Commitments And Contingencies (Narrative) (Details) $ in Millions	12 Months Ended
	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.