Derivative and Hedging Activities Derivative and Hedging Activities - Oil, Natural Gas and NGL Revenues Table (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Oil and Gas Revenue	$ 1,049	$ 1,048	$ 3,275	$ 2,744
Oil and Gas Sales Revenue	979	1,177	3,727	2,610
Oil, Natural Gas and NGL Sales [Member]
Derivative [Line Items]
Gain (Loss) on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net	(8)	(7)	(25)	(24)
Oil, Natural Gas and NGL Sales [Member] | Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (62)	$ 136	$ 477	$ (110)