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Summary of Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2013
Midwest Generation LLC [Member]
MW
Dec. 31, 2012
Midwest Generation LLC [Member]
Dec. 31, 2013
Midwest Generation LLC [Member]
Powerton, Joliet, Will County and Waukegan Stations of Midwest Generation LLC.
MW
Dec. 31, 2013
Midwest Generation LLC [Member]
Fisk and Waukegan Stations of Midwest Generation LLC.
MW
Aug. 31, 2000
Powerton and Joliet Power Stations
Midwest Generation LLC [Member]
Dec. 31, 2013
Powerton Station
Midwest Generation LLC [Member]
Dec. 31, 2013
Joliet Units 7 and 8
Midwest Generation LLC [Member]
Property, Plant and Equipment [Line Items]                  
Generating capacity (in megawatts)     4,619   4,314 305      
Debt issuance             $ 1,147    
Sale leaseback transaction lease period (years)               33 years 9 months 30 years
Write off of unamortized deferred financing costs and debt discounts $ 0 $ 15 $ 0 $ 0