Commitments and Contingencies (Contingencies) (Details) (USD $)	1 Months Ended			1 Months Ended	3 Months Ended	1 Months Ended
	Jan. 31, 2012 Midwest Generation LLC claims	Oct. 31, 2011 Midwest Generation LLC claims	Jun. 30, 2013 Midwest Generation LLC sites	Aug. 31, 2009 Midwest Generation LLC Violation of certain operating permit requirements sites	Mar. 31, 2011 Midwest Generation LLC Violation of certain operating permit requirements claims	Jan. 31, 2011 Homer City owners residents	Jan. 31, 2011 Homer City Violations of the PSD and Title V provisions of the CAA
Contingencies
Number of coal-fired electric generating stations (in sites)				6
Penalties sought, per violation, per day, minimum end of range				$ 25,000			$ 32,500
Penalties sought, per violation, per day, maximum end of range				37,500			37,500
Number of fully dismissed claims in the complaint filed by the US EPA and the State of Illinois (in claims)					9
Number of claims in the complaint filed by the US EPA and the State of Illinois (in claims)					10
Number of complaints filed asserting claims of nuisance, negligence, trespass, and strict liability (in claims)	2
Similar number of complaints previously filed asserting claims of nuisance, negligence, trespass, and strict liability that were dismissed		2
Number of prior owners of facilities (in owners)						2
Number of plaintiffs (in residents)						2
Accrued liability for environmental remediation			$ 8,000,000
Identified sites for environmental remediation (in number of sites)			2