Employee Benefits - Costs by Plans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 73	$ 61
Amortization of prior service cost (credit)	15	15
Expected return on plan assets	(297)	(282)
Interest cost	140	178
Remeasurement loss (gain), net	182	(96)
Other components	40	(185)
Total	113	(124)
Pension | Cost of services
Defined Benefit Plan Disclosure [Line Items]
Service cost	59	50
Pension | Selling, general and administrative expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	11
Health Care and Life
Defined Benefit Plan Disclosure [Line Items]
Service cost	27	24
Amortization of prior service cost (credit)	(241)	(243)
Expected return on plan assets	(7)	(9)
Interest cost	107	157
Remeasurement loss (gain), net	0	0
Other components	(141)	(95)
Total	(114)	(71)
Health Care and Life | Cost of services
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	20
Health Care and Life | Selling, general and administrative expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4