Commitments and Contingencies (Environmental) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended		1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Nov. 30, 2012 Homer City, Pennsylvania	Dec. 31, 2012 Homer City, Pennsylvania	Dec. 31, 2012 Duncan, Oklahoma environmental matter	Dec. 31, 2012 Superfund sites Superfund_Site
Site Contingency [Line Items]
Period since occurrence	25 years
Accrual for site contingency					$ 25	$ 6
Number of superfund sites						9
Accrual for Environmental Loss Contingencies Disclosure [Abstract]
Accrued liabilities for environmental matters		81		72
Penalty in excess of $100,000			$ 0.1