Employee Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	9	11	27	31
Expected return on assets	(11)	(12)	(33)	(34)
Prior service credit
Recognized actuarial net (gain) loss	3	3	10	9
Net periodic benefit cost (credit)	2	3	6	8
Other Benefits [Member]
Components of net periodic benefit cost
Service cost		1		1
Interest cost	1	1	3	5
Expected return on assets
Prior service credit			(1)
Recognized actuarial net (gain) loss	(2)	(2)	(5)	(6)
Net periodic benefit cost (credit)	$ (1)		$ (3)