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		21 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020
Restructuring Reserve [Roll Forward]
Costs charged to expense	$ 9			$ 24	$ 39	$ 104
Costs charged to expense	9			24	39	104
2019 Restructuring
Restructuring Reserve [Roll Forward]
Balance, beginning	49	$ 50	$ 35		35
Costs charged to expense	9	4	23	24	36	104	$ 173
Cash payments	(7)	(5)	(8)
Non-cash charge adjustment	(3)
Balance, ending	48	49	50		48		48
Costs charged to expense	9	4	23	$ 24	36	$ 104	173
2019 Restructuring | Severance and employee-related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	49	49	32		32
Costs charged to expense	6	3	23				108
Cash payments	(7)	(3)	(6)
Non-cash charge adjustment	0
Balance, ending	48	49	49		48		48
Costs charged to expense	6	3	23				108
2019 Restructuring | Facilities and related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	0	0	0		0
Costs charged to expense	3	0	0				32
Cash payments	0	0	0
Non-cash charge adjustment	(3)
Balance, ending	0	0	0		0		0
Costs charged to expense	3	0	0				32
2019 Restructuring | Other costs
Restructuring Reserve [Roll Forward]
Balance, beginning	0	1	3		3
Costs charged to expense	0	1	0				33
Cash payments	0	(2)	(2)
Non-cash charge adjustment	0
Balance, ending	0	0	1		$ 0		0
Costs charged to expense	$ 0	$ 1	$ 0				$ 33