Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 16	$ 18	$ 32	$ 35
Interest cost	28	26	56	52
Expected return on plan assets	(42)	(43)	(84)	(85)
Amortization of unrecognized net actuarial losses	16	20	32	39
Settlement loss	0	5	0	5
Pension expense	$ 18	$ 26	$ 36	$ 46