Expense (Income) Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Foreign-exchange contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	$ 9.9	$ (9.1)	$ 36.4	$ (7.9)
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.1	0.1	0.7	1.1
Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income) expense, net
Derivative [Line Items]
(Income) Expense recognized in earnings	0.7	0.9	4.2	0.8
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	11.4	(10.6)	44.6	(8.2)
Foreign-exchange contracts | Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	(2.3)	0.5	(13.1)	(1.6)
Interest-Rate Contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	(0.1)	0.0	(0.1)	0.0
Interest-Rate Contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0	0.0
Interest-Rate Contracts | Truck, Parts and Other | Interest and other (income) expense, net
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0	0.0
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	(0.1)	0.0	(0.1)	0.0
Interest-Rate Contracts | Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	$ 0.0	$ 0.0	$ 0.0	$ 0.0