Description of Business, Accounting Policies, and Supplemental Disclosures - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Cash paid for interest on debt	$ 916	$ 875	$ 854
Cash paid for operating leases	4,475	3,361	0
Cash paid for interest on finance leases	612	647	381
Cash paid for interest on financing obligations	102	39	194
Cash paid for income taxes, net of refunds	1,713	881	1,184
Assets acquired under operating leases	16,217	7,870	0
Property and equipment acquired under finance leases	11,588	13,723	10,615
Property and equipment acquired under build-to-suit arrangements	$ 2,267	$ 1,362	$ 3,641