Summary of Impaired Loans (Detail) - Financial Services - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	$ 24.7	$ 14.0
Associated allowance	(1.9)	(2.7)
Net carrying amount of impaired loans with specific reserve	22.8	11.3
Impaired loans with no specific reserve	1.2	9.4
Net carrying amount of impaired loans	24.0	20.7
Average amortized cost basis	30.9	27.3
Dealer | Wholesale
Financing Receivable, Impaired [Line Items]
Average amortized cost basis		4.9
Dealer | Retail
Financing Receivable, Impaired [Line Items]
Impaired loans with no specific reserve	1.2	2.3
Net carrying amount of impaired loans	1.2	2.3
Average amortized cost basis	1.6	2.4
Customer Retail | Fleet
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	22.6	10.9
Associated allowance	(1.6)	(2.1)
Net carrying amount of impaired loans with specific reserve	21.0	8.8
Impaired loans with no specific reserve		6.7
Net carrying amount of impaired loans	21.0	15.5
Average amortized cost basis	26.5	16.6
Customer Retail | Owner/Operator
Financing Receivable, Impaired [Line Items]
Impaired loans with a specific reserve	2.1	3.1
Associated allowance	(0.3)	(0.6)
Net carrying amount of impaired loans with specific reserve	1.8	2.5
Impaired loans with no specific reserve		0.4
Net carrying amount of impaired loans	1.8	2.9
Average amortized cost basis	$ 2.8	$ 3.4