Debt - Changes to Debt (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Changes To Debt [Roll Forward]
Debt Maturing within One Year, beginning balance	$ 3,453
Long-term Debt, beginning balance	113,642
Total debt, beginning balance	117,095
Proceeds from long-term borrowings	5,932	$ 21,915
Proceeds from asset-backed long-term borrowings	3,216	2,878
Repayments of long-term borrowings and capital leases obligations	(9,776)	(16,457)
Repayments of asset-backed long-term borrowings	(2,915)	$ 0
Reclassifications of long-term debt	0
Other	(610)
Debt Maturing within One Year, ending balance	6,502
Long-term Debt, ending balance	106,440
Total debt, ending balance	112,942
Long-term Debt
Changes To Debt [Roll Forward]
Long-term Debt, beginning balance	113,642
Proceeds from long-term borrowings	5,685
Proceeds from asset-backed long-term borrowings	3,216
Repayments of long-term borrowings and capital leases obligations	(8,341)
Repayments of asset-backed long-term borrowings	(640)
Reclassifications of long-term debt	(6,549)
Other	(573)
Long-term Debt, ending balance	106,440
Debt Maturing within One Year
Changes To Debt [Roll Forward]
Debt Maturing within One Year, beginning balance	3,453
Proceeds from long-term borrowings	247
Proceeds from asset-backed long-term borrowings	0
Repayments of long-term borrowings and capital leases obligations	(1,435)
Repayments of asset-backed long-term borrowings	(2,275)
Reclassifications of long-term debt	6,549
Other	(37)
Debt Maturing within One Year, ending balance	$ 6,502