Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 571	$ 271	$ 578	$ 463
Average amount outstanding (based on daily outstanding balances)	$ 452	$ 121	$ 438	$ 252
Weighted average interest rates	0.20%	0.50%	0.20%	1.50%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 19	$ 8	$ 19	$ 8
Average amount outstanding (based on daily outstanding balances)	$ 1	$ 0	$ 0	$ 0
Weighted average interest rates	0.20%	0.50%	0.20%	0.50%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 232	$ 182	$ 275	$ 212
Average amount outstanding (based on daily outstanding balances)	$ 177	$ 9	$ 183	$ 88
Weighted average interest rates	0.10%	0.50%	0.10%	1.70%