Financial Instruments and Risk Management (Earnings Impact of Realized and Unrealized Gains (Losses) On Risk Management Positions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	$ 51	$ 353	$ 901
Unrealized Gain (Loss) on Derivatives	474	(615)	(331)
Realized and Unrealized Gain (Loss) on Risk Management	525	(262)	570
Revenue [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	40	361	917
Unrealized Gain (Loss) on Derivatives	442	(636)	(325)
Realized and Unrealized Gain (Loss) on Risk Management	482	(275)	592
Transportation and Processing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	(4)	(8)	(16)
Unrealized Gain (Loss) on Derivatives		22	(6)
Realized and Unrealized Gain (Loss) on Risk Management	(4)	14	$ (22)
Foreign Currency Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gain (Loss) on Derivatives	15
Unrealized Gain (Loss) on Derivatives	32	(1)
Realized and Unrealized Gain (Loss) on Risk Management	$ 47	$ (1)