Finance Receivables by Credit Quality Indicator and Portfolio Class (Detail) - Financial Services - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 10,060.4	$ 9,653.2
Performing
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	9,864.6	9,524.7
Watch
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	120.0	73.6
At-risk
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	75.8	54.9
Dealer | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,103.9	1,880.6
Dealer | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,367.1	1,358.7
Dealer | Performing | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	2,098.3	1,874.5
Dealer | Performing | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,363.1	1,354.7
Dealer | Watch | Wholesale
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5.5	6.0
Dealer | Watch | Retail
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables		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	4.0
Customer Retail | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,545.1	5,397.9
Customer Retail | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,044.3	1,016.0
Customer Retail | Performing | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	5,373.3	5,290.3
Customer Retail | Performing | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	1,029.9	1,005.2
Customer Retail | Watch | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	107.2	62.9
Customer Retail | Watch | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	7.3	4.7
Customer Retail | At-risk | Fleet
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	64.6	44.7
Customer Retail | At-risk | Owner/Operator
Financing Receivable, Recorded Investment [Line Items]
Financing Receivables	$ 7.1	$ 6.1