Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 10		$ 14	$ 24	$ 28
Interest cost	24		26	47	52
Expected return on plan assets	(49)		(42)	(98)	(83)
Amortization of unrecognized net actuarial losses	9		16	21	33
Curtailment gains	0	$ (2)	0	(2)	0
Settlement loss	0		7	0	7
Pension (income) expense	$ (6)		$ 21	$ (8)	$ 37