UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 11-K [X] ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2004 or [ ] TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from _____________ to _____________ Commission File Number: 1-9894 A. Full title of the plan and address of the plan, if different from that of the issuer named below: ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN B. Name of issuer of the securities held pursuant to the plan and the address of its principal executive office: ALLIANT ENERGY CORPORATION 4902 North Biltmore Lane Madison, Wisconsin 53718 REQUIRED INFORMATION The following financial statements and schedules of the Alliant Energy Corporation 401(k) Savings Plan, prepared in accordance with the financial reporting requirements of the Employee Retirement Income Security Act of 1974, as amended, are filed herewith. Page 1 of 19 pages Exhibit Index is on page 18 1 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN FINANCIAL STATEMENTS AS OF DECEMBER 31, 2004 AND 2003 AND FOR THE YEAR ENDED DECEMBER 31, 2004, SUPPLEMENTAL SCHEDULES FOR THE YEAR ENDED DECEMBER 31, 2004, AND REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM 2 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN TABLE OF CONTENTS Page No. REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM 4 FINANCIAL STATEMENTS Statements of Net Assets Available for Plan Benefits as of December 31, 2004 and 2003 5 Statement of Changes in Net Assets Available for Plan Benefits for the Year Ended December 31, 2004 6 NOTES TO FINANCIAL STATEMENTS 7-12 SUPPLEMENTAL SCHEDULES Form 5500, Schedule H, Part IV, line 4i - Schedule of Assets (Held at End of Year) as of December 31, 2004 13-15 Form 5500, Schedule H, Part IV, line 4j - Schedule of Reportable Transactions for the Year Ended December 31, 2004 16 SIGNATURES 17 EXHIBIT INDEX 18 Consent of Independent Registered Public Accounting Firm 19 3 Report of Independent Registered Public Accounting Firm To the Total Compensation Committee and Participants of the Alliant Energy Corporation 401(k) Savings Plan: We have audited the accompanying statements of net assets available for plan benefits of the Alliant Energy Corporation 401(k) Savings Plan (the "Plan") as of December 31, 2004 and 2003, and the related statement of changes in net assets available for plan benefits for the year ended December 31, 2004. These financial statements are the responsibility of the Plan's management. Our responsibility is to express an opinion on these financial statements based on our audits. We conducted our audits in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. The Plan is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. Our audits included consideration of internal control over financial reporting as a basis for designing audit procedures that are appropriate in the circumstances, but not for the purpose of expressing an opinion on the effectiveness of the Plan's internal control over financial reporting. Accordingly, we express no such opinion. An audit also includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion. In our opinion, such financial statements present fairly, in all material respects, the net assets available for plan benefits of the Plan as of December 31, 2004 and 2003, and the changes in net assets available for plan benefits for the year ended December 31, 2004, in conformity with accounting principles generally accepted in the United States of America. Our audits were conducted for the purpose of forming an opinion on the basic financial statements taken as a whole. The supplemental schedules of (1) assets (held at end of year) as of December 31, 2004, and (2) reportable transactions for the year ended December 31, 2004, are presented for the purpose of additional analysis and are not a required part of the basic financial statements, but are supplementary information required by the Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. These schedules are the responsibility of the Plan's management. Such schedules have been subjected to the auditing procedures applied in our audit of the basic 2004 financial statements and, in our opinion, are fairly stated in all material respects when considered in relation to the basic financial statements taken as a whole. /s/ Deloitte & Touche LLP Milwaukee, Wisconsin June 16, 2005 4 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN STATEMENTS OF NET ASSETS AVAILABLE FOR PLAN BENEFITS December 31, 2004 2003 --------------------- -------------------- Investment income receivable $8,564,250 $6,819,703 Contributions receivable 374,368 424,518 --------------------- -------------------- Total receivables 8,938,618 7,244,221 --------------------- -------------------- Investments, other than participant promissory notes (Refer to Note 7) 445,595,364 385,431,715 Participant promissory notes 8,742,835 8,213,703 --------------------- -------------------- Total investments 454,338,199 393,645,418 --------------------- -------------------- Net assets available for plan benefits $463,276,817 $400,889,639 ===================== ==================== The accompanying Notes to Financial Statements are an integral part of these statements. 5 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR PLAN BENEFITS For the Year Ended December 31, 2004 Net assets available for plan benefits - beginning of year $400,889,639 Contributions: Cash contributions from employees 26,470,660 Employer contributions: Cash for purchase of Alliant Energy Corporation common stock 7,750,725 Cash 692,957 Rollovers from other qualified plans 537,947 Investment activity: Net appreciation in fair value of investments (Refer to Note 7) 38,741,362 Investment income 9,343,320 Distributions to participants (21,149,793) ---------------- Net assets available for plan benefits - end of year $463,276,817 ================ The accompanying Notes to Financial Statements are an integral part of this statement. 6 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN NOTES TO FINANCIAL STATEMENTS FOR THE YEAR ENDED DECEMBER 31, 2004 Note 1. Description of the Plan The Alliant Energy Corporation 401(k) Savings Plan (the Plan) is a qualified defined contribution plan under Section 401(k) of the Internal Revenue Code (the Code), as amended, and meets the applicable requirements of the Employee Retirement Income Security Act of 1974, as amended. The following brief description of the Plan is provided for general information purposes only. More complete information regarding the Plan is provided in the summary plan description, which has been made available to all eligible Plan participants (participants). The Plan is administered by the Total Compensation Committee (the Committee) and the Plan sponsor is Alliant Energy Corporate Services, Inc. (a direct subsidiary of Alliant Energy Corporation), which reserves the right to terminate, amend or modify the Plan if future conditions warrant such action. Any regular employee of Alliant Energy Corporation and its participating subsidiaries (the Company) age 18 and over may participate in the Plan. Regular full-time employees and regular part-time employees customarily scheduled to work at least half-time may participate immediately following 30 days of service. Part-time employees customarily scheduled to work less than half-time may participate after 12 months of service during which he or she has earned at least 1,000 paid hours. An Employee Stock Ownership Plan (ESOP) is in place within the Plan. Under these provisions, participants have the option to elect to receive cash for any dividends paid on Company common stock within the Plan or to have the dividends reinvested in additional shares based on the current market price. Also, the Company is eligible for the dividend deduction provisions of Section 404(k) of the Code for Company common stock held in the ESOP. The Company provides matching contributions for each $1 contributed by participants up to a maximum of the first 6% of each respective participant's eligible compensation. Other than the exceptions noted below, Company match information and employee contribution limits for 2004 were as follows: Company match for each $1 contributed up to the maximum $0.50 Eligible employee annual contribution limit as a percentage of compensation 50% Maximum annual contribution limit $13,000 Company contributions for Alliant Energy Resources, Inc. (Resources) and Cedar Rapids and Iowa City Railway Company (CRANDIC) employees are calculated based on a percentage of base pay, without overtime or incentive pay, and there is a "basic" Company contribution equal to 4% and 2%, respectively, of base pay. Resources and CRANDIC employees may be eligible for a "discretionary" Company contribution of $0.50 for every $1 contributed up to a maximum of the first 6% of pay in addition to the "basic" Company contribution. The "discretionary" contribution for both Resources and CRANDIC employees is based on goals established by Resources and is typically determined and paid during the first quarter of the following year. The "discretionary" Company contributions for 2004 and 2003 were $374,368 and $424,518, respectively. An "additional" Company contribution is allocated to the accounts of active participants, except for Resources and CRANDIC employees, as of the last day of the Plan year, who contributed at least 6% of compensation during the Plan year and did not receive a Company matching contribution equal to 3% of compensation. The amount of the "additional" Company contribution is the difference between 3% of compensation during the Plan year and the amount of Company matching contributions previously received during the Plan year. 7 Participants who were at least age 50 by Dec. 31, 2004 were eligible to make catch-up contributions of up to $3,000 in 2004. These catch-up contributions were not eligible for any Company match. All Company contributions are invested in the Alliant Energy Corporation Common Stock Fund, except for Company "basic" contributions for Resources and CRANDIC employees which are invested at each participant's discretion. Participants are immediately vested in their respective employee and employer contributions. Contributions under the Plan are held and invested, until distribution, in a Trust Fund maintained by American Express Trust Company (the Trustee), a division of American Express Financial Advisors Inc. Participants may subsequently redesignate the distribution of future contributions or transfer existing balances between investment funds on a daily basis, subject to the limits set forth in the Plan. As previously described, Company matching contributions invested in the Alliant Energy Corporation Company Stock Fund may not be transferred to any other investment fund, except for "basic" contributions made for CRANDIC and Resources employees. However, Company matching contributions may be transferred by certain participants during the 30-day period immediately prior to retirement and participants age 55 with 10 years of service are eligible to diversify up to 100% of their ESOP account to one or more of the investment options. The Plan has provisions under which participants who are active employees may take loans up to the lesser of $50,000 or 50% of their total account balance (a $1,000 minimum loan amount and a maximum of three loans for each participant also apply). The Committee determines the loan interest rate pursuant to the Plan. Interest rates on participant loans ranged from 5.0% to 10.5% at both Dec. 31, 2004 and 2003. Principal and interest are repaid bi-weekly through employee payroll deductions. Note 2. Summary of Significant Accounting Policies (a) Basis of Accounting - The financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). (b) Valuation of Investments and Income Recognition - All Guaranteed Investment Contracts (GIC's) held by the Plan are fully benefit responsive and are valued at contract value, which represents contributions made under the contract, plus interest at the contract rate (less funds used to pay plan benefits). The carrying value of all GIC investments was $35,339,962 and $38,189,962 at Dec. 31, 2004 and 2003, respectively. The approximate fair value of these investments was $43,639,028 and $46,026,501 at Dec. 31, 2004 and 2003, respectively, based on the discounted cash flows valuation method. Under the terms of the GIC's, the weighted average crediting interest rate was 5.00% and 4.08% on Dec. 31, 2004 and 2003, respectively, and is reset quarterly for all contracts. The GIC's earned an average rate of 4.80% in 2004. Participant loans are carried at unpaid principal balances due. All other Plan investments are carried at fair value as determined by quoted market prices, except for the American Express Trust Income Fund I. The American Express Trust Income Fund I is a common collective trust fund, which includes investments in fully benefit responsive GIC's and is reported at contract value, which approximates fair value. Interest income is accrued when earned. Dividend income is recorded on the ex-dividend date. Investment transactions are recorded on the trade date. (c) Net Appreciation in Fair Value of Investments - Net realized and unrealized appreciation is recorded in the accompanying statement of changes in net assets available for plan benefits as "Net appreciation in fair value of investments." (d) Payment of Benefits - Benefit payments to participants are recorded when paid. 8 (e) Expenses - Investment management fees are paid from investment earnings prior to crediting earnings to the individual participant account balances. Most other Plan administrative expenses are absorbed by the Company. Expenses incurred in maintaining Self-Managed Brokerage Accounts are the responsibility of the respective Plan participants. (f) Use of Estimates - The preparation of financial statements in conformity with GAAP requires the Plan administrator to make estimates and assumptions that affect the reported amounts of net assets available for plan benefits at the date of the financial statements and the reported amounts of changes in net assets available for plan benefits during the reporting period. Actual results could differ from those estimates. (g) Risk and Uncertainties - The Plan invests in various investments, including common investment funds, mutual funds, common stock of the Company and investment contracts. The Plan also offers a Self-Managed Brokerage Account option which allows participants to invest in a wide range of mutual funds. Investments, in general, are exposed to various risks, such as interest rate, credit, and overall market volatility. Due to the level of risk associated with certain investments, it is reasonably possible that changes in the values of certain investments will occur in the near term and that such changes could materially affect the amounts reported in the financial statements. Note 3. Tax Status The Internal Revenue Service has determined and informed the Company by a letter dated Aug. 25, 2003, that the Plan and related trust are designed in accordance with the applicable sections of the Code. It is the intention of the Company to adopt any amendments necessary to maintain the qualified status of the Plan. Note 4. Plan Termination Provisions Upon termination of the Plan in its entirety, each participant is entitled to receive, in accordance with the terms of the Plan, the entire balance in their account. The Company has no intention to terminate the Plan. Note 5. Withdrawals and Distributions Withdrawals from participants' account balances are allowed when participants who are actively employed reach age 70-1/2 (or age 59-1/2 for certain participants). Withdrawals are also allowed due to special "hardship" circumstances. Distributions from the Plan will be made upon termination of employment (by retirement, death, disability or otherwise) if the participant's account balance is less than $5,000. If the participant's account balance exceeds $5,000, the participant may elect to defer payment until he or she is age 70-1/2. Distributions can be either in the form of a lump sum or substantially equal annual installments. The unpaid portion of all loans made to the participant, including accrued interest, will be deducted from the amount of the participant account to be distributed. Distributions payable to participants at Dec. 31, 2004 and 2003 were $25,656 and $0, respectively. Distributions payable are not recorded in the accompanying financial statements, however, they are recorded in the Plan's Form 5500 (refer to Note 10). Note 6. Derivative Financial Instruments The Plan did not invest in any material derivative financial instruments during 2004 and 2003. 9 Note 7. Other Investment Information Investments held which were greater than 5% of the Plan's net assets available for plan benefits as of Dec. 31 were as follows: 2004 2003 -------------- -------------- Alliant Energy Corporation Common Stock* $108,063,758 $89,235,309 (non-participant directed: $63,508,962 (2,220,593 shares) and $48,442,726 (1,945,491 shares), respectively) (participant directed: $44,554,796 (1,557,860 shares) and $40,792,583 (1,638,256 shares), respectively) American Express Trust Equity Index Fund III*, 2,340,750 and 2,449,624 shares, respectively 76,942,777 72,695,049 American Funds Growth Fund of America, 2,572,065 and 2,509,599 shares, respectively 70,423,142 61,585,565 American Express Trust Long-Term Horizon (65:35) Fund*, 2,660,902 and 2,729,903 shares, respectively 33,931,822 31,904,378 Dodge & Cox Stock Fund, 196,080 and 127,389 shares, respectively 25,533,595 14,494,303 Brown Capital Management Small Company Fund, 822,599 and 895,853 shares, respectively 24,513,456 26,633,723 PIMCO Total Return Fund, 1,941,165 and 1,887,924 shares, respectively 20,712,227 20,219,670 * Represents party known to be a party-in-interest to the Plan. During 2004, the Plan's investments, including gains and losses on investments acquired and disposed of, as well as held during the year, appreciated (depreciated) in value as follows: Alliant Energy Corporation Common Stock $13,866,178 American Express Trust Equity Index Fund III 7,563,061 American Funds Growth Fund of America 7,216,827 American Express Trust Long-Term Horizon (65:35) Fund 2,835,135 Dodge & Cox Stock Fund 2,698,166 American Funds EuroPacific Growth Fund 2,599,976 Dreyfus Premier Emerging Markets Fund 653,655 State Street Global Advisors S&P Midcap Index Fund 528,085 Evergreen Small Cap Value Fund 365,571 American Express Trust Income Fund I 262,515 Vanguard Mid-Cap Index Fund 150,758 American Express Trust Long-Term Horizon (80:20) Fund 115,326 American Express Trust Short-Term Horizon (25:75) Fund 40,824 American Express Trust Bond Index Fund II 12,814 Self-Managed Brokerage Accounts 11,582 Brown Capital Management Small Company Fund (89,258) PIMCO Total Return Fund (89,853) ------------ Net appreciation in fair value of investments $38,741,362 ============ 10 Note 8. Non-Participant Directed Investments Information about the net assets and the significant components of the changes in net assets relating to the non-participant directed investments was as follows: As of Dec. 31, Net assets: 2004 2003 ------------- ------------- Alliant Energy Corporation Common Stock* $63,508,962 $48,442,726 American Express Trust Money Market Fund I* 993,002 605,615 Contributions receivable 374,368 424,518 Investment income receivable 697 441 ------------- ------------- $64,877,029 $49,473,300 ============= ============= For the Year Ended Changes in net assets: Dec. 31, 2004 ------------------ Employer contributions $7,750,725 Investment activity: Net appreciation in fair value of investments 7,936,617 Investment income 2,133,932 Transfers to participant directed investments (482,303) Distributions to participants (1,935,242) ------------ $15,403,729 ============ * Represents party known to be a party-in-interest to the Plan. Note 9. Related Party Transactions Certain Plan investments are shares of mutual funds and common trust funds managed by an affiliate of the Trustee and shares of common stock of the Company. As of Dec. 31, 2004 and 2003, the Plan held 3,778,453 and 3,583,747 shares of Alliant Energy Corporation common stock with a cost basis of $92,640,650 and $87,615,743, respectively. During the years ended Dec. 31, 2004 and 2003, the Plan recorded dividend income of $3,705,802 and $3,344,162, respectively, from investments in common stock of the Company. These transactions qualify as party-in-interest. Note 10. Reconciliation to Form 5500 Distributions payable to participants are not included in the accompanying financial statements, however, they are recorded in the Plan's Form 5500. The following table reconciles net assets available for plan benefits per the financial statements to the Plan's Form 5500 as filed by the Company for the year ended Dec. 31: 2004 2003 -------------- ------------ Net assets available for plan benefits per financial statements $463,276,817 $400,889,639 Adjustments: Benefits requested not yet paid (25,656) -- -------------- ------------ Amounts reported per Form 5500 $463,251,161 $400,889,639 ============== ============ 11 The following table reconciles certain changes in net assets available for plan benefits per the financial statements to the Form 5500 as filed by the Company for the year ended Dec. 31, 2004: Distributions to Participants ---------------- Amounts reported per financial statements ($21,149,793) Adjustments: Changes in benefits requested not yet paid (25,656) ----------------- Amounts reported per Form 5500 ($21,175,449) ================= Note 11. Subsequent Event On Aug. 1, 2005, it is expected that the Trustee will change its name to Ameriprise Trust Company, and American Express Financial Advisors Inc. will begin operating as Ameriprise Financial Services, Inc. 12 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN FORM 5500, SCHEDULE H, PART IV, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR) AS OF DECEMBER 31, 2004 Identity of issue, borrower, Description of investment including maturity date, Current lessor, or similar party rate of interest, collateral, par or maturity value Cost Value ---------------------------------- ------------------------------------------------------------------ ------------- -------------- Registered Investment Companies Evergreen Small Cap Value Fund, 216,771 shares $4,520,031 $5,074,605 American Funds Growth Fund of America, 2,572,065 shares 50,263,175 70,423,142 PIMCO Total Return Fund, 1,941,165 shares 20,952,129 20,712,227 Dodge & Cox Stock Fund, 196,080 shares 20,500,585 25,533,595 Brown Capital Management Small Company Fund, 822,599 shares 19,402,020 24,513,456 Dreyfus Premier Emerging Markets Fund, 354,871 shares 6,277,245 6,959,020 American Funds EuroPacific Growth Fund, 526,727 shares 16,035,870 18,572,401 Common/Collective Trusts American Express Trust Money Market Fund I*, 3,547,995 shares 3,547,995 3,547,995 American Express Trust Short-Term Horizon (25:75) Fund*, 42,155 shares 810,431 852,918 American Express Trust Long-Term Horizon (65:35) Fund*, 2,660,902 shares 26,570,252 33,931,822 American Express Trust Long-Term Horizon (80:20) Fund*, 54,546 shares 1,302,834 1,419,236 American Express Trust Equity Index Fund III*, 2,340,750 shares 68,063,447 76,942,777 American Express Trust Income Fund I*, 137,429 shares 8,297,933 9,081,602 American Express Trust Investment Grade Bond Fund*, 273,592 shares 4,070,987 4,447,234 American Express Trust Bond Index Fund II*, 33,412 shares 465,077 475,489 State Street Global Advisors S&P Midcap Index Fund, 176,674 shares 4,794,443 5,337,675 Corporate Stocks: Common Alliant Energy Corporation common stock*, 3,778,453 shares 92,640,650 108,063,758 Corporate Bonds AMCAR 2002-C AR, 3.55%, 2/12/08, par value $100,000 99,982 100,347 AMCAR 2003-CF A3, 2.75%, 10/9/07, par value $175,000 177,728 174,558 AMCAR 2004-AF A3, 2.18%, 7/7/08, par value $200,000 199,988 198,313 AMCAR 2004-CA A3, 3.00%, 3/6/09, par value $150,000 149,985 148,687 AMSI 2004-R7 A2, 2.55%, 8/25/34, par value $89,078 89,078 89,085 BOAA 2003-1-A1, 5.00%, 2/25/33, par value $151,156 152,171 152,598 BOAMS 2004-E 2A6, 4.13%, 6/25/34, par value $150,000 148,781 147,842 CWL 2004-5 4A1, 2.53%, 8/25/23, par value $112,411 112,411 112,415 COAFT 2002-B A4A, 3.32%, 4/15/09, par value $100,000 101,969 100,089 COAFT 2003-A A3A, 1.83%, 10/15/07, par value $130,578 130,124 129,886 COAFT 2004-A A3, 3.07%, 7/15/08, par value $100,000 99,999 99,446 Centex Home Eq 2004-A AF3, 3.26%, 4/25/28, par value $150,000 149,996 147,695 CFAB 2004-2 2A1, 2.55%, 1/25/25, par value $99,731 99,731 99,716 CSFB 2004-C1 A2, 3.52%, 1/15/37, par value $100,000 100,500 98,467 FSPC T-17 A4 ABS HEL, 6.93%, 1/25/26, par value $66,469 66,467 66,484 GMACC 2002-C2 A1, 4.32%, 10/15/38, par value $151,862 154,567 153,470 GSMS 2004-GG2 A2, 4.29%, 8/1/38, par value $150,000 150,747 151,636 HART 2003-A A3, 2.33%, 11/15/07, par value $150,000 149,998 148,727 LBUBS 2004-C4 A2, 4.57%, 5/15/34, par value $150,000 153,697 152,853 LB-UBS 2002-A2, 4.90%, 6/15/26, par value $200,000 200,995 206,021 LBUBS 2004-C6 A2, 4.19%, 8/15/29, par value $200,000 200,995 200,076 LBUBS 2003-C7 A2, 4.06%, 9/15/27, par value $185,000 186,356 185,080 LBUBS 2003-C8 A2, 4.21%, 11/15/27, par value $150,000 150,744 151,101 LBUBS 2004-C2 A2, 3.25%, 3/15/29, par value $150,000 144,686 145,460 LBMLT 2004-3 A2, 2.54%, 7/25/34, par value $107,419 107,419 107,421 MARM 2004-3 3A2, 4.50%, 4/25/34, par value $129,431 132,019 129,165 MSCI 2004-IQ8-A2, 3.96%, 6/15/40, par value $250,000 252,676 250,211 MSM 2004-2AR 3A, 5.05%, 2/25/34, par value $161,695 165,585 163,129 MSM 2004-10AR 1A, 4.82%, 11/25/34, par value $141,712 144,280 143,815 RALI SER 2003-QS4 ABS, 5.50%, 9/25/33, par value $179,562 184,598 181,173 RASC 2004-KS8 A13, 3.84%, 9/25/34, par value $125,000 124,980 124,395 RASC SER 2002-KS1, 5.864%, 11/25/29, par value $192,758 205,468 193,762 SASCO CMO 2004-12H, 5.56%, 4/25/34, par value $110,288 112,774 112,291 VWALT 2004-A-A3, 2.84%, 7/20/07, par value $150,000 149,997 149,133 WESTO 2002-1 A4A, 4.87%, 9/20/09, par value $150,000 156,633 152,032 WESTO 2002-2 A4, 4.50%, 2/20/10, par value $150,000 155,865 151,927 WESTO 2003-4 A3, 2.39%, 1/22/08, par value $150,000 149,994 149,320 WBCMT 2003-C8 A2, 3.89%, 11/15/35, par value $150,000 150,745 149,525 13 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN FORM 5500, SCHEDULE H, PART IV, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR) AS OF DECEMBER 31, 2004 (Continued) Identity of issue, borrower, Description of investment including maturity date, Current lessor, or similar party rate of interest, collateral, par or maturity value Cost Value ---------------------------------- ------------------------------------------------------------------ ------------- -------------- Government and Agency Obligations FHLMC Gold #E91326, 6.50%, 9/1/17, par value $91,927 97,385 97,345 FHLMC Gold #E96180, 4.50%, 5/1/13, par value $138,779 143,984 139,699 FHLMC Gold #E96579, 4.50%, 6/1/13, par value $161,377 167,353 162,437 FHLMC Gold #E97247, 5.00%, 6/1/18, par value $121,903 124,494 123,978 FHLMC MTN, 3.525%, 12/20/07, par value $370,000 370,000 370,226 FHLMC, 2.85%, 2/23/07, par value $300,000 296,670 296,697 FHLMC Gold #C66932, 6.00%, 5/1/32, par value $77,995 78,166 80,681 FHLMC Gold #B10258, 5.00%, 10/1/18, par value $290,539 295,715 295,287 FHLMC Gold #B10776, 5.00%, 11/1/13, par value $123,046 126,314 125,852 FHLB, 3.00%, 5/15/06, par value $290,000 291,134 289,586 FHLB, 2.50%, 3/13/06, par value $300,000 300,102 298,038 Fed Home Loan Bank, 2.88%, 5/22/06, par value $475,000 474,069 473,482 Fed Home Loan Bank, 3.25%, 12/17/07, par value $170,000 169,466 168,657 Federal Farm Credit Bank, 2.38%, 10/2/06, par value $150,000 150,473 147,912 Federal Farm Credit Bank, 2.13%, 7/17/06, par value $250,000 249,522 246,092 FHLMC 2393-A CMO, 5.50%, 4/15/30, par value $22,549 22,973 22,657 FHLMC, 5.50%, 7/15/06, par value $150,000 157,088 155,228 FHLMC Reference Notes, 4.25%, 7/15/09, par value $475,000 487,774 483,391 FHLMC ARM #781884, 5.20%, 8/1/34, par value $98,650 99,960 99,521 FHLMC (Non Gold) Arm #782436, 5.01%, 10/1/34, par value $147,481 150,799 149,671 FNMA, 3.88%, 11/17/08, par value $350,000 349,202 349,496 FNMA Benchmark, 2.25%, 2/28/06, par value $145,000 143,912 143,676 FNMA, 3.00%, 3/2/07, par value $220,000 219,593 218,627 FNMA Benchmark, 3.13%, 12/15/07, par value $65,000 64,994 64,360 FNMA 15yr #252260, 6.00%, 3/1/10, par value $512,781 510,297 538,474 FNMA #254187, 5.00%, 12/1/08, par value $318,937 317,193 324,467 FNMA #254291, 7.00%, 4/1/17, par value $120,175 128,174 127,409 FNMA #254757, 5.00%, 3/31/13, par value $133,650 139,664 136,610 FNMA #535170, 5.50%, 9/1/14, par value $140,518 144,997 145,622 FNMA #545701, 7.00%, 7/1/12, par value $158,408 169,298 165,721 FNMA #545864, 5.50%, 8/1/17, par value $220,934 224,196 229,222 FNMA #555655, 4.45%, 7/1/33, par value $254,080 257,057 255,193 FNMA #555740, 4.50%, 9/1/18, par value $258,383 253,135 258,303 FNMA #640996, 7.50%, 5/1/32, par value $79,659 85,235 85,286 FNMA #648349, 6.00%, 6/1/17, par value $93,746 98,053 98,705 FNMA 2002-W3 A3, 6.00%, 7/25/24, par value $164,624 165,068 165,746 FNMA 2002-W5 A6, 6.00%, 8/25/32, par value $166,553 167,724 167,023 FNMA 2002-W4 A3, 5.30%, 4/25/42, par value $323,694 324,503 326,098 FNMA 2002-W9 A3, 5.00%, 8/25/42, par value $153,438 154,313 154,150 FNMA CMO 03-W2-2A6, 5.50%, 7/25/42, par value $68,709 71,071 68,723 FHLMC 2492-B, 5.50%, 5/15/13, par value $332,019 346,597 338,746 FNMA #200394, 5.50%, 7/25/23, par value $300,000 313,172 308,311 FHLMC 2617 HD, 7.00%, 6/15/16, par value $118,399 128,611 127,380 FNMA 2003-109 CX, 4.00%, 7/25/16, par value $150,000 150,791 149,245 FNMA 2003-106 B, 4.50%, 10/25/19, par value $191,463 195,352 192,466 FNMA 2003-W16 AF3, 2.91%, 1/25/29, par value $150,000 149,997 149,766 FNMA 2003-133 GB, 8.00%, 12/25/26, par value $73,127 80,131 78,563 FHLMC_2641, 6.50%, 1/15/18, par value $120,327 128,402 127,975 FNMA 2004-21 AC, 4.00%, 5/25/16, par value $200,000 204,687 200,625 FNMA 2004-W3 A2, 3.75%, 5/25/34, par value $125,000 127,344 123,640 FNMA 2004-W3 A14, 3.50%, 5/25/34, par value $85,343 85,610 85,063 FNMA 2004-W3 A15, 5.00%, 5/25/34, par value $100,000 104,641 101,751 FNMA 2004-W4 A2, 5.00%, 6/25/34, par value $150,000 157,242 152,800 FNMA 2004-W8, 7.50%, 6/25/44, par value $83,710 89,315 89,956 FNMA 2004-60 PA, 5.50%, 4/25/34, par value $146,796 151,647 151,777 FHLMC 2657 NT, 5.00%, 1/15/16, par value $150,000 156,117 153,865 FHLMC 2663 BA, 4.00%, 8/15/16, par value $82,544 81,461 82,194 FHLMC 2672 NT, 5.00%, 2/15/16, par value $200,000 208,289 205,039 FHLMC 2662 DB, 5.00%, 2/15/16, par value $150,000 156,047 153,875 FHLMC 2681 PJ, 5.00%, 10/15/15, par value $300,000 313,734 308,212 14 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN FORM 5500, SCHEDULE H, PART IV, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR) AS OF DECEMBER 31, 2004 (Continued) Identity of issue, borrower, Description of investment including maturity date, Current lessor, or similar party rate of interest, collateral, par or maturity value Cost Value ---------------------------------- ------------------------------------------------------------------ ------------ -------------- FHLMC 2688 DE, 4.50%, 2/15/20, par value $150,000 151,359 151,216 FHLMC 2716 UA, 4.50%, 7/15/20, par value $268,388 267,717 270,502 FHLMC 2750 DB, 4.50%, 5/15/15, par value $150,000 153,586 152,593 FHLMC 2822 ZN, 5.00%, 1/15/33, par value $41,574 41,288 40,878 FHLMC 2843-BA, 5.00%, 1/15/18, par value $140,442 143,915 142,538 FHLMC 2907-AG, 4.50%, 3/15/19, par value $125,000 124,961 126,256 FHLMC, 3.50%, 9/15/07, par value $725,000 716,894 727,071 FNMA #685433, 6.50%, 3/1/33, par value $187,532 198,037 197,185 FNMA #705304, 4.90%, 6/1/33, par value $174,887 177,442 179,939 FNMA ARM #722781, 4.27%, 9/1/33, par value $459,008 453,987 458,374 FNMA #725090, 4.80%, 11/1/33, par value $139,469 138,729 139,638 FNMA ARM #725737, 4.53%, 8/1/34, par value $98,575 97,389 99,045 FNMA #732002, 4.25%, 8/1/33, par value $105,295 107,039 106,038 FNMA #764082, 4.78%, 1/1/34, par value $127,987 130,087 129,593 FNMA ARM #768193, 4.58%, 3/1/34, par value $161,085 164,703 162,216 FNMA ARM #799769, 5.07%, 11/1/34, par value $149,983 152,983 152,424 FNMA ARM #801344, 5.10%, 10/1/34, par value $145,752 148,394 148,102 FNMA 2003-W18 1A5, 4.61%, 8/25/43, par value $100,000 101,172 100,556 FNMA 2004-W10 A23, 5.00%, 8/25/34, par value $125,000 128,770 126,750 VENDEE 2003-2 C, 5.00%, 7/15/20, par value $100,000 103,406 101,040 U.S. Treasury Note, 3.25%, 8/15/07, par value $265,000 274,813 265,393 U.S. Treasury Note, 1.88%, 1/31/06, par value $1,525,000 1,516,717 1,510,346 U.S. Treasury Note, 2.25%, 2/15/07, par value $1,065,000 1,073,830 1,046,945 U.S. Treasury Note, 2.75%, 8/15/07, par value $800,000 792,167 791,218 U.S. Treasury Note, 4.25%, 8/15/04, par value $475,000 477,448 476,058 U.S. Treasury Note, 2.88%, 11/30/06, par value $600,000 598,969 598,125 U.S. Treasury Note, 3.63%, 12/15/09, par value $1,785,000 1,782,404 1,776,353 Investment Contracts Monumental Life Insurance Company, 4.09%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - (41,973) Bank of America NA, 5.45%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - (87,448) Rabobank International, 4.80%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - 35,617 IXIS Capital Markets, 3.31%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - 25,405 JP Morgan Chase & Co., 3.94%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - (14,458) UBS Warburg, 3.61%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - (5,096) State Street Bank and Trust Company, 3.23%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - 27,852 AIG Financial Products Corp., 3.32%, 12/31/50 Synthetic Guaranteed Investment Contract Wrapper - (81,860) United of Omaha, 2.48%, 5/20/05 2,004,213 2,004,213 John Hancock Life Insurance Company, 7.69%, 3/31/05 2,115,241 2,115,241 New York Life Insurance Company, 7.41%, 8/15/05 2,056,032 2,056,032 Hartford, 5.21%, 11/15/06 2,012,842 2,012,842 Protective Life Insurance Company, 6.12%, 6/15/06 2,066,167 2,066,167 Participant-Directed Brokerage Accounts Self-Managed Brokerage Accounts 115,152 126,092 Participant Promissory Notes Maximum allowable loan -- $50,000 Various interest rates -- 5.0% to 10.5% Primarily maturing within 5 years - 8,742,835 ------------ --------------- $386,237,992 $462,094,753(1) ============ =============== (1) The difference between the total current value on this Schedule H, Part IV, Line 4i and the total investments on the Statement of Net Assets Available for Plan Benefits as of Dec. 31, 2004 is equal to accrued interest on the Guaranteed Investment Contracts. * Represents party known to be a party-in-interest to the Alliant Energy Corporation 401(k) Savings Plan. 15 ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN FORM 5500, SCHEDULE H, PART IV LINE 4j - SCHEDULE OF REPORTABLE TRANSACTIONS FOR THE YEAR ENDED DECEMBER 31, 2004 Identity Total Total Total Net Adjusted Net of Party Involved and Number of Value of Number Selling Cost of Gain Description of Assets Purchases Purchases (1) of Sales Price (1) Assets Sold (Loss) ----------------------------------------------------------------------------------------------------------------------------------- Single Transaction Exceeds 5% of Value: None. ----------------------------------------------------------------------------------------------------------------------------------- Series of Transactions With Same Broker Exceeds 5% of Value: None. ----------------------------------------------------------------------------------------------------------------------------------- Series of Transactions In Same Security Exceeds 5% of Value: American Express Trust Money Market Fund I 384 $47,425,374 455 $48,010,220 $48,010,220 $ - ----------------------------------------------------------------------------------------------------------------------------------- Single Transaction With One Broker Exceeds 5% of Value: None. ----------------------------------------------------------------------------------------------------------------------------------- (1) The purchase/selling price was equal to the fair value on the date of purchase/sale. 16 SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the Total Compensation Committee, which administers the Plan, has duly caused this Annual Report to be signed on its behalf by the undersigned, thereunto duly authorized, on this 29th day of June 2005. ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN /s/ Jonathan C. Day -------------------- Jonathan C. Day The foregoing person is the Director - Total Compensation of Alliant Energy Corporation and the Chairperson of the Alliant Energy Corporation Total Compensation Committee. 17 EXHIBIT INDEX TO ANNUAL REPORT ON FORM 11-K ALLIANT ENERGY CORPORATION 401(k) SAVINGS PLAN FOR THE YEAR ENDED DECEMBER 31, 2004 Page Number in Sequentially Numbered Exhibit No. Exhibit Form 11-K ----------- ------- -------------- 23 Consent of Independent Registered 19 Public Accounting Firm 18