Mortgage Loans by Geographic Region (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Mortgage Loans on Real Estate
Mortgage Loans	$ 1,843.3	$ 1,815.1
Percent of Total	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans	122.5	100.9
Percent of Total	6.70%	5.60%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	186.2	191.5
Percent of Total	10.10%	10.50%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans	227.4	244.3
Percent of Total	12.30%	13.50%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans	172.8	162.3
Percent of Total	9.40%	8.90%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	441.1	447.7
Percent of Total	23.90%	24.70%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans	66.5	67.7
Percent of Total	3.60%	3.70%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans	206.5	190.9
Percent of Total	11.20%	10.50%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans	114.7	101.9
Percent of Total	6.20%	5.60%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans	$ 305.6	$ 307.9
Percent of Total	16.60%	17.00%