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Summary Of Significant Accounting Policies (Policy) | 9 Months Ended
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Sep. 30, 2025
General, Basis of Accounting | The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (SEC). Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025.
General, Use of Estimates | A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification | Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
Cash and Cash Equivalents | At September 30, 2025, cash and cash equivalents included money market fund investments of $477 million and $194 million for Alliant Energy and IPL, respectively, with weighted average interest rates of 4%.
Short-term investments | Short-term investments include investments that have original maturities of greater than 90 days and remaining maturities of less than one year, and are convertible to known amounts of cash. At September 30, 2025, short-term investments included time deposits of $250 million for Alliant Energy, with weighted average interest rates of 4%.
Asset Retirement Obligations | In the second quarter of 2024, substantially due to the enactment of the revised Coal Combustion Residuals Rule, Alliant Energy and IPL recorded a pre-tax non-cash charge of $20 million to “Other operation and maintenance” in their income statements for the nine months ended September 30, 2024 for the AROs allocated to IPL’s steam business for its Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews.
IPL [Member] |
General, Basis of Accounting | The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (SEC). Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025.
General, Use of Estimates | A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification | Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
Cash and Cash Equivalents | At September 30, 2025, cash and cash equivalents included money market fund investments of $477 million and $194 million for Alliant Energy and IPL, respectively, with weighted average interest rates of 4%.
Asset Retirement Obligations | In the second quarter of 2024, substantially due to the enactment of the revised Coal Combustion Residuals Rule, Alliant Energy and IPL recorded a pre-tax non-cash charge of $20 million to “Other operation and maintenance” in their income statements for the nine months ended September 30, 2024 for the AROs allocated to IPL’s steam business for its Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews.
WPL [Member] |
General, Basis of Accounting | The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (SEC). Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2024 Form 10-K. In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2025 are not necessarily indicative of results that may be expected for the year ending December 31, 2025.
General, Use of Estimates | A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
General, Reclassification | Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

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- Definition Disclosure of accounting policy for legal obligation associated with retirement of long-lived asset that results from acquisition, construction, or development or from normal operation of long-lived asset. Excludes environmental remediation liability from improper or other-than-normal operation of long-lived asset, obligation arising in connection with leased property that meets definition of lease payments or variable lease payments and from plan to sell or otherwise dispose of a long-lived asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/410-20/tableOfContent + Details
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- Definition Disclosure of accounting policy for basis of accounting, or basis of presentation, used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483426/235-10-50-4 + Details
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- Definition Entity's cash and cash equivalents accounting policy with respect to restricted balances. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(1)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482913/230-10-50-1 + Details
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