Auto Loans Held for Investment (By Major Credit Grade) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	May 31, 2025	May 31, 2024	Feb. 28, 2025
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 1,986.4		$ 6,907.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,913.1		4,726.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,224.4		3,278.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,870.7		1,929.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,615.5		593.6
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	544.4		160.3
Financing Receivable, before Allowance for Credit Loss	$ 17,154.5		$ 17,594.6
Total ending managed receivables as percentage by major credit grade	100.00%		100.00%
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 141.7	$ 133.1	$ 589.2
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	43.5		196.2
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	31.6		193.2
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	38.2		107.2
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	20.5		30.3
Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff	7.8		17.6
Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff	0.1		44.7
Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,928.7		6,595.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,686.3		4,548.9
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,070.9		3,161.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,775.6		1,883.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,581.9		588.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	536.1		153.6
Financing Receivable, before Allowance for Credit Loss	$ 16,579.5		$ 16,930.3
Total ending managed receivables as percentage by major credit grade	96.60%		96.20%
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 120.2	113.0
Tier 2 & Tier 3
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	21.5	$ 20.1
Credit Grade A | Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,291.7		$ 4,132.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	3,716.6		2,607.9
Financing Receivable, Originated Two Years before Latest Fiscal Year	2,320.3		1,673.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,453.4		894.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	736.0		243.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	199.6		48.9
Financing Receivable, before Allowance for Credit Loss	$ 9,717.6		$ 9,600.7
Total ending managed receivables as percentage by major credit grade	56.60%		54.50%
Credit Grade B | Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 511.5		$ 2,041.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,657.2		1,664.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,500.2		1,163.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,033.8		746.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	638.7		244.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	234.1		69.7
Financing Receivable, before Allowance for Credit Loss	$ 5,575.5		$ 5,929.1
Total ending managed receivables as percentage by major credit grade	32.50%		33.70%
Credit Grade C And Other | Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 125.5		$ 422.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	312.5		277.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	250.4		324.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	288.4		242.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	207.2		99.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	102.4		35.0
Financing Receivable, before Allowance for Credit Loss	$ 1,286.4		$ 1,400.5
Total ending managed receivables as percentage by major credit grade	7.50%		8.00%
Credit Grade C And Other | Tier 2 & Tier 3
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 57.7		$ 311.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	226.8		177.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	153.5		116.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	95.1		46.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	33.6		5.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	8.3		6.7
Financing Receivable, before Allowance for Credit Loss	$ 575.0		$ 664.3
Total ending managed receivables as percentage by major credit grade	3.40%		3.80%