Leases (Lease Cost and Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 93	$ 99	$ 282	$ 288
Short-term lease cost	1	1	4	3
Variable lease cost	38	28	101	92
Sublease income	(3)	(5)	(16)	(15)
Net lease cost	$ 129	$ 123	371	368
Operating cash outflows from operating leases			310	306
Right of use assets obtained in exchange for new operating lease liabilities			$ 282	$ 162
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	9 years	8 years 4 months 24 days	9 years	8 years 4 months 24 days
Weighted-average discount rate, percent	2.75%	3.02%	2.75%	3.02%