Amortized Cost Basis of Impaired Loans and Specific Reserve (Detail) - Financial Services - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2020		Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	$ 29.3		$ 14.0
Associated allowance	(1.9)		(2.7)
Net carrying amount of impaired loans with specific reserve	27.4		11.3
Impaired loans with no specific reserve	2.6		9.4
Net carrying amount of impaired loans	30.0		20.7
Average recorded investment	34.3	[1]	28.8	[2]
Dealer | Wholesale
Financing Receivable, Impaired [Line Items]
Average recorded investment	4.9	[1]	4.9	[2]
Dealer | Retail
Financing Receivable, Impaired [Line Items]
Impaired loans with no specific reserve	1.5		2.3
Net carrying amount of impaired loans	1.5		2.3
Average recorded investment	1.9	[1]	2.4	[2]
Customer Retail | Fleet
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	27.4		10.9
Associated allowance	(1.7)		(2.1)
Net carrying amount of impaired loans with specific reserve	25.7		8.8
Impaired loans with no specific reserve	1.0		6.7
Net carrying amount of impaired loans	26.7		15.5
Average recorded investment	24.5	[1]	18.1	[2]
Customer Retail | Owner/Operator
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	1.9		3.1
Associated allowance	(0.2)		(0.6)
Net carrying amount of impaired loans with specific reserve	1.7		2.5
Impaired loans with no specific reserve	0.1		0.4
Net carrying amount of impaired loans	1.8		2.9
Average recorded investment	$ 3.0	[1]	$ 3.4	[2]

[1] Represents the average during the 12 months ended September 30, 2020.

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