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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3	$ 6	$ 5
Interest cost	4	3	7	7
Expected return on plan assets	(5)	(4)	(9)	(8)
Amortization of actuarial loss and prior service cost	2	0	3	1
Net periodic benefit cost	$ 4	$ 2	$ 7	$ 5