Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Contingency [Line Items]
Income tax provision (benefit)	$ 168	$ 34
Effective Income Tax Rate Reconciliation, Percent	32.00%	213.00%
Effective income tax rate excluding Libya	2.00%	16.00%
Libya, Dinars
Income Tax Contingency [Line Items]
Income tax provision (benefit)	$ 162	$ 45
ALASKA
Income Tax Contingency [Line Items]
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority		$ 13