Invested Assets - Change in Unrealized Appreciation or Depreciation of Investments Carried at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedule of Available-For-Sale Securities [Line Items]
Change in unrealized appreciation of fixed maturities	$ 295	$ 478	$ 411	$ 731
Change in unrealized appreciation of equity securities	57	(276)	131	(170)
Change in unrealized appreciation of fixed maturities and equity securities	352	202	542	561
Deferred income tax	123	70	190	196
Total change in unrealized appreciation of fixed maturities and equity securities, Net of tax	$ 229	$ 132	$ 352	$ 365