CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment, accumulated depreciation (in dollars)	$ 1,431	$ 1,295
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	10,000	10,000
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100
Midwest Generation LLC
Property, Plant and Equipment, accumulated depreciation (in dollars)	$ 1,260	$ 1,152
Membership interests, no par value	$ 0	$ 0
Common stock, shares authorized	100	100
Common stock, shares issued	100	100
Common stock, shares outstanding	100	100