Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2010 orders	Sep. 30, 2012 zones	Jul. 05, 2012 owners	Dec. 31, 2011	Nov. 14, 2006
Regulatory Matters Disclosure [Abstract]
Under-scheduling charges					$ 4
ERCOT's number of congestion zones		4
Number of Significant Orders Issued by Authority	2
SECA charges owed by BP Energy				22
Loss Contingencies [Line Items]
Number of PJM Transmission Owners Who Filed Motion			3
Regulatory Charges Settled by Third Party			24
Regulatory Charges Settled by Third Party, Additional			$ 1