Pension and Other Postretirement Benefits - Schedule of Obligations and Funded Status (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 11,833	$ 10,421
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	13,730
Service cost	166	194	186
Interest cost	630	602	639
Settlements	26	9
Benefit obligation at end of year	15,019	13,730
Funded status	(3,302)	(3,150)
Less: Amounts attributed to joint venture partners	(33)	(25)
Net funded status	(3,269)	(3,125)
Noncurrent assets	53	88
Current liabilities	(31)	(30)
Noncurrent liabilities	(3,291)	(3,183)
Net amount recognized	(3,269)	(3,125)
Net actuarial loss	5,379	5,198
Prior service cost (benefit)	102	94
Total, before tax effect	5,481	5,292
Less: Amounts attributed to joint venture partners	43	38
Net amount recognized, before tax effect	5,438	5,254
Net actuarial (gain) loss	572	(193)
Amortization of accumulated net actuarial loss	(391)	(489)	(384)
Prior service cost	26
Amortization of prior service (cost) benefit	(18)	(25)
Total, before tax effect	189	(707)
Less: Amounts attributed to joint venture partners	5	(16)
Net amount recognized, before tax effect	184	(691)
Pension Benefits [Member] | Change in Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	13,730	14,751
Service cost	182	213
Interest cost	640	611
Amendments	33	82
Actuarial (gains) losses	1,552	(849)
Acquisitions	455
Divestitures	(142)
Settlements	(134)	(13)
Benefits paid	(1,051)	(841)
Foreign currency translation impact	(246)	(224)
Benefit obligation at end of year	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	10,580	11,043
Actual return on plan assets	1,764	109
Employer contributions	507	473
Participants' contributions	25	27
Settlements	(134)	(17)
Benefits paid	(1,038)	(825)
Administrative expenses	(54)	(40)
Acquisitions	431
Divestitures	(164)
Foreign currency translation impact	(200)	(190)
Fair value of plan assets at end of year	11,717	10,580
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	15	17	14
Interest cost	114	114	131
Funded status	(2,368)	(2,592)
Less: Amounts attributed to joint venture partners		(4)
Net funded status	(2,368)	(2,588)
Current liabilities	(213)	(234)
Noncurrent liabilities	(2,155)	(2,354)
Net amount recognized	(2,368)	(2,588)
Net actuarial loss	392	389
Prior service cost (benefit)	(144)	(57)
Total, before tax effect	248	332
Less: Amounts attributed to joint venture partners		(1)
Net amount recognized, before tax effect	248	333
Net actuarial (gain) loss	15	(169)
Amortization of accumulated net actuarial loss	(13)	(35)	(25)
Prior service cost	(112)
Amortization of prior service (cost) benefit	25	19
Total, before tax effect	(85)	(185)
Net amount recognized, before tax effect	(85)	(185)
Other Postretirement Benefits [Member] | Change in Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	2,592	2,863
Service cost	15	17
Interest cost	114	114
Amendments	(111)
Actuarial (gains) losses	16	(170)
Divestitures	(10)
Benefits paid	(264)	(249)
Medicare Part D subsidy receipts	19	20
Foreign currency translation impact	(3)	(3)
Benefit obligation at end of year	$ 2,368	$ 2,592