Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Financing Receivable, Accrued Interest, Writeoff	$ (2.7)	$ 1.5
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	8,869.2	8,528.6
Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	1,826.5	1,944.4
Residential Mortgage [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	2,244.3	2,188.3
Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	716.8	794.9
Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	13,656.8	13,456.2
Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	769.4	708.3
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	2,906.8	2,882.6
Loans held for investment
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	18,292.1	18,114.8
Indirect consumer
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	740.9	829.7
Other consumer
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	141.6	152.9
Collateral
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	52.6	39.1
Collateral | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	26.6	17.5
Collateral | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	17.0	3.2
Collateral | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	1.2	6.0
Collateral | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	45.3	27.2
Collateral | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.7	7.3
Collateral | Residential Real Estate
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.5	0.5
Collateral | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	6.6	4.6
Business Assets Pledged as Collateral | Collateral
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	5.2	7.1
Business Assets Pledged as Collateral | Collateral | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	1.7
Business Assets Pledged as Collateral | Collateral | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Business Assets Pledged as Collateral | Collateral | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.2
Business Assets Pledged as Collateral | Collateral | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	1.9
Business Assets Pledged as Collateral | Collateral | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.7	2.1
Business Assets Pledged as Collateral | Collateral | Residential Real Estate
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Business Assets Pledged as Collateral | Collateral | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	4.5	3.1
Real Property Pledged as Collateral | Collateral
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	46.7	32.0
Real Property Pledged as Collateral | Collateral | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	26.6	15.8
Real Property Pledged as Collateral | Collateral | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	17.0	3.2
Real Property Pledged as Collateral | Collateral | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	1.2	5.8
Real Property Pledged as Collateral | Collateral | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	45.3	25.3
Real Property Pledged as Collateral | Collateral | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	5.2
Real Property Pledged as Collateral | Collateral | Residential Real Estate
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.5	0.5
Real Property Pledged as Collateral | Collateral | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	1.4	1.5
Other Property | Collateral
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.7	0.0
Other Property | Collateral | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Other Property | Collateral | Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Other Property | Collateral | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Other Property | Collateral | Real Estate Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Other Property | Collateral | Agricultural Financing Receivable [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Other Property | Collateral | Residential Real Estate
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.0	0.0
Other Property | Collateral | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 0.7	$ 0.0