Schedule of Participating Mortgage Loans by Internal Credit Rating and Loan to Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 2,434.4	$ 2,397.0
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,256.0	$ 1,215.1
Mortgage Loans, Percent of Total	51.50%	50.70%
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,065.4	$ 1,053.0
Mortgage Loans, Percent of Total	43.80%	43.90%
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 40.2	$ 91.4
Mortgage Loans, Percent of Total	1.70%	3.80%
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 72.8	$ 37.5
Mortgage Loans, Percent of Total	3.00%	1.60%
Total
Mortgage Loans on Real Estate
Mortgage Loans, Percent of Total	100.00%	100.00%
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 476.1	$ 485.6
Mortgage Loans, Percent of Total	19.60%	20.30%
BBB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 1,912.2	$ 1,911.4
Mortgage Loans, Percent of Total	78.50%	79.70%
BB Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 29.6	$ 0.0
Mortgage Loans, Percent of Total	1.20%	0.00%
B Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans, Carrying Amount	$ 16.5	$ 0.0
Mortgage Loans, Percent of Total	0.70%	0.00%
Total
Mortgage Loans on Real Estate
Mortgage Loans, Percent of Total	100.00%	100.00%