(Income) Expense Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - Foreign-exchange contracts - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
(Income) expense recognized in earnings	$ 2.4	$ (9.3)	$ (2.1)	$ (3.0)
Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) expense recognized in earnings	(0.2)			1.2
Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
(Income) expense recognized in earnings	1.1	0.3	2.6	3.7
Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) expense recognized in earnings	$ 1.5	(8.9)	$ (4.7)	(8.4)
Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) expense recognized in earnings		$ (0.7)		$ 0.5