Retirement Plans - Change in Benefit Obligation, Fair Value of Plan Assets, and Funded Status of Pension Plans and Postretirement Medical Plan (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Change in Fair Value of Plan Assets
Beginning balance	$ 2,732
Ending balance	3,043	$ 2,732
Lump-sum settlement payment included in Benefit payments	23	27
Funded Pension Plans
Change in Benefit Obligation
Beginning balance	2,667	2,492
Service cost	37	33
Interest cost	68	82
Actuarial (gains) loss	385	401
Single premium annuity contract payment	0	(249)
Benefit payments	(93)	(113)
Foreign currency exchange rate changes	21	21
Ending balance	3,085	2,667
Change in Fair Value of Plan Assets
Beginning balance	2,732	2,568
Actual return on plan assets	378	462
Employer contributions	4	40
Single premium annuity contract payment	0	(249)
Benefit payments	(93)	(113)
Foreign currency exchange rate changes	22	24
Ending balance	3,043	2,732
Funded Status (Plan assets greater (less) than benefit obligations) at December 31,	(42)	65
Unrecognized Net Actuarial (Gains) Losses	900	756
Actuarial gains/losses resulted from a change	(385)	(401)
Accumulated benefit obligation	2,993	2,580
Unfunded Pension Plan
Change in Benefit Obligation
Beginning balance	242	216
Service cost	13	11
Interest cost	5	7
Actuarial (gains) loss	26	22
Single premium annuity contract payment	0	0
Benefit payments	(17)	(14)
Foreign currency exchange rate changes	0	0
Ending balance	269	242
Change in Fair Value of Plan Assets
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	17	14
Single premium annuity contract payment	0	0
Benefit payments	(17)	(14)
Foreign currency exchange rate changes	0	0
Ending balance	0	0
Funded Status (Plan assets greater (less) than benefit obligations) at December 31,	(269)	(242)
Unrecognized Net Actuarial (Gains) Losses	86	65
Actuarial gains/losses resulted from a change	(26)	(22)
Accumulated benefit obligation	228	194
Postretirement Medical Plan
Change in Benefit Obligation
Beginning balance	75	59
Service cost	3	2
Interest cost	1	2
Actuarial (gains) loss	(8)	19
Single premium annuity contract payment	0	0
Benefit payments	(6)	(7)
Foreign currency exchange rate changes	0	0
Ending balance	65	75
Change in Fair Value of Plan Assets
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	6	7
Single premium annuity contract payment	0	0
Benefit payments	(6)	(7)
Foreign currency exchange rate changes	0	0
Ending balance	0	0
Funded Status (Plan assets greater (less) than benefit obligations) at December 31,	(65)	(75)
Unrecognized Net Actuarial (Gains) Losses	(19)	(12)
Actuarial gains/losses resulted from a change	8	(19)
Changes in Discount Rate
Change in Benefit Obligation
Actuarial (gains) loss	(387)	(465)
Change in Fair Value of Plan Assets
Actuarial gains/losses resulted from a change	387	465
Changes in Mortality Improvement
Change in Benefit Obligation
Actuarial (gains) loss	(18)	(13)
Change in Fair Value of Plan Assets
Actuarial gains/losses resulted from a change	$ 18	$ 13

Defined benefit plan plan assets single premium annuity contract payment.

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Defined benefit plan single premium annuity contract payment.

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Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of foreign currency translation gain (loss) which (increases) decreases benefit obligation of defined benefit plan.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement.

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