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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Investments Debt And Equity Securities [Abstract]
Change in unrealized appreciation of fixed maturities	$ (99)	$ 295	$ (1,314)	$ 411
Change in unrealized appreciation of equity securities	94	57	239	131
Change in unrealized appreciation of fixed maturities and equity securities	(5)	352	(1,075)	542
Deferred income tax (credit)	(2)	123	(376)	190
Total change in unrealized appreciation (depreciation) of fixed maturities and equity securities, Net of tax	$ (3)	$ 229	$ (699)	$ 352