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Loans Held for Investment - Schedule of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	$ 7.2	$ 2.8	$ 9.0	$ 5.4
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)	0.1	18.6	20.3	27.0
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	209.6	232.8	209.6	232.8	$ 204.1	$ 215.3	$ 227.7	$ 227.7
Financing Receivable, Allowance for Credit Loss, Writeoff	13.0	16.3	23.8	27.3	114.7
Provision for Loan, Lease, and Other Losses	(0.3)	9.0	19.7	14.3
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			2.8		25.4
Agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	0.1	0.0	0.1	0.3
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	6.0	5.4	6.0	5.4	9.0	7.1	4.2	4.4
Financing Receivable, Allowance for Credit Loss, Writeoff	2.0	0.0	4.9	0.0	0.3
Provision for Loan, Lease, and Other Losses	0.8	1.2	1.8	0.7
Residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.7		1.0
Total real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	5.2	0.2	5.3	0.9
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	148.7	139.7	148.7	139.7	139.4	146.0	152.9	160.1
Financing Receivable, Allowance for Credit Loss, Writeoff	3.2	10.1	3.5	13.3	39.6
Provision for Loan, Lease, and Other Losses	0.7	(3.3)	7.5	(8.0)
Indirect consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			4.8		8.5
Total consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	1.5	1.3	2.7	2.3
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	12.0	18.5	12.0	18.5	16.8	15.9	12.6	13.0
Financing Receivable, Allowance for Credit Loss, Writeoff	5.6	4.0	10.3	7.8	15.4
Provision for Loan, Lease, and Other Losses	0.2	8.6	2.8	11.0
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	0.4	1.3	0.9	1.9
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	42.9	69.2	42.9	69.2	38.9	$ 46.3	$ 58.0	$ 50.2
Financing Receivable, Allowance for Credit Loss, Writeoff	2.2	2.2	5.1	6.2	$ 59.4
Provision for Loan, Lease, and Other Losses	$ (1.6)	$ 12.1	$ 8.2	$ 23.3