Property, Plant and Equipment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 3,270.4	$ 2,883.8	$ 2,480.9
Truck, Parts and Other
Property, Plant and Equipment [Line Items]
Land	286.4	271.8
Buildings and improvements	1,474.7	1,382.2
Machinery, equipment and production tooling	4,234.4	3,998.2
Construction in progress	1,081.8	741.7
Property, Plant and Equipment, Gross, Total	7,077.3	6,393.9
Less allowance for depreciation	(3,806.9)	(3,510.1)
Property, plant and equipment, net	$ 3,270.4	$ 2,883.8
Truck, Parts and Other | Minimum | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Truck, Parts and Other | Minimum | Machinery Equipment And Production Tooling
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Truck, Parts and Other | Maximum | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Truck, Parts and Other | Maximum | Machinery Equipment And Production Tooling
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	12 years