Shareholders' Equity - Accumulated Other Comprehensive Loss, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 86,893
Other comprehensive income/(loss) adjustments, net of tax	(154)	$ (65)
Ending balance	86,917		$ 86,893
Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(647)	(587)	(587)
Other comprehensive income/(loss) adjustments, net of tax	(16)		(60)
Ending balance	(663)		(647)
Debt Valuation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(239)	305	305
Other comprehensive income/(loss) adjustments, net of tax	(139)		(544)
Ending balance	(378)		(239)
Pension and Postretirement Liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(330)	(131)	(131)
Other comprehensive income/(loss) adjustments, net of tax	1		(199)
Ending balance	(329)		(330)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,216)	(718)	(718)
Other comprehensive income/(loss) adjustments, net of tax	(154)		(803)
Ending balance	$ (1,370)		(1,216)
Accumulated Other Comprehensive Loss [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (413)	$ (413)