Restructuring Costs - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		18 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 2	$ 8	$ 5	$ 33
IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1		1		$ 1	$ 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		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			5		7
Consulting Fees | Other segment | IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring costs			2		4
Other Restructuring Costs | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring costs	3
Contract Termination | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	17		$ 17		$ 17
Restructuring costs	$ 4