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Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | $ 857 | $ 857
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 857 | 857
Fair value of plan assets | 732 | 706
Plans with projected benefit obligations in excess of plan assets: |  |
Projected benefit obligations | 876 | 875
Fair value of plan assets | 732 | 706
Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 160 | 168
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 160 | 168
Fair value of plan assets | 83 | 83
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 377 | 379
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 377 | 379
Fair value of plan assets | 352 | 344
Plans with projected benefit obligations in excess of plan assets: |  |
Projected benefit obligations | 387 | 389
Fair value of plan assets | 352 | 344
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 65 | 68
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 65 | 68
Fair value of plan assets | 61 | 58
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 373 | 373
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 373 | 373
Fair value of plan assets | 306 | 291
Plans with projected benefit obligations in excess of plan assets: |  |
Projected benefit obligations | 381 | 381
Fair value of plan assets | 306 | 291
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Accumulated benefit obligations | 61 | 65
Plans with accumulated benefit obligations in excess of plan assets: |  |
Accumulated benefit obligations | 61 | 65
Fair value of plan assets | $ 14 | $ 14

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