Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Change in Benefit Obligation Table (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Pension Plans, Defined Benefit [Member]
Change in benefit obligation
Benefit obligation at beginning of year	$ 2,528	[1]	$ 2,158
Service cost	118		99		$ 85
Interest cost	101		99		78
Plan amendments	0		0
Actuarial (gain) loss	(115)		337
Participant contributions	0		1
Benefit payments	(194)		(159)
Foreign-currency exchange-rate changes	(7)		(7)
Benefit obligation at end of year (1)	2,431	[1]	2,528	[1]	2,158
Accumulated benefit obligation for all defined-benefit pension plans	2,100		2,100
Other Postretirement Benefit Plans, Defined Benefit [Member]
Change in benefit obligation
Benefit obligation at beginning of year	373		294
Service cost	9		7		9
Interest cost	15		15		14
Plan amendments	(89)		0
Actuarial (gain) loss	(27)		72
Participant contributions	5		4
Benefit payments	(20)		(19)
Foreign-currency exchange-rate changes	0		0
Benefit obligation at end of year (1)	$ 266		$ 373		$ 294

[1] The accumulated benefit obligation for all defined-benefit pension plans was $2.1 billion at both December 31, 2015 and December 31, 2014.