Commitments and Contingencies (Contingencies) (Details) (USD $)	1 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended
	Jan. 31, 2012 claims	Oct. 31, 2011 claims	Jun. 30, 2012 sites	Aug. 31, 2009 Violation of certain operating permit requirements sites	Jun. 30, 2012 Violation of certain operating permit requirements claims	Feb. 29, 2012 Homer City Alleged violations of emissions standards and limitations under the CAA and the Pennsylvania Air Pollution Control Act	Jan. 31, 2011 Homer City Violations of the PSD and Title V provisions of the CAA residents owners
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 plaintiffs (in residents)							2
Number of prior owners of facilities (in owners)							2
Notice of intent to sue, notice time period						60 days
Accrued liability for environmental remediation			$ 9,000,000
Identified sites for environmental remediation (in number of sites)			4