Accumulated Other Comprehensive Loss - Schedule of AOCI Rollforward (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	$ (138)		$ (94)
OCI before reclassifications	67		(23)
Amount reclassified from AOCI	(10)		21
Balance, at the end of period	(61)		(138)
Commodity contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses), after-tax recorded in accumulated other comprehensive income (loss)	0		(1)
Interest rate contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses), after-tax recorded in accumulated other comprehensive income (loss)	(37)		(75)
Unrealized Gain (Losses) on Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(76)		(34)
OCI before reclassifications	34		(17)
Amount reclassified from AOCI	(5)		25
Balance, at the end of period	(37)		(76)
Unrecognized Losses and Prior Service Adjustments, Net
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(56)		(60)
OCI before reclassifications	33		0
Amount reclassified from AOCI	(5)		(4)
Balance, at the end of period	(18)		(56)
Valuation Allowance on Deferred Tax Asset
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(6)		0
OCI before reclassifications	0		(6)
Amount reclassified from AOCI	0		0
Balance, at the end of period	(6)		(6)
Midwest Generation LLC [Member]
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(50)		(17)
OCI before reclassifications	24		(9)
Amount reclassified from AOCI	(5)		24
Balance, at the end of period	(21)		(50)
Midwest Generation LLC [Member] | Unrealized Gain (Losses) on Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(1)		21
OCI before reclassifications	(1)		4
Amount reclassified from AOCI	(2)		26
Balance, at the end of period	0		(1)
Midwest Generation LLC [Member] | Unrecognized Losses and Prior Service Adjustments, Net
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(37)	[1]	(38)	[1]
OCI before reclassifications	25	[1]	(1)	[1]
Amount reclassified from AOCI	(3)	[1]	(2)	[1]
Balance, at the end of period	(9)	[1]	(37)	[1]
Midwest Generation LLC [Member] | Valuation Allowance on Deferred Tax Asset
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(12)		0
OCI before reclassifications	0		(12)
Amount reclassified from AOCI	0		0
Balance, at the end of period	$ (12)		$ (12)

[1] 1 For further detail, see Note 8—Compensation and Benefit Plans.