Sales and Revenues - Additional Information (Detail) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Entity Wide Information Revenue From External Customer [Line Items]
Term used to calculate historical weighted average return rate		4 years
Estimated value of returned trucks	$ 250.7	$ 250.7
Estimated sales returned liabilites		258.0
Revenue deferred		832.4
Maturities of the residual value guarantees, reminder in 2018	48.9	48.9
Annual maturities of the residual value guarantees, in 2019	185.8	185.8
Annual maturities of the residual value guarantees, in 2020	252.8	252.8
Annual maturities of the residual value guarantees, in 2021	199.5	199.5
Annual maturities of the residual value guarantees, in 2022	125.6	125.6
Annual maturities of the residual value guarantees, thereafter	19.8	19.8
Estimated value of returned goods	47.9	47.9
Sales returns liabilities in estimated returns.		101.7
Parts
Entity Wide Information Revenue From External Customer [Line Items]
Decrease in parts sales due to change in reserve balance	$ 6.8	$ 10.4
Minimum
Entity Wide Information Revenue From External Customer [Line Items]
Lease and guarantee periods (in years)		3 years
Maximum
Entity Wide Information Revenue From External Customer [Line Items]
Lease and guarantee periods (in years)		5 years
Warranty period		5 years