Company Restructuring - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	$ 109	$ 30	$ 39
Employee costs
Restructuring Cost and Reserve [Line Items]
Cumulative amount incurred to date for active programs	103
Exit costs
Restructuring Cost and Reserve [Line Items]
Cumulative amount incurred to date for active programs	$ 104