Auto Loan Receivables (Ending Managed Receivables By Major Credit Grade) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Aug. 31, 2024	Aug. 31, 2023	Aug. 31, 2024	Aug. 31, 2023	Feb. 29, 2024
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 4,046.9		$ 4,046.9		$ 6,936.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,735.9		5,735.9		5,074.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,118.3		4,118.3		3,333.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,577.9		2,577.9		1,308.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	917.4		917.4		600.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	373.0		373.0		137.4
Financing Receivable, before Allowance for Credit Loss	$ 17,769.4		$ 17,769.4		$ 17,391.8
Total ending managed receivables as percentage by major credit grade	100.00%		100.00%		100.00%
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 163.8	$ 143.2	$ 296.9	$ 253.0	$ 561.5
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff			106.5		129.8
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff			97.7		248.6
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff			59.6		41.0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff			16.9		19.7
Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff			12.3		11.4
Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff			3.9		111.0
Core managed receivables
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	3,879.1		3,879.1		6,637.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,521.9		5,521.9		4,898.0
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,974.1		3,974.1		3,261.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,519.6		2,519.6		1,299.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	910.3		910.3		588.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	361.8		361.8		128.2
Financing Receivable, before Allowance for Credit Loss	$ 17,166.8		$ 17,166.8		$ 16,813.3
Total ending managed receivables as percentage by major credit grade	96.60%		96.60%		96.70%
Financing Receivable, Allowance for Credit Loss, Writeoff	$ 131.1	118.7	$ 244.1	211.8
Other managed receivables
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Allowance for Credit Loss, Writeoff	32.7	$ 24.5	52.8	$ 41.2
Credit Grade A \| Core managed receivables
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	2,432.5		2,432.5		$ 3,922.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	3,204.6		3,204.6		2,660.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	2,137.6		2,137.6		1,635.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,237.3		1,237.3		614.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	410.1		410.1		268.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	139.3		139.3		40.0
Financing Receivable, before Allowance for Credit Loss	$ 9,561.4		$ 9,561.4		$ 9,141.1
Total ending managed receivables as percentage by major credit grade	53.80%		53.80%		52.60%
Credit Grade B \| Core managed receivables
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 1,194.6		$ 1,194.6		$ 2,370.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,987.3		1,987.3		1,738.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,432.4		1,432.4		1,225.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	968.0		968.0		493.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	358.6		358.6		233.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	155.7		155.7		61.3
Financing Receivable, before Allowance for Credit Loss	$ 6,096.6		$ 6,096.6		$ 6,123.5
Total ending managed receivables as percentage by major credit grade	34.30%		34.30%		35.20%
Credit Grade C And Other \| Core managed receivables
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 252.0		$ 252.0		$ 344.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	330.0		330.0		498.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	404.1		404.1		400.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	314.3		314.3		192.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	141.6		141.6		86.6
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	66.8		66.8		26.9
Financing Receivable, before Allowance for Credit Loss	$ 1,508.8		$ 1,508.8		$ 1,548.7
Total ending managed receivables as percentage by major credit grade	8.50%		8.50%		8.90%
Credit Grade C And Other \| Other managed receivables
Financing Receivable, By Major Credit Grade [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 167.8		$ 167.8		$ 299.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	214.0		214.0		176.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	144.2		144.2		72.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	58.3		58.3		9.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	7.1		7.1		12.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	11.2		11.2		9.2
Financing Receivable, before Allowance for Credit Loss	$ 602.6		$ 602.6		$ 578.5
Total ending managed receivables as percentage by major credit grade	3.40%		3.40%		3.30%

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