Loans Held for Investment - Schedule of Contractual Aging of Loans by Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Nonaccrual loans	$ 53.1		$ 59.8
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	14,728.4		15,201.6
Financing Receivable, Allowance for Credit Loss, Writeoff	6.5	$ 10.8	55.0
Financing Receivable, Nonaccrual, Interest Income	(1.3)	(0.4)
Accrued interest reversal	(0.5)	(1.5)
Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	37.8		40.1
Nonaccrual loans	34.6		35.6
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	289.0		1,204.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,119.1		1,021.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	985.0		1,172.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	1,139.4		1,412.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1,378.1		1,194.3
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	2,996.8		2,029.7
Financing Receivable, Excluding Accrued Interest, Revolving	61.0		59.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	72.1		49.5
Financing Receivable, Allowance for Credit Loss, Writeoff			22.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	8,040.5		8,144.4
Commercial real estate | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	255.1		1,025.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	991.1		948.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	947.9		1,095.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	1,058.0		1,344.8
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1,276.4		1,101.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	2,772.6		1,892.9
Financing Receivable, Excluding Accrued Interest, Revolving	60.4		59.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	72.1		49.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	7,433.6		7,517.2
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	2.8		96.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	59.3		28.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	24.1		43.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	46.8		35.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	69.3		64.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	156.1		88.4
Financing Receivable, Excluding Accrued Interest, Revolving	0.6		0.6
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	359.0		357.9
Commercial real estate | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	31.1		81.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	66.8		41.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	8.0		27.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	28.5		32.7
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	31.6		27.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	67.7		48.4
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	233.7		259.1
Commercial real estate | Doubtful
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	0.0		1.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	1.9		2.2
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	5.0		5.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	6.1		0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.8		0.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.4		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	14.2		10.2
Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.9		13.5
Nonaccrual loans	4.3		4.3
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	25.8		254.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	210.5		217.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	155.8		110.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	68.5		107.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	120.6		27.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	45.7		21.4
Financing Receivable, Excluding Accrued Interest, Revolving	41.1		86.1
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	1.1		12.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	669.1		837.2
Total construction loans | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	24.1		240.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	198.3		211.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	148.7		110.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	68.3		92.3
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	106.0		25.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	44.8		21.3
Financing Receivable, Excluding Accrued Interest, Revolving	40.7		85.9
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	1.1		12.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	632.0		799.4
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	0.0		3.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	9.4		5.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.6		0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.0		14.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.1		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	10.1		23.2
Total construction loans | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	1.7		10.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	2.8		0.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	5.2		0.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.2		0.3
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	14.5		1.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.2		0.1
Financing Receivable, Excluding Accrued Interest, Revolving	0.4		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	25.0		12.6
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
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.0		1.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	1.3		0.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.0		0.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.0		0.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.7		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	2.0		2.0
Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	9.1		10.9
Nonaccrual loans	13.7		13.9
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	9.9		46.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	55.9		36.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	40.1		72.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	70.3		399.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	391.0		451.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	1,021.2		601.6
Financing Receivable, Excluding Accrued Interest, Revolving	489.4		494.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	6.5		7.4
Financing Receivable, Allowance for Credit Loss, Writeoff	0.5		1.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	2,084.3		2,108.8
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	9.9		45.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	55.2		35.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	39.2		71.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	69.0		394.6
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	386.8		449.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	1,014.6		596.8
Financing Receivable, Excluding Accrued Interest, Revolving	489.4		494.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	6.5		7.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	2,070.6		2,094.8
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	0.0		0.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.7		1.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.9		1.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	1.3		4.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	4.2		2.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	6.6		4.8
Financing Receivable, Excluding Accrued Interest, Revolving	0.0		0.1
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	13.7		14.0
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	5.0		0.2
Nonaccrual loans	27.5		27.1
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	50.8		126.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	96.9		88.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	80.3		46.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	44.0		111.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	107.8		90.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	211.2		143.2
Financing Receivable, Excluding Accrued Interest, Revolving	27.3		21.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.9		0.6
Financing Receivable, Allowance for Credit Loss, Writeoff			0.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	619.2		629.0
Agricultural | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	29.9		100.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	92.6		68.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	57.8		36.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	34.6		104.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	99.9		73.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	175.8		121.6
Financing Receivable, Excluding Accrued Interest, Revolving	22.7		19.7
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.9		0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	514.2		524.8
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	1.1		10.2
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	1.8		10.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	8.3		3.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	2.9		4.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	3.6		8.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	18.9		13.8
Financing Receivable, Excluding Accrued Interest, Revolving	3.9		2.1
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	40.5		52.8
Agricultural | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	19.8		15.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	2.5		9.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	14.2		6.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	6.5		2.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	4.3		8.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	13.8		7.8
Financing Receivable, Excluding Accrued Interest, Revolving	0.7		0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	61.8		51.4
Agricultural | Doubtful
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	2.7
Financing Receivable, Excluding Accrued Interest, Revolving	0.0
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	2.7
Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	52.8		64.7
Nonaccrual loans	80.1		80.9
Financing Receivable, Allowance for Credit Loss, Writeoff	0.5	0.3	23.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	11,413.1		11,719.4
Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	6.3		8.3
Nonaccrual loans	4.3		5.6
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	1.2		31.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	27.2		171.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	150.2		75.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	65.3		103.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	90.4		40.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	85.1		55.7
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, Allowance for Credit Loss, Writeoff	2.7		9.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	419.4		477.5
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	1.2		30.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	26.5		169.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	149.0		74.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	64.4		102.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	89.7		39.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	84.1		54.9
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	414.9		471.8
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	0.0		0.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.7		1.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	1.2		1.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.9		1.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.7		0.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	1.0		0.8
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	4.5		5.7
Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	7.1		9.4
Nonaccrual loans	5.0		6.3
Financing Receivable, Allowance for Credit Loss, Writeoff	3.8	4.7	17.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	547.4		609.0
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	8.6		8.9
Nonaccrual loans	42.8		21.7
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	111.1		321.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	295.3		325.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	257.8		239.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	209.6		299.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	279.0		233.8
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	434.6		261.5
Financing Receivable, Excluding Accrued Interest, Revolving	689.3		672.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	66.2		6.1
Financing Receivable, Allowance for Credit Loss, Writeoff	2.2	2.9	8.9
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	2,342.9		2,359.6
Commercial | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	102.8		301.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	278.9		287.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	224.4		228.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	204.6		277.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	257.9		225.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	427.1		260.4
Financing Receivable, Excluding Accrued Interest, Revolving	625.9		593.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	48.3		4.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	2,169.9		2,178.5
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	0.2		6.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	3.4		23.7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	24.3		3.3
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	2.8		1.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	5.4		3.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	1.8		0.4
Financing Receivable, Excluding Accrued Interest, Revolving	54.5		52.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	92.4		91.4
Commercial | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	8.1		9.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	8.0		13.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	7.8		6.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	2.2		14.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	10.3		4.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	5.2		0.7
Financing Receivable, Excluding Accrued Interest, Revolving	8.9		26.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.2		1.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	50.7		76.6
Commercial | Doubtful
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	0.0		4.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	5.0		1.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	1.3		0.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.0		6.3
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	5.4		0.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.5		0.0
Financing Receivable, Excluding Accrued Interest, Revolving	0.0		0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	17.7		0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	29.9		13.1
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.5		1.1
Nonaccrual loans	26.9		24.6
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	35.5		97.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	78.9		30.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	23.8		21.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	16.2		28.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	24.6		7.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	9.7		5.1
Financing Receivable, Excluding Accrued Interest, Revolving	237.1		315.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	1.0		14.6
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	$ 2.9	5.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	426.8		520.2
Agricultural | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	31.7		80.2
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	46.7		25.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	19.5		15.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	12.4		25.6
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	22.0		7.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	9.1		4.7
Financing Receivable, Excluding Accrued Interest, Revolving	195.7		277.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.1		5.6
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	337.2		441.5
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	0.3		7.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	13.8		1.4
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	1.2		2.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.4		2.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1.3		0.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.0		0.0
Financing Receivable, Excluding Accrued Interest, Revolving	24.5		26.0
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	41.5		40.4
Agricultural | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	3.5		3.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	3.8		3.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	3.1		0.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.8		0.8
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1.3		0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.6		0.4
Financing Receivable, Excluding Accrued Interest, Revolving	14.9		9.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.9		1.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	28.9		19.5
Agricultural | Doubtful
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	0.0		6.2
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	14.6		0.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.0		2.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	2.6		0.0
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	2.0		2.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		8.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	19.2		18.8
Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.0		0.0
Nonaccrual loans	0.0		0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	5.8		1.7
Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	73.0		84.1
Nonaccrual loans	154.8		133.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	14,736.0		15,209.9
Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.8		1.1
Nonaccrual loans	0.7		0.7
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	13.0		47.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	40.7		25.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	22.2		13.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	11.4		10.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	8.2		5.3
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	9.2		5.1
Financing Receivable, Excluding Accrued Interest, Revolving	23.1		23.9
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.2		0.2
Financing Receivable, Allowance for Credit Loss, Writeoff	1.1		4.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	128.0		131.5
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	13.0		47.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	40.6		25.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	22.0		13.3
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	11.3		9.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	8.1		5.3
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	9.0		5.0
Financing Receivable, Excluding Accrued Interest, Revolving	23.1		23.9
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.2		0.1
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	127.3		130.8
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	0.0		0.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.1		0.2
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.2		0.1
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.1		0.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.1		0.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.2		0.1
Financing Receivable, Excluding Accrued Interest, Revolving	0.0		0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.1
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, Fee, and Loan in Process	0.7		0.7
Credit Card Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			3.5
30 to 59 Days Past Due
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Nonaccrual loans	8.0		4.5
30 to 59 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	12.5		34.1
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		13.4
30 to 59 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	8.6		8.3
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.6		0.2
30 to 59 Days Past Due | Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	26.0		56.0
30 to 59 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.7		6.5
30 to 59 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	5.2		7.4
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	6.2		3.1
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.1		0.5
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
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	41.5		67.0
30 to 59 Days Past Due | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.5		0.9
60 to 89 Days Past Due
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Nonaccrual loans	6.8		3.8
60 to 89 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	25.3		5.7
60 to 89 Days Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.6		0.1
60 to 89 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.5		2.5
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.3		0.0
60 to 89 Days Past Due | Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	26.7		8.3
60 to 89 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.4		1.7
60 to 89 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.7		1.9
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.6		4.9
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.4		0.6
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
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	30.4		15.7
60 to 89 Days Past Due | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.3		0.2
Equal to or Greater than 90 Days Past Due
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Nonaccrual loans	80.8		60.5
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		0.3
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
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		0.1
Equal to or Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.1		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	0.1		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	0.2		0.1
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	0.2		0.1
Equal to or Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.8		0.9
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
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
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	1.1		1.4
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
Financial Asset, Not Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	7,968.1		8,068.7
Financial Asset, Not Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	663.9		819.4
Financial Asset, Not Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,061.5		2,084.0
Financial Asset, Not Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	586.7		601.7
Financial Asset, Not Past Due | Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	11,280.2		11,573.8
Financial Asset, Not Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	408.8		463.6
Financial Asset, Not Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	535.3		593.3
Financial Asset, Not Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,291.5		2,329.0
Financial Asset, Not Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	395.4		494.5
Financial Asset, Not Past Due | Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	5.8		1.7
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	14,508.2		14,992.3
Financial Asset, Not Past Due | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	126.5		129.7
Year One, Originated, Current Fiscal Year
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0		3.8
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
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		0.1
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		0.1
Year One, Originated, Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0		0.6
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	0.0		1.0
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		0.7
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
Year One, Originated, Current Fiscal Year | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0		0.4
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
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	1.0		8.4
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			0.4
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	0.0		0.5
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	0.0		0.9
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	0.5		2.4
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	0.7		3.6
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	0.3		1.0
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
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	0.2		1.2
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
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	1.8		5.9
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			0.1
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		0.1
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			0.2
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	0.1		0.4
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	0.8		2.4
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	1.0		3.0
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	0.7		2.5
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
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	0.2		0.6
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
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	1.2		20.5
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			16.2
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	0.2		0.4
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	0.2		16.6
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	0.4		2.4
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	0.6		2.6
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	0.4		1.3
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
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
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	0.8		6.5
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			5.1
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	0.2		0.2
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	0.2		5.3
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	0.5		0.8
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	0.5		0.9
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	0.1		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 | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0		0.1
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
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	1.0		3.6
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			0.2
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	0.0		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
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	0.0		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	0.5		1.0
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	1.0		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	0.0		0.4
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 | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.5		1.9
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
Revolving
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.7		6.1
Revolving | Commercial real estate
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	0.0		3.5
Revolving | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.7		2.5
Revolving | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.1
Revolving | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 0.0		0.0
Revolving | Credit Card Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			3.5
Revolving, Converted to Term
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.2
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
Revolving, Converted to Term | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			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
Revolving, Converted to Term | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			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
Revolving, Converted to Term | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.2
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 | Consumer Loan
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.0
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