Balance Sheet Classifications, Fair Value, Gross and Pro Forma Net Amounts of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
ASSETS
Derivative assets	$ 65.8	$ 59.7
Pro forma net amount	55.8	44.0
LIABILITIES
Derivative liabilities	146.3	88.5
Pro forma net amount	136.3	72.8
Interest-Rate Contracts | Financial Services
ASSETS
Less amounts not offset in financial instruments	(7.1)	(12.8)
LIABILITIES
Less amounts not offset in financial instruments	(7.1)	(12.8)
Foreign-exchange contracts | Financial Services
ASSETS
Less amounts not offset in financial instruments		(0.2)
LIABILITIES
Less amounts not offset in financial instruments		(0.2)
Foreign-exchange contracts | Truck, Parts and Other
ASSETS
Less amounts not offset in financial instruments	(2.9)	(2.7)
LIABILITIES
Less amounts not offset in financial instruments	(2.9)	(2.7)
Designated under hedge accounting
ASSETS
Derivative assets	64.3	58.6
LIABILITIES
Derivative liabilities	144.0	87.2
Designated under hedge accounting | Interest-Rate Contracts | Financial Services | Other Assets
ASSETS
Derivative assets	24.0	30.8
Designated under hedge accounting | Interest-Rate Contracts | Financial Services | Deferred Taxes and Other Liabilities
LIABILITIES
Derivative liabilities	80.4	54.4
Designated under hedge accounting | Foreign-exchange contracts | Financial Services | Other current assets
ASSETS
Derivative assets		2.5
Designated under hedge accounting | Foreign-exchange contracts | Financial Services | Deferred Taxes and Other Liabilities
LIABILITIES
Derivative liabilities	14.6	0.1
Designated under hedge accounting | Foreign-exchange contracts | Truck, Parts and Other | Other current assets
ASSETS
Derivative assets	8.9	25.3
Designated under hedge accounting | Foreign-exchange contracts | Truck, Parts and Other | Accounts payable, accrued expenses and other
LIABILITIES
Derivative liabilities	49.0	15.8
Designated under hedge accounting | Commodity Contract | Truck, Parts and Other | Other current assets
ASSETS
Derivative assets	31.4
Designated under hedge accounting | Commodity Contract | Truck, Parts and Other | Accounts payable, accrued expenses and other
LIABILITIES
Derivative liabilities		16.9
Not designated as hedging instruments
ASSETS
Derivative assets	1.5	1.1
LIABILITIES
Derivative liabilities	2.3	1.3
Not designated as hedging instruments | Foreign-exchange contracts | Financial Services | Other Assets
ASSETS
Derivative assets		0.1
Not designated as hedging instruments | Foreign-exchange contracts | Financial Services | Deferred Taxes and Other Liabilities
LIABILITIES
Derivative liabilities	0.5	0.2
Not designated as hedging instruments | Foreign-exchange contracts | Truck, Parts and Other | Other current assets
ASSETS
Derivative assets	1.5	1.0
Not designated as hedging instruments | Foreign-exchange contracts | Truck, Parts and Other | Accounts payable, accrued expenses and other
LIABILITIES
Derivative liabilities	$ 1.8	$ 1.1