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Investment Securities - Mortgage-backed Asset Securities Table (Details) - USD ($) $ in Millions | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | $ 241.9 | $ 256.5
Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 22.2 | 21.1
Total mortgage and asset-backed securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 264.1 | 277.6
Collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 133.4 | 135.0
Total mortgage and asset-backed securities and collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 397.5 | 412.6
Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 241.9 | 256.5
Level 2 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 22.2 | 21.1
Level 2 | Total mortgage and asset-backed securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 264.1 | 277.6
Level 2 | Collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 133.4 | 135.0
Level 2 | Total mortgage and asset-backed securities and collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 397.5 | 412.6
Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Level 3 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Level 3 | Total mortgage and asset-backed securities |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Level 3 | Collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Level 3 | Total mortgage and asset-backed securities and collateralized loan obligations |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
FNMA | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 119.3 | 125.4
FNMA | Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 119.3 | 125.4
FNMA | Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
FHLMC | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 86.5 | 90.5
FHLMC | Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 86.5 | 90.5
FHLMC | Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
GNMA | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 35.6 | 40.1
GNMA | Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 35.6 | 40.1
GNMA | Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Total agency | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 241.4 | 256.0
Total agency | Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 241.4 | 256.0
Total agency | Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Non-agency: Residential | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.5 | 0.5
Non-agency: Residential | Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.5 | 0.5
Non-agency: Residential | Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Total non-agency | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.5 | 0.5
Total non-agency | Level 2 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.5 | 0.5
Total non-agency | Level 3 | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Credit card receivables | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 9.8 | 12.3
Credit card receivables | Level 2 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 9.8 | 12.3
Credit card receivables | Level 3 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | 0.0
Vehicle receivables | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 12.4 | 8.8
Vehicle receivables | Level 2 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 12.4 | 8.8
Vehicle receivables | Level 3 | Other asset-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | 0.0 | $ 0.0
Collateralized mortgage obligations | Mortgage-backed securities: |  |
Debt and Equity Securities, FV-NI [Line Items] |  |
Fair value investments | $ 133.4 |

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