Leases - Lease Cost and Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Leases [Abstract]
Operating lease cost	$ 92	$ 82
Short-term lease cost	1	1
Variable lease cost	37	37
Sublease income	(5)	(4)
Net lease cost	125	116
Operating cash outflows from operating leases	103	87
Right of use assets obtained in exchange for new operating lease liabilities	$ 79	$ 0
Weighted-average remaining lease term	8 years 7 months 28 days	7 years 8 months 12 days
Weighted-average discount rate	3.06%	3.12%