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Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
May 31, 2020 | Jun. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  |  | $ 1,270 |
IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  |  | 690 |
WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  |  | 549 |
Capital Purchase Commitment [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  |  | 60 |
Capital Purchase Commitment [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  |  | 8 |
Capital Purchase Commitment [Member] | WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  |  | 52 |
Purchased Power [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments | [1] |  |  | 39 |
Purchased Power [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments | [1] |  |  | 38 |
Purchased Power [Member] | WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments | [1] |  |  | 1 |
Indemnification Agreement [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Obligations, maximum |  |  | $ 82 | 82 |
Indemnification Agreement [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Obligations, maximum |  |  | 17 | 17 |
Indemnification Agreement [Member] | Purchased Power [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Obligations, maximum |  |  | 17 | $ 17 |
Workforce Subject to Collective Bargaining Arrangements [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Employees covered by collective bargaining agreement |  |  |  | 53.00% |
Workforce Subject to Collective Bargaining Arrangements [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Employees covered by collective bargaining agreement |  |  |  | 60.00% |
Workforce Subject to Collective Bargaining Arrangements [Member] | WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Employees covered by collective bargaining agreement |  |  |  | 82.00% |
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Employees covered by collective bargaining agreement |  |  |  | 18.00% |
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Employees covered by collective bargaining agreement |  |  |  | 44.00% |
Credit Losses ASU [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  |  |  |  | $ 12
Whiting Petroleum Affiliate [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Partnership share, percent |  |  |  | 6.00% |
Obligations, maximum |  |  | 63 | $ 63 |
Credit loss liability |  |  | 20 | 20 |
Credit loss expense |  |  | 0 | $ 8 |
Whiting Petroleum Affiliate [Member] | Credit Losses ASU [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  |  |  |  | $ 12
FederalEnergyRegulatoryCommission [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
MISO base return on equity, percentage |  | 10.02% |  |  | 9.88%
FederalEnergyRegulatoryCommission [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Refunds related to MISO base return on equity complaints |  |  | 10 |  |
FederalEnergyRegulatoryCommission [Member] | WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Refunds related to MISO base return on equity complaints |  |  | $ 3 |  |
[1] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of an amendment to shorten the term of the DAEC PPA, Alliant Energy’s and IPL’s amounts include minimum future commitments related to IPL’s purchase of capacity and the resulting energy from DAEC through September 2020, and do not include the September 2020 buyout payment of $110 million.

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