Commitments and Contingencies (Commitments) (Details) (USD $)										6 Months Ended			1 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Southern California Edison Company Environmental Indemnities	Jun. 30, 2012 Southern California Edison Company Power Purchase Agreements	Jul. 31, 2012 Southern California Edison Company Power Purchase Agreements Operating Leases, Purchase Power Contracts Subsequent Event	Jun. 30, 2012 Edison Mission Energy Indemnities under International Asset Sale Agreements	Jun. 30, 2012 Homer City	Jun. 30, 2012 Homer City Senior Secured Bonds due 2019	Jun. 30, 2012 Homer City Senior Secured Bonds due 2026	Jun. 30, 2012 Homer City Minimum	Jun. 30, 2012 Homer City Maximum	Jun. 30, 2012 Edison Mission Marketing and Trading, Inc	Feb. 20, 2003 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement	Jun. 30, 2012 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement cases	Jun. 30, 2012 Midwest Generation LLC. Coal Transportation Agreements	Jun. 30, 2012 Senior Rent Reserve Letter of Credit Homer City plant
Third-Party Power Purchase Agreements
Estimated additional commitments, 2014					$ 51,000,000
Estimated additional commitments, 2015				21,000,000	53,000,000
Estimated additional commitments, 2016				45,000,000	50,000,000
Estimated additional commitments, thereafter				944,000,000	199,000,000
Power Plant and Other Lease Commitments
Letter of credit																48,000,000
Estimated Capital Costs For SO2 Reduction Technology										700,000,000	750,000,000
Interest rate on debt (as a percent)								8.137%	8.734%
Assets	49,388,000,000	48,039,000,000					181,000,000
Liabilities	37,443,000,000	36,953,000,000					97,000,000
Intercompany accounts receivable due from Homer City												37,000,000
Guarantees and Indemnities
Percentage reimbursement obligation for asbestos claims (as a percent)													50.00%
Term of asbestos supplemental agreement													5 years
Term of asbestos supplemental agreement, automatic renewal period (in years)													1 year
Number of cases not settled and dismissed creating potential liability (in cases)														218
Liability under indemnities						27,000,000								53,000,000
Maximum liability under indemnity per Mountainview purchase agreement for damages and other amounts			60,000,000
Coal Transportation Commitments
Coal transportation agreements, aggregate															2,400,000,000
Coal transportation agreements, remainder of 2012															229,000,000
Coal transportation agreements, 2013															292,000,000
Coal transportation agreements, 2014															287,000,000
Coal transportation agreements, 2015															261,000,000
Coal transportation agreements, 2016															261,000,000
Coal transportation agreements, thereafter															$ 1,100,000,000