Invested Assets - Components of Unrealized Appreciation or Depreciation of Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Fixed maturities, Gross Unrealized Appreciation	$ 1,629	$ 1,884
Fixed maturities, Gross Unrealized Depreciation	82	62
Fixed maturities, Unrealized appreciation (depreciation), Net	1,547	1,822
Equity securities, Gross Unrealized Appreciation	742	894
Equity securities, Gross Unrealized Depreciation	31	19
Equity securities, Unrealized appreciation (depreciation), Net	711	875
Total fixed maturities and equity securities, Unrealized appreciation (depreciation), Net	2,258	2,697
Deferred income tax liability	790	944
Total fixed maturities and equity securities, Unrealized appreciation (depreciation), Net of tax	$ 1,468	$ 1,753