Property, Plant and Equipment (Asset Retirement Obligations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 80	$ 70	$ 47
Accretion expense	6	5	5
Revisions	0	0	(1)
Liabilities added	8	5	19
Ending balance	94	80	70
Midwest Generation LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	2	2	2
Accretion expense	0	0	1
Revisions	0	0	(1)
Ending balance	2	2	2
Fair value of legally restricted assets for purposes of settling AROs	4
Plant and equipment under lease financing \| Midwest Generation LLC [Member]
Property, Plant and Equipment [Line Items]
Accumulated depreciation on sale leaseback transactions	$ 555	$ 514

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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- Definition

The accumulated depreciation and amortization related to the asset(s) sold in connection with the property sold to another party and leased back to the seller.

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