Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits
Components of net periodic benefit cost
Service cost			$ 1	$ 1
Interest cost	9	10	18	20
Expected return on assets	(11)	(11)	(22)	(22)
Recognized actuarial net (gain) loss	4	4	7	6
Net periodic benefit cost (credit)	2	3	4	5
Other Benefits
Components of net periodic benefit cost
Interest cost	1	2	2	4
Prior service cost	(1)		(1)
Recognized actuarial net (gain) loss	(1)	(2)	(3)	(4)
Net periodic benefit cost (credit)	$ (1)		$ (2)