Restructuring - Schedule of Accrued Restructuring Included in Accrued Expenses and Other Liabilities by Cost Type (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Balance, beginning	$ 27	$ 34	$ 0		$ 0
Costs charged to expense	24	22	57	$ 0	104	$ 0
Cash payments	(11)	(20)	(12)
Non-cash charge adjustment	(13)	(9)	(11)
Balance, ending	27	27	34		27
Severance and employee related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	26	32	0		0
Costs charged to expense	5	9	43
Cash payments	(8)	(15)	(11)
Non-cash charge adjustment	0	0	0
Balance, ending	23	26	32		23
Facilities and related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	0	0	0		0
Costs charged to expense	13	9	0
Cash payments	0	0	0
Non-cash charge adjustment	(13)	(9)	0
Balance, ending	0	0	0		0
Other costs
Restructuring Reserve [Roll Forward]
Balance, beginning	1	2	0		0
Costs charged to expense	6	4	14
Cash payments	(3)	(5)	(1)
Non-cash charge adjustment	0	0	(11)
Balance, ending	$ 4	$ 1	$ 2		$ 4