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Loans Held for Investment - Schedule of Contractual Aging of Loans by Portfolio (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Nonaccrual loans $ 101.0   $ 101.0   $ 56.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss 15,834.4   15,834.4   17,844.9
Financing Receivable, Allowance for Credit Loss, Writeoff 6.7 $ 29.1 30.5 $ 56.4 114.7
Financing Receivable, Nonaccrual, Interest Income (2.0) (1.0) (3.5) (1.8)  
Accrued interest reversal (0.4) (0.4) (2.9) (2.4)  
Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 5.2   5.2   7.7
Nonaccrual loans 74.2   74.2   55.4
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 931.5   931.5   1,368.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 1,175.8   1,175.8   1,369.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 1,217.8   1,217.8   1,946.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 1,537.6   1,537.6   1,397.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 1,261.4   1,261.4   1,084.8
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 2,295.6   2,295.6   1,901.0
Financing Receivable, Excluding Accrued Interest, Revolving 67.3   67.3   75.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 9.4   9.4   119.6
Financing Receivable, Allowance for Credit Loss, Writeoff     3.0   25.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 8,496.4   8,496.4   9,263.2
Commercial real estate | Pass          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 734.7   734.7   1,208.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 1,041.1   1,041.1   1,340.2
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 1,154.3   1,154.3   1,909.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 1,457.5   1,457.5   1,344.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 1,146.4   1,146.4   1,069.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 2,136.1   2,136.1   1,778.3
Financing Receivable, Excluding Accrued Interest, Revolving 67.0   67.0   74.1
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 9.4   9.4   109.8
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 7,746.5   7,746.5   8,833.8
Commercial real estate | Other Assets Especially Mentioned          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 170.4   170.4   78.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 92.4   92.4   17.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 16.7   16.7   15.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 37.9   37.9   16.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 77.6   77.6   4.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 110.3   110.3   79.2
Financing Receivable, Excluding Accrued Interest, Revolving 0.1   0.1   0.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   9.8
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 505.4   505.4   222.3
Commercial real estate | Substandard          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 24.5   24.5   81.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 39.5   39.5   12.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 41.1   41.1   22.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 26.3   26.3   37.3
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 37.4   37.4   10.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 49.2   49.2   43.5
Financing Receivable, Excluding Accrued Interest, Revolving 0.2   0.2   0.5
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 218.2   218.2   207.1
Commercial real estate | Doubtful          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 1.9   1.9    
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 2.8   2.8    
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 5.7   5.7    
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 15.9   15.9    
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.0   0.0    
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0    
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0    
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0    
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 26.3   26.3    
Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.3   0.3   3.7
Nonaccrual loans 4.2   4.2   3.3
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 233.4   233.4   443.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 278.6   278.6   233.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 114.1   114.1   326.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 195.8   195.8   76.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 32.5   32.5   17.3
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 24.1   24.1   20.9
Financing Receivable, Excluding Accrued Interest, Revolving 82.3   82.3   124.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   1.8
Financing Receivable, Allowance for Credit Loss, Writeoff         13.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 960.8   960.8   1,244.6
Total construction loans | Pass          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 225.2   225.2   438.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 271.4   271.4   233.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 113.9   113.9   320.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 185.6   185.6   76.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 30.7   30.7   17.3
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 24.0   24.0   20.9
Financing Receivable, Excluding Accrued Interest, Revolving 82.1   82.1   124.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   1.8
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 932.9   932.9   1,232.5
Total construction loans | Other Assets Especially Mentioned          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 6.4   6.4   2.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 1.0   1.0   0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 0.2   0.2   6.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 0.1   0.1   0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 7.7   7.7   8.5
Total construction loans | Substandard          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 1.8   1.8    
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 4.9   4.9    
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 0.0   0.0    
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 10.1   10.1    
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 1.0   1.0    
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.1   0.1    
Financing Receivable, Excluding Accrued Interest, Revolving 0.2   0.2    
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0    
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 18.1   18.1    
Total construction loans | Doubtful          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 0.0   0.0   3.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 1.3   1.3   0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.8   0.8   0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 2.1   2.1   3.6
Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 3.2   3.2   9.7
Nonaccrual loans 16.1   16.1   15.4
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 25.8   25.8   23.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 35.0   35.0   75.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 76.7   76.7   414.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 404.3   404.3   489.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 461.8   461.8   441.3
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 621.1   621.1   257.4
Financing Receivable, Excluding Accrued Interest, Revolving 503.1   503.1   477.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 8.2   8.2   12.5
Financing Receivable, Allowance for Credit Loss, Writeoff     1.1   1.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 2,136.0   2,136.0   2,191.6
Residential | Performing Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 25.3   25.3   22.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 34.0   34.0   73.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 74.9   74.9   409.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 399.1   399.1   487.3
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 459.5   459.5   440.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 615.9   615.9   252.5
Financing Receivable, Excluding Accrued Interest, Revolving 503.0   503.0   477.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 8.2   8.2   12.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 2,119.9   2,119.9   2,175.8
Residential | Nonperforming Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 0.5   0.5   1.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 1.0   1.0   1.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 1.8   1.8   4.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 5.2   5.2   2.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 2.3   2.3   1.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 5.2   5.2   4.9
Financing Receivable, Excluding Accrued Interest, Revolving 0.1   0.1   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 16.1   16.1   15.8
Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2.4   2.4   10.4
Nonaccrual loans 26.9   26.9   5.3
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 84.4   84.4   132.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 94.5   94.5   61.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 50.9   50.9   131.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 116.7   116.7   117.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 97.6   97.6   78.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 162.1   162.1   145.7
Financing Receivable, Excluding Accrued Interest, Revolving 16.8   16.8   33.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.5
Financing Receivable, Allowance for Credit Loss, Writeoff     0.2    
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 623.0   623.0   701.1
Agricultural | Pass          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 58.9   58.9   118.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 83.2   83.2   53.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 40.9   40.9   104.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 111.0   111.0   107.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 83.7   83.7   66.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 139.0   139.0   144.1
Financing Receivable, Excluding Accrued Interest, Revolving 15.7   15.7   33.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 532.4   532.4   628.2
Agricultural | Other Assets Especially Mentioned          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 9.1   9.1   1.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 10.5   10.5   0.2
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 3.5   3.5   6.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 3.4   3.4   6.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 8.6   8.6   8.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 12.3   12.3   0.7
Financing Receivable, Excluding Accrued Interest, Revolving 1.1   1.1   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 48.5   48.5   23.4
Agricultural | Substandard          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 16.4   16.4   12.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 0.8   0.8   8.2
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 6.5   6.5   19.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 2.3   2.3   3.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 5.3   5.3   4.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 10.8   10.8   0.9
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 42.1   42.1   49.5
Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 11.1   11.1   31.5
Nonaccrual loans 121.4   121.4   79.4
Financing Receivable, Allowance for Credit Loss, Writeoff 0.8 22.2 4.3 35.5 39.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 12,216.2   12,216.2   13,400.5
Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 8.2   8.2   11.7
Nonaccrual loans 4.8   4.8   3.9
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 31.4   31.4   267.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 193.7   193.7   128.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 88.6   88.6   168.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 117.4   117.4   69.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 46.8   46.8   44.8
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 62.4   62.4   46.1
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Allowance for Credit Loss, Writeoff     7.4   8.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 540.3   540.3   725.0
Indirect consumer | Performing Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 31.1   31.1   266.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 192.6   192.6   127.2
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 87.5   87.5   167.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 116.5   116.5   68.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 46.2   46.2   44.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 61.6   61.6   45.6
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 535.5   535.5   720.4
Indirect consumer | Nonperforming Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 0.3   0.3   0.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 1.1   1.1   1.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 1.1   1.1   1.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 0.9   0.9   0.6
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.6   0.6   0.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.8   0.8   0.5
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 4.8   4.8   4.6
Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 9.4   9.4   15.0
Nonaccrual loans 5.4   5.4   4.5
Financing Receivable, Allowance for Credit Loss, Writeoff 3.8 4.1 14.1 11.9 15.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 674.6   674.6   936.6
Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 7.5   7.5   14.8
Nonaccrual loans 40.0   40.0   33.5
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 230.0   230.0   473.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 366.2   366.2   373.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 269.2   269.2   392.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 329.5   329.5   324.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 251.0   251.0   173.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 287.0   287.0   259.2
Financing Receivable, Excluding Accrued Interest, Revolving 707.0   707.0   821.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 7.5   7.5   10.4
Financing Receivable, Allowance for Credit Loss, Writeoff 2.1 2.5 7.2 8.7 59.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 2,447.4   2,447.4   2,829.4
Commercial | Pass          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 211.9   211.9   438.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 329.8   329.8   353.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 256.7   256.7   375.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 297.0   297.0   316.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 242.7   242.7   165.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 284.9   284.9   255.2
Financing Receivable, Excluding Accrued Interest, Revolving 625.1   625.1   767.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 7.3   7.3   8.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 2,255.4   2,255.4   2,681.0
Commercial | Other Assets Especially Mentioned          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 8.6   8.6   3.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 22.4   22.4   13.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 4.2   4.2   3.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 2.3   2.3   2.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 3.9   3.9   6.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.2   0.2   0.6
Financing Receivable, Excluding Accrued Interest, Revolving 37.7   37.7   19.1
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 79.3   79.3   49.0
Commercial | Substandard          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 8.0   8.0   30.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 11.6   11.6   5.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 7.8   7.8   12.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 23.9   23.9   5.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 4.0   4.0   1.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 1.9   1.9   3.4
Financing Receivable, Excluding Accrued Interest, Revolving 44.2   44.2   35.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.2   0.2   1.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 101.6   101.6   96.2
Commercial | Doubtful          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 1.5   1.5   0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 2.4   2.4   1.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 0.5   0.5   1.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 6.3   6.3   0.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.4   0.4   0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 11.1   11.1   3.2
Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 1.1   1.1   5.2
Nonaccrual loans 14.8   14.8   20.9
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 82.8   82.8   136.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 48.6   48.6   61.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 25.4   25.4   40.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 32.2   32.2   16.8
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 10.9   10.9   14.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 7.3   7.3   5.9
Financing Receivable, Excluding Accrued Interest, Revolving 288.3   288.3   410.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   1.4
Financing Receivable, Allowance for Credit Loss, Writeoff 0.0 $ 0.3 4.9 $ 0.3 0.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 495.5   495.5   687.9
Agricultural | Pass          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 62.6   62.6   109.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 41.8   41.8   34.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 19.3   19.3   39.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 29.3   29.3   16.6
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 10.3   10.3   13.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 6.8   6.8   5.8
Financing Receivable, Excluding Accrued Interest, Revolving 246.1   246.1   379.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   1.1
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 416.2   416.2   599.5
Agricultural | Other Assets Especially Mentioned          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 13.1   13.1   4.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 3.3   3.3   1.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 2.8   2.8   0.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 2.8   2.8   0.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.6   0.6   0.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0   0.1
Financing Receivable, Excluding Accrued Interest, Revolving 33.3   33.3   5.1
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 55.9   55.9   12.7
Agricultural | Substandard          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 1.6   1.6   4.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 3.4   3.4   25.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 0.7   0.7   0.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 0.1   0.1   0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.0   0.0   0.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.5   0.5   0.0
Financing Receivable, Excluding Accrued Interest, Revolving 6.9   6.9   25.9
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 13.2   13.2   56.8
Agricultural | Doubtful          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 5.5   5.5   18.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 0.1   0.1   0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 2.6   2.6   0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving 2.0   2.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 10.2   10.2   18.9
Other, including overdrafts          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
Nonaccrual loans 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 10.2   10.2   1.6
Loans And Leases Held For Investment [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 29.1   29.1   66.5
Nonaccrual loans 181.6   181.6   138.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 15,843.9   15,843.9   17,856.0
Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 1.2   1.2   1.1
Nonaccrual loans 0.6   0.6   0.6
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 40.4   40.4   46.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 30.3   30.3   25.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 16.1   16.1   18.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 11.8   11.8   10.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 6.2   6.2   4.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 6.1   6.1   5.3
Financing Receivable, Excluding Accrued Interest, Revolving 23.2   23.2   23.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.2   0.2   0.1
Financing Receivable, Allowance for Credit Loss, Writeoff     3.2   3.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 134.3   134.3   134.0
Consumer Loan | Performing Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 40.2   40.2   46.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 30.1   30.1   25.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 16.0   16.0   18.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 11.7   11.7   10.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 6.2   6.2   4.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 6.1   6.1   5.2
Financing Receivable, Excluding Accrued Interest, Revolving 23.2   23.2   23.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.2   0.2   0.1
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 133.7   133.7   133.1
Consumer Loan | Nonperforming Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year 0.2   0.2   0.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year 0.2   0.2   0.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year 0.1   0.1   0.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year 0.1   0.1   0.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year 0.0   0.0   0.1
Financing Receivable, Excluding Accrued Interest, Revolving 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 0.6   0.6   0.9
Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   2.2
Nonaccrual loans 0.0   0.0   0.0
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Revolving         77.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan         0.0
Financing Receivable, Allowance for Credit Loss, Writeoff     3.5   3.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process 0.0   0.0   77.6
Credit Card Receivable [Member] | Performing Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Revolving         76.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan         0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process         76.6
Credit Card Receivable [Member] | Nonperforming Financial Instruments [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year         0.0
Financing Receivable, Excluding Accrued Interest, Revolving         1.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan         0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process         1.0
30 to 59 Days Past Due          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Nonaccrual loans 13.0   13.0   13.5
30 to 59 Days Past Due | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 5.0   5.0   4.9
30 to 59 Days Past Due | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.3   0.3   3.7
30 to 59 Days Past Due | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2.1   2.1   6.6
30 to 59 Days Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2.4   2.4   7.6
30 to 59 Days Past Due | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 9.8   9.8   22.8
30 to 59 Days Past Due | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 6.0   6.0   8.4
30 to 59 Days Past Due | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 6.7   6.7   9.7
30 to 59 Days Past Due | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 5.3   5.3   11.2
30 to 59 Days Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 1.1   1.1   2.4
30 to 59 Days Past Due | Other, including overdrafts          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
30 to 59 Days Past Due | Loans And Leases Held For Investment [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 22.9   22.9   46.1
30 to 59 Days Past Due | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.7   0.7   0.6
30 to 59 Days Past Due | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.7
60 to 89 Days Past Due          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Nonaccrual loans 5.5   5.5   6.2
60 to 89 Days Past Due | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.2   0.2   2.8
60 to 89 Days Past Due | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
60 to 89 Days Past Due | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 1.1   1.1   2.7
60 to 89 Days Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   2.8
60 to 89 Days Past Due | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 1.3   1.3   8.3
60 to 89 Days Past Due | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2.2   2.2   2.6
60 to 89 Days Past Due | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2.7   2.7   3.3
60 to 89 Days Past Due | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 1.6   1.6   3.0
60 to 89 Days Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   2.8
60 to 89 Days Past Due | Other, including overdrafts          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
60 to 89 Days Past Due | Loans And Leases Held For Investment [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 5.6   5.6   17.4
60 to 89 Days Past Due | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.5   0.5   0.2
60 to 89 Days Past Due | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.5
Equal to or Greater than 90 Days Past Due          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Nonaccrual loans 88.6   88.6   40.5
Equal to or Greater than 90 Days Past Due | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
Equal to or Greater than 90 Days Past Due | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
Equal to or Greater than 90 Days Past Due | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.4
Equal to or Greater than 90 Days Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
Equal to or Greater than 90 Days Past Due | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.4
Equal to or Greater than 90 Days Past Due | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.7
Equal to or Greater than 90 Days Past Due | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   2.0
Equal to or Greater than 90 Days Past Due | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.6   0.6   0.6
Equal to or Greater than 90 Days Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
Equal to or Greater than 90 Days Past Due | Other, including overdrafts          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.0
Equal to or Greater than 90 Days Past Due | Loans And Leases Held For Investment [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.6   0.6   3.0
Equal to or Greater than 90 Days Past Due | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   0.3
Equal to or Greater than 90 Days Past Due | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 0.0   0.0   1.0
Financial Asset, Not Past Due | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 8,417.0   8,417.0   9,200.1
Financial Asset, Not Past Due | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 956.3   956.3   1,237.6
Financial Asset, Not Past Due | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2,116.7   2,116.7   2,166.5
Financial Asset, Not Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 593.7   593.7   685.4
Financial Asset, Not Past Due | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 12,083.7   12,083.7   13,289.6
Financial Asset, Not Past Due | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 527.3   527.3   709.4
Financial Asset, Not Past Due | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 659.8   659.8   917.1
Financial Asset, Not Past Due | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 2,399.9   2,399.9   2,781.1
Financial Asset, Not Past Due | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 479.6   479.6   661.8
Financial Asset, Not Past Due | Other, including overdrafts          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 10.2   10.2   1.6
Financial Asset, Not Past Due | Loans And Leases Held For Investment [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 15,633.2   15,633.2   17,651.2
Financial Asset, Not Past Due | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process 132.5   132.5   132.3
Financial Asset, Not Past Due | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Loan in Process $ 0.0   0.0   75.4
Year One, Originated, Current Fiscal Year          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.5   22.5
Year One, Originated, Current Fiscal Year | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.2
Year One, Originated, Current Fiscal Year | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.0
Year One, Originated, Current Fiscal Year | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year One, Originated, Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Year One, Originated, Current Fiscal Year | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.2
Year One, Originated, Current Fiscal Year | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.4   0.5
Year One, Originated, Current Fiscal Year | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.5   0.7
Year One, Originated, Current Fiscal Year | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   21.6
Year One, Originated, Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.0   0.0
Year One, Originated, Current Fiscal Year | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   0.2
Year One, Originated, Current Fiscal Year | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     6.9   10.7
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   5.7
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.5   0.2
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.5   5.9
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     1.8   2.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.6   2.6
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.9   2.2
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.9   0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.8   0.6
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Three, Originated, Two Years before Current Fiscal Year          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     5.0   18.7
Year Three, Originated, Two Years before Current Fiscal Year | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Three, Originated, Two Years before Current Fiscal Year | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         13.1
Year Three, Originated, Two Years before Current Fiscal Year | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   0.2
Year Three, Originated, Two Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.2    
Year Three, Originated, Two Years before Current Fiscal Year | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.3   13.3
Year Three, Originated, Two Years before Current Fiscal Year | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     1.8   3.4
Year Three, Originated, Two Years before Current Fiscal Year | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.3   4.3
Year Three, Originated, Two Years before Current Fiscal Year | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.4   1.1
Year Three, Originated, Two Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Three, Originated, Two Years before Current Fiscal Year | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.5   0.9
Year Three, Originated, Two Years before Current Fiscal Year | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Four, Originated, Three Years before Current Fiscal Year          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     3.9   21.4
Year Four, Originated, Three Years before Current Fiscal Year | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.2   19.4
Year Four, Originated, Three Years before Current Fiscal Year | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.0
Year Four, Originated, Three Years before Current Fiscal Year | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.3   0.1
Year Four, Originated, Three Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Year Four, Originated, Three Years before Current Fiscal Year | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.5   19.5
Year Four, Originated, Three Years before Current Fiscal Year | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.0   1.1
Year Four, Originated, Three Years before Current Fiscal Year | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.2   1.3
Year Four, Originated, Three Years before Current Fiscal Year | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     1.2   0.3
Year Four, Originated, Three Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.3
Year Four, Originated, Three Years before Current Fiscal Year | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.2   0.2
Year Four, Originated, Three Years before Current Fiscal Year | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Five, Originated, Four Years before Current Fiscal Year          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     3.7   0.9
Year Five, Originated, Four Years before Current Fiscal Year | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.5   0.0
Year Five, Originated, Four Years before Current Fiscal Year | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.1
Year Five, Originated, Four Years before Current Fiscal Year | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   0.3
Year Five, Originated, Four Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Year Five, Originated, Four Years before Current Fiscal Year | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.6   0.4
Year Five, Originated, Four Years before Current Fiscal Year | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.7   0.4
Year Five, Originated, Four Years before Current Fiscal Year | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.8   0.4
Year Five, Originated, Four Years before Current Fiscal Year | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.3   0.1
Year Five, Originated, Four Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Year Five, Originated, Four Years before Current Fiscal Year | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   0.0
Year Five, Originated, Four Years before Current Fiscal Year | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Originated, More than Five Years before Current Fiscal Year          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     3.0   3.3
Originated, More than Five Years before Current Fiscal Year | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.3   0.1
Originated, More than Five Years before Current Fiscal Year | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.0
Originated, More than Five Years before Current Fiscal Year | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   0.2
Originated, More than Five Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Originated, More than Five Years before Current Fiscal Year | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.4   0.3
Originated, More than Five Years before Current Fiscal Year | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.7   1.1
Originated, More than Five Years before Current Fiscal Year | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     2.2   2.9
Originated, More than Five Years before Current Fiscal Year | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.4   0.1
Originated, More than Five Years before Current Fiscal Year | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Originated, More than Five Years before Current Fiscal Year | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     1.5   1.8
Originated, More than Five Years before Current Fiscal Year | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     5.4   34.2
Revolving | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.0
Revolving | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Revolving | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     3.5   3.1
Revolving | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     1.9   31.1
Revolving | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.1
Revolving | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     3.5   3.0
Revolving, Converted to Term          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   3.0
Revolving, Converted to Term | Commercial real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving, Converted to Term | Total construction loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff         0.0
Revolving, Converted to Term | Residential          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving, Converted to Term | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0    
Revolving, Converted to Term | Total real estate          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving, Converted to Term | Indirect consumer          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving, Converted to Term | Total consumer loans          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.1
Revolving, Converted to Term | Commercial          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.1   2.9
Revolving, Converted to Term | Agricultural          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.0
Revolving, Converted to Term | Consumer Loan          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     0.0   0.1
Revolving, Converted to Term | Credit Card Receivable [Member]          
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]          
Financing Receivable, Allowance for Credit Loss, Writeoff     $ 0.0   $ 0.0