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Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Dec. 31, 2021
--- | --- | ---
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 3,487.6 | $ 1,687.6
AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 3,292.9 | 1,626.2
AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 93.8 | 31.6
A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 12.0 | 18.7
BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 65.1 | 7.0
Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 13.8 | 4.1
BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 10.0 |
U.S. Treasury notes |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 396.1 |
U.S. Treasury notes | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 396.1 |
U.S. Treasury notes | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
U.S. Treasury notes | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
U.S. Treasury notes | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
U.S. Treasury notes | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
U.S. Treasury notes | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
State, county, and municipal securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 184.0 | 67.6
State, county, and municipal securities | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 69.4 | 17.2
State, county, and municipal securities | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 93.8 | 31.6
State, county, and municipal securities | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 12.0 | 14.7
State, county, and municipal securities | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
State, county, and municipal securities | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 8.8 | 4.1
State, county, and municipal securities | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Obligations of U.S. government agencies |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 350.8 |
Obligations of U.S. government agencies | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 350.8 |
Obligations of U.S. government agencies | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Obligations of U.S. government agencies | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Obligations of U.S. government agencies | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Obligations of U.S. government agencies | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Obligations of U.S. government agencies | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Corporate securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 80.1 | 11.0
Corporate securities | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Corporate securities | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Corporate securities | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 4.0
Corporate securities | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 65.1 | 7.0
Corporate securities | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 5.0 | 0.0
Corporate securities | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 10.0 |
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,476.6 | 1,609.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,261.3 | 1,439.1
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,261.3 | 1,439.1
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 215.3 | 169.9
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 215.3 | 169.9
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | $ 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 0.0 |

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