Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 37,261	$ 41,529
Other comprehensive gain (loss) before reclassifications	(112)	(40)
Amounts reclassified from accumulated other comprehensive loss	81	125
Net other comprehensive income	(31)	85
Balance	36,897	39,952
Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,139)	(2,136)
Other comprehensive gain (loss) before reclassifications	(81)	(26)
Net other comprehensive income	(81)	(26)
Balance	(2,220)	(2,162)
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	13	21
Other comprehensive gain (loss) before reclassifications	(21)	(25)
Net other comprehensive income	(21)	(25)
Balance	(8)	(4)
Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	3	(19)
Other comprehensive gain (loss) before reclassifications	(10)	11
Amounts reclassified from accumulated other comprehensive loss	(5)	8
Net other comprehensive income	(15)	19
Balance	(12)
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	86	117
Net other comprehensive income	86	117
Balance	(2,065)	(2,392)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(4,274)	(4,643)
Balance	$ (4,305)	$ (4,558)