Stockholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 41,529	$ 35,905	$ 38,049
Other comprehensive income (loss) before reclassifications	145	(452)	(960)
Amounts reclassified from accumulated other comprehensive loss	239	380	682
Income taxes	(15)	(13)	(74)
Balance	37,261	41,529	35,905
Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,136)	(2,053)	(1,531)
Other comprehensive income (loss) before reclassifications	(3)	(83)	(522)
Balance	(2,139)	(2,136)	(2,053)
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	21		10
Other comprehensive income (loss) before reclassifications	(8)	21	(50)
Amounts reclassified from accumulated other comprehensive loss			40
Balance	13	21
Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(19)	(39)	(96)
Other comprehensive income (loss) before reclassifications	22	(101)	(178)
Amounts reclassified from accumulated other comprehensive loss		121	235
Balance	3	(19)	(39)
Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,509)	(2,466)	(2,589)
Other comprehensive income (loss) before reclassifications	134	(289)	(210)
Amounts reclassified from accumulated other comprehensive loss	239	259	407
Income taxes	(15)	(13)	(74)
Balance	(2,151)	(2,509)	(2,466)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(4,643)	(4,558)	(4,206)
Balance	$ (4,274)	$ (4,643)	$ (4,558)