Leases (Schedule of Aggregate Lease Maturities) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Future Minimum Lease Payments For Operating Leases [Abstract]
Minimum operating lease payments - 2020	$ 366
Minimum operating lease payments - 2021	293
Minimum operating lease payments - 2022	258
Minimum operating lease payments - 2023	217
Minimum operating lease payments - 2024	208
Minimum operating lease payments - later years	775
Total operating lease payments	2,117
Operating lease paymetns - amount representing interest	(284)
Operating lease liabilities - present value of minimum lease liabilities	1,833
Future Minimum Lease Payments For Finance Leases [Abstract]
Minimum finance lease payments - 2020	143
Minimum finance lease payments - 2021	147
Minimum finance lease payments - 2022	130
Minimum finance lease payments - 2023	88
Minimum finance lease payments - 2024	75
Minimum finance lease payments - later years	124
Total finance lease payments	707
Finance lease payments - amount representing interest	(102)
Finance lease liabilities - present value of minimum lease liabilities	605
Minimum lease payments - 2020	509
Minimum lease payments - 2021	440
Minimum lease payments - 2022	388
Minimum lease payments - 2023	305
Minimum lease payments - 2024	283
Minimum lease payments - later years	899
Total minimum lease payments	2,824
Lease payments - amount representing interest	(386)
Total lease liabilities	$ 2,438