Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Pension And Other Postretirment Benefits Recgonized In Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest cost	$ 10	$ 11	$ 12
Expected return on assets	(13)	(15)	(14)
Amortization of net actuarial loss	14	11	12
Amortization of net prior service cost		1	1
Settlement	(6)	(6)
Net periodic pension cost	17	14	11
Net actuarial loss (gain)	7	50	2
Amortization of net actuarial loss	(14)	(11)	(12)
Amortization of prior service cost		(1)	(1)
Settlement	(6)	(6)
Total recognized in other comprehensive income	(13)	32	(11)
Total recognized in net periodic benefit cost and other comprehensive income	$ 4	$ 46