Loans Held for Investment - Schedule of Contractual Aging of Loans by Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	$ 1.2		$ 1.2
Less loans charged-off	16.3	$ 14.1	27.3	$ 23.0
Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	6.5		6.5		$ 18.8
Nonaccrual loans	37.7		37.7		28.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	9,054.5		9,054.5		8,869.2
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	623.2		623.2		1,337.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,385.6		1,385.6		2,085.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	2,008.7		2,008.7		1,675.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	1,555.9		1,555.9		1,215.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1,184.8		1,184.8		774.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	2,194.6		2,194.6		1,706.1
Financing Receivable, Excluding Accrued Interest, Revolving	51.7		51.7		47.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	50.0		50.0		28.1
Total	9,054.5		9,054.5		8,869.2
Less loans charged-off			5.7		7.6
Commercial real estate | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	599.5		599.5		1,268.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,360.8		1,360.8		2,065.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	1,985.1		1,985.1		1,612.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	1,482.6		1,482.6		1,200.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1,171.9		1,171.9		716.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	2,114.2		2,114.2		1,660.5
Financing Receivable, Excluding Accrued Interest, Revolving	51.6		51.6		46.5
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	40.9		40.9		28.1
Total	8,806.6		8,806.6		8,596.9
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	6.2		6.2		4.2
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	6.6		6.6		9.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	19.2		19.2		42.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	17.8		17.8		12.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	3.4		3.4		27.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	29.3		29.3		17.1
Financing Receivable, Excluding Accrued Interest, Revolving	0.1		0.1		0.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	82.6		82.6		113.7
Commercial real estate | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	17.5		17.5		65.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	18.2		18.2		11.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	4.4		4.4		18.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	55.5		55.5		2.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	9.5		9.5		30.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	51.1		51.1		28.5
Financing Receivable, Excluding Accrued Interest, Revolving	0.0		0.0		0.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	9.1		9.1		0.0
Total	165.3		165.3		157.3
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
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					1.3
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					0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan					0.0
Total					1.3
Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2.3		2.3		3.5
Nonaccrual loans	9.4		9.4		17.2
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	1,519.9		1,519.9		1,826.5
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	210.1		210.1		501.2
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	373.3		373.3		758.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	617.5		617.5		356.9
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	121.8		121.8		36.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	20.2		20.2		16.8
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	27.6		27.6		36.8
Financing Receivable, Excluding Accrued Interest, Revolving	121.1		121.1		104.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	28.3		28.3		14.6
Total	1,519.9		1,519.9		1,826.5
Less loans charged-off			7.0		10.3
Total construction loans | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	206.3		206.3		493.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	369.0		369.0		735.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	604.8		604.8		331.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	121.8		121.8		36.7
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	20.2		20.2		16.8
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	27.0		27.0		36.2
Financing Receivable, Excluding Accrued Interest, Revolving	121.1		121.1		104.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	28.3		28.3		13.7
Total	1,498.5		1,498.5		1,768.0
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	1.9		1.9		0.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.9		0.9		6.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	6.5		6.5		1.3
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	0.2		0.2		0.2
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		0.9
Total	9.5		9.5		9.5
Total construction loans | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	1.9		1.9		7.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	3.4		3.4		4.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	6.2		6.2		24.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.0		0.0		0.2
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	0.4		0.4		0.4
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
Total	11.9		11.9		36.0
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
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year					13.0
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					0.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan					0.0
Total					13.0
Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	8.7		8.7		15.6
Nonaccrual loans	13.3		13.3		10.7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	2,246.4		2,246.4		2,244.3
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	8.4		8.4		45.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	61.4		61.4		359.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	418.7		418.7		522.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	508.0		508.0		501.7
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	473.2		473.2		89.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	284.7		284.7		222.2
Financing Receivable, Excluding Accrued Interest, Revolving	481.6		481.6		471.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	10.4		10.4		32.1
Total	2,246.4		2,246.4		2,244.3
Less loans charged-off			0.6		0.6
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	7.9		7.9		44.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	60.6		60.6		356.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	415.1		415.1		521.3
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	506.0		506.0		500.6
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	471.8		471.8		88.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	278.6		278.6		217.1
Financing Receivable, Excluding Accrued Interest, Revolving	481.6		481.6		471.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	10.4		10.4		32.1
Total	2,232.0		2,232.0		2,233.0
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		1.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.8		0.8		2.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	3.6		3.6		1.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	2.0		2.0		1.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1.4		1.4		0.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	6.1		6.1		5.1
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
Total	14.4		14.4		11.3
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.1		4.1		1.8
Nonaccrual loans	4.8		4.8		5.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	723.5		723.5		716.8
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	77.6		77.6		96.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	81.1		81.1		154.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	141.7		141.7		133.3
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	131.6		131.6		98.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	90.7		90.7		58.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	174.6		174.6		136.7
Financing Receivable, Excluding Accrued Interest, Revolving	26.2		26.2		32.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		7.0
Total	723.5		723.5		716.8
Less loans charged-off			0.0		0.0
Agricultural | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	64.4		64.4		86.2
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	70.1		70.1		123.7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	117.6		117.6		126.2
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	124.7		124.7		93.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	84.3		84.3		56.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	172.4		172.4		124.3
Financing Receivable, Excluding Accrued Interest, Revolving	26.2		26.2		31.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		7.0
Total	659.7		659.7		649.4
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		1.1		2.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	6.6		6.6		9.5
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	4.5		4.5		3.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	3.2		3.2		1.9
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	5.0		5.0		1.5
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	1.3		1.3		11.3
Financing Receivable, Excluding Accrued Interest, Revolving	0.0		0.0		0.5
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	21.7		21.7		30.8
Agricultural | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	12.1		12.1		8.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	4.4		4.4		20.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	19.6		19.6		3.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	3.7		3.7		2.6
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1.4		1.4		0.4
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.9		0.9		1.1
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
Total	42.1		42.1		36.6
Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	21.6		21.6		39.7
Nonaccrual loans	65.2		65.2		61.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	13,544.3		13,544.3		13,656.8
Less loans charged-off	10.1	10.0	13.3	14.8
Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	9.0		9.0		10.6
Nonaccrual loans	3.2		3.2		2.7
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	733.7		733.7		740.9
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	130.4		130.4		195.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	164.6		164.6		265.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	217.3		217.3		116.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	93.9		93.9		81.5
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	63.8		63.8		33.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	63.7		63.7		49.4
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
Total	733.7		733.7		740.9
Less loans charged-off			4.5		7.3
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	130.3		130.3		194.9
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	163.9		163.9		264.7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	216.4		216.4		115.4
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	93.4		93.4		81.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	63.4		63.4		32.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	63.1		63.1		48.8
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
Total	730.5		730.5		737.8
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	0.1		0.1		0.4
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.7		0.7		0.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.9		0.9		0.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.5		0.5		0.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.4		0.4		0.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.6		0.6		0.6
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
Total	3.2		3.2		3.1
Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.8		0.8		1.1
Nonaccrual loans	0.5		0.5		0.3
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	139.0		139.0		141.6
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	27.3		27.3		44.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	34.1		34.1		33.0
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	25.5		25.5		18.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	13.9		13.9		9.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	6.6		6.6		3.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	7.2		7.2		6.0
Financing Receivable, Excluding Accrued Interest, Revolving	24.3		24.3		26.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.1		0.1		0.2
Total	139.0		139.0		141.6
Less loans charged-off			1.9		4.1
Direct and advance lines | Performing Financial Instruments [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	27.2		27.2		44.5
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	34.0		34.0		32.9
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	25.3		25.3		18.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	13.8		13.8		9.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	6.6		6.6		3.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	7.2		7.2		6.0
Financing Receivable, Excluding Accrued Interest, Revolving	24.3		24.3		26.2
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.1		0.1		0.2
Total	138.5		138.5		141.3
Direct and advance lines | Nonperforming Financial Instruments [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	0.1		0.1		0.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.1		0.1		0.1
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.2		0.2		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		0.0
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
Total	0.5		0.5		0.3
Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.7		1.7		1.8
Nonaccrual loans	0.0		0.0		0.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	76.1		76.1		76.5
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	0.0		0.0		0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.0		0.0		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	0.0		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	76.1		76.1		76.5
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	76.1		76.1		76.5
Less loans charged-off			1.4		2.6
Credit card | 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		0.0		0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.0		0.0		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	0.0		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	75.5		75.5		75.9
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	75.5		75.5		75.9
Credit card | 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		0.0		0.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	0.0		0.0		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	0.0		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	0.6		0.6		0.6
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	0.6		0.6		0.6
Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	11.5		11.5		13.5
Nonaccrual loans	3.7		3.7		3.0
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	948.8		948.8		959.0
Less loans charged-off	4.0	3.3	7.8	6.7
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	13.9		13.9		15.9
Nonaccrual loans	72.6		72.6		11.5
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	3,052.9		3,052.9		2,906.8
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	352.2		352.2		508.0
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	440.0		440.0		533.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	458.8		458.8		407.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	364.8		364.8		225.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	200.5		200.5		111.2
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	321.2		321.2		277.9
Financing Receivable, Excluding Accrued Interest, Revolving	912.0		912.0		836.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	3.4		3.4		8.2
Total	3,052.9		3,052.9		2,906.8
Less loans charged-off	2.2	0.8	6.2	1.5	3.4
Commercial | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	320.3		320.3		481.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	424.5		424.5		507.7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	439.9		439.9		389.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	356.4		356.4		215.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	190.8		190.8		108.7
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	316.9		316.9		272.9
Financing Receivable, Excluding Accrued Interest, Revolving	847.3		847.3		762.3
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	1.9		1.9		7.6
Total	2,898.0		2,898.0		2,745.7
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	1.4		1.4		7.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	7.9		7.9		4.7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	8.6		8.6		6.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	2.9		2.9		3.1
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	1.2		1.2		0.9
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	1.3		1.3		1.9
Financing Receivable, Excluding Accrued Interest, Revolving	16.1		16.1		14.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.2
Total	39.4		39.4		39.5
Commercial | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	29.3		29.3		15.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	5.9		5.9		19.6
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	9.4		9.4		9.0
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	4.9		4.9		7.0
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	8.5		8.5		1.6
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	3.0		3.0		3.0
Financing Receivable, Excluding Accrued Interest, Revolving	7.5		7.5		58.8
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	1.5		1.5		0.4
Total	70.0		70.0		115.2
Commercial | Doubtful
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	1.2		1.2		3.3
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	1.7		1.7		1.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.9		0.9		1.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.6		0.6		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		0.1
Financing Receivable, Excluding Accrued Interest, Revolving	41.1		41.1		0.1
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	45.5		45.5		6.4
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2.0		2.0		3.1
Nonaccrual loans	24.1		24.1		30.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	698.2		698.2		769.4
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	117.6		117.6		152.1
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	88.3		88.3		58.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	46.6		46.6		34.8
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	22.4		22.4		23.3
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	19.1		19.1		35.0
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	11.8		11.8		9.5
Financing Receivable, Excluding Accrued Interest, Revolving	392.3		392.3		449.4
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.1		0.1		6.5
Total	698.2		698.2		769.4
Less loans charged-off	0.0	$ 0.0	0.0	$ 0.0	0.0
Agricultural | Pass
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	64.7		64.7		105.7
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	60.1		60.1		57.7
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	45.7		45.7		31.6
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	21.7		21.7		22.4
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	18.4		18.4		6.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	11.6		11.6		7.2
Financing Receivable, Excluding Accrued Interest, Revolving	364.6		364.6		421.9
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.1		0.1		3.4
Total	586.9		586.9		656.0
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	0.4		0.4		2.6
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	3.4		3.4		0.8
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.7		0.7		0.5
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.1		0.1		0.2
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.1		0.1		0.1
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.2		0.2		0.1
Financing Receivable, Excluding Accrued Interest, Revolving	4.2		4.2		9.0
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		3.1
Total	9.1		9.1		16.4
Agricultural | Substandard
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year	52.5		52.5		43.8
Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year	24.8		24.8		0.3
Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year	0.2		0.2		2.7
Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year	0.1		0.1		0.7
Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year	0.6		0.6		28.8
Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year	0.0		0.0		2.2
Financing Receivable, Excluding Accrued Interest, Revolving	23.5		23.5		18.5
Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan	0.0		0.0		0.0
Total	101.7		101.7		97.0
Agricultural | 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		0.0
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	0.5		0.5
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
Total	0.5		0.5
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	3.1		3.1		0.1
Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	49.0		49.0		72.2
Nonaccrual loans	165.6		165.6		106.4
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss	18,247.3		18,247.3		18,292.1
30 to 59 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.1		4.1		12.7
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		3.1
30 to 59 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	3.3		3.3		11.9
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.3		1.3		1.8
30 to 59 Days Past Due | Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	9.0		9.0		29.5
30 to 59 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	6.5		6.5		8.0
30 to 59 Days Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.6		0.6		0.9
30 to 59 Days Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.7		0.7		0.7
30 to 59 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	7.8		7.8		9.6
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	11.3		11.3		14.5
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.7		1.7		0.1
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	29.8		29.8		53.7
60 to 89 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2.3		2.3		6.1
60 to 89 Days Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2.0		2.0		0.4
60 to 89 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4.3		4.3		3.1
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2.8		2.8		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	11.4		11.4		9.6
60 to 89 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2.5		2.5		2.2
60 to 89 Days Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.2		0.2		0.2
60 to 89 Days Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.4		0.4		0.5
60 to 89 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	3.1		3.1		2.9
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.8		1.8		1.1
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.3		0.3		0.0
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	16.6		16.6		13.6
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	0.1		0.1		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	1.1		1.1		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 | Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1.2		1.2		0.6
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		0.4
Equal to or Greater than 90 Days Past Due | Direct and advance lines
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 | Credit card
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 | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.6		0.6		1.0
Equal to or Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0.8		0.8		0.3
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		3.0
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	2.6		2.6		4.9
Financial Asset, Not Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	9,010.3		9,010.3		8,822.2
Financial Asset, Not Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,508.2		1,508.2		1,805.8
Financial Asset, Not Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,224.4		2,224.4		2,218.0
Financial Asset, Not Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	714.6		714.6		709.6
Financial Asset, Not Past Due | Total real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	13,457.5		13,457.5		13,555.6
Financial Asset, Not Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	721.5		721.5		727.6
Financial Asset, Not Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	137.7		137.7		140.2
Financial Asset, Not Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	74.4		74.4		74.7
Financial Asset, Not Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	933.6		933.6		942.5
Financial Asset, Not Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,966.4		2,966.4		2,879.4
Financial Asset, Not Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	672.1		672.1		735.9
Financial Asset, Not Past Due | Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	3.1		3.1		0.1
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	$ 18,032.7		18,032.7		18,113.5
Year One, Originated, Current Fiscal Year | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		1.7
Year One, Originated, Current Fiscal Year | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year One, Originated, Current Fiscal Year | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.3
Year One, Originated, Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year One, Originated, Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.5
Year One, Originated, Current Fiscal Year | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.2
Year One, Originated, Current Fiscal Year | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year One, Originated, Current Fiscal Year | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.2
Year One, Originated, Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			5.6		0.3
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.2		0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.7		3.2
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.3		0.5
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.8		0.4
Year Two, Originated, Fiscal Year Before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Three, Originated, Two Years before Current Fiscal Year | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		1.7
Year Three, Originated, Two Years before Current Fiscal Year | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			6.9		0.1
Year Three, Originated, Two Years before Current Fiscal Year | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.1
Year Three, Originated, Two Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Three, Originated, Two Years before Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			2.3		1.8
Year Three, Originated, Two Years before Current Fiscal Year | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.5		0.2
Year Three, Originated, Two Years before Current Fiscal Year | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Three, Originated, Two Years before Current Fiscal Year | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.8		0.5
Year Three, Originated, Two Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Four, Originated, Three Years before Current Fiscal Year | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		2.6
Year Four, Originated, Three Years before Current Fiscal Year | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Four, Originated, Three Years before Current Fiscal Year | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.1
Year Four, Originated, Three Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Four, Originated, Three Years before Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.6		0.8
Year Four, Originated, Three Years before Current Fiscal Year | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.2		0.4
Year Four, Originated, Three Years before Current Fiscal Year | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Four, Originated, Three Years before Current Fiscal Year | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.2		0.5
Year Four, Originated, Three Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Five, Originated, Four Years before Current Fiscal Year | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Five, Originated, Four Years before Current Fiscal Year | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.6
Year Five, Originated, Four Years before Current Fiscal Year | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.0
Year Five, Originated, Four Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Five, Originated, Four Years before Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.2		0.3
Year Five, Originated, Four Years before Current Fiscal Year | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.1
Year Five, Originated, Four Years before Current Fiscal Year | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Year Five, Originated, Four Years before Current Fiscal Year | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.2
Year Five, Originated, Four Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Originated, More than Five Years before Current Fiscal Year | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		1.3
Originated, More than Five Years before Current Fiscal Year | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Originated, More than Five Years before Current Fiscal Year | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.1		0.1
Originated, More than Five Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Originated, More than Five Years before Current Fiscal Year | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.7		0.7
Originated, More than Five Years before Current Fiscal Year | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.8		2.6
Originated, More than Five Years before Current Fiscal Year | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Originated, More than Five Years before Current Fiscal Year | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.1
Originated, More than Five Years before Current Fiscal Year | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.1
Revolving | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			1.4		2.6
Revolving | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			1.4		1.4
Revolving | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		9.6
Revolving, Converted to Term | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			0.0		0.0
Revolving, Converted to Term | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			2.9		0.1
Revolving, Converted to Term | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Less loans charged-off			$ 0.0		$ 0.0