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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the period	$ 2	$ 1	$ 6	$ 5
Interest cost on projected benefit obligation	14	14	42	35
Expected return on assets	(16)	(19)	(52)	(46)
Recognized losses	8	11	30	23
Curtailment gain	0	(4)	0	(4)
Pension expense	8	3	26	13
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the period	0	0	0	0
Interest cost on projected benefit obligation	2	2	6	5
Pension expense	$ 2	$ 2	$ 6	$ 5