Employee Benefit Plans (Changes in Projected Benefit Obligations, Plan Assets and Funded Status) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	$ 2,965
Company contributions		$ 75
End balance	3,216	2,965
Amounts recognized in the Consolidated Balance Sheet:
Accounts payable and accrued liabilities	(85)	(85)
Other postretirement benefits	(733)	(661)
Accrued pensions	(945)	(745)
Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, Beginning of year	3,561	3,100
Service cost	24	23	$ 28
Interest cost	87	105	97
Actuarial losses - net	416	449
Benefits paid	(193)	(144)
Foreign currency translation adjustments	87	34
Settlements and curtailments	(6)	(4)
Other	(1)	(2)
Projected benefit obligation, End of year	3,975	3,561	3,100
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	2,965	2,618
Actual return on plan assets	342	409
Company contributions	17	13
Benefits paid	(164)	(111)
Plan settlements	(19)	(4)
Foreign currency translation adjustments	78	42
Other	(3)	(2)
End balance	3,216	2,965	2,618
Funded Status	(759)	(596)
Amounts recognized in the Consolidated Balance Sheet:
Other assets (long-term)	218	183
Accounts payable and accrued liabilities	(32)	(34)
Accrued pensions	(945)	(745)
Net liability recognized	(759)	(596)
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, Beginning of year	712	681
Service cost	10	8	10
Interest cost	20	26	24
Plan amendments	4	(17)
Actuarial losses - net	82	60
Benefits paid	(44)	(49)
Foreign currency translation adjustments	2	4
Other	0	(1)
Projected benefit obligation, End of year	786	712	681
Amounts recognized in the Consolidated Balance Sheet:
Accounts payable and accrued liabilities	(53)	(51)
Other postretirement benefits	(733)	(661)
Net liability recognized	(786)	(712)
United States
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Company contributions	0	0	75
United States | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, Beginning of year	1,842	1,582
Service cost	13	13
Interest cost	54	64
Actuarial losses - net	251	263
Benefits paid	(133)	(80)
Foreign currency translation adjustments	0	0
Settlements and curtailments	13	0
Other	2	0
Projected benefit obligation, End of year	2,042	1,842	1,582
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	1,304	1,140
Actual return on plan assets	144	219
Company contributions	0	0
Benefits paid	(113)	(55)
Plan settlements	0	0
Foreign currency translation adjustments	0	0
Other	0	0
End balance	1,335	1,304	1,140
Funded Status	(707)	(538)
Amounts recognized in the Consolidated Balance Sheet:
Other assets (long-term)	0	0
Accounts payable and accrued liabilities	(23)	(26)
Accrued pensions	(684)	(512)
Net liability recognized	(707)	(538)
United States | Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, Beginning of year	616	587
Service cost	9	8
Interest cost	17	23
Plan amendments	4	(17)
Actuarial losses - net	75	59
Benefits paid	(39)	(44)
Foreign currency translation adjustments	0	0
Other	0	0
Projected benefit obligation, End of year	682	616	587
Amounts recognized in the Consolidated Balance Sheet:
Accounts payable and accrued liabilities	(48)	(46)
Other postretirement benefits	(634)	(570)
Net liability recognized	(682)	(616)
International
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Company contributions	17	13	24
International | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, Beginning of year	1,719	1,518
Service cost	11	10
Interest cost	33	41
Actuarial losses - net	165	186
Benefits paid	(60)	(64)
Foreign currency translation adjustments	87	34
Settlements and curtailments	(19)	(4)
Other	(3)	(2)
Projected benefit obligation, End of year	1,933	1,719	1,518
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	1,661	1,478
Actual return on plan assets	198	190
Company contributions	17	13
Benefits paid	(51)	(56)
Plan settlements	(19)	(4)
Foreign currency translation adjustments	78	42
Other	(3)	(2)
End balance	1,881	1,661	1,478
Funded Status	(52)	(58)
Amounts recognized in the Consolidated Balance Sheet:
Other assets (long-term)	218	183
Accounts payable and accrued liabilities	(9)	(8)
Accrued pensions	(261)	(233)
Net liability recognized	(52)	(58)
International | Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, Beginning of year	96	94
Service cost	1	0
Interest cost	3	3
Plan amendments	0	0
Actuarial losses - net	7	1
Benefits paid	(5)	(5)
Foreign currency translation adjustments	2	4
Other	0	(1)
Projected benefit obligation, End of year	104	96	$ 94
Amounts recognized in the Consolidated Balance Sheet:
Accounts payable and accrued liabilities	(5)	(5)
Other postretirement benefits	(99)	(91)
Net liability recognized	$ (104)	$ (96)