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, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule Of Pension And Other Postretirment Benefits Recgonized In Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest cost	$ 11	$ 12	$ 12
Expected return on assets	(15)	(14)	(12)
Amortization of actuarial loss	11	12	15
Amortization of net prior service cost	1	1	1
Settlement	6		13
Net periodic pension cost	14	11	29
Net actuarial loss (gain)	50	2	(10)
Net prior service cost	0
Amortization of net actuarial loss	11	(12)	(15)
Amortization of prior service cost	1	(1)	(1)
Settlement	(6)		(13)
Total recognized in other comprehensive income	32	(11)	(39)
Total recognized in net periodic benefit cost and other comprehensive income	$ 46		$ (10)