Investments (Net Unrealized Gains (Losses), Including Portion Of Other-Than-Temporary Impairments Included In Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Gross unrealized gains	$ 251	$ 263
Gross unrealized losses	(152)	(478)
Foreign exchange	24	(5)
Net	123	(220)
Deferred income tax provision (benefit)	31	(86)
Unrealized gains (losses), net	$ 92	$ (134)