Commitments and Contingencies (Commitments) (Details) (USD $)						1 Months Ended			1 Months Ended		9 Months Ended
	Sep. 30, 2012 Southern California Edison Environmental Indemnities	Sep. 30, 2012 Southern California Edison Operating Leases, Purchase Power Agreements	Sep. 30, 2012 Southern California Edison Power Purchase Contracts	Sep. 30, 2012 Edison Mission Group	Sep. 30, 2012 Edison Mission Energy Indemnities under International Asset Sale Agreements	Oct. 31, 2012 Homer City	Apr. 30, 2012 Homer City	Sep. 30, 2012 Homer City Senior Rent Reserve Letter of Credit	Feb. 20, 2003 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement	Sep. 30, 2012 Midwest Generation LLC. Environmental Indemnities under Acquisition Agreement claims	Sep. 30, 2012 Midwest Generation LLC. Coal Transportation Agreements
Third-Party Power Purchase Agreements
Estimated additional commitments, 2014			$ 17,000,000
Estimated additional commitments, 2015		21,000,000	43,000,000
Estimated additional commitments, 2016		45,000,000	66,000,000
Estimated additional commitments, thereafter		942,000,000	970,000,000
Coal Transportation Commitments
Coal transportation agreements, aggregate											2,300,000,000
Coal transportation agreements, remainder of 2012											118,000,000
Coal transportation agreements, 2013											292,000,000
Coal transportation agreements, 2014											286,000,000
Coal transportation agreements, 2015											260,000,000
Coal transportation agreements, 2016											260,000,000
Coal transportation agreements, thereafter											1,100,000,000
Firm commitments for capital expenditures, remainder of 2012				92,000,000
Firm commitments for capital expenditures, 2013				44,000,000
Firm commitments for capital expenditures, 2015				17,000,000
Guarantees and Indemnities
Percentage reimbursement obligation for asbestos claims (as a percent)									50.00%
Term of asbestos supplemental agreement (in years)									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)										230
Liability under indemnities					20,000,000					53,000,000
Maximum liability under indemnity per Mountainview purchase agreement for damages and other amounts	60,000,000
Senior rent payment						47,000,000	48,000,000
Equity rent payment							65,000,000
Rent Reserve Letter Of Credit Outstanding Amount								$ 48,000,000