Invested Assets and Related Income - Change in Unrealized Appreciation or Depreciation of Investments Carried at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-For-Sale Securities [Line Items]
Change in unrealized appreciation of fixed maturities	$ 256	$ 964	$ 70
Change in unrealized appreciation of equity securities	171	(17)	47
Change in unrealized appreciation of fixed maturities and equity securities	427	947	117
Deferred income tax	150	331	41
Total change in unrealized appreciation of fixed maturities and equity securities, Net of tax	$ 277	$ 616	$ 76