Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Administrative and General Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 47	$ 43	$ 137	$ 128
Administrative and General Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	36	33	104	100
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	23	11	50	34
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	2	7	6	16
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	93	95	251	268
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 32	$ 19	$ 91	$ 56