Invested Assets - Change in Unrealized Appreciation or Depreciation of Investments Carried at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investments Debt And Equity Securities [Abstract]
Change in unrealized appreciation of fixed maturities	$ (1,019)	$ 133	$ (1,215)	$ 116
Change in unrealized appreciation of equity securities	(57)	(28)	145	74
Change in unrealized appreciation of fixed maturities and equity securities	(1,076)	105	(1,070)	190
Deferred income tax (credit)	(376)	37	(374)	67
Total change in unrealized appreciation (depreciation) of fixed maturities and equity securities, Net of tax	$ (700)	$ 68	$ (696)	$ 123