v3.26.1
Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Total mortgage and asset-backed securities and collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value $ 747.7 $ 740.0
Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 402.5 393.0
Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 357.4 354.0
Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 45.1 39.0
Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 345.2 347.0
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 747.7 740.0
Level 2 | Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 402.5 393.0
Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 357.4 354.0
Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 45.1 39.0
Level 2 | Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 345.2 347.0
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 agency | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 357.4 354.0
Total agency | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 357.4 354.0
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 201.2 192.1
FNMA | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 201.2 192.1
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 136.2 141.3
FHLMC | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 136.2 141.3
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 20.0 20.6
GNMA | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 20.0 20.6
GNMA | 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 26.2 21.9
Vehicle receivables | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 26.2 21.9
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 13.9 14.0
Credit card receivables | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 13.9 14.0
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 5.0 3.1
Other | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 5.0 3.1
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