Retirement Plans - Components of Net Periodic Pension Cost (Detail) - Pension Plans [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18	$ 13	$ 35	$ 25
Interest cost	26	24	52	49
Expected return on plan assets	(43)	(40)	(85)	(80)
Amortization of unrecognized net actuarial losses	20	7	39	15
Settlement loss	5	8	5	8
Pension expense	$ 26	$ 12	$ 46	$ 17