Commitments and Contingencies (Lease Commitments) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended		0 Months Ended	12 Months Ended
	Dec. 31, 2013		Jan. 02, 2013	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011	Jan. 02, 2014	Jul. 02, 2013
Commitments and Guarantees
Capital Leased Assets, Gross						$ 4
Future minimum payments for lease financing:
Operating lease expense				102		108	110
Capital leases, accumulated amortization						1
Midwest Generation LLC [Member]
Commitments and Guarantees
Capital Leased Assets, Gross						4
Future minimum payments for lease financing:
Operating lease expense				7		14	16
Lease payments not paid			76					76	76
Rent paid for sales leaseback transaction	10		7	30
Capital leases, accumulated amortization						1
Current portion of lease financings	0			0		6
Powerton and Joliet Power Stations
Future minimum payments for operating leases:
Operating Leases, 2014	272	[1]		272	[1]
Operating Leases, 2015	67	[1]		67	[1]
Operating Leases, 2016	26	[1]		26	[1]
Operating Leases, 2017	1	[1]		1	[1]
Operating Leases, 2018	1	[1]		1	[1]
Operating Leases, thereafter	239	[1]		239	[1]
Operating Leases, total future commitments	606	[1]		606	[1]
Other Operating Leases
Future minimum payments for operating leases:
Operating Leases, 2014	15			15
Operating Leases, 2015	12			12
Operating Leases, 2016	10			10
Operating Leases, 2017	10			10
Operating Leases, 2018	8			8
Operating Leases, thereafter	115			115
Operating Leases, total future commitments	170			170
Other Operating Leases | Midwest Generation LLC [Member]
Future minimum payments for operating leases:
Operating Leases, 2014	2			2
Operating Leases, 2015	1			1
Operating Leases, 2016	1			1
Operating Leases, 2017	0			0
Operating Leases, 2018	0			0
Operating Leases, thereafter	0			0
Operating Leases, total future commitments	4			4
LSTC
Future minimum payments for operating leases:
Operating Leases, 2014	32			32
Operating Leases, 2015	0			0
Operating Leases, 2016	0			0
Operating Leases, 2017	0			0
Operating Leases, 2018	0			0
Operating Leases, thereafter	0			0
Operating Leases, total future commitments	32			32
LSTC | Midwest Generation LLC [Member]
Future minimum payments for lease financing:
LSTC, 2014	283			283
LSTC, 2015	59			59
LSTC, 2016	23			23
LSTC, 2017	0			0
LSTC, 2018	0			0
LSTC, thereafter	101			101
LSTC, total future commitments	466			466
Railcars | Midwest Generation LLC [Member]
Future minimum payments for lease financing:
Number of units under rejected operating lease contract	2,282			2,282
Barges | Midwest Generation LLC [Member]
Future minimum payments for lease financing:
Number of units under rejected operating lease contract	11			11
Accrued Liabilities and Other
Future minimum payments for lease financing:
Current portion of lease financings						1
Other Long-Term Liabilities
Future minimum payments for lease financing:
Lease financings, net of current portion						2
Current Portion of Lease Financings | Midwest Generation LLC [Member]
Future minimum payments for lease financing:
Current portion of lease financings						1
Lease Financings, Net of Current Portion | Midwest Generation LLC [Member]
Future minimum payments for lease financing:
Lease financings, net of current portion						$ 2

[1] Reflects principal and interest payments related to the Powerton and Joliet Sale Leaseback.