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Regulatory Matters (Narrative) (Details) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2020 USD ($) | Aug. 31, 2020 customer | Dec. 31, 2021 USD ($) MW | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets |  |  | $ 1,940 | $ 2,010 |
Credits issued to customers |  |  | (66) | (113) | $ (40)
Regulatory liabilities |  |  | 1,271 | 1,306 |
Electric transmission cost recovery [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory liabilities |  |  | 51 | 68 |
IPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets not earning a return |  |  | 75 |  |
Regulatory assets |  |  | 1,443 | 1,483 |
Credits issued to customers |  |  | $ 1 | (20) | 2
Electric capacity of wind farm (in megawatts) | MW |  |  | 1,000 |  |
Regulatory liabilities |  |  | $ 691 | 676 |
IPL [Member] | Electric transmission cost recovery [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Credits issued to customers |  |  |  | 42 |
Regulatory liabilities |  |  | 27 | 39 |
IPL [Member] | Derecho windstorm [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Number of customers without power, derecho windstorm (number of customers) | customer |  | 250,000 |  |  |
Derecho windstorm repair and rebuilding costs |  |  | 140 |  |
Net regulatory liability, derecho windstorm |  |  | 8 |  |
WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets not earning a return |  |  | 13 |  |
Regulatory assets |  |  | 497 | 527 |
Credits issued to customers |  |  | (67) | (93) | (42)
Regulatory liabilities |  |  | 580 | 630 |
WPL [Member] | Electric transmission cost recovery [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory liabilities |  |  | 24 | 29 |
2020 Test Period Retail Electric [Member] | IPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Interim rate increase (decrease), amount |  |  |  |  | $ 90
Authorized increase (decrease) in final rates, amount |  |  |  | 127 |
2020 Test Period Retail Electric [Member] | IPL [Member] | Tax-related [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory liabilities |  |  |  | 27 |
2020 Test Period Retail Electric [Member] | IPL [Member] | Revenue subject to refund [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory liabilities |  |  |  | 8 |
2020 Test Period Retail Electric [Member] | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  |  |  | $ 29 |
Authorized increase (decrease) in final rates, percentage |  |  |  | 2.00% |
2020 Test Period Retail Gas [Member] | IPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  |  |  | $ 12 |
2019 Test Period Retail Electric [Member] | WPL [Member] | Revenue subject to refund [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Credits issued to customers |  |  |  | $ 12 |
Deferred Fuel Costs | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets |  |  | $ 37 |  |
DAEC PPA [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Buyout payment | $ 110 |  |  |  |
PPA term amendment |  |  | 5 years |  |

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