Postretirement Benefit Plans - Schedule of Net Periodic Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Qualified Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 630	$ 635	$ 671
Interest cost	1,740	1,835	1,890
Expected return on plan assets	(2,395)	(2,249)	(2,539)
Recognized net actuarial losses	1,777	1,506	1,359
Amortization of net prior service (credit) cost	(321)	(355)	(362)
Total net periodic benefit cost	1,431	1,372	1,019
Qualified Defined Benefit Pension Plans | Discontinued Operations | Information Systems & Global Solutions
Defined Benefit Plan Disclosure [Line Items]
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts			14
Retiree Medical and Life Insurance Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	19	23
Interest cost	91	103	120
Expected return on plan assets	(135)	(128)	(138)
Recognized net actuarial losses	5	19	34
Amortization of net prior service (credit) cost	15	15	22
Total net periodic benefit cost	$ (5)	$ 28	$ 61