Commitments and Contingencies (Commitments) (Details) (USD $) In Millions, unless otherwise specified										1 Months Ended		3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Homer City plant Senior Rent Reserve Letter of Credit	Mar. 31, 2012 Southern California Edison Company	Mar. 31, 2012 Southern California Edison Company Environmental Indemnities	Mar. 31, 2012 Edison Mission Energy	Mar. 31, 2012 Edison Mission Energy Indemnities under International Asset Sale Agreements	Mar. 31, 2012 Homer City	Mar. 31, 2012 Edison Mission Marketing and Trading, Inc	Feb. 20, 2003 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement	Mar. 31, 2012 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement cases	Mar. 31, 2012 Minimum Homer City	Mar. 31, 2012 Maximum Homer City
Power Plant and Other Lease Commitments
Letter of credit			$ 48			$ 71
Estimated Capital Costs For So2 Reduction Technology												700	750
Assets	49,384	48,039						209
Liabilities	37,777	36,953						84
Intercompany accounts receivable due from Homer City									13
Guarantees and Indemnities
Percentage reimbursement obligation for asbestos claims (as a percent)										50.00%
Term of asbestos supplemental agreement										5 years
Number of cases not settled and dismissed creating potential liability (in cases)											245
Estimated liability range, minimum				3
Liability under indemnities							34				54
Maximum liability under indemnity per Mountainview purchase agreement for damages and other amounts					$ 60