Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 422	$ 472	$ 463	$ 601
Average amount outstanding (based on daily outstanding balances)	$ 252	$ 400	$ 252	$ 476
Weighted average interest rates	0.20%	2.50%	1.10%	2.60%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 0	$ 0	$ 8	$ 50
Average amount outstanding (based on daily outstanding balances)	0	0	$ 0	$ 0
Weighted average interest rates			0.50%	2.80%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	139	90	$ 212	$ 195
Average amount outstanding (based on daily outstanding balances)	$ 83	$ 27	$ 86	$ 102
Weighted average interest rates	0.20%	2.30%	1.20%	2.50%