Restructuring - Schedule of Accrued Restructuring Included in Accrued Expenses and Other Liabilities by Cost Type (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		18 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020
Restructuring Reserve [Roll Forward]
Costs charged to expense	$ 6		$ 22	$ 29	$ 79
Costs charged to expense	6		22	29	79
2019 Restructuring
Restructuring Reserve [Roll Forward]
Balance, beginning	50	$ 35		35
Costs charged to expense	4	23	22	27	79	$ 164
Cash payments	(5)	(8)
Balance, ending	49	50		49		49
Costs charged to expense	4	23	$ 22	27	$ 79	164
2019 Restructuring | Severance and employee-related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	49	32		32
Costs charged to expense	3	23				102
Cash payments	(3)	(6)
Balance, ending	49	49		49		49
Costs charged to expense	3	23				102
2019 Restructuring | Facilities and related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	0	0		0
Costs charged to expense	0	0				29
Cash payments	0	0
Balance, ending	0	0		0		0
Costs charged to expense	0	0				29
2019 Restructuring | Other costs
Restructuring Reserve [Roll Forward]
Balance, beginning	1	3		3
Costs charged to expense	1	0				33
Cash payments	(2)	(2)
Balance, ending	0	1		$ 0		0
Costs charged to expense	$ 1	$ 0				$ 33