Commitments and Contingencies (Sale-Leaseback Commitments) (Details) (Midwest Generation LLC [Member], USD $) In Millions, unless otherwise specified	1 Months Ended	0 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2013	Jan. 02, 2013	Dec. 31, 2013	Dec. 31, 2013	Jan. 02, 2014	Jul. 02, 2013
Sale Leaseback Transaction [Line Items]
Lease payments not paid		$ 76			$ 76	$ 76
PoJoCureAmount	147		147	147
Rent paid for sales leaseback transaction	10	7		30
Sale Leaseback Transaction, Monthly Rental Payments			3.75
Powerton-Joliet Stations, Sale-Leaseback
Sale Leaseback Transaction [Line Items]
Remaining lessor debt held by pass-through trustees	$ 345		$ 345	$ 345
Fixed interest rate				8.56%