STATEMENTS OF COMPREHENSIVE INCOME AND RETAINED EARNINGS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024		Sep. 30, 2023
Income Statement [Abstract]
Interest and fee income	$ 174.9	$ 125.5	$ 482.9		$ 338.2
Operating lease and rental revenues	45.4	54.9	140.1		186.8
Used truck sales and other revenues	8.1	3.8	25.6		15.5
TOTAL INTEREST AND OTHER REVENUES	228.4	184.2	648.6		540.5
Interest and other borrowing costs	112.0	74.9	299.5		192.1
Depreciation and other rental expenses	43.2	47.1	132.3		138.8
Cost of used truck sales and other expenses	7.4	2.6	24.5		11.2
Selling, general and administrative expenses	18.1	16.3	53.3		47.9
Provision for losses on receivables	9.9	0.8	23.1		2.2
TOTAL EXPENSES	190.6	141.7	532.7		392.2
INCOME BEFORE INCOME TAXES	37.8	42.5	115.9		148.3
Income taxes	9.3	10.3	28.2		36.7
NET INCOME	28.5	32.2	87.7		111.6
COMPREHENSIVE INCOME	22.8	34.3	83.2		112.2
RETAINED EARNINGS AT BEGINNING OF PERIOD	1,712.3	1,643.0	1,703.1	[1]	1,813.6
RETAINED EARNINGS AT END OF PERIOD	$ 1,740.8	$ 1,675.2	$ 1,740.8		$ 1,675.2

[1] The December 31, 2023 balance sheet has been derived from audited financial statements.