Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 648	$ 422	$ 648	$ 463
Average amount outstanding (based on daily outstanding balances)	$ 560	$ 252	$ 479	$ 252
Weighted average interest rates	0.20%	0.20%	0.20%	1.10%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 8	$ 0	$ 19	$ 8
Average amount outstanding (based on daily outstanding balances)	$ 0	0	$ 0	$ 0
Weighted average interest rates	0.20%		0.20%	0.50%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 320	139	$ 320	$ 212
Average amount outstanding (based on daily outstanding balances)	$ 221	$ 83	$ 196	$ 86
Weighted average interest rates	0.10%	0.20%	0.10%	1.20%