Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Contingency [Line Items]
Income from operations before income taxes	$ (458)	$ (313)	$ (586)	$ (1,118)
Income tax provision (benefit)	$ 141	$ (107)	$ 216	$ (414)
Effective Income Tax Rate Reconciliation, Percent	31.00%	(34.00%)	37.00%	(37.00%)
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ (160)	$ (109)	$ (205)	$ (390)
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount	31	(8)	29	(39)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	228	11	361	17
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	0	(2)	(13)	(4)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	$ 42	$ 1	$ 44	$ 2
Effective income tax rate excluding Libya	7.00%	(31.00%)	5.00%	(35.00%)
Libya, Dinars
Income Tax Contingency [Line Items]
Income tax provision (benefit)	$ 102	$ (16)	$ 179	$ (39)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			90.00%
Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Deferred Tax Assets, Valuation Allowance	41		$ 41
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Valuation Allowances and Reserves, Additions for Charges to Cost and Expense	228		361
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Deferred Foreign Income Tax Expense (Benefit)	31		29
Foreign Tax Authority [Member] | UK Government [Member]
Income Tax Contingency [Line Items]
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	130		$ 130
UNITED STATES
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
ALASKA
Income Tax Contingency [Line Items]
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	$ 13		$ 13