Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 10,532.4	$ 9,653.2
Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	10,392.7	9,524.7
Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	95.0	73.6
At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	44.7	54.9
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,229.6	1,880.6
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,373.0	1,358.7
Dealer | Performing | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,219.6	1,874.5
Dealer | Performing | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,370.6	1,354.7
Dealer | Watch | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	9.9	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	2.4	4.0
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,846.5	5,397.9
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,083.3	1,016.0
Customer Retail | Performing | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,734.3	5,290.3
Customer Retail | Performing | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,068.2	1,005.2
Customer Retail | Watch | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	78.7	62.9
Customer Retail | Watch | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	6.4	4.7
Customer Retail | At-risk | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	33.5	44.7
Customer Retail | At-risk | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 8.7	$ 6.1