Restructuring - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) position	Dec. 31, 2018 USD ($)
2019 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce reduction | position	170
Restructuring reserve balance	$ 20
Restructuring charges paid	$ 20
2018 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce reduction | position	160
Restructuring reserve balance	$ 6	$ 24
Restructuring charges paid	$ 18