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Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
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Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | $ 3,208.7 | $ 3,453.7
AAA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 3,041.5 | 3,260.7
AA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 92.3 | 92.8
A Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 10.6 | 11.5
BBB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 47.0 | 65.1
BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 5.0 | 10.0
Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 12.3 | 13.6
US Treasury Securities [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 399.0 | 396.6
US Treasury Securities [Member] | AAA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 399.0 | 396.6
US Treasury Securities [Member] | AA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Treasury Securities [Member] | A Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Treasury Securities [Member] | BBB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Treasury Securities [Member] | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Treasury Securities [Member] | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
State, county and municipal securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 179.2 | 181.2
State, county and municipal securities | AAA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 69.0 | 68.3
State, county and municipal securities | AA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 92.3 | 92.8
State, county and municipal securities | A Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 10.6 | 11.5
State, county and municipal securities | BBB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
State, county and municipal securities | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
State, county and municipal securities | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 7.3 | 8.6
US Government Agencies Debt Securities [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 354.5 | 351.7
US Government Agencies Debt Securities [Member] | AAA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 354.5 | 351.7
US Government Agencies Debt Securities [Member] | AA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Government Agencies Debt Securities [Member] | A Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Government Agencies Debt Securities [Member] | BBB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Government Agencies Debt Securities [Member] | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
US Government Agencies Debt Securities [Member] | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Corporate Debt Securities [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 57.0 | 80.1
Corporate Debt Securities [Member] | AAA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Corporate Debt Securities [Member] | AA Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Corporate Debt Securities [Member] | A Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Corporate Debt Securities [Member] | BBB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 47.0 | 65.1
Corporate Debt Securities [Member] | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 5.0 | 10.0
Corporate Debt Securities [Member] | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 5.0 | 5.0
Commercial Mortgage Backed Securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 510.5 | 526.8
Commercial Mortgage Backed Securities | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 359.7 | 364.9
Commercial Mortgage Backed Securities | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 150.8 | 161.9
Commercial Mortgage Backed Securities | AAA Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 359.7 | 364.9
Commercial Mortgage Backed Securities | AAA Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 150.8 | 161.9
Commercial Mortgage Backed Securities | AA Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | AA Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | A Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | A Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | BBB Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | BBB Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | BB Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | BB Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | Not Rated | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Commercial Mortgage Backed Securities | Not Rated | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 1,232.6 | 1,391.5
Residential Mortgage-Backed Securities | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 1,189.8 | 1,342.9
Residential Mortgage-Backed Securities | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 42.8 | 48.6
Residential Mortgage-Backed Securities | AAA Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 1,189.8 | 1,342.9
Residential Mortgage-Backed Securities | AAA Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 42.8 | 48.6
Residential Mortgage-Backed Securities | AA Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | AA Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | A Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | A Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | BBB Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | BBB Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | BB Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | BB Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | Not Rated | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Residential Mortgage-Backed Securities | Not Rated | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Collateralized Mortgage Obligations |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 475.9 | 525.8
Collateralized Mortgage Obligations | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 334.1 | 525.8
Collateralized Mortgage Obligations | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 141.8 |
Collateralized Mortgage Obligations | AAA Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 334.1 | 525.8
Collateralized Mortgage Obligations | AAA Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 141.8 |
Collateralized Mortgage Obligations | AA Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | AA Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 |
Collateralized Mortgage Obligations | A Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | A Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 |
Collateralized Mortgage Obligations | BBB Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | BBB Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 |
Collateralized Mortgage Obligations | BB Rating | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | BB Rating | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 |
Collateralized Mortgage Obligations | Not Rated | FNMA and FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | 0.0 | $ 0.0
Collateralized Mortgage Obligations | Not Rated | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Debt Securities, Held-to-maturity | $ 0.0 |

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