Commitments And Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,222
Present value abandonment obligation	36
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,565
Indemnification obligations, maximum	17
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	643
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	82
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	26
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	56
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,089	[1]
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,063	[1]
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	26	[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

[1] Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. 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 December 2025. 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, which is not included in Alliant Energy’s and IPL’s amounts. The amendment to the DAEC PPA is contingent upon IUB approval of IPL’s July 2018 application regarding recovery of the buyout payment.