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	6 Months Ended
	Jun. 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 Period	$ 0