Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 37,261	$ 41,529
Other comprehensive gain (loss) before reclassifications	(167)	2
Amounts reclassified from accumulated other comprehensive loss	128	183
Income taxes		(2)
Net other comprehensive income	(39)	183
Balance	36,948	40,010
Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,139)	(2,136)
Other comprehensive gain (loss) before reclassifications	(128)	49
Net other comprehensive income	(128)	49
Balance	(2,267)	(2,087)
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	13	21
Other comprehensive gain (loss) before reclassifications	(33)	(66)
Net other comprehensive income	(33)	(66)
Balance	(20)	(45)
Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	3	(19)
Other comprehensive gain (loss) before reclassifications	(6)	19
Amounts reclassified from accumulated other comprehensive loss	(2)	4
Net other comprehensive income	(8)	23
Balance	(5)	4
Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,151)	(2,509)
Amounts reclassified from accumulated other comprehensive loss	130	179
Income taxes		(2)
Net other comprehensive income	130	177
Balance	(2,021)	(2,332)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(4,274)	(4,643)
Balance	$ (4,313)	$ (4,460)