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Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2017
Cumulative Effect, Period of Adoption, Adjustment [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  | $ 12 |
Whiting Petroleum Affiliate [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Partnership share, percent | 6.00% |  |
Obligations, maximum | $ 68 |  |
Credit loss liability | 5 |  |
Credit loss expense | 7 |  |
Capital Purchase Commitment [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Minimum future commitments | 8 |  |
WPL [Member] | Capital Purchase Commitment [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Minimum future commitments | 7 |  |
Indemnification Agreement [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Obligations, maximum | 74 |  |
Indemnification Agreement [Member] | Purchased Power [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Obligations, maximum | 17 |  |
FERC [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Base return on equity, percentage |  | 9.88% | 10.02%
FERC [Member] | IPL [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Refunds related to MISO base return on equity complaints | 15 |  |
FERC [Member] | WPL [Member] |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Refunds related to MISO base return on equity complaints | $ 5 |  |

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