Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 10,780.0	$ 9,653.2
Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	10,649.9	9,524.7
Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	90.8	73.6
At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	39.3	54.9
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,342.3	1,880.6
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,464.6	1,358.7
Dealer | Performing | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,329.5	1,874.5
Dealer | Performing | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,462.1	1,354.7
Dealer | Watch | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	12.6	6.0
Dealer | Watch | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	0.0	0.0
Dealer | At-risk | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	0.2	0.1
Dealer | At-risk | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2.5	4.0
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,857.5	5,397.9
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,115.6	1,016.0
Customer Retail | Performing | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,759.0	5,290.3
Customer Retail | Performing | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,099.3	1,005.2
Customer Retail | Watch | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	70.0	62.9
Customer Retail | Watch | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	8.2	4.7
Customer Retail | At-risk | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	28.5	44.7
Customer Retail | At-risk | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 8.1	$ 6.1