Leases (Assets and Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Operating right-of-use assets, net of amortization	$ 196	$ 213
Operating lease liabilities	$ 223	$ 240
Weighted average remaining lease term, operating leases	8 years 7 months 6 days	8 years 10 months 24 days
Weighted average remaining lease term, finance leases	18 years 6 months	19 years 2 months 12 days
Weighted average discount rate, operating leases	2.80%	2.90%
Weighted average discount rate, finance leases	3.10%	3.10%