Employee Benefits - Costs by Plans (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 73		$ 62	$ 146	$ 123
Amortization of prior service cost (credit)	15		16	30	31
Expected return on plan assets	(296)		(282)	(593)	(564)
Interest cost	137		176	277	354
Remeasurement loss, net	153	$ 182	0	335	(96)
Other components	9		(90)	49	(275)
Total	82		(28)	195	(152)
Pension | Cost of services
Defined Benefit Plan Disclosure [Line Items]
Service cost	59		50	118	100
Pension | Selling, general and administrative expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	14		12	28	23
Health Care and Life
Defined Benefit Plan Disclosure [Line Items]
Service cost	28		24	55	48
Amortization of prior service cost (credit)	(242)		(243)	(483)	(486)
Expected return on plan assets	(6)		(10)	(13)	(19)
Interest cost	107		158	214	315
Remeasurement loss, net	0		0	0	0
Other components	(141)		(95)	(282)	(190)
Total	(113)		(71)	(227)	(142)
Health Care and Life | Cost of services
Defined Benefit Plan Disclosure [Line Items]
Service cost	23		19	45	39
Health Care and Life | Selling, general and administrative expense
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5		$ 5	$ 10	$ 9