Restructuring Costs (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 0	$ 5,000,000	$ 5,000,000	$ 38,000,000
IT Restructuring
Restructuring Cost and Reserve [Line Items]
Expected restructuring costs	15,000,000		15,000,000
Decrease to estimated expected costs remaining			20,000,000
Accrued liabilities under restructuring plan	0		0		$ 6,000,000
Restructuring costs			2,000,000
Cumulative restructuring costs	11,000,000		11,000,000
2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Accrued liabilities under restructuring plan					$ 18,000,000
One-Time Termination Benefits | IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring costs			5,000,000
Cumulative restructuring costs	7,000,000		7,000,000
Consulting Fees | IT Restructuring
Restructuring Cost and Reserve [Line Items]
Restructuring costs			3,000,000
Cumulative restructuring costs	4,000,000		4,000,000
Other Restructuring Costs | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Restructuring costs			3,000,000
Contract Termination | 2017 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Accrued liabilities under restructuring plan	$ 14,000,000		14,000,000
Restructuring costs			$ 7,000,000