Commitments And Contingencies (Other Purchase Obligations) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended
		Sep. 30, 2020	Mar. 31, 2019
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 1,351
Individual commitments incurred			1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			752
Individual commitments incurred			1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			586
Individual commitments incurred			1
Purchased Power [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		221
Purchased Power [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		219
Purchased Power [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[1]		2
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			879
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			388
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			491
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		163
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		96
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[2]		67
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		88
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		49
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	[3]		$ 26
Scenario, Forecast [Member] | DAEC PPA [Member]
Commitments and Contingencies [Line Items]
Buyout payment		$ 110

[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.

[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 March 31, 2019 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 March 31, 2019.