Debt - Assets and Liabilities Related to Asset-backed Debt Arrangements (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Account receivable, net	$ 22,617	$ 25,429
Prepaid expenses and other	5,515	8,028
Other assets	11,669	10,141
Accounts payable and accrued liabilities	17,391	21,806
Short-term portion of long-term debt	5,770	10,777
Long-term debt	109,790	100,712
Variable Interest Entity, Primary Beneficiary
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Account receivable, net	9,438	10,525
Prepaid expenses and other	1,013	1,180
Other assets	3,011	3,856
Accounts payable and accrued liabilities	8	11
Short-term portion of long-term debt	3,589	5,578
Long-term debt	$ 6,503	$ 6,791