Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 10	$ 14
Interest cost	24	23
Expected return on plan assets	(45)	(49)
Amortization of unrecognized net actuarial losses	11	12
Curtailment gains	0	(2)
Pension (income) expense	$ 0	$ (2)