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Loans Held for Investment - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Jun. 30, 2021 | Dec. 31, 2020 | Jun. 30, 2020 | Dec. 31, 2019
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | $ 0.0 | $ (5.2) | $ 5.1 | $ (53.7) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 135.1 | 145.5 | 135.1 | 145.5 | $ 135.5 | $ 144.3 | $ 146.1 | $ 73.0
Collateral dependent borrowings | 13.2 |  | 13.2 |  |  | 17.5 |  |
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal) | 0.2 | 4.0 |  | 52.5 |  |  |  |
Balance of defaulted loans under trouble debt restructurings | 0.0 |  | 0.0 |  |  |  |  |
Impaired Financing Receivable, Interest Income, Accrual Method | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Agriculture Portfolio Segment [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | 0.0 | 0.0 |  | 0.0 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 0.4 | 0.9 | 0.4 | 0.9 | 0.4 |  | 0.9 |
Total real estate loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | (0.7) | (3.2) | (0.1) | (21.3) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 78.9 | 78.6 | 78.9 | 78.6 | 79.4 | 80.5 | 75.2 | 28.9
Collateral dependent borrowings | 8.5 |  | 8.5 |  |  | 8.9 |  |
Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | (0.1) | (1.1) | (5.5) | (23.8) |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 33.9 | 42.0 | 33.9 | 42.0 | 33.7 | 39.2 | 46.5 | 32.6
Collateral dependent borrowings | 4.0 |  | 4.0 |  |  | 7.8 |  |
Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Provision charged to operating expense | 0.0 | 0.0 | (0.1) | 0.0 |  |  |  |
Accounts Receivable, Allowance for Credit Loss | 0.4 | $ 0.9 | 0.4 | $ 0.9 | $ 0.4 | 0.7 | $ 0.9 | $ 1.6
Collateral dependent borrowings | 0.7 |  | 0.7 |  |  | 0.8 |  |
Business Assets Pledged as Collateral [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 4.3 |  | 4.3 |  |  | 7.4 |  |
Business Assets Pledged as Collateral [Member] | Total real estate loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 1.2 |  | 1.2 |  |  | 1.3 |  |
Business Assets Pledged as Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 3.1 |  | 3.1 |  |  | 6.1 |  |
Business Assets Pledged as Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 0.0 |  | 0.0 |  |  | 0.0 |  |
Real Property Pledged as Collateral [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 8.9 |  | 8.9 |  |  | 8.6 |  |
Real Property Pledged as Collateral [Member] | Total real estate loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 7.3 |  | 7.3 |  |  | 6.5 |  |
Real Property Pledged as Collateral [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 0.9 |  | 0.9 |  |  | 1.3 |  |
Real Property Pledged as Collateral [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 0.7 |  | 0.7 |  |  | 0.8 |  |
Other Property [Member] |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 0.0 |  | 0.0 |  |  | 1.5 |  |
Other Property [Member] | Total real estate loans |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 0.0 |  | 0.0 |  |  | 1.1 |  |
Other Property [Member] | Commercial |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | 0.0 |  | 0.0 |  |  | 0.4 |  |
Other Property [Member] | Agricultural |  |  |  |  |  |  |  |
Loans and Leases Receivable Recorded Investment, Impaired [Line Items] |  |  |  |  |  |  |  |
Collateral dependent borrowings | $ 0.0 |  | $ 0.0 |  |  | $ 0.0 |  |

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