Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Loan to Value Ratio (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 1,815.1	[1]	$ 1,712.7
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	777.4		624.7
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	867.5		858.8
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	107.6		142.5
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 62.6		$ 86.7

[1] (1)The amortized cost for fixed maturity securities and mortgage loans represents original cost reduced by repayments, write-downs from other-than-temporary declines in fair value, amortization of premiums, and/or accretion of discounts.