Derivatives - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) on commodity derivatives	$ 16	$ (152)	$ (75)	$ (254)
Commodity
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) on commodity derivatives	11	(45)	(102)	(88)
Net gain (loss) on settlements, net	5	(107)	27	(166)
Operating Segments | United States E&P
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) on commodity derivatives	$ 5	$ (107)	$ 27	$ (166)