Commitments, Contingencies and Uncertainties (Narrative) (Details)	12 Months Ended
	Dec. 31, 2012
Time to terminate contract, in Years	2 years
Number of criteria emissions established under the Clear Air Act	6
Frequency of Review by Environmental Protection Agency	5 years
Operating Lease Renewal Option, Term	25 years
Collective Bargaining Agreements Expire Date	September 2013
Minimum
Mercury and Air Toxics Standards Required Compliance Period, in Years	3 years
Maximum
Mercury and Air Toxics Standards Required Compliance Period, in Years	4 years
NRG
Long-term Purchase Commitment, Time Period	P20Y
Sun Edison 1 and Sun Edison 2
Long-term Purchase Commitment, Time Period	P25Y
Hatch Solar Energy Center I
Long-term Purchase Commitment, Time Period	P25Y
Newman Power Station [Member]
Lease Expiration Date	June 2033
Other Operating Facilities [Member]
Range Of Years Lease Agreements Expires	5 years
Warehouse Facilities [Member]
Lease Expiration Date	December 2014