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Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2021 USD ($) customer MW | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Cash, Cash Equivalents and Restricted Cash [Abstract] |  |  |
Money market fund investments | $ 32 | $ 44 |
Money market fund investments interest rate, percentage | 0.04% |  |
Current and Expected Credit Loss Estimates: |  |  |
Adoption of new accounting standard, net of tax | $ (3,250) | (2,994) |
Cumulative Effect, Period of Adoption, Adjustment [Member] |  |  |
Current and Expected Credit Loss Estimates: |  |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  |  | $ 12
Adoption of new accounting standard, net of tax |  |  | $ 9
IPL [Member] |  |  |
General: |  |  |
Generation and distribution of steam, number of customers served (in customers) | customer | 2 |  |
Electric capacity of wind farm (in megawatts) | MW | 1,000 |  |
Cash, Cash Equivalents and Restricted Cash [Abstract] |  |  |
Money market fund investments | $ 32 | 44 |
Money market fund investments interest rate, percentage | 0.04% |  |
Property, Plant and Equipment: |  |  |
AFUDC accrual recorded, percentage of estimated CWIP | 100.00% |  |
Current and Expected Credit Loss Estimates: |  |  |
Adoption of new accounting standard, net of tax | $ (929) | (979) |
WPL [Member] |  |  |
Property, Plant and Equipment: |  |  |
AFUDC accrual recorded, percentage of estimated CWIP | 50.00% |  |
AFUDC rates, projects with approval | 100.00% |  |
Current and Expected Credit Loss Estimates: |  |  |
Adoption of new accounting standard, net of tax | $ (1,053) | $ (953) |
Alliant Energy Finance, LLC [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 |  |
Finance lease, lease term | 20 years |  |

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