v3.26.3
Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($)
$ in Millions
Sep. 30, 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 $ 771.2 $ 740.0
Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 392.8 393.0
Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 328.7 354.0
Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 64.1 39.0
Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 378.4 347.0
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 771.2 740.0
Level 2 | Total mortgage and asset-backed securities    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 392.8 393.0
Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 328.7 354.0
Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 64.1 39.0
Level 2 | Collateralized loan obligations    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 378.4 347.0
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 328.7 354.0
Total agency | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 328.7 354.0
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 190.7 192.1
FNMA | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 190.7 192.1
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 120.4 141.3
FHLMC | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 120.4 141.3
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 17.6 20.6
GNMA | Level 2 | Mortgage-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 17.6 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 41.6 21.9
Vehicle receivables | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 41.6 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 13.5 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 13.5 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 9.0 3.1
Other | Level 2 | Other asset-backed securities:    
Debt and Equity Securities, FV-NI [Line Items]    
Fixed maturity investments, at fair value 9.0 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