Debt - Assets and Liabilities Related to Asset-backed Debt Arrangements (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Account receivable, net	$ 22,195	$ 23,917
Prepaid expenses and other	5,843	6,710
Other assets	10,679	10,879
Accounts payable and accrued liabilities	20,153	20,658
Debt maturing within one year	7,623	5,889
Long-term debt	143,352	123,173
Variable Interest Entity, Primary Beneficiary
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Account receivable, net	8,845	9,257
Prepaid expenses and other	1,073	1,128
Other assets	3,309	2,950
Accounts payable and accrued liabilities	7	8
Debt maturing within one year	4,429	4,191
Long-term debt	$ 4,996	$ 6,413