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Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 USD ($) customer MW | Dec. 31, 2023 USD ($) | Dec. 31, 2022
Cash, Cash Equivalents and Restricted Cash: |  |  |  |
Money market fund investments |  | $ 52 | $ 45 |
Money market fund investments interest rate, percentage |  | 4.00% |  |
Non-utility wind farm in Oklahoma [Member] |  |  |  |
General: |  |  |  |
Ownership interest |  | 50.00% |  |
IPL [Member] |  |  |  |
General: |  |  |  |
Generation and distribution of steam, number of customers served (in customers) | customer |  | 2 |  |
Cash, Cash Equivalents and Restricted Cash: |  |  |  |
Money market fund investments |  | $ 9 | 45 |
Money market fund investments interest rate, percentage |  | 4.00% |  |
Property, Plant and Equipment: |  |  |  |
AFUDC accrual recorded, percentage of estimated CWIP |  | 100.00% |  |
WPL [Member] |  |  |  |
Cash, Cash Equivalents and Restricted Cash: |  |  |  |
Money market fund investments |  | $ 43 | $ 0 |
Money market fund investments interest rate, percentage |  | 4.00% |  |
Property, Plant and Equipment: |  |  |  |
AFUDC accrual recorded, percentage of estimated CWIP |  | 50.00% |  |
AFUDC accrual recorded, percentage earning a return as part of rate base |  | 50.00% |  |
AFUDC rates, projects with approval, percent |  | 100.00% |  |
Alliant Energy Finance, LLC [Member] | Non-utility wind farm in Oklahoma [Member] |  |  |  |
General: |  |  |  |
Ownership interest |  | 50.00% |  |
Electric capacity of wind farm (in megawatts) | MW |  | 225 |  |
Sheboygan Falls Energy Facility [Member] |  |  |  |
General: |  |  |  |
Fossil-fueled EGU capacity (in megawatts) | MW |  | 347 |  |
Electric - generation [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation, percent |  | 3.30% | 3.30% | 3.40%
Electric - generation [Member] | WPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation, percent |  | 3.40% | 3.00% | 3.40%
Electric - distribution [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation, percent |  | 2.80% | 2.80% | 2.80%
Electric - distribution [Member] | WPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation, percent |  | 2.70% | 2.70% | 2.50%
Forecast [Member] | Electric - generation [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation, percent | 3.80% |  |  |
Forecast [Member] | Electric - distribution [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation, percent | 3.00% |  |  |

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