Derivative and Hedging Activities Derivative and Hedging Activities - Oil, Natural Gas and NGL Revenues Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Oil, natural gas and NGL revenues	$ 1,360	$ 1,147
Gains (losses) on undesignated oil, natural gas and NGL derivatives	(117)
Oil, natural gas and NGL	1,243	1,469
Oil, Natural Gas and NGL Sales [Member]
Derivative [Line Items]
Losses on terminated cash flow hedges	(10)	(10)
Oil, Natural Gas and NGL Sales [Member] | Commodity contract [Member] | Not designated as hedging instrument [Member]
Derivative [Line Items]
Gains (losses) on undesignated oil, natural gas and NGL derivatives	$ (107)	$ 332