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Investment Securities - Debt Securities Issued By Corporation (Details) - Debt securities issued by corporations - USD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Investment securities |  |
Fair value investments | $ 1,018.8 | $ 992.9
AAA |  |
Investment securities |  |
Fair value investments | 11.3 | 12.0
AA |  |
Investment securities |  |
Fair value investments | 96.0 | 85.0
A |  |
Investment securities |  |
Fair value investments | 567.9 | 490.4
BBB |  |
Investment securities |  |
Fair value investments | 337.7 | 396.8
Other |  |
Investment securities |  |
Fair value investments | $ 5.9 | $ 8.7

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