Basis of Presentation Basis of Presentation, Condensed Consolidated Statements of Cash Flows Restatements Table (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss	$ (17)	$ (1,214)	$ 619	$ (4,058)
Impairment of oil and natural gas properties	$ 0	497	$ 0	2,564
Scenario, Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss		(1,154)		(3,825)
Impairment of oil and natural gas properties		433		2,331
Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss		(60)		(233)
Impairment of oil and natural gas properties		$ 64		$ 233