Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012		Dec. 31, 2011
Property, plant and equipment:
Gross property, plant and equipment	$ 5,191	$ 5,947
Less accumulated depreciation and amortization	1,314	1,431
Net property, plant and equipment	3,877	4,516
Construction work in progress related to new gas and wind projects under construction		466
Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	2,534	3,338
Less accumulated depreciation and amortization	1,011	1,260
Net property, plant and equipment	1,523	2,078
Land
Property, plant and equipment:
Gross property, plant and equipment	34	36
Land | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	31	32
Power plant facilities
Property, plant and equipment:
Gross property, plant and equipment	4,453	4,612
Power plant facilities | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	613	1,293
Leasehold improvements
Property, plant and equipment:
Gross property, plant and equipment	4	4
Leasehold improvements | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	0	0
Emission allowances
Property, plant and equipment:
Gross property, plant and equipment	541	672
Emission allowances | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	496	639
Construction in progress
Property, plant and equipment:
Gross property, plant and equipment	54	495	[1]
Construction in progress | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	53	28
Equipment, furniture and fixtures
Property, plant and equipment:
Gross property, plant and equipment	105	128
Equipment, furniture and fixtures | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	8	13
Plant and equipment under lease financing
Property, plant and equipment:
Gross property, plant and equipment	0	0
Plant and equipment under lease financing | Midwest Generation LLC [Member]
Property, plant and equipment:
Gross property, plant and equipment	1,333	1,333
Amortization expense	42	42		42
Accumulated depreciation on sale leaseback transactions	555	514
Power sales agreements
Property, plant and equipment:
Gross property, plant and equipment	1,700
Less accumulated depreciation and amortization	$ 362

[1] Included $466 million at December 31, 2012 for EME's new gas and wind projects under construction.