Finance Receivables within Credit Quality Indicator and Portfolio Class (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	$ 2,234.0	$ 1,299.4
2023	2,824.4	2,449.0
2022	1,875.9	1,670.9
2021	1,133.1	1,061.3
2020	659.5	667.5
2019	323.7	235.3
Prior	150.5	147.3
Total	9,201.1	7,530.7
Dealer
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	2,234.0	1,299.4
2023	677.3	546.2
2022	467.2	315.5
2021	267.6	182.7
2020	135.2	214.9
2019	146.3	97.5
Prior	106.6	105.0
Total	4,034.2	2,761.2
Dealer | Wholesale
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	1,953.3	1,093.2
Total	1,953.3	1,093.2
Dealer | Wholesale | Performing
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	1,951.4	1,087.0
Total	1,951.4	1,087.0
Dealer | Wholesale | Watch
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	1.9	6.2
Total	1.9	6.2
Dealer | Retail
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	280.7	206.2
2023	677.3	546.2
2022	467.2	315.5
2021	267.6	182.7
2020	135.2	214.9
2019	146.3	97.5
Prior	106.6	105.0
Total	2,080.9	1,668.0
Dealer | Retail | Performing
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	280.7	206.2
2023	677.3	546.2
2022	467.2	315.5
2021	267.6	182.7
2020	135.2	214.9
2019	146.3	97.5
Prior	106.6	105.0
Total	2,080.9	1,668.0
Customer Retail
Financing Receivable Recorded Investment [Line Items]
2023	2,147.1	1,902.8
2022	1,408.7	1,355.4
2021	865.5	878.6
2020	524.3	452.6
2019	177.4	137.8
Prior	43.9	42.3
Total	5,166.9	4,769.5
Customer Retail | Gross Charge-Offs
Financing Receivable Recorded Investment [Line Items]
2023	0.7
2022	3.1
2021	1.6
2020	0.4
2019	3.8
Prior	0.2
Total	9.8
Customer Retail | Fleet
Financing Receivable Recorded Investment [Line Items]
2023	1,993.8	1,702.7
2022	1,265.5	1,137.9
2021	733.1	753.7
2020	457.3	395.9
2019	152.6	119.8
Prior	39.9	39.6
Total	4,642.2	4,149.6
Customer Retail | Fleet | Performing
Financing Receivable Recorded Investment [Line Items]
2023	1,967.2	1,698.2
2022	1,244.9	1,130.2
2021	725.3	751.7
2020	453.3	382.6
2019	151.5	113.7
Prior	38.9	38.6
Total	4,581.1	4,115.0
Customer Retail | Fleet | Watch
Financing Receivable Recorded Investment [Line Items]
2023	24.2	2.9
2022	16.6	1.7
2021	3.3	0.3
2020	2.0	2.9
2019	0.5	2.0
Prior	0.9	0.6
Total	47.5	10.4
Customer Retail | Fleet | At-risk
Financing Receivable Recorded Investment [Line Items]
2023	2.4	1.6
2022	4.0	6.0
2021	4.5	1.7
2020	2.0	10.4
2019	0.6	4.1
Prior	0.1	0.4
Total	13.6	24.2
Customer Retail | Fleet | Gross Charge-Offs
Financing Receivable Recorded Investment [Line Items]
2023	0.5
2022	2.4
2021	0.8
2020	0.2
2019	3.8
Total	7.7
Customer Retail | Owner/Operator
Financing Receivable Recorded Investment [Line Items]
2023	153.3	200.1
2022	143.2	217.5
2021	132.4	124.9
2020	67.0	56.7
2019	24.8	18.0
Prior	4.0	2.7
Total	524.7	619.9
Customer Retail | Owner/Operator | Performing
Financing Receivable Recorded Investment [Line Items]
2023	151.8	199.2
2022	140.5	216.8
2021	130.5	124.7
2020	66.3	56.5
2019	24.5	17.9
Prior	4.0	2.7
Total	517.6	617.8
Customer Retail | Owner/Operator | Watch
Financing Receivable Recorded Investment [Line Items]
2023	0.9	0.5
2022	1.9	0.4
2021	1.1	0.1
2020	0.5
2019	0.2
Total	4.6	1.0
Customer Retail | Owner/Operator | At-risk
Financing Receivable Recorded Investment [Line Items]
2023	0.6	0.4
2022	0.8	0.3
2021	0.8	0.1
2020	0.2	0.2
2019	0.1	0.1
Total	2.5	$ 1.1
Customer Retail | Owner/Operator | Gross Charge-Offs
Financing Receivable Recorded Investment [Line Items]
2023	0.2
2022	0.7
2021	0.8
2020	0.2
Prior	0.2
Total	$ 2.1