Schedule of Participating Mortgage Loans by Internal Credit Rating and Loan to Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Mortgage Loans on Real Estate
Mortgage Loans	$ 2,432.1	$ 2,397.0
Percent of Total	100.00%	100.00%
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans	$ 1,189.4	$ 1,215.1
Percent of Total	48.90%	50.70%
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans	$ 1,000.3	$ 1,053.0
Percent of Total	41.10%	43.90%
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans	$ 155.8	$ 91.4
Percent of Total	6.40%	3.80%
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans	$ 86.6	$ 37.5
Percent of Total	3.60%	1.60%
Total
Mortgage Loans on Real Estate
Percent of Total	100.00%	100.00%
AA Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	$ 3.5	$ 0.0
Percent of Total	0.10%	0.00%
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	$ 510.0	$ 485.6
Percent of Total	21.00%	20.30%
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	$ 1,863.0	$ 1,911.4
Percent of Total	76.60%	79.70%
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	$ 39.4	$ 0.0
Percent of Total	1.60%	0.00%
B Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	$ 16.2	$ 0.0
Percent of Total	0.70%	0.00%
Total
Mortgage Loans on Real Estate
Percent of Total	100.00%	100.00%