Investments (Schedule of Amortized Cost of Mortgage Participations and Other Loans by Credit Ratings and Year of Origination) (Details) $ in Millions	Dec. 31, 2023 USD ($)
Schedule of Investments [Line Items]
Allowance for credit losses	$ (10.0)
Amortized cost, net of allowance for credit losses	371.4
Amortized Cost
Schedule of Investments [Line Items]
Prior to 2019	228.9
2019	47.2
2020	33.1
2021	62.2
2022	10.0
Total	381.4
Aaa/Aa/A
Schedule of Investments [Line Items]
Prior to 2019	140.2
2019	34.8
2020	9.7
2021	62.2
2022	10.0
Total	256.9
Baa
Schedule of Investments [Line Items]
Prior to 2019	41.3
2019	12.4
2020	17.5
Total	71.2
Ba and lower
Schedule of Investments [Line Items]
Prior to 2019	47.4
2020	5.9
Total	$ 53.3