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Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Financial assets: |  |
Held-to-maturity investment securities, estimated fair value | $ 2,874.0 | $ 3,052.2
Derivative Assets, Estimated Fair Value | 37.4 | 45.2
Deferred compensation plan assets | 19.2 | 18.7
Financial liabilities: |  |
Derivative Liabilities, Estimated Fair Value | 127.3 | 159.6
Deferred compensation plan liabilities | 19.2 | 18.7
Carrying Amount |  |
Financial assets: |  |
Cash and cash equivalents | 578.0 | 870.5
Estimated Fair Value | 5,841.5 | 6,946.1
Held-to-maturity investment securities, estimated fair value | 3,207.9 | 3,451.8
Accrued interest receivable | 129.1 | 118.3
Mortgage servicing rights, net | 28.3 | 31.1
Loans Held-for-sale, Fair Value Disclosure | 47.4 | 79.9
Net loans held for investment | 18,051.9 | 17,879.1
Derivative Assets, Estimated Fair Value | 37.4 | 45.2
Deferred compensation plan assets | 19.2 | 18.7
Total financial assets | 27,940.7 | 29,440.7
Financial liabilities: |  |
Total deposits, excluding time deposits | 20,313.2 | 23,145.2
Time deposits | 3,009.9 | 1,928.4
Securities sold under repurchase agreements | 782.7 | 1,052.9
Federal Home Loan Bank Borrowings, Fair Value Disclosure | 2,603.0 | 2,327.0
Accrued interest payable | 52.2 | 14.5
Long-term debt | 120.8 | 120.8
Subordinated debentures held by subsidiary trusts | 163.1 | 163.1
Derivative Liabilities, Estimated Fair Value | 127.3 | 159.6
Deferred compensation plan liabilities | 19.2 | 18.7
Total financial liabilities | 27,191.4 | 28,930.2
Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 578.0 | 870.5
Estimated Fair Value | 5,841.5 | 6,946.1
Held-to-maturity investment securities, estimated fair value | 2,874.0 | 3,052.2
Accrued interest receivable | 129.1 | 118.3
Mortgage servicing rights, net | 38.8 | 37.4
Loans Held-for-sale, Fair Value Disclosure | 47.4 | 79.9
Net loans held for investment | 17,334.4 | 17,552.1
Derivative Assets, Estimated Fair Value | 37.4 | 45.2
Deferred compensation plan assets | 19.2 | 18.7
Total financial assets | 26,899.8 | 28,720.4
Financial liabilities: |  |
Total deposits, excluding time deposits | 20,313.2 | 23,145.2
Time deposits | 2,981.7 | 1,876.1
Securities sold under repurchase agreements | 782.7 | 1,052.9
Federal Home Loan Bank Borrowings, Fair Value Disclosure | 2,603.0 | 2,327.0
Accrued interest payable | 52.2 | 14.5
Long-term debt | 115.6 | 116.3
Subordinated debentures held by subsidiary trusts | 151.1 | 155.8
Derivative Liabilities, Estimated Fair Value | 127.3 | 159.6
Deferred compensation plan liabilities | 19.2 | 18.7
Total financial liabilities | 27,146.0 | 28,866.1
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 578.0 | 870.5
Estimated Fair Value | 0.0 | 0.0
Held-to-maturity investment securities, estimated fair value | 0.0 | 0.0
Accrued interest receivable | 0.0 | 0.0
Mortgage servicing rights, net | 0.0 | 0.0
Loans Held-for-sale, Fair Value Disclosure | 0.0 | 0.0
Net loans held for investment | 0.0 | 0.0
Derivative Assets, Estimated Fair Value | 0.0 | 0.0
Deferred compensation plan assets | 0.0 | 0.0
Total financial assets | 578.0 | 870.5
Financial liabilities: |  |
Total deposits, excluding time deposits | 20,313.2 | 23,145.2
Time deposits | 0.0 | 0.0
Securities sold under repurchase agreements | 0.0 | 0.0
Federal Home Loan Bank Borrowings, Fair Value Disclosure | 0.0 | 0.0
Accrued interest payable | 0.0 | 0.0
Long-term debt | 0.0 | 0.0
Subordinated debentures held by subsidiary trusts | 0.0 | 0.0
Derivative Liabilities, Estimated Fair Value | 0.0 | 0.0
Deferred compensation plan liabilities | 0.0 | 0.0
Total financial liabilities | 20,313.2 | 23,145.2
Significant Other Observable Inputs (Level 2) | Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 0.0 | 0.0
Estimated Fair Value | 5,841.5 | 6,946.1
Held-to-maturity investment securities, estimated fair value | 2,874.0 | 3,052.2
Accrued interest receivable | 129.1 | 118.3
Mortgage servicing rights, net | 38.8 | 37.4
Loans Held-for-sale, Fair Value Disclosure | 0.5 | 6.9
Net loans held for investment | 17,281.8 | 17,513.0
Derivative Assets, Estimated Fair Value | 37.4 | 45.2
Deferred compensation plan assets | 19.2 | 18.7
Total financial assets | 26,222.3 | 27,737.8
Financial liabilities: |  |
Total deposits, excluding time deposits | 0.0 | 0.0
Time deposits | 2,981.7 | 1,876.1
Securities sold under repurchase agreements | 782.7 | 1,052.9
Federal Home Loan Bank Borrowings, Fair Value Disclosure | 2,603.0 | 2,327.0
Accrued interest payable | 52.2 | 14.5
Long-term debt | 115.6 | 116.3
Subordinated debentures held by subsidiary trusts | 151.1 | 155.8
Derivative Liabilities, Estimated Fair Value | 127.3 | 159.6
Deferred compensation plan liabilities | 19.2 | 18.7
Total financial liabilities | 6,832.8 | 5,720.9
Significant Unobservable Inputs (Level 3) | Estimated Fair Value |  |
Financial assets: |  |
Cash and cash equivalents | 0.0 | 0.0
Estimated Fair Value | 0.0 | 0.0
Held-to-maturity investment securities, estimated fair value | 0.0 | 0.0
Accrued interest receivable | 0.0 | 0.0
Mortgage servicing rights, net | 0.0 | 0.0
Loans Held-for-sale, Fair Value Disclosure | 46.9 | 73.0
Net loans held for investment | 52.6 | 39.1
Derivative Assets, Estimated Fair Value | 0.0 | 0.0
Deferred compensation plan assets | 0.0 | 0.0
Total financial assets | 99.5 | 112.1
Financial liabilities: |  |
Total deposits, excluding time deposits | 0.0 | 0.0
Time deposits | 0.0 | 0.0
Securities sold under repurchase agreements | 0.0 | 0.0
Federal Home Loan Bank Borrowings, Fair Value Disclosure | 0.0 | 0.0
Accrued interest payable | 0.0 | 0.0
Long-term debt | 0.0 | 0.0
Subordinated debentures held by subsidiary trusts | 0.0 | 0.0
Derivative Liabilities, Estimated Fair Value | 0.0 | 0.0
Deferred compensation plan liabilities | 0.0 | 0.0
Total financial liabilities | $ 0.0 | $ 0.0

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