Before-Tax Credit Related Portion of Other-Than-Temporary Impairments on Fixed Maturity Securities Still Held and Recognized in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Balance at Beginning of Year	$ 8.5
Sales or Maturities of Securities in the Period	8.5
Balance at End of Year	$ 0