Auto Loans Held for Investment (By Major Credit Grade) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Aug. 31, 2025	Aug. 31, 2024	Aug. 31, 2025	Aug. 31, 2024	Feb. 28, 2025
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 3,550.8		$ 3,550.8		$ 6,907.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,332.2		5,332.2		4,726.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,749.6		3,749.6		3,278.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,485.7		2,485.7		1,929.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,310.7		1,310.7		593.6
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	350.7		350.7		160.3
Financing Receivable, before Allowance for Credit Loss	$ 16,779.7		$ 16,779.7		$ 17,594.6
Total ending managed receivables as percentage by major credit grade	100.00%		100.00%		100.00%
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 168.7	$ 163.8	$ 310.4	$ 296.9	$ 589.2
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff			94.8		196.2
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff			75.0		193.2
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff			80.9		107.2
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff			42.0		30.3
Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff			14.8		17.6
Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff			2.9		44.7
Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	3,461.7		3,461.7		6,595.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,122.2		5,122.2		4,548.9
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,612.8		3,612.8		3,161.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,403.1		2,403.1		1,883.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,285.0		1,285.0		588.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	344.4		344.4		153.6
Financing Receivable, before Allowance for Credit Loss	$ 16,229.2		$ 16,229.2		$ 16,930.3
Total ending managed receivables as percentage by major credit grade	96.70%		96.70%		96.20%
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 141.3	131.1	$ 261.5	244.1
Tier 2 & Tier 3
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	27.4	$ 32.7	48.9	$ 52.8
Credit Grade A | Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	2,333.0		2,333.0		$ 4,132.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	3,349.7		3,349.7		2,607.9
Financing Receivable, Originated Two Years before Latest Fiscal Year	2,047.4		2,047.4		1,673.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,244.6		1,244.6		894.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	590.6		590.6		243.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	126.8		126.8		48.9
Financing Receivable, before Allowance for Credit Loss	$ 9,692.1		$ 9,692.1		$ 9,600.7
Total ending managed receivables as percentage by major credit grade	57.70%		57.70%		54.50%
Credit Grade B | Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 885.4		$ 885.4		$ 2,041.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,481.2		1,481.2		1,664.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,340.8		1,340.8		1,163.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	906.8		906.8		746.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	522.2		522.2		244.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	143.5		143.5		69.7
Financing Receivable, before Allowance for Credit Loss	$ 5,279.9		$ 5,279.9		$ 5,929.1
Total ending managed receivables as percentage by major credit grade	31.50%		31.50%		33.70%
Credit Grade C And Other | Tier 1
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 243.3		$ 243.3		$ 422.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	291.3		291.3		277.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	224.6		224.6		324.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	251.7		251.7		242.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	172.2		172.2		99.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	74.1		74.1		35.0
Financing Receivable, before Allowance for Credit Loss	$ 1,257.2		$ 1,257.2		$ 1,400.5
Total ending managed receivables as percentage by major credit grade	7.50%		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	$ 89.1		$ 89.1		$ 311.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	210.0		210.0		177.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	136.8		136.8		116.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	82.6		82.6		46.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	25.7		25.7		5.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	6.3		6.3		6.7
Financing Receivable, before Allowance for Credit Loss	$ 550.5		$ 550.5		$ 664.3
Total ending managed receivables as percentage by major credit grade	3.30%		3.30%		3.80%