Invested Assets - Components of Unrealized Appreciation or Depreciation of Investments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Fixed maturities, Gross unrealized appreciation	$ 1,816	$ 1,457
Fixed maturities, Gross unrealized depreciation	65	325
Fixed maturities, Unrealized appreciation (depreciation), Net	1,751	1,132
Equity securities, Gross Unrealized Appreciation	804	756
Equity securities, Gross Unrealized Depreciation	14	3
Equity securities, Unrealized appreciation (depreciation), Net	790	753
Total fixed maturities and equity securities, Unrealized appreciation (depreciation), Net	2,541	1,885
Deferred income tax liability	889	660
Total fixed maturities and equity securities, Unrealized appreciation (depreciation), Net of tax	$ 1,652	$ 1,225