Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ (454)	$ (1,164)	$ (2,439)
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	(159)	(407)	(854)
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount	140	47	(55)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	446	1,270	95
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	(19)	9	(15)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	(35)	6	(3)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount	0	0	94
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	3	(2)	0
Income Tax Expense (Benefit)	$ 376	$ 923	$ (738)
Libya Statutory Income Tax Rate	93.50%
Effective income tax rate excluding Libya	5.00%	79.00%	29.00%
Federal
Current	$ (32)	$ 2	$ (41)
Deferred	41	836	(684)
Total	9	838	(725)
State and local
Current	(14)	2	(8)
Deferred	2	8	(18)
Total	(12)	10	(26)
Foreign
Current	483	91	115
Deferred	(104)	(16)	(102)
Total	379	75	13
Current Income Tax Expense (Benefit)	437	95	66
Deferred Income Tax Expense (Benefit)	$ (61)	$ 828	$ (804)
Effective Tax Rate Reconciliation [Abstract]
Effective income tax rate on continuing operations	83.00%	79.00%	(30.00%)