Mortgage Loans by Geographic Region (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
Percent of Total	100.00%		100.00%
New England
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	100.9		114.3
Percent of Total	5.60%		6.70%
Mid-Atlantic
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	191.5		160.0
Percent of Total	10.50%		9.30%
East North Central
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	244.3		224.7
Percent of Total	13.50%		13.10%
West North Central
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	162.3		160.8
Percent of Total	8.90%		9.40%
South Atlantic
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	447.7		440.9
Percent of Total	24.70%		25.70%
East South Central
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	67.7		79.6
Percent of Total	3.70%		4.70%
West South Central
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	190.9		159.5
Percent of Total	10.50%		9.30%
Mountain
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	101.9		90.5
Percent of Total	5.60%		5.30%
Pacific
Mortgage Loans on Real Estate [Line Items]
Mortgage Loans	$ 307.9		$ 282.4
Percent of Total	17.00%		16.50%

[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.