v3.25.1
Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Total mortgage and asset-backed securities and collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value $ 635.9 $ 610.6
Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 379.9 373.9
Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 374.6 370.0
Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 5.3 3.9
Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 256.0 236.7
Level 2 | Total mortgage and asset-backed securities and collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 635.9 610.6
Level 2 | Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 379.9 373.9
Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 374.6 370.0
Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 5.3 3.9
Level 2 | Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 256.0 236.7
Level 3 | Total mortgage and asset-backed securities and collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Level 3 | Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Level 3 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Level 3 | Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Total non-agency | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.4 0.4
Total non-agency | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.4 0.4
Total non-agency | Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Total agency | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 374.2 369.6
Total agency | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 374.2 369.6
Total agency | Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
FNMA | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 202.7 198.3
FNMA | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 202.7 198.3
FNMA | Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
FHLMC | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 147.5 147.1
FHLMC | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 147.5 147.1
FHLMC | Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
GNMA | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 24.0 24.2
GNMA | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 24.0 24.2
GNMA | Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Non-agency: Commercial | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.4 0.4
Non-agency: Commercial | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.4 0.4
Non-agency: Commercial | Level 3 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Vehicle receivables | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 3.1 1.7
Vehicle receivables | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 3.1 1.7
Vehicle receivables | Level 3 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Credit card receivables | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.2 0.2
Credit card receivables | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.2 0.2
Credit card receivables | Level 3 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 0.0 0.0
Other | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 2.0 2.0
Other | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 2.0 2.0
Other | Level 3 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value $ 0.0 $ 0.0