STATEMENTS OF COMPREHENSIVE INCOME AND RETAINED EARNINGS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024		Jun. 30, 2023
Income Statement [Abstract]
Interest and fee income	$ 160.9	$ 112.1	$ 308.0		$ 212.7
Operating lease and rental revenues	42.4	62.0	94.7		131.9
Used truck sales and other revenues	5.7	4.7	17.5		11.7
TOTAL INTEREST AND OTHER REVENUES	209.0	178.8	420.2		356.3
Interest and other borrowing costs	97.8	64.1	187.5		117.2
Depreciation and other rental expenses	41.5	43.5	89.1		91.7
Cost of used truck sales and other expenses	5.6	3.4	17.1		8.6
Selling, general and administrative expenses	18.0	16.0	35.2		31.6
Provision for losses on receivables	6.1	0.8	13.2		1.4
TOTAL EXPENSES	169.0	127.8	342.1		250.5
INCOME BEFORE INCOME TAXES	40.0	51.0	78.1		105.8
Income taxes	10.0	12.7	18.9		26.4
NET INCOME	30.0	38.3	59.2		79.4
COMPREHENSIVE INCOME	29.3	45.0	60.4		77.9
RETAINED EARNINGS AT BEGINNING OF PERIOD	1,682.3	1,604.7	1,703.1	[1]	1,813.6
RETAINED EARNINGS AT END OF PERIOD	$ 1,712.3	$ 1,643.0	$ 1,712.3		$ 1,643.0

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