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Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($) $ in Millions	Dec. 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	$ 740.0	$ 610.6
Total mortgage and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	393.0	373.9
Mortgage-backed securities:
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	354.0	370.0
Mortgage-backed securities: | Total non-agency
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.4
Mortgage-backed securities: | Total agency
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	354.0	369.6
Mortgage-backed securities: | FNMA
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	192.1	198.3
Mortgage-backed securities: | FHLMC
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	141.3	147.1
Mortgage-backed securities: | GNMA
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	20.6	24.2
Mortgage-backed securities: | Non-agency: Commercial
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.4
Other asset-backed securities:
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	39.0	3.9
Other asset-backed securities: | Vehicle receivables
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	21.9	1.7
Other asset-backed securities: | Credit card receivables
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	14.0	0.2
Other asset-backed securities: | Other
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	3.1	2.0
Collateralized loan obligations
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	347.0	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	740.0	610.6
Level 2 | Total mortgage and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	393.0	373.9
Level 2 | Mortgage-backed securities:
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	354.0	370.0
Level 2 | Mortgage-backed securities: | Total non-agency
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.4
Level 2 | Mortgage-backed securities: | Total agency
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	354.0	369.6
Level 2 | Mortgage-backed securities: | FNMA
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	192.1	198.3
Level 2 | Mortgage-backed securities: | FHLMC
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	141.3	147.1
Level 2 | Mortgage-backed securities: | GNMA
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	20.6	24.2
Level 2 | Mortgage-backed securities: | Non-agency: Commercial
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.4
Level 2 | Other asset-backed securities:
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	39.0	3.9
Level 2 | Other asset-backed securities: | Vehicle receivables
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	21.9	1.7
Level 2 | Other asset-backed securities: | Credit card receivables
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	14.0	0.2
Level 2 | Other asset-backed securities: | Other
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	3.1	2.0
Level 2 | Collateralized loan obligations
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	347.0	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 | Mortgage-backed securities: | Total non-agency
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Mortgage-backed securities: | Total agency
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Mortgage-backed securities: | FNMA
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Mortgage-backed securities: | FHLMC
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Mortgage-backed securities: | GNMA
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Mortgage-backed securities: | Non-agency: Commercial
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 | Other asset-backed securities: | Vehicle receivables
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Other asset-backed securities: | Credit card receivables
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	0.0	0.0
Level 3 | Other asset-backed securities: | Other
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

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