Restructuring Costs - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		15 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 3	$ 25
IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	5		$ 5	$ 6
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve				$ 18
Other segment | IT Restructuring
Restructuring Cost and Reserve [Line Items]
Expected restructuring costs	15		15
Decrease to estimated expected costs remaining	20
Restructuring costs	2		11
One-Time Termination Benefits | Other segment | IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2		7
Consulting Fees | Other segment | IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring costs	1		4
Other Restructuring Costs | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring costs	1
Contract Termination | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring costs	3
Restructuring Reserve	$ 16		$ 16