Loans Held for Investment - Schedule of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	$ 4.1	$ 1.8
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)	6.8	20.2
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	195.8	215.3	$ 191.4	$ 204.1
Financing Receivable, Allowance for Credit Loss, Writeoff	6.5	10.8	55.0
Provision for Loan, Lease, and Other Losses	6.7	20.0
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			22.0
Agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	0.1	0.0
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	13.2	7.1	12.1	9.0
Financing Receivable, Allowance for Credit Loss, Writeoff	0.0	2.9	5.0
Provision for Loan, Lease, and Other Losses	1.0	1.0
Residential
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff	0.5		1.4
Agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff			0.2
Total real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	1.5	0.1
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	128.9	146.0	131.2	139.4
Financing Receivable, Allowance for Credit Loss, Writeoff	0.5	0.3	23.6
Provision for Loan, Lease, and Other Losses	(3.3)	6.8
Indirect consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss, Writeoff	2.7		9.6
Total consumer loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	1.0	1.2
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	12.3	15.9	11.2	16.8
Financing Receivable, Allowance for Credit Loss, Writeoff	3.8	4.7	17.5
Provision for Loan, Lease, and Other Losses	3.9	2.6
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Recoveries Collected	1.5	0.5
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	41.4	46.3	36.9	$ 38.9
Financing Receivable, Allowance for Credit Loss, Writeoff	2.2	2.9	$ 8.9
Provision for Loan, Lease, and Other Losses	$ 5.2	$ 9.8

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

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