Income Taxes - Deferred income taxes (assets and liabilities netted by jurisdiction) as classified in the Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred income taxes
Deferred tax assets — non-current	$ 389	$ 325
Deferred tax liabilities — non-current	(127)	(101)
Net deferred tax asset	$ 262	$ 224