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Commitments And Contingencies (Narrative) (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2019 USD ($)
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | $ 1,351 |
Present value abandonment obligation | 37 |
IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 752 |
Indemnification obligations, maximum | 17 |
WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 586 |
Capital Purchase Obligation [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 65 |
Capital Purchase Obligation [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 33 |
Capital Purchase Obligation [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 32 |
Purchased Power [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 221 | [1]
Purchased Power [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 219 | [1]
Purchased Power [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 2 | [1]
Indemnification Agreement [Member] |  |
Commitments and Contingencies [Line Items] |  |
Indemnification obligations, maximum | 90 |
Indemnification Agreement [Member] | Purchased Power [Member] |  |
Commitments and Contingencies [Line Items] |  |
Indemnification obligations, maximum | $ 17 |
Workforce Subject to Collective Bargaining Arrangements [Member] |  |
Commitments and Contingencies [Line Items] |  |
Employees covered by collective bargaining agreement | 55.00% |
Workforce Subject to Collective Bargaining Arrangements [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Employees covered by collective bargaining agreement | 62.00% |
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 | 26.00% |
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Employees covered by collective bargaining agreement | 82.00% |
[1] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. As a result of amendments to shorten the term of the DAEC PPA, which were approved by the IUB and effective in January 2019, 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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