Restructuring - Schedule of Accrued Restructuring Included in Accrued Expenses and Other Liabilities by Cost Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Restructuring Reserve [Roll Forward]
Costs charged to expense	$ 30	$ 23
Cumulative charges	251
2019 Restructuring
Restructuring Reserve [Roll Forward]
Balance, beginning	91
Costs charged to expense	27	$ 23
Cash payments	(10)
Non-cash charge adjustment	(4)
Balance, ending	104
Cumulative charges	246
2019 Restructuring | Severance and employee-related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	88
Costs charged to expense	24
Cash payments	(9)
Non-cash charge adjustment	(2)
Balance, ending	101
Cumulative charges	176
2019 Restructuring | Facilities and related costs
Restructuring Reserve [Roll Forward]
Balance, beginning	0
Costs charged to expense	1
Cash payments	0
Non-cash charge adjustment	(1)
Balance, ending	0
Cumulative charges	36
2019 Restructuring | Other costs
Restructuring Reserve [Roll Forward]
Balance, beginning	3
Costs charged to expense	2
Cash payments	(1)
Non-cash charge adjustment	(1)
Balance, ending	3
Cumulative charges	$ 34