Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Retirement Benefits [Abstract]
Service cost	$ 14	$ 14
Interest cost	14	18
Expected return on plan assets	(50)	(45)
Amortization of unrecognized net actuarial losses	15	12
Settlement loss	1	0
Pension (income) expense	(6)	(1)
Net non-service pension (income) costs included in other, net	$ 20	$ (15)