Commitments And Contingencies (Other Purchase Obligations) (Details) - USD ($) $ in Millions		1 Months Ended		9 Months Ended
		Sep. 30, 2020	Jul. 31, 2018	Sep. 30, 2018
Commitments and Contingencies [Line Items]
Minimum future commitments				$ 2,222
Individual commitments incurred				1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				1,565
Individual commitments incurred				1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				643
Individual commitments incurred				1
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]			1,089
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]			1,063
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]			26
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				921
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				394
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments				527
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]			169
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]			84
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]			85
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]			43
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]			24
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]			$ 5
DAEC PPA [Member]
Commitments and Contingencies [Line Items]
PPA term amendment			5 years
Scenario, Forecast [Member] | DAEC PPA [Member]
Commitments and Contingencies [Line Items]
PPA buyout payment		$ 110

[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.

[2] Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of September 30, 2018 regarding expected future usage, which is subject to change.

[3] Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2018.