Summary of Impaired Loans (Detail) - Financial Services - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	$ 19.9	$ 20.8
Associated allowance	(3.3)	(3.2)
Net carrying amount of impaired loans with specific reserve	16.6	17.6
Impaired loans with no specific reserve	17.2	11.0
Net carrying amount of impaired loans	33.8	28.6
Average recorded investment	37.2	33.2
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	2.8
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	3.9	0.0
Net carrying amount of impaired loans	3.9	0.0
Average recorded investment	4.0	0.0
Customer Retail | Fleet
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	18.8	18.9
Associated allowance	(3.0)	(2.8)
Net carrying amount of impaired loans with specific reserve	15.8	16.1
Impaired loans with no specific reserve	13.1	10.8
Net carrying amount of impaired loans	28.9	26.9
Average recorded investment	31.3	28.0
Customer Retail | Owner/Operator
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	1.0	1.8
Associated allowance	(0.2)	(0.3)
Net carrying amount of impaired loans with specific reserve	0.8	1.5
Impaired loans with no specific reserve	0.2	0.2
Net carrying amount of impaired loans	1.0	1.7
Average recorded investment	$ 1.8	$ 2.4