Related Parties (Sales Credited And Purchases Billed) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
SCOA Sales Credited [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 3	$ 6	$ 7	$ 26
SCOA Sales Credited [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	4	7	10	23
SCOA Purchases Billed [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	87	93	237	238
SCOA Purchases Billed [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 13	$ 20	$ 50	$ 56