Organization and Summary of Significant Accounting Policies - Business Overview (Details) $ in Millions		1 Months Ended	12 Months Ended
	Sep. 07, 2017	Jul. 31, 2019 item	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies
Total revenues | $			$ 23,179.4	$ 22,785.1	$ 21,386.9
Receivables from manufacturers | $			$ 244.6	211.3
Number of reportable segments			4
PTL
Significant Accounting Policies
Ownership acquired (as a percent)	5.50%
Ownership interest in Penske Truck Leasing Co (as a percent)			28.90%
German Automotive Dealership Group
Significant Accounting Policies
Ownership acquired (as a percent)			12.40%
Ownership interest (as a percent)			91.80%
U.S.
Significant Accounting Policies
Total revenues | $			$ 13,511.8	12,607.8	12,487.2
Penske Corporation | PTL
Significant Accounting Policies
Ownership interest in Penske Truck Leasing Co (as a percent)			41.10%
Mitsui and Co | PTL
Significant Accounting Policies
Ownership acquired (as a percent)	10.00%
Ownership interest in Penske Truck Leasing Co (as a percent)			30.00%
Retail Automotive Dealership
Significant Accounting Policies
Total number of owned and operated franchises			321
Number of owned and operated franchises in US			145
Number of owned and operated franchises outside US			176
Number of franchises disposed			25
Number of franchises awarded to the reporting entity			1
Number of used vehicle supercenters operated in the U.S. and U.K.			16
Retail Automotive Dealership | UK
Significant Accounting Policies
Number of franchises disposed			8
Number of used vehicle supercenters opened			1
Retail Automotive Dealership | U.S.
Significant Accounting Policies
Number of franchises disposed			10
Number of used vehicle supercenters opened			1
Retail Automotive Dealership | U.S. | Bentley, Ferrari, Maserati
Significant Accounting Policies
Number of franchises disposed			3
Ownership percentage of equity method investment			20.00%
Retail Automotive Dealership | Germany
Significant Accounting Policies
Number of franchises disposed			7
Retail Automotive Dealership | CarSense
Significant Accounting Policies
Number of retail locations operated			6
Retail Automotive Dealership | CarShop
Significant Accounting Policies
Number of retail locations operated			10
Retail Commercial Truck Dealership
Significant Accounting Policies
Number of locations acquired		6
Retail Commercial Truck Dealership | PTG
Significant Accounting Policies
Number of operating locations			25
Audi/Volkswagen/Porsche/Bentley | Automotive dealership revenues
Significant Accounting Policies
Percentage of total			23.00%
BMW, MINI | Automotive dealership revenues
Significant Accounting Policies
Percentage of total			23.00%
Toyota/Lexus | Automotive dealership revenues
Significant Accounting Policies
Percentage of total			13.00%
Retail Automotive Dealership
Significant Accounting Policies
Total revenues | $			$ 20,615.8	20,849.2	19,824.3
Number of reportable segments			1
Retail Automotive Dealership | UK
Significant Accounting Policies
Total revenues | $			$ 7,559.4	7,961.4	7,048.7
Retail Automotive Dealership | U.S.
Significant Accounting Policies
Total revenues | $			11,697.6	11,504.3	11,610.1
Retail Commercial Truck Dealership
Significant Accounting Policies
Total revenues | $			2,050.5	1,374.5	1,048.0
Commercial Vehicle Distribution and Other
Significant Accounting Policies
Total revenues | $			$ 513.1	$ 561.4	$ 514.6