Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Receivables [Line Items]
Customer	$ 95	$ 92
Unbilled utility revenues	62	82
Deferred proceeds	201	188
Other	54	47
Allowance for expected credit losses	(13)	(7)
Accounts receivable, less allowance for expected credit losses	399	402
IPL [Member]
Receivables [Line Items]
Customer	0	0
Unbilled utility revenues	0	0
Deferred proceeds	201	188
Other	20	16
Allowance for expected credit losses	(2)	(1)
Accounts receivable, less allowance for expected credit losses	219	203
WPL [Member]
Receivables [Line Items]
Customer	86	84
Unbilled utility revenues	62	82
Other	33	31
Allowance for expected credit losses	(11)	(6)
Accounts receivable, less allowance for expected credit losses	$ 170	$ 191