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Commitments And Contingencies (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($)
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 2,192 |
Present value abandonment obligation | $ 36 |
Workforce Subject to Collective Bargaining Arrangements [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Employees covered by collective bargaining agreement | 55.00% |
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Employees covered by collective bargaining agreement | 26.00% |
Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 1,045 | [1]
Capital Purchase Commitment [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 40 |
IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,546 |
Maximum indemnification limit | $ 17 |
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Employees covered by collective bargaining agreement | 63.00% |
IPL [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 1,030 | [1]
IPL [Member] | Capital Purchase Commitment [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 14 |
WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 632 |
WPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Employees covered by collective bargaining agreement | 82.00% |
WPL [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Employees covered by collective bargaining agreement | 82.00% |
WPL [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 15 |
WPL [Member] | Capital Purchase Commitment [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 26 |
Indemnification Agreement [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Maximum indemnification limit | 90 |
Indemnification Agreement [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Maximum indemnification limit | $ 17 |
[1] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. In July 2018, IPL entered into an amendment to shorten the term of the DAEC PPA by five years in exchange for a $110 million buyout payment by IPL in September 2020, subject to IUB approval. In December 2018, IPL received an order from the IUB, which was effective in January 2019, approving recovery of the buyout payment. As a result, Alliant Energy’s and IPL’s amounts in the above table do not include the September 2020 buyout payment, and the minimum future commitments reflect IPL’s purchase of capacity and the resulting energy from DAEC through December 2025, the original term of the PPA prior to the amendment. Amounts in the above table for 2021 and beyond relate to the DAEC PPA.

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