Leases (Lease Cost and Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 95	$ 97	$ 189	$ 189
Short-term lease cost	2	1	3	2
Variable lease cost	26	27	63	64
Sublease income	(5)	(5)	(13)	(10)
Net lease cost	$ 118	$ 120	242	245
Operating cash outflows from operating leases			204	197
Right of use assets obtained in exchange for new operating lease liabilities			$ 251	$ 129
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	9 years 1 month 6 days	8 years 6 months	9 years 1 month 6 days	8 years 6 months
Weighted-average discount rate, percent	2.76%	3.05%	2.76%	3.05%