Postretirement Benefit Plans - Reconciliation of Benefit Obligations, Plan Assets, and Unfunded or Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets
Beginning balance at fair value	$ 40,566
Ending balance at fair value	37,361	$ 40,566
Changes in longevity assumptions	250
Qualified Defined  Benefit Pension Plans
Change in benefit obligation
Beginning balance	51,352	48,674
Service cost	106	101	$ 516
Interest cost	1,220	1,538	1,806
Actuarial losses (gains)	(2,045)	4,610
Settlements	(4,885)	(1,392)
Plan amendments and curtailments	2	9
Benefits paid	(2,303)	(2,188)
Medicare Part D subsidy	0	0
Participants’ contributions	0	0
Ending balance	43,447	51,352	48,674
Change in plan assets
Beginning balance at fair value	38,481	35,442
Actual return on plan assets	3,899	5,594
Settlements	(4,885)	(1,392)
Benefits paid	(2,303)	(2,188)
Company contributions	0	1,025
Medicare Part D subsidy	0	0
Participants’ contributions	0	0
Ending balance at fair value	35,192	38,481	$ 35,442
Net (unfunded) funded status of the plans	$ (8,255)	$ (12,871)
Weighted average discount rate	2.875%	2.50%	3.25%
Actual return on plan assets (percent)	10.50%
Qualified Defined  Benefit Pension Plans | Qualified Plan
Change in plan assets
Weighted average discount rate	2.875%	2.50%
Increased (decrease) in benefit obligation		$ 2,300
Retiree Medical and Life Insurance Plans
Change in benefit obligation
Beginning balance	$ 2,271	2,226
Service cost	13	13	$ 14
Interest cost	53	70	97
Actuarial losses (gains)	(352)	117
Settlements	0	0
Plan amendments and curtailments	0	(8)
Benefits paid	(217)	(220)
Medicare Part D subsidy	4	3
Participants’ contributions	67	70
Ending balance	1,839	2,271	2,226
Change in plan assets
Beginning balance at fair value	2,085	1,889
Actual return on plan assets	224	298
Settlements	0	0
Benefits paid	(217)	(220)
Company contributions	6	45
Medicare Part D subsidy	4	3
Participants’ contributions	67	70
Ending balance at fair value	2,169	2,085	$ 1,889
Net (unfunded) funded status of the plans	$ 330	$ (186)
Weighted average discount rate	2.75%	2.375%	3.25%
Retiree Medical and Life Insurance Plans | Qualified Plan
Change in plan assets
Weighted average discount rate	2.75%	2.375%
Increased (decrease) in benefit obligation	$ 70
Demographic experience gain	$ 282
Actual return on plan assets (percent)	10.50%	16.50%