Amortized Cost Basis of Impaired Loans and Specific Reserve (Detail) - Financial Services - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2021		Dec. 31, 2020		Dec. 31, 2019	[2]
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve		$ 20.7		$ 24.7
Associated allowance		(1.8)		(1.9)
Net carrying amount of impaired loans with specific reserve		18.9		22.8
Impaired loans with no specific reserve		6.6		1.2
Net carrying amount of impaired loans		25.5		24.0
Average recorded investment		31.7	[1]			$ 29.9
Dealer | Wholesale
Financing Receivable, Impaired [Line Items]
Average recorded investment	[2]			4.9
Dealer | Retail
Financing Receivable, Impaired [Line Items]
Impaired loans with no specific reserve		1.1		1.2
Net carrying amount of impaired loans		1.1		1.2
Average recorded investment		1.4	[1]	2.3	[2]
Customer Retail | Fleet
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve		18.7		22.6
Associated allowance		(1.5)		(1.6)
Net carrying amount of impaired loans with specific reserve		17.2		21.0
Impaired loans with no specific reserve		5.4
Net carrying amount of impaired loans		22.6		21.0
Average recorded investment		27.8	[1]	19.5	[2]
Customer Retail | Owner/Operator
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve		2.0		2.1
Associated allowance		(0.3)		(0.3)
Net carrying amount of impaired loans with specific reserve		1.7		1.8
Impaired loans with no specific reserve		0.1
Net carrying amount of impaired loans		1.8		1.8
Average recorded investment		$ 2.5	[1]	$ 3.2	[2]

[1] Represents the average during the 12 months ended March 31, 2021.

[2] Represents the average during the 12 months ended March 31, 2020.