Schedule of Participating Mortgage Loans by Internal Credit Rating and Loan to Value (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 2,476.4	$ 2,560.4
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,317.6	$ 1,346.1
Mortgage Loans, Percent of Total	53.30%	52.60%
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,043.3	$ 1,076.8
Mortgage Loans, Percent of Total	42.10%	42.00%
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 109.9	$ 114.9
Mortgage Loans, Percent of Total	4.40%	4.50%
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 5.6	$ 22.6
Mortgage Loans, Percent of Total	0.20%	0.90%
Total
Mortgage Loans on Real Estate
Mortgage Loans, Percent of Total	100.00%	100.00%
AA Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 30.1	$ 27.3
Mortgage Loans, Percent of Total	1.20%	1.10%
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 695.5	$ 709.6
Mortgage Loans, Percent of Total	28.10%	27.70%
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,730.6	$ 1,802.6
Mortgage Loans, Percent of Total	69.90%	70.40%
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 20.2	$ 20.9
Mortgage Loans, Percent of Total	0.80%	0.80%
Total
Mortgage Loans on Real Estate
Mortgage Loans, Percent of Total	100.00%	100.00%