Postretirement Benefit Plans - Reconciliation of Benefit Obligations, Plan Assets, and Unfunded or Funded Status (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jun. 26, 2022
Change in plan assets
Beginning balance at fair value		$ 24,884
Settlements	$ (414)
Ending balance at fair value	24,515	24,515	$ 24,884
Qualified Defined Benefit Pension Plans
Change in benefit obligation
Beginning balance		28,698	43,447
Service cost		65	87	$ 106
Interest cost		1,459	1,289	1,220
Actuarial losses (gains)		731	(10,270)
Settlements		(414)	(4,309)
Plan amendments		6	186
Benefits paid		(1,586)	(1,732)
Medicare Part D subsidy		0	0
Participants’ contributions		0	0
Ending balance	28,959	28,959	28,698	43,447
Change in plan assets
Beginning balance at fair value		23,228	35,192
Actual return on plan assets		1,572	(5,923)
Settlements		(414)	(4,309)
Benefits paid		(1,586)	(1,732)
Company contributions		0	0
Medicare Part D subsidy		0	0
Participants’ contributions		0	0
Ending balance at fair value	22,800	22,800	23,228	$ 35,192
Net (unfunded) funded status of the plans	$ (6,159)	$ (6,159)	$ (5,470)
Weighted average discount rate	5.00%	5.00%	5.25%	2.875%	4.75%
Increased (decrease) in benefit obligation		$ 765	$ (10,200)
Actual return on plan assets (percent)	7.00%	7.00%
Qualified Defined Benefit Pension Plans \| Qualified Plan
Change in plan assets
Weighted average discount rate	5.00%	5.00%	5.25%	2.875%
Retiree Medical and Life Insurance Plans
Change in benefit obligation
Beginning balance		$ 1,359	$ 1,839
Service cost		5	9	$ 13
Interest cost		68	49	53
Actuarial losses (gains)		27	(396)
Settlements		0	0
Plan amendments		1	1
Benefits paid		(192)	(207)
Medicare Part D subsidy		1	3
Participants’ contributions		59	61
Ending balance	$ 1,328	1,328	1,359	1,839
Change in plan assets
Beginning balance at fair value		1,656	2,169
Actual return on plan assets		190	(381)
Settlements		0	0
Benefits paid		(192)	(207)
Company contributions		1	11
Medicare Part D subsidy		1	3
Participants’ contributions		59	61
Ending balance at fair value	1,715	1,715	1,656	$ 2,169
Net (unfunded) funded status of the plans	$ 387	$ 387	$ 297
Weighted average discount rate	5.00%	5.00%	5.25%	2.75%
Increased (decrease) in benefit obligation			$ (335)
Actual return on plan assets (percent)	7.00%	7.00%	(18.00%)
Retiree Medical and Life Insurance Plans \| Qualified Plan
Change in plan assets
Weighted average discount rate	5.00%	5.00%	5.25%	2.75%

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Actual Return on Plan Assets

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Amount of (increase) decrease in accumulated benefit obligation of defined benefit plan from effects of settlement and curtailment.

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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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Amount of payment, which decreases benefit obligation of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. Excludes decreases to benefit obligation for remeasurement due to settlement.

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Amount of increase (decrease) in benefit obligation of defined benefit plan.

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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 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 receipt from prescription drug subsidy which increases plan assets of defined benefit postretirement 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 payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

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