Financing Receivables by Credit Quality Indicator and Portfolio Class (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 6,261.6	$ 6,032.8
Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	6,184.1	5,972.3
Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	63.5	45.1
At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	14.0	15.4
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,336.4	1,179.0
Dealer | Wholesale | Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,335.3	1,177.9
Dealer | Wholesale | Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1.1	1.1
Dealer | Wholesale | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,245.2	1,256.1
Dealer | Retail | Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,245.2	1,256.1
Dealer | Retail | Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables
Dealer | Retail | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	3,201.1	3,092.5
Customer Retail | Fleet | Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	3,128.1	3,037.1
Customer Retail | Fleet | Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	61.7	43.3
Customer Retail | Fleet | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	11.3	12.1
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	478.9	505.2
Customer Retail | Owner/Operator | Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	475.5	501.2
Customer Retail | Owner/Operator | Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	0.7	0.7
Customer Retail | Owner/Operator | At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 2.7	$ 3.3