Invested Assets - Change in Unrealized Appreciation or Depreciation of Investments Carried at Fair Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Change in unrealized appreciation of fixed maturities	$ 152	$ 362
Change in unrealized appreciation of equity securities	15	(1)
Change in unrealized appreciation of fixed maturities and equity securities	167	361
Deferred income tax	58	126
Total change in unrealized appreciation (depreciation) of fixed maturities and equity securities, Net of tax	$ 109	$ 235