Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 14	$ 10
Interest cost	18	24
Expected return on plan assets	(45)	(45)
Amortization of unrecognized net actuarial losses	12	11
Pension (income) expense	$ (1)	$ 0