Commitments And Contingencies (Other Purchase Commitments) (Details) - USD ($) $ in Millions		1 Months Ended
		Sep. 30, 2020	Dec. 31, 2019
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			$ 499
Minimum future commitments, 2021			223
Minimum future commitments, 2022			160
Minimum future commitments, 2023			128
Minimum future commitments, 2024			84
Minimum future commitments, Thereafter			199
Minimum future commitments, Total			1,293
Individual commitments incurred			1
Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[1]		111
Minimum future commitments, 2021	[1]		0
Minimum future commitments, 2022	[1]		0
Minimum future commitments, 2023	[1]		0
Minimum future commitments, 2024	[1]		0
Minimum future commitments, Thereafter	[1]		0
Minimum future commitments, Total	[1]		111
Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			257
Minimum future commitments, 2021			183
Minimum future commitments, 2022			139
Minimum future commitments, 2023			109
Minimum future commitments, 2024			77
Minimum future commitments, Thereafter			187
Minimum future commitments, Total			952
Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[2]		75
Minimum future commitments, 2021	[2]		27
Minimum future commitments, 2022	[2]		10
Minimum future commitments, 2023	[2]		10
Minimum future commitments, 2024	[2]		0
Minimum future commitments, Thereafter	[2]		0
Minimum future commitments, Total	[2]		122
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[3]		56
Minimum future commitments, 2021	[3]		13
Minimum future commitments, 2022	[3]		11
Minimum future commitments, 2023	[3]		9
Minimum future commitments, 2024	[3]		7
Minimum future commitments, Thereafter	[3]		12
Minimum future commitments, Total	[3]		108
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			315
Minimum future commitments, 2021			126
Minimum future commitments, 2022			91
Minimum future commitments, 2023			80
Minimum future commitments, 2024			56
Minimum future commitments, Thereafter			99
Minimum future commitments, Total			767
IPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[1]		110
Minimum future commitments, 2021	[1]		0
Minimum future commitments, 2022	[1]		0
Minimum future commitments, 2023	[1]		0
Minimum future commitments, 2024	[1]		0
Minimum future commitments, Thereafter	[1]		0
Minimum future commitments, Total	[1]		110
IPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			135
Minimum future commitments, 2021			101
Minimum future commitments, 2022			77
Minimum future commitments, 2023			67
Minimum future commitments, 2024			55
Minimum future commitments, Thereafter			89
Minimum future commitments, Total			524
IPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[2]		46
Minimum future commitments, 2021	[2]		21
Minimum future commitments, 2022	[2]		10
Minimum future commitments, 2023	[2]		10
Minimum future commitments, 2024	[2]		0
Minimum future commitments, Thereafter	[2]		0
Minimum future commitments, Total	[2]		87
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[3]		24
Minimum future commitments, 2021	[3]		4
Minimum future commitments, 2022	[3]		4
Minimum future commitments, 2023	[3]		3
Minimum future commitments, 2024	[3]		1
Minimum future commitments, Thereafter	[3]		10
Minimum future commitments, Total	[3]		46
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			176
Minimum future commitments, 2021			89
Minimum future commitments, 2022			63
Minimum future commitments, 2023			43
Minimum future commitments, 2024			23
Minimum future commitments, Thereafter			99
Minimum future commitments, Total			493
WPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			1
Minimum future commitments, 2021			0
Minimum future commitments, 2022			0
Minimum future commitments, 2023			0
Minimum future commitments, 2024			0
Minimum future commitments, Thereafter			0
Minimum future commitments, Total			1
WPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020			122
Minimum future commitments, 2021			82
Minimum future commitments, 2022			62
Minimum future commitments, 2023			42
Minimum future commitments, 2024			22
Minimum future commitments, Thereafter			98
Minimum future commitments, Total			428
WPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[2]		29
Minimum future commitments, 2021	[2]		6
Minimum future commitments, 2022	[2]		0
Minimum future commitments, 2023	[2]		0
Minimum future commitments, 2024	[2]		0
Minimum future commitments, Thereafter	[2]		0
Minimum future commitments, Total	[2]		35
WPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2020	[3]		24
Minimum future commitments, 2021	[3]		1
Minimum future commitments, 2022	[3]		1
Minimum future commitments, 2023	[3]		1
Minimum future commitments, 2024	[3]		1
Minimum future commitments, Thereafter	[3]		1
Minimum future commitments, Total	[3]		$ 29
Forecast [Member] | DAEC PPA [Member]
Long-term Purchase Commitment [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 an amendment to shorten the term of the DAEC PPA, 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 has historically entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. Such commitments were assigned to IPL and WPL based on information available as of December 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 December 31, 2019.