Stockholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 24,176	$ 36,586	$ 37,261
Reclassification to Retained Earnings of stranded tax effects resulting from US tax reform			(109)
Other comprehensive income (loss) before reclassifications	(576)	162	(404)
Amounts reclassified from accumulated other comprehensive loss	168	93	183
Income taxes	(38)	(71)	(18)
Balance	12,489	24,176	36,586
Currency Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,263)	(2,330)	(2,139)
Other comprehensive income (loss) before reclassifications	(239)	67	(191)
Balance	(2,502)	(2,263)	(2,330)
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	2	2	13
Other comprehensive income (loss) before reclassifications			(11)
Balance	2	2	2
Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(34)	(12)	3
Other comprehensive income (loss) before reclassifications	(90)	(32)	(16)
Amounts reclassified from accumulated other comprehensive loss	54	10	1
Balance	(70)	(34)	(12)
Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(2,143)	(2,282)	(2,151)
Reclassification to Retained Earnings of stranded tax effects resulting from US tax reform			(109)
Other comprehensive income (loss) before reclassifications	(247)	127	(186)
Amounts reclassified from accumulated other comprehensive loss	114	83	182
Income taxes	(38)	(71)	(18)
Balance	(2,314)	(2,143)	(2,282)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(4,438)	(4,622)	(4,274)
Reclassification to Retained Earnings of stranded tax effects resulting from US tax reform			(109)
Balance	$ (4,884)	$ (4,438)	$ (4,622)