Pension and Other Postretirement Benefits - Schedule of Obligations and Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Settlements	$ (74)	$ (341)
Fair value of plan assets at beginning of year	4,591
Company's contribution		725
Fair value of plan assets at end of year	5,007	4,591
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	5,997
Service cost	48	54	$ 71
Interest cost	221	227	244
Settlements	73	410	5
Benefit obligation at end of year	6,532	5,997
Funded status	1,517	1,387
Less: Amounts attributed to joint venture partners	(34)	(33)
Net funded status	1,483	1,354
Noncurrent assets	33	63
Current liabilities	(11)	(10)
Noncurrent liabilities	(1,505)	(1,407)
Net amount recognized	(1,483)	(1,354)
Net actuarial loss	3,364	3,261
Prior service cost (benefit)	5	21
Total, before tax effect	3,369	3,282
Less: Amounts attributed to joint venture partners	42	40
Net amount recognized, before tax effect	3,327	3,242
Net actuarial loss (benefit)	350	132
Amortization of accumulated net actuarial (loss) benefit	(247)	(614)
Prior service cost (benefit)	26	(1)
Amortization of prior service (cost) benefit	(42)	(13)
Total, before tax effect	87	(496)
Less: Amounts attributed to joint venture partners	2	(5)
Net amount recognized, before tax effect	85	(491)
Pension Benefits [Member] | Change In Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	5,997	7,639
Service cost	49	60
Interest cost	226	232
Amendments	26
Actuarial losses (gains)	746	(346)
Settlements	(177)	(1,009)
Curtailments		(22)
Benefits paid	(379)	(407)
Foreign currency translation impact	44	(150)
Benefit obligation at end of year	6,532	5,997	7,639
Pension Benefits [Member] | Change In Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlements	(177)	(1,030)
Benefits paid	(379)	(403)
Foreign currency translation impact	31	(127)
Fair value of plan assets at beginning of year	4,610	5,322
Actual return on plan assets	763	(129)
Company's contribution	175	996
Participant contributions	11	12
Administrative expenses	(19)	(31)
Fair value of plan assets at end of year	5,015	4,610	5,322
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5	5
Interest cost	36	34	38
Settlements	8	(56)
Company's contribution	7	8	8
Funded status	848	973
Net funded status	848	973
Current liabilities	(99)	(105)
Noncurrent liabilities	(749)	(868)
Net amount recognized	(848)	(973)
Net actuarial loss	261	176
Prior service cost (benefit)	(154)	(4)
Total, before tax effect	107	172
Net amount recognized, before tax effect	107	172
Net actuarial loss (benefit)	103	(88)
Amortization of accumulated net actuarial (loss) benefit	(18)	(17)
Prior service cost (benefit)	(150)	(62)
Amortization of prior service (cost) benefit		88
Total, before tax effect	(65)	(79)
Net amount recognized, before tax effect	(65)	(79)
Other Postretirement Benefits [Member] | Change In Benefit Obligation [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	973	1,218
Service cost	4	5
Interest cost	36	34
Amendments	(150)	(5)
Actuarial losses (gains)	103	(88)
Settlements	(14)	(57)
Benefits paid	(111)	(140)
Medicare Part D subsidy receipts	7	7
Foreign currency translation impact		(1)
Benefit obligation at end of year	$ 848	$ 973	$ 1,218