Mortgage Loans by Property Type and Geographic Region (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Mortgage Loans on Real Estate
Mortgage Loans	$ 2,224.5	$ 2,318.2
Percent of Total	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans	$ 52.6	$ 55.1
Percent of Total	2.40%	2.40%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	$ 167.2	$ 155.1
Percent of Total	7.50%	6.70%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 297.2	$ 314.4
Percent of Total	13.40%	13.60%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 151.1	$ 163.5
Percent of Total	6.80%	7.00%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	$ 532.5	$ 553.0
Percent of Total	23.90%	23.80%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 95.1	$ 110.7
Percent of Total	4.30%	4.80%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 193.6	$ 200.9
Percent of Total	8.70%	8.70%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans	$ 278.7	$ 282.7
Percent of Total	12.50%	12.20%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans	$ 456.5	$ 482.8
Percent of Total	20.50%	20.80%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans	$ 658.2	$ 685.8
Percent of Total	29.60%	29.60%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans	$ 690.4	$ 706.0
Percent of Total	31.00%	30.50%
Office
Mortgage Loans on Real Estate
Mortgage Loans	$ 338.4	$ 379.9
Percent of Total	15.20%	16.40%
Retail
Mortgage Loans on Real Estate
Mortgage Loans	$ 496.2	$ 503.9
Percent of Total	22.30%	21.70%
Other Property
Mortgage Loans on Real Estate
Mortgage Loans	$ 41.3	$ 42.6
Percent of Total	1.90%	1.80%