Revenues - Commercial Vehicle Distribution and Other (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Total revenues	$ 5,439.3	$ 5,658.6	$ 5,940.3	$ 5,746.9	$ 5,398.0	$ 5,524.4	$ 5,383.4	$ 5,081.1	$ 22,785.1	$ 21,386.9	$ 20,118.5
Commercial Vehicle Distribution and Other
Revenues
Total revenues									561.4	514.6	444.6
Commercial Vehicle Distribution and Other | Penske Commercial Vehicles Australia
Revenues
Total revenues									558.5
Commercial Vehicle Distribution and Other | Other
Revenues
Total revenues									$ 2.9
Without Adoption of ASC 606 | Commercial Vehicle Distribution and Other
Revenues
Total revenues										514.6	444.6
Without Adoption of ASC 606 | Commercial Vehicle Distribution and Other | Penske Commercial Vehicles Australia
Revenues
Total revenues										511.0	428.8
Without Adoption of ASC 606 | Commercial Vehicle Distribution and Other | Other
Revenues
Total revenues										$ 3.6	$ 15.8