Accounting Policies and Supplemental Disclosures - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Cash paid for interest on debt	$ 179	$ 139	$ 455	$ 430	$ 942	$ 872
Cash paid for operating leases	1,577	1,086	3,217	2,115	5,577	3,929
Cash paid for interest on finance leases	129	161	286	329	569	662
Cash paid for interest on financing obligations	35	21	68	43	127	77
Cash paid for income taxes, net of refunds	1,803	486	2,604	791	3,526	1,221
Assets acquired under operating leases	5,578	3,347	9,114	5,755	19,576	10,530
Property and equipment acquired under finance leases	1,642	3,155	3,709	5,321	9,976	13,110
Property and equipment acquired under build-to-suit arrangements	$ 1,094	$ 482	$ 1,981	$ 861	$ 3,387	$ 1,504