Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 10,140.4	$ 9,653.2
Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	9,992.3	9,524.7
Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	100.2	73.6
At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	47.9	54.9
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,069.7	1,880.6
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,360.6	1,358.7
Dealer | Performing | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,064.8	1,874.5
Dealer | Performing | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,357.6	1,354.7
Dealer | Watch | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	4.8	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	0.1	0.1
Dealer | At-risk | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	3.0	4.0
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,648.2	5,397.9
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,061.9	1,016.0
Customer Retail | Performing | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,520.9	5,290.3
Customer Retail | Performing | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,049.0	1,005.2
Customer Retail | Watch | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	90.0	62.9
Customer Retail | Watch | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5.4	4.7
Customer Retail | At-risk | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	37.3	44.7
Customer Retail | At-risk | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 7.5	$ 6.1