Leases - Lease Cost and Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 97	$ 100	$ 189	$ 182
Short-term lease cost	1	2	2	3
Variable lease cost	27	39	64	76
Sublease income	(5)	(4)	(10)	(8)
Net lease cost	$ 120	$ 137	245	253
Operating cash outflows from operating leases			197	187
Right of use assets obtained in exchange for new operating lease liabilities			$ 129	$ 67
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	8 years 6 months 10 days	8 years 11 months 26 days	8 years 6 months 10 days	8 years 11 months 26 days
Weighted-average discount rate	3.05%	3.08%	3.05%	3.08%