Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 37	$ 43
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	32	33
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	15	15
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	2	1
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	81	84
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 20	$ 30