Leases (Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating right-of-use assets, net of amortization	$ 213	$ 218
Operating lease liabilities	$ 240	$ 246
Weighted average remaining lease term, operating leases	8 years 10 months 24 days	9 years 1 month 6 days
Weighted average remaining lease term, finance leases	19 years 2 months 12 days	20 years 2 months 12 days
Weighted average discount rate, operating leases	2.90%	3.20%
Weighted average discount rate, finance leases	3.10%	3.10%