Summary of Significant Accounting Policies (Notes Receivable From Related Party) (Details) (Midwest Generation LLC, USD $) In Millions, unless otherwise specified			0 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jan. 02, 2013 Edison Mission Energy	Jun. 30, 2013 Notes Receivable Edison Mission Energy	Jun. 30, 2012 Notes Receivable Edison Mission Energy	Jun. 30, 2013 Notes Receivable Edison Mission Energy	Jun. 30, 2012 Notes Receivable Edison Mission Energy
Related Party Transaction [Line Items]
Current portion of notes receivable from affiliate, gross	$ 19	$ 12
Current portion of notes receivable from affiliate, valuation allowance	(19)	(12)
Current portion of notes receivable from affiliate, carrying value	0	0
Interest receivable from affiliate, gross	55	55
Interest receivable from affiliate, valuation allowance	(55)	(55)
Interest receivable from affiliate, carrying value	0	0
Notes receivable from affiliate, gross	1,304	1,311
Notes receivable from affiliate, valuation allowance	(1,304)	(1,311)
Notes receivable from affiliate, carrying value	0	0
Total due from affiliates, gross	1,378	1,378
Total due from affiliates, valuation allowance	1,378	1,378
Total due from affiliates, carrying amount	0	0
Interest income from related parties				0	27	0	55
Debt principal and interest payment			$ 61