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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Investments Debt And Equity Securities [Abstract]
Change in unrealized appreciation of fixed maturities	$ 255	$ (1,019)	$ 617	$ (1,215)
Change in unrealized appreciation of equity securities	111	(57)	110	145
Change in unrealized appreciation of fixed maturities and equity securities	366	(1,076)	727	(1,070)
Deferred income tax (credit)	128	(376)	254	(374)
Total change in unrealized appreciation (depreciation) of fixed maturities and equity securities, Net of tax	$ 238	$ (700)	$ 473	$ (696)