Pension and Other Postretirement Benefits - Schedule of Obligations and Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 11,833
Fair value of plan assets at end of year	10,926	$ 11,833
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	15,019
Service cost	175	166	$ 194
Interest cost	577	630	602
Settlements	16	26	9
Curtailments	(9)		(6)
Benefit obligation at end of year	14,247	15,019
Funded status	(3,319)	(3,302)
Less: Amounts attributed to joint venture partners	(30)	(33)
Net funded status	(3,289)	(3,269)
Noncurrent assets	44	53
Current liabilities	(35)	(31)
Noncurrent liabilities	(3,298)	(3,291)
Net amount recognized	(3,289)	(3,269)
Net actuarial loss	5,351	5,379
Prior service cost (benefit)	70	102
Total, before tax effect	5,421	5,481
Less: Amounts attributed to joint venture partners	38	43
Net amount recognized, before tax effect	5,383	5,438
Net actuarial loss	440	572
Amortization of accumulated net actuarial loss	(468)	(391)
Prior service (benefit) cost	(7)	26
Amortization of prior service (cost) benefit	(25)	(18)
Total, before tax effect	(60)	189
Less: Amounts attributed to joint venture partners	(5)	5
Net amount recognized, before tax effect	(55)	184
Pension Benefits [Member] | Change in Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	15,019	13,730
Service cost	187	182
Interest cost	583	640
Amendments	18	33
Actuarial (gains) losses	(222)	1,552
Acquisitions	188	455
Divestitures		(142)
Settlements	(72)	(134)
Curtailments	(12)
Benefits paid	(1,033)	(1,051)
Foreign currency translation impact	(409)	(246)
Benefit obligation at end of year	14,247	15,019	13,730
Pension Benefits [Member] | Change in Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	11,717	10,580
Actual return on plan assets	24	1,764
Employer contributions	479	507
Participants' contributions	21	25
Settlements	(72)	(134)
Benefits paid	(1,015)	(1,038)
Administrative expenses	(55)	(54)
Acquisitions	164	431
Divestitures		(164)
Foreign currency translation impact	(335)	(200)
Fair value of plan assets at end of year	10,928	11,717	10,580
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	15	17
Interest cost	92	114	114
Curtailments	4
Funded status	(2,319)	(2,368)
Net funded status	(2,319)	(2,368)
Current liabilities	(213)	(213)
Noncurrent liabilities	(2,106)	(2,155)
Net amount recognized	(2,319)	(2,368)
Net actuarial loss	398	392
Prior service cost (benefit)	(106)	(144)
Total, before tax effect	292	248
Net amount recognized, before tax effect	292	248
Net actuarial loss	23	15
Amortization of accumulated net actuarial loss	(17)	(13)
Prior service (benefit) cost	1	(112)
Amortization of prior service (cost) benefit	37	25
Total, before tax effect	44	(85)
Net amount recognized, before tax effect	44	(85)
Other Postretirement Benefits [Member] | Change in Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	2,368	2,592
Service cost	14	15
Interest cost	92	114
Amendments		(111)
Actuarial (gains) losses	26	16
Acquisitions	48
Divestitures		(10)
Curtailments	(6)
Benefits paid	(235)	(264)
Medicare Part D subsidy receipts	15	19
Foreign currency translation impact	(3)	(3)
Benefit obligation at end of year	$ 2,319	$ 2,368	$ 2,592