Mortgage Loans by Property Type and Geographic Region (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Mortgage Loans on Real Estate
Mortgage Loans	$ 2,435.4	$ 2,560.4
Percent of Total	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans	$ 52.4	$ 54.9
Percent of Total	2.20%	2.10%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	$ 192.4	$ 214.7
Percent of Total	7.90%	8.40%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 313.0	$ 298.4
Percent of Total	12.90%	11.70%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 181.4	$ 193.1
Percent of Total	7.40%	7.50%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	$ 539.3	$ 582.1
Percent of Total	22.10%	22.70%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 101.8	$ 120.7
Percent of Total	4.20%	4.70%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 212.6	$ 243.2
Percent of Total	8.70%	9.60%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans	$ 298.7	$ 290.6
Percent of Total	12.30%	11.30%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans	$ 543.8	$ 562.7
Percent of Total	22.30%	22.00%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans	$ 688.6	$ 780.0
Percent of Total	28.30%	30.50%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans	$ 745.3	$ 734.4
Percent of Total	30.60%	28.70%
Office
Mortgage Loans on Real Estate
Mortgage Loans	$ 423.0	$ 467.2
Percent of Total	17.40%	18.20%
Retail
Mortgage Loans on Real Estate
Mortgage Loans	$ 534.5	$ 533.3
Percent of Total	21.90%	20.80%
Other Property
Mortgage Loans on Real Estate
Mortgage Loans	$ 44.0	$ 45.5
Percent of Total	1.80%	1.80%