Income Taxes (Narrative) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) assessment	Mar. 31, 2017	Dec. 31, 2017
Income Tax Contingency [Line Items]
Effective income tax rate	14.70%	25.80%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Effective Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Percent	21.00%
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)	$ (14)
Brazilian Federal Revenue Service [Member]
Income Tax Contingency [Line Items]
Number of separate tax assessments | assessment	3
Income tax assessment	$ 127
Income tax assessment - Interest and Penalties	348
Argentine Tax Authorities [Member]
Income Tax Contingency [Line Items]
Income tax assessment	30
Income tax assessment - Interest and Penalties	92
Estimated Additional Tax Assessment	95
Additional income tax assessment - Interest and Penalties	79
Tax and Customs Administration, Netherlands [Member]
Income Tax Contingency [Line Items]
Income tax assessment	100
Additional income tax assessment - Interest and Penalties	$ 30