Postretirement Benefit Plans - Schedule of Net Periodic Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Qualified Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 516	$ 630	$ 635
Interest cost	1,806	1,740	1,835
Expected return on plan assets	(2,300)	(2,395)	(2,249)
Recognized net actuarial losses	1,404	1,777	1,506
Amortization of net prior service (credit) cost	(333)	(321)	(355)
Total net periodic benefit cost	1,093	1,431	1,372
Retiree Medical and Life Insurance Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	19	19
Interest cost	97	91	103
Expected return on plan assets	(110)	(135)	(128)
Recognized net actuarial losses	2	5	19
Amortization of net prior service (credit) cost	42	15	15
Total net periodic benefit cost	$ 45	$ (5)	$ 28