EME Liquidity and Restructuring Activities (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Restructuring Cost and Reserve [Line Items]
Cash and cash equivalents	$ 1,080,000,000	$ 1,390,000,000	$ 1,280,000,000	$ 1,261,000,000
Edison Mission Energy
Restructuring Cost and Reserve [Line Items]
Corporate cash and cash equivalents, without contractual dividend restrictions	627,000,000
Unsecured notes outstanding	3,700,000,000
Unsecured bonds, general grace period (in days)	30 days
Investment in consolidated subsidiary Edison Mission Energy	1,240,000,000
Accumulated other comprehensive loss, due to deconsolidation	128,000,000
Edison Mission Energy | Unsecured Notes Maturing June 2013
Restructuring Cost and Reserve [Line Items]
Unsecured notes outstanding	500,000,000
Edison Mission Energy | Bonds due 2017, 2019 and 2027 | Interest Payment Due November 15, 2012
Restructuring Cost and Reserve [Line Items]
Interest payments due	97,000,000
Midwest Generation LLC.
Restructuring Cost and Reserve [Line Items]
Cash and cash equivalents	$ 142,000,000