Price Risk Management Price Risk Management (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Collateral, Master Netting Arrangements, Letters of Credit	$ 13		$ 13		$ 11
Net gain or (loss) recognized in the statement of income offset by regulatory accounting	33	$ 52	116	$ 64
Derivative, Net Liability Position, Aggregate Fair Value	274		274
Collateral Posted, Aggregate Fair Value	56		56
Letters of Credit Outstanding, Amount	44		44
Restricted Cash and Cash Equivalents, Current	12		12
Collateral cash requirement	$ 261		$ 261