Employee Retirement Benefits - Components of Net Periodic Costs for Qualified and Supplemental Pension Plans (Detail) - Qualified Pension Plans [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3	$ 8	$ 9
Interest cost	4	3	11	10
Expected return on plan assets	(5)	(4)	(14)	(13)
Amortization of actuarial loss and prior service cost	0	1	2	4
Net periodic benefit cost	$ 2	$ 3	$ 7	$ 10