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Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | $ 1,214 | $ 1,305
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 1,214 | 1,305
Fair value of plan assets | 1,011 | 984
Plans with projected benefit obligations in excess of plan assets: |  |
Projected benefit obligations | 1,251 | 1,351
Fair value of plan assets | 1,011 | 984
Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 210 | 227
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 210 | 227
Fair value of plan assets | 106 | 108
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 546 | 589
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 546 | 589
Fair value of plan assets | 462 | 453
Plans with projected benefit obligations in excess of plan assets: |  |
Projected benefit obligations | 567 | 615
Fair value of plan assets | 462 | 453
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 84 | 91
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 84 | 91
Fair value of plan assets | 74 | 74
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 532 | 573
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 532 | 573
Fair value of plan assets | 450 | 436
Plans with projected benefit obligations in excess of plan assets: |  |
Projected benefit obligations | 546 | 588
Fair value of plan assets | 450 | 436
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 81 | 89
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 81 | 89
Fair value of plan assets | $ 17 | $ 18

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