Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Effective income tax expense (benefit) rate from continuing operations	29.00%	31.00%	31.00%	37.00%
Deferred tax expense from reduction in estimated costs for U.K. asset retirement obligation	$ 76		$ 76
Income tax provision (benefit)	103	$ 141	$ 315	$ 216
Effective income tax rate excluding Libya			17.00%	5.00%
Income tax receivable related to refundable AMT credits	$ 136		$ 136
Foreign Tax Authority | Libya Tax Authority
Income Tax Contingency [Line Items]
Income tax provision (benefit)		102	$ 162	$ 179
Domestic Tax Authority
Income Tax Contingency [Line Items]
Tax benefit from settlement with taxing authority		$ 13		$ 13