(Income) Expense Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - Foreign-exchange contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
(Income) expense recognized in earnings	$ (5.5)	$ (0.8)	$ (7.6)	$ (3.8)
Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) expense recognized in earnings	0.8	(1.1)	0.8	0.1
Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
(Income) expense recognized in earnings	2.0	(0.3)	4.6	3.4
Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) expense recognized in earnings	$ (8.3)	(0.5)	$ (13.0)	(8.9)
Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) expense recognized in earnings		$ 1.1		$ 1.6