Accounting Policies and Supplemental Disclosures - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Accounting Policies [Abstract]
Cash paid for interest on debt	$ 279	$ 276	$ 1,101	$ 902
Cash paid for operating leases	2,367	1,640	7,449	5,086
Cash paid for interest on finance leases	107	157	471	601
Cash paid for interest on financing obligations	58	33	178	113
Cash paid for income taxes, net of refunds	453	801	3,340	2,209
Assets acquired under operating leases	2,175	3,536	24,008	17,345
Property and equipment acquired under finance leases	166	2,067	5,160	11,489
Property and equipment acquired under build-to-suit lease arrangements	$ 1,332	$ 887	$ 6,061	$ 2,775