Pension and Other Postretirement Benefits - Components of Pension Expense for Defined Benefit Pension Plan (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain	$ 4		$ 4
Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the period	1	1	5	4
Interest cost on projected benefit obligation	14	8	35	25
Expected return on assets	(19)	(10)	(46)	(29)
Recognized losses	11	4	23	12
Curtailment gain	(4)		(4)
Pension expense	$ 3	$ 3	$ 13	$ 12