Mortgage Loans by Property Type (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%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans	80.4	61.1
Percent of Total	4.40%	3.30%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans	533.3	567.8
Percent of Total	29.30%	31.30%
Office
Mortgage Loans on Real Estate
Mortgage Loans	799.1	776.5
Percent of Total	43.80%	42.80%
Retail
Mortgage Loans on Real Estate
Mortgage Loans	$ 411.0	$ 409.7
Percent of Total	22.50%	22.60%