Leases (Supplemental Balance Sheet Information) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Property leases
Operating lease ROU assets	$ 2,309	$ 2,560
Short-term operating lease liabilities	484	514
Long-term operating lease liabilities	1,862	2,078
Operating lease liabilities	$ 2,346	$ 2,592
Weighted average remaining lease term	8 years 2 months 12 days	8 years 4 months 24 days
Weighted average discount rate	3.86%	3.86%
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accounts Payable and Accrued Liabilities, Current	Accounts Payable and Accrued Liabilities, Current