Schedule I - Condensed Financial Information Of Parent (Impairment and Other Charges) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended										1 Months Ended	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2012 Merchant Generation [Member]	Dec. 31, 2010 Merchant Generation [Member]	Dec. 31, 2012 Parent Company [Member] Merchant Generation [Member]	Dec. 31, 2010 Parent Company [Member] Merchant Generation [Member]	Jul. 31, 2011 SO2 Emission Allowances [Member]	Dec. 31, 2010 SO2 Emission Allowances [Member]	Dec. 31, 2010 SO2 Emission Allowances [Member] Parent Company [Member]
Impairment and Other Charges [Line Items]
Impairment charge on long-lived assets and related charges	$ 2,578	[1]	$ 123	[1]	$ 101	[1]	$ 1,950	$ 101	$ 1,880
Impairment charge on goodwill	0	[1]	0	[1]	420	[1]		420		345
Impairment charge on emission allowances	$ 0	[1]	$ 2	[1]	$ 68	[1]					$ 2	$ 68	$ 27

[1] Includes amounts for registrant and nonregistrant subsidiaries.