Derivatives and Risk Management Activities - Offsetting (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative Asset Positions
Gross Position - Asset	$ 108	$ 280
Netting Adjustment	(350)	(38)
Cash collateral received		(156)
Cash collateral paid	410
Net Position - Asset	168	86
Derivative Liability Positions
Gross Position - Liability	(481)	(110)
Netting Adjustment	350	38
Net Position - Liability	(131)	(72)
Other current assets
Derivative Asset Positions
Net Position - Asset	167	76
Other long-term assets, net
Derivative Asset Positions
Net Position - Asset	1	10
Other current liabilities
Derivative Liability Positions
Net Position - Liability	(40)	(38)
Other long-term liabilities and deferred credits
Derivative Liability Positions
Net Position - Liability	$ (91)	$ (34)