Summary of Impaired Loans (Detail) - Financial Services - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2019		Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	$ 38.4		$ 18.0
Associated allowance	(4.4)		(3.4)
Net carrying amount of impaired loans with specific reserve	34.0		14.6
Impaired loans with no specific reserve	4.3		7.7
Net carrying amount of impaired loans	38.3		22.3
Average recorded investment	28.8	[1]	37.0	[2]
Dealer | Wholesale
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	24.3		0.1
Associated allowance	(2.0)		(0.1)
Net carrying amount of impaired loans with specific reserve	22.3
Net carrying amount of impaired loans	22.3
Average recorded investment	4.9	[1]	0.1	[2]
Dealer | Retail
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	0.0
Net carrying amount of impaired loans with specific reserve	0.0
Impaired loans with no specific reserve	2.3		2.5
Net carrying amount of impaired loans	2.3		2.5
Average recorded investment	2.4	[1]	3.5	[2]
Customer Retail | Fleet
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	11.2		14.5
Associated allowance	(1.8)		(2.3)
Net carrying amount of impaired loans with specific reserve	9.4		12.2
Impaired loans with no specific reserve	1.6		4.9
Net carrying amount of impaired loans	11.0		17.1
Average recorded investment	18.1	[1]	31.1	[2]
Customer Retail | Owner/Operator
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	2.9		3.4
Associated allowance	(0.6)		(1.0)
Net carrying amount of impaired loans with specific reserve	2.3		2.4
Impaired loans with no specific reserve	0.4		0.3
Net carrying amount of impaired loans	2.7		2.7
Average recorded investment	$ 3.4	[1]	$ 2.3	[2]

[1] Represents the average during the 12 months ended September 30, 2019.

[2] Represents the average during the 12 months ended September 30, 2018.