Reorganization and Business Transformation (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 12	$ 23
Cash payments for restructuring	16	11
Restructuring Reserve [Roll Forward]
Balance at December 31, 2018	12
Expense accruals	6
Cash payments	(16)	(11)
Balance at June 30, 2019	2	12
Accelerated depreciation	6
Employee separation benefits costs related to headquarter transition and business transformation
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring	13
Restructuring Reserve [Roll Forward]
Balance at December 31, 2018	11
Expense accruals	4
Cash payments	(13)
Balance at June 30, 2019	2	11
Transition support and other exit related costs for the headquarter transition and business transformation
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring	3
Restructuring Reserve [Roll Forward]
Balance at December 31, 2018	1
Expense accruals	2
Cash payments	(3)
Balance at June 30, 2019	0	$ 1
Minimum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost	35
Maximum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost	$ 40