Leases (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leased Assets [Line Items]
Operating Lease, Right-of-Use Asset	$ 1,102	$ 971
Operating Lease, Liability, Current	261	215
Operating Lease, Liability, Noncurrent	$ 863	$ 781
Minimum [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Renewal Term	10 months
Maximum [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Renewal Term	49 years