Commitments and Contingencies - Additional Information (Detail) € in Millions, $ in Millions			3 Months Ended		6 Months Ended		9 Months Ended
	Jul. 19, 2016 USD ($)	Jul. 19, 2016 EUR (€)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2016 EUR (€)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Commitments and Contingencies Disclosure [Line Items]
European Commission charge					$ 833.0
Truck, Parts and Other
Commitments and Contingencies Disclosure [Line Items]
European Commission charge			$ 0.0	$ 0.0	$ 833.0	€ 752.7	$ 0.0	$ 833.0
Litigation settlement amount	$ 833.0	€ 752.7