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
Total recognized in other comprehensive income, pre-tax	$ 95	$ 382	$ (106)
Pension Plans, Defined Benefit
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	64
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	(25)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Settlements Recognized in Net Periodic Benefit Cost, before tax	(2)
Total recognized in other comprehensive income, pre-tax	37
Defined Benefit Plans Amount Recognized In Periodic Benefit Cost And Accumulated Other Comprehensive Income	11
Other Postretirement Benefit Plans, Defined Benefit
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	(12)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	0
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Settlements Recognized in Net Periodic Benefit Cost, before tax	0
Total recognized in other comprehensive income, pre-tax	(12)
Defined Benefit Plans Amount Recognized In Periodic Benefit Cost And Accumulated Other Comprehensive Income	$ (12)