Summary of Impaired Loans (Detail) - Financial Services - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018		Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	$ 32.4		$ 19.9
Associated allowance	(4.7)		(3.3)
Net carrying amount of impaired loans with specific reserve	27.7		16.6
Impaired loans with no specific reserve	16.4		17.2
Net carrying amount of impaired loans	44.1		33.8
Average recorded investment	39.5	[1]	37.4	[2]
Dealer | Wholesale
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	0.1		0.1
Associated allowance	(0.1)		(0.1)
Net carrying amount of impaired loans with specific reserve	0.0		0.0
Impaired loans with no specific reserve	0.0		0.0
Net carrying amount of impaired loans	0.0		0.0
Average recorded investment	0.1	[1]	1.8	[2]
Dealer | Retail
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	0.0		0.0
Associated allowance	0.0		0.0
Net carrying amount of impaired loans with specific reserve	0.0		0.0
Impaired loans with no specific reserve	4.0		3.9
Net carrying amount of impaired loans	4.0		3.9
Average recorded investment	4.0	[1]	3.6	[2]
Customer Retail | Fleet
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	29.5		18.8
Associated allowance	(4.0)		(3.0)
Net carrying amount of impaired loans with specific reserve	25.5		15.8
Impaired loans with no specific reserve	12.2		13.1
Net carrying amount of impaired loans	37.7		28.9
Average recorded investment	33.4	[1]	29.6	[2]
Customer Retail | Owner/Operator
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	2.8		1.0
Associated allowance	(0.6)		(0.2)
Net carrying amount of impaired loans with specific reserve	2.2		0.8
Impaired loans with no specific reserve	0.2		0.2
Net carrying amount of impaired loans	2.4		1.0
Average recorded investment	$ 2.0	[1]	$ 2.4	[2]

[1] Represents the average during the 12 months ended March 31, 2018.

[2] Represents the average during the 12 months ended March 31, 2017.