Revenues - Other Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenues
Aggregate reserves relating to chargeback activity	$ 26.0	$ 24.9
Vehicle Sales | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period	30 days
Service and parts | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period	30 days
Customer return period, parts sales	30 days
Finance and insurance, net | Retail Automotive and Retail Commercial Truck Dealership
Revenues
Payment period	30 days
Aggregate reserves relating to chargeback activity	$ 26.0	$ 24.9
Penske Commercial Vehicles Australia | Commercial Vehicle Distribution and Other
Revenues
Payment period	30 days
Penske Power Systems | Commercial Vehicle Distribution and Other
Revenues
Payment period	30 days