Derivatives and Risk Management Activities - Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivative Asset Positions
Gross Position - Asset	$ 96	$ 108
Netting adjustment	(92)	(350)
Cash collateral received	95	410
Net Position - Asset	99	168
Derivative Liability Positions
Gross Position - Liability	(183)	(481)
Netting adjustment	92	350
Net Position - Liability	(91)	(131)
Other current assets
Derivative Asset Positions
Net Position - Asset	94	167
Other long-term assets, net
Derivative Asset Positions
Net Position - Asset	5	1
Other current liabilities
Derivative Liability Positions
Net Position - Liability	(28)	(40)
Other long-term liabilities and deferred credits
Derivative Liability Positions
Net Position - Liability	$ (63)	$ (91)