Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounts Receivable [Line Items]
Customer	$ 101	$ 92
Unbilled utility revenues	82	82
Deferred proceeds	188	188
Other	59	47
Allowance for expected credit losses	(18)	(7)
Accounts receivable, less allowance for expected credit losses	412	402
IPL [Member]
Accounts Receivable [Line Items]
Customer	0	0
Unbilled utility revenues	0	0
Deferred proceeds	188	188
Other	23	16
Allowance for expected credit losses	(1)	(1)
Accounts receivable, less allowance for expected credit losses	210	203
WPL [Member]
Accounts Receivable [Line Items]
Customer	92	84
Unbilled utility revenues	82	82
Other	35	31
Allowance for expected credit losses	(17)	(6)
Accounts receivable, less allowance for expected credit losses	$ 192	$ 191