Finance Receivables within Credit Quality Indicator and Portfolio Class (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	$ 950.7	$ 939.5
2022	726.4	2,285.9
2021	2,127.9	1,577.6
2020	1,414.8	1,089.9
2019	976.6	507.3
2018	429.0	218.7
Prior	278.6	123.8
Total	6,904.0	6,742.7
Dealer
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	950.7	939.5
2022	213.2	396.9
2021	367.6	262.2
2020	221.5	280.2
2019	265.2	139.6
2018	128.7	98.5
Prior	161.9	83.4
Total	2,308.8	2,200.3
Dealer | Wholesale
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	762.1	737.6
Total	762.1	737.6
Dealer | Wholesale | Performing
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	756.8	731.8
Total	756.8	731.8
Dealer | Wholesale | Watch
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	5.3	5.8
Total	5.3	5.8
Dealer | Retail
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	188.6	201.9
2022	213.2	396.9
2021	367.6	262.2
2020	221.5	280.2
2019	265.2	139.6
2018	128.7	98.5
Prior	161.9	83.4
Total	1,546.7	1,462.7
Dealer | Retail | Performing
Financing Receivable Recorded Investment [Line Items]
Revolving Loans	188.6	201.9
2022	213.2	389.9
2021	367.6	258.5
2020	221.5	271.0
2019	265.2	135.2
2018	128.7	97.4
Prior	161.9	83.4
Total	1,546.7	1,437.3
Dealer | Retail | Watch
Financing Receivable Recorded Investment [Line Items]
2022		7.0
2021		3.7
2020		9.2
2019		4.4
2018		1.1
Total		25.4
Customer Retail
Financing Receivable Recorded Investment [Line Items]
2022	513.2	1,889.0
2021	1,760.3	1,315.4
2020	1,193.3	809.7
2019	711.4	367.7
2018	300.3	120.2
Prior	116.7	40.4
Total	4,595.2	4,542.4
Customer Retail | Fleet
Financing Receivable Recorded Investment [Line Items]
2022	444.7	1,573.2
2021	1,469.9	1,113.9
2020	1,016.3	704.9
2019	621.1	320.9
2018	263.3	105.8
Prior	104.4	36.5
Total	3,919.7	3,855.2
Customer Retail | Fleet | Performing
Financing Receivable Recorded Investment [Line Items]
2022	444.2	1,568.6
2021	1,466.2	1,109.5
2020	1,012.7	691.9
2019	609.2	312.1
2018	255.0	103.8
Prior	102.9	36.2
Total	3,890.2	3,822.1
Customer Retail | Fleet | Watch
Financing Receivable Recorded Investment [Line Items]
2022		0.5
2021		1.2
2020	3.0	1.1
2019	1.0	2.3
2018	2.2	0.3
Prior	0.2	0.1
Total	6.4	5.5
Customer Retail | Fleet | At-risk
Financing Receivable Recorded Investment [Line Items]
2022	0.5	4.1
2021	3.7	3.2
2020	0.6	11.9
2019	10.9	6.5
2018	6.1	1.7
Prior	1.3	0.2
Total	23.1	27.6
Customer Retail | Owner Operator
Financing Receivable Recorded Investment [Line Items]
2022	68.5	315.8
2021	290.4	201.5
2020	177.0	104.8
2019	90.3	46.8
2018	37.0	14.4
Prior	12.3	3.9
Total	675.5	687.2
Customer Retail | Owner Operator | Performing
Financing Receivable Recorded Investment [Line Items]
2022	68.5	315.5
2021	290.3	201.5
2020	176.9	104.5
2019	90.0	46.3
2018	36.7	14.4
Prior	12.1	3.8
Total	674.5	686.0
Customer Retail | Owner Operator | Watch
Financing Receivable Recorded Investment [Line Items]
2022		0.3
2021	0.1
2019	0.1	0.2
Total	0.2	0.5
Customer Retail | Owner Operator | At-risk
Financing Receivable Recorded Investment [Line Items]
2020	0.1	0.3
2019	0.2	0.3
2018	0.3
Prior	0.2	0.1
Total	$ 0.8	$ 0.7