Restructuring - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) position	Dec. 31, 2018 USD ($)
2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce reduction | position	170
Restructuring charges paid	$ 20
Increase (decrease) in restructuring reserve	(4)
Restructuring reserve balance	$ 16
2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce reduction | position	160
Restructuring charges paid	$ 22
Restructuring reserve balance	$ 2	$ 24