Restructuring Activities (Liabilities Subject to Compromise) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 16, 2012	Nov. 15, 2012
Liabilities Subject to Compromise
Senior notes, net	$ 3,700	$ 3,700
Accounts payable and accrued liabilities	53	32
Interest payable	154	154	38	97
Other	108	73
Total liabilities subject to compromise	4,015	3,959
Midwest Generation LLC [Member]
Liabilities Subject to Compromise
Accounts payable and accrued liabilities	42	29
Interest payable	11	13
Lease financing	434	434
Other	53	53
Total liabilities subject to compromise	$ 540	$ 529