Restructuring - Narrative (Details) $ in Millions		12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Positions	Dec. 31, 2017 USD ($) Positions	Dec. 31, 2016 USD ($)
Restructuring Plan, 2018
Restructuring Cost and Reserve [Line Items]
Workforce reduction, positions | Positions		160
Restructuring charges paid		$ 1
Restructuring Plan, 2017
Restructuring Cost and Reserve [Line Items]
Workforce reduction, positions | Positions			520
Restructuring reserves	$ 6		$ 6
Restructuring charges paid	$ 44	29	$ 5
Restructuring Plan, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserves				$ 7
Restructuring charges paid		$ 30