Debt - Changes to Debt (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 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	4,584	$ 16,009
Proceeds from asset-backed long-term borrowings	1,716	2,878
Repayments of long-term borrowings and capital leases obligations	(6,568)	(10,294)
Repayments of asset-backed long-term borrowings	(2,000)	0
Decrease in short-term obligations, excluding current maturities	(210)	$ (152)
Reclassifications of long-term debt	0
Other	23
Debt Maturing within One Year, ending balance	5,466
Long-term Debt, ending balance	109,174
Total debt, ending balance	114,640
Long-term Debt
Changes To Debt [Roll Forward]
Long-term Debt, beginning balance	113,642
Proceeds from long-term borrowings	4,337
Proceeds from asset-backed long-term borrowings	1,716
Repayments of long-term borrowings and capital leases obligations	(6,051)
Repayments of asset-backed long-term borrowings	(311)
Decrease in short-term obligations, excluding current maturities	0
Reclassifications of long-term debt	(3,508)
Other	(651)
Long-term Debt, ending balance	109,174
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	(517)
Repayments of asset-backed long-term borrowings	(1,689)
Decrease in short-term obligations, excluding current maturities	(210)
Reclassifications of long-term debt	3,508
Other	674
Debt Maturing within One Year, ending balance	$ 5,466