Environmental Developments (Details) (Midwest Generation LLC, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Joliet unit 6
Environmental developments
Estimated cost of retrofitting	$ 75
Joliet Unit 7
Environmental developments
Estimated cost of retrofitting	111
Joliet Unit 8
Environmental developments
Estimated cost of retrofitting	124
Powerton 5
Environmental developments
Estimated cost of retrofitting	127
Powerton 6
Environmental developments
Estimated cost of retrofitting	69
Waukegan Station 7
Environmental developments
Estimated cost of retrofitting	59
Waukegan Station 8
Environmental developments
Estimated cost of retrofitting	64
Will County 3
Environmental developments
Estimated cost of retrofitting	104
Will County 4
Environmental developments
Estimated cost of retrofitting	$ 90