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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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	$ 4.3	$ 7.2	$ 8.4	$ 9.0
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)	(3.9)	0.1	2.9	20.3
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	182.2	209.6	182.2	209.6	$ 191.4	$ 195.8	$ 215.3	$ 204.1
Financing Receivable, Allowance for Credit Loss, Writeoff	14.0	13.0	20.5	23.8	55.0
Provision for Loan, Lease, and Other Losses	(3.2)	(0.3)	3.5	19.7
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.4		22.0
Agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	0.1	0.1	0.2	0.1
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	3.5	6.0	3.5	6.0	12.1	13.2	7.1	9.0
Financing Receivable, Allowance for Credit Loss, Writeoff	8.5	2.0	8.5	4.9	5.0
Provision for Loan, Lease, and Other Losses	(1.3)	0.8	(0.3)	1.8
Residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			1.0		1.4
Agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.1		0.2
Total real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	2.5	5.2	4.0	5.3
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	127.9	148.7	127.9	148.7	131.2	128.9	146.0	139.4
Financing Receivable, Allowance for Credit Loss, Writeoff	1.0	3.2	1.5	3.5	23.6
Provision for Loan, Lease, and Other Losses	(2.5)	0.7	(5.8)	7.5
Indirect consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			4.0		9.6
Total consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	1.1	1.5	2.1	2.7
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	10.5	12.0	10.5	12.0	11.2	12.3	15.9	16.8
Financing Receivable, Allowance for Credit Loss, Writeoff	2.4	5.6	6.2	10.3	17.5
Provision for Loan, Lease, and Other Losses	(0.5)	0.2	3.4	2.8
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	0.6	0.4	2.1	0.9
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	40.3	42.9	40.3	42.9	36.9	$ 41.4	$ 46.3	$ 38.9
Financing Receivable, Allowance for Credit Loss, Writeoff	2.1	2.2	4.3	5.1	$ 8.9
Provision for Loan, Lease, and Other Losses	$ 0.4	$ (1.6)	$ 5.6	$ 8.2