Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Libya statutory income tax rate	93.50%
Effective income tax rate excluding Libya	14.00%	5.00%	79.00%
Change in valuation allowance	$ (177)	$ 446	$ 1,270
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,304	1,030
Deferred tax liability, property, plant and equipment	1,018	1,332
Income tax receivable	146
Income tax receivable, current	73
Income tax receivable, noncurrent	73
Interest and penalties recorded	2	27	$ 1
Interest and penalties accrued	27	$ 25
United States
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, subject to expiration	655
Operating loss carryforwards, not subject to expiration	472
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	151
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 26