Restructuring Activities (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2013 positions	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 claims	Jun. 30, 2012	Dec. 31, 2012	Dec. 16, 2012	Nov. 15, 2012
Restructuring Cost and Reserve [Line Items]
Senior notes, net		$ 3,700		$ 3,700		$ 3,700
Interest payable on liabilities subject to compromise		154		154		154	38	97
Contractual interest expense on liabilities subject to compromise not reflected in statement of operations				73
Number claims received (claims)				1,835
Provision for allowable claims		19		19
Professional fees		28		56
Total reorganization items		47	0	75	0
Number of positions eliminated	150
Severance costs		7
Midwest Generation LLC
Restructuring Cost and Reserve [Line Items]
Interest payable on liabilities subject to compromise		13		13		13
Number claims received (claims)				275
Provision for allowable claims		19		19
Professional fees		7		15
Total reorganization items		26	0	34	0
Number of positions eliminated	120
Severance costs		5
Other EME Subsidiaries
Restructuring Cost and Reserve [Line Items]
Provision for allowable claims		0		0
Professional fees		21		41
Total reorganization items		$ 21		$ 41