Derivative and Hedging Activities Derivative and Hedging Activities - Oil, Natural Gas and NGL Revenues Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Oil and Gas Revenue	$ 4,574	$ 3,866	$ 4,767
Oil, natural gas and NGL	4,985	3,288	5,391
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	(34)	(33)	(37)
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	$ 445	$ (545)	$ 661