Sales and Revenues - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 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	$ 199.9
Estimated sales returned liabilites	208.8
Revenue deferred	686.8
Maturities of the residual value guarantees, reminder in 2018	149.2
Annual maturities of the residual value guarantees, in 2019	236.5
Annual maturities of the residual value guarantees, in 2020	198.3
Annual maturities of the residual value guarantees, in 2021	64.2
Annual maturities of the residual value guarantees, in 2022	35.5
Annual maturities of the residual value guarantees, thereafter	3.1
Estimated value of returned goods	44.1
Sales returns liabilities in estimated returns.	91.2
Parts
Entity Wide Information Revenue From External Customer [Line Items]
Increase in parts sales due to change in reserve balance	$ 2.3
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