Mortgage Loans by Geographic Region (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Mortgage Loans on Real Estate
Mortgage Loans	$ 1,823.8	$ 1,815.1
Percent of Total	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans	113.2	100.9
Percent of Total	6.20%	5.60%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	182.3	191.5
Percent of Total	10.00%	10.50%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans	232.0	244.3
Percent of Total	12.70%	13.50%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans	169.0	162.3
Percent of Total	9.30%	8.90%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	447.0	447.7
Percent of Total	24.50%	24.70%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans	66.1	67.7
Percent of Total	3.60%	3.70%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans	202.5	190.9
Percent of Total	11.10%	10.50%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans	108.4	101.9
Percent of Total	6.00%	5.60%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans	$ 303.3	$ 307.9
Percent of Total	16.60%	17.00%