Employee Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 1	$ 1	$ 2
Interest cost	10	9	29	27
Expected return on assets	(12)	(11)	(36)	(33)
Recognized actuarial net (gain) loss	3	3	8	10
Net periodic benefit cost (credit)	1	2	2	6
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	2	1	4	3
Prior service credit	(1)		(1)	(1)
Recognized actuarial net (gain) loss	(2)	(2)	(6)	(5)
Net periodic benefit cost (credit)	$ (1)	$ (1)	$ (3)	$ (3)