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Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 USD ($) customer MW | Dec. 31, 2019 USD ($)
Cash, Cash Equivalents and Restricted Cash [Abstract] |  |
Money market fund investments | $ 44 | $ 5
Money market fund investments interest rate, percentage | 0.04% |
New Accounting Standards: |  |
New accounting standard, cumulative effect adjustment to retained earnings, after-tax | $ (2,994) | (2,766)
Cumulative Effect, Period of Adoption, Adjustment [Member] |  |
New Accounting Standards: |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  | 12
New accounting standard, cumulative effect adjustment to retained earnings, after-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 | $ 44 | 5
Money market fund investments interest rate, percentage | 0.04% |
Property, Plant and Equipment: |  |
AFUDC accrual recorded, percentage of estimated CWIP | 100.00% |
New Accounting Standards: |  |
New accounting standard, cumulative effect adjustment to retained earnings, after-tax | $ (979) | (891)
WPL [Member] |  |
Property, Plant and Equipment: |  |
AFUDC accrual recorded, percentage of estimated CWIP | 50.00% |
AFUDC rates, projects with approval | 100.00% |
New Accounting Standards: |  |
New accounting standard, cumulative effect adjustment to retained earnings, after-tax | $ (953) | $ (864)
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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