Basis of Presentation and Significant Accounting Policies Basis of Presentation and Significant Accounting Policies, Condensed Consolidated Statements of Cash Flows Restatements Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss	$ 141	$ (1,068)
Depreciation, depletion and amortization	218	292
Impairment of oil and natural gas properties	0	997
Provision for legal contingencies	(2)	33
Net cash used in operating activities	$ 99	(421)
Scenario, Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss		(921)
Depreciation, depletion and amortization		300
Impairment of oil and natural gas properties		853
Provision for legal contingencies		22
Net cash used in operating activities		(421)
Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net loss		(147)
Depreciation, depletion and amortization		(8)
Impairment of oil and natural gas properties		144
Provision for legal contingencies		11
Net cash used in operating activities		$ 0