Leasing Arrangements - Supplemental Disclosure for Statement of Cash Flows related to Operating and Finance Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating cash flows for operating leases	$ (4,813)	$ (4,392)
Operating cash flows for finance leases	(39)	(38)
Financing cash flows for finance leases	(394)	(352)
Operating lease right-of-use assets obtained in exchange for new operating lease liabilities	3,800	3,510
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 562	$ 564