Long-term Debt - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt, fair value	$ 16,200	$ 16,800
Short-term borrowings and current portion of long-term debt	1,289	3,153
Long-term debt, carrying amount	15,871	16,463
Commercial paper borrowings
Debt Instrument [Line Items]
Long-term debt, fair value	184
Short-term borrowings and current portion of long-term debt		200
Long-term debt, carrying amount	2,393	2,421
Long-term debt	$ 2,400	$ 2,600