Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 13	$ 14	$ 40	$ 42
Interest cost	14	19	42	56
Expected return on plan assets	(49)	(45)	(148)	(135)
Amortization of unrecognized net actuarial losses	15	11	43	35
Settlement loss	1	0	5	0
Pension (income) expense	(6)	(1)	(18)	(2)
Net non-service pension (income) costs included in other, net	$ (19)	$ (15)	$ (58)	$ (44)