Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 9,653.2	$ 8,797.7
Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	9,524.7	8,710.8
Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	73.6	29.5
At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	54.9	57.4
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,880.6	1,528.5
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,358.7	1,406.0
Dealer | Performing | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,874.5	1,519.3
Dealer | Performing | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,354.7	1,406.0
Dealer | Watch | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	6.0	9.1
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	4.0	0.0
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,397.9	4,928.7
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,016.0	934.5
Customer Retail | Performing | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,290.3	4,863.4
Customer Retail | Performing | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,005.2	922.1
Customer Retail | Watch | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	62.9	14.9
Customer Retail | Watch | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	4.7	5.5
Customer Retail | At-risk | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	44.7	50.4
Customer Retail | At-risk | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 6.1	$ 6.9