Pension and Other Postretirement Benefits - Components of Pension Expense for Defined Benefit Pension Plan (Detail) (Pension benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the period	$ 4	$ 5	$ 12
Interest cost on projected benefit obligation	47	33	39
Expected return on assets	(65)	(39)	(39)
Recognized losses	33	18	23
Curtailment gain	(4)	(1)
Amortization of prior service costs	(1)
Pension expense	$ 14	$ 16	$ 35