Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified						12 Months Ended					12 Months Ended										0 Months Ended	12 Months Ended					12 Months Ended					12 Months Ended								12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Edison Mission Operation and Maintenance, Inc	Dec. 31, 2012 Administrative Services Agreements	Dec. 31, 2011 Administrative Services Agreements	Dec. 31, 2012 Administrative Services Agreements Edison International	Dec. 31, 2011 Administrative Services Agreements Edison International	Dec. 31, 2010 Administrative Services Agreements Edison International	Dec. 31, 2012 Operation and Maintenance Agreements	Dec. 31, 2011 Operation and Maintenance Agreements	Dec. 31, 2012 Operation and Maintenance Agreements Edison Mission Operation and Maintenance, Inc	Dec. 31, 2011 Operation and Maintenance Agreements Edison Mission Operation and Maintenance, Inc	Dec. 31, 2010 Operation and Maintenance Agreements Edison Mission Operation and Maintenance, Inc	Dec. 31, 2012 Power Sales Contract Southern California Edison Company	Dec. 31, 2011 Power Sales Contract Southern California Edison Company	Dec. 31, 2010 Power Sales Contract Southern California Edison Company	Dec. 31, 2012 Power Sales Contract Walnut Creek MW	Dec. 31, 2012 Midwest Generation LLC	Dec. 31, 2011 Midwest Generation LLC	Dec. 31, 2010 Midwest Generation LLC	Jan. 02, 2013 Midwest Generation LLC Edison Mission Energy	Dec. 31, 2011 Midwest Generation LLC Edison Mission Energy	Dec. 31, 2010 Midwest Generation LLC Edison Mission Energy	Aug. 24, 2000 Midwest Generation LLC Edison Mission Energy notes_pledged	Dec. 31, 2012 Midwest Generation LLC Administrative Services Agreements	Dec. 31, 2011 Midwest Generation LLC Administrative Services Agreements	Dec. 31, 2012 Midwest Generation LLC Administrative Services Agreements Edison International	Dec. 31, 2011 Midwest Generation LLC Administrative Services Agreements Edison International	Dec. 31, 2010 Midwest Generation LLC Administrative Services Agreements Edison International	Dec. 31, 2012 Midwest Generation LLC Master Purchase, Sale and Services Agreement	Dec. 31, 2011 Midwest Generation LLC Master Purchase, Sale and Services Agreement	Dec. 31, 2012 Midwest Generation LLC Master Purchase, Sale and Services Agreement Edison Mission Marketing and Trading, Inc	Dec. 31, 2011 Midwest Generation LLC Master Purchase, Sale and Services Agreement Edison Mission Marketing and Trading, Inc	Dec. 31, 2010 Midwest Generation LLC Master Purchase, Sale and Services Agreement Edison Mission Marketing and Trading, Inc	Dec. 31, 2012 Midwest Generation LLC Notes Receivable Edison Mission Energy	Dec. 31, 2011 Midwest Generation LLC Notes Receivable Edison Mission Energy	Dec. 31, 2010 Midwest Generation LLC Notes Receivable Edison Mission Energy	Dec. 31, 2012 Midwest Generation LLC Management and Support Services Agreement	Dec. 31, 2011 Midwest Generation LLC Management and Support Services Agreement	Dec. 31, 2012 Midwest Generation LLC Management and Support Services Agreement Midwest Generation EME LLC	Dec. 31, 2011 Midwest Generation LLC Management and Support Services Agreement Midwest Generation EME LLC	Dec. 31, 2010 Midwest Generation LLC Management and Support Services Agreement Midwest Generation EME LLC
Related Party Transaction [Line Items]
Ownership percentage			50.00%
Revenues from related parties											$ 24	$ 23	$ 23	$ 233	$ 277	$ 367																$ 1	$ 1	$ 1
Receivables from affiliates	8	4							4	3								40	109											39	98
Number Of Notes Pledged																								4
Power sales contract, term of contract																	10 years
Power sales contract, output of gas-fired peaking facility (in megawatts)																	479
Intercompany notes pledged																								1,367
Fixed interest rate (percent)																								8.30%
Debt Instrument, Periodic Payment																					61
Impairment of loan to affiliate																		1,378	0	0
Interest income from related parties																																			110	111	112
Expenses, reimbursed to related party						60	60	52														14	14				27	30	18											23	24	26
Payables to affiliates	$ 34	$ 187		$ (1)	$ 13		$ 13											$ 3	$ 18						$ 1	$ 4												$ 2	$ 1