Organization and Summary of Significant Accounting Policies - Business Overview (Details) $ in Millions				1 Months Ended						3 Months Ended								12 Months Ended
	Sep. 07, 2017 USD ($)	Jul. 27, 2016 USD ($)	Jul. 26, 2016	Jan. 31, 2018 item	Sep. 30, 2017	Dec. 31, 2016 USD ($) item	Jul. 31, 2016	Jun. 30, 2016	Apr. 30, 2016 item	Dec. 31, 2017 USD ($) item	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Significant Accounting Policies
Total revenues | $										$ 5,398.0	$ 5,524.4	$ 5,383.4	$ 5,081.1	$ 4,887.8	$ 5,152.0	$ 5,254.1	$ 4,824.6	$ 21,386.9	$ 20,118.5	$ 19,284.9
Ownership interest in Penske Truck Leasing Co (as a percent)							23.40%	9.00%										28.90%
Ownership acquired (as a percent)					5.50%		14.40%
Receivables from manufacturers | $						$ 196.5				$ 230.1				$ 196.5				$ 230.1	196.5
Minimum
Significant Accounting Policies
Ownership percentage of equity method investment										20.00%								20.00%
Maximum
Significant Accounting Policies
Ownership percentage of equity method investment										50.00%								50.00%
PTL
Significant Accounting Policies
Ownership interest in Penske Truck Leasing Co (as a percent)		23.40%	9.00%															28.90%
Ownership acquired (as a percent)	5.50%	14.40%			5.50%
Cost of acquisition | $	$ 239.1	$ 498.5
Ownership percentage of equity method investment										28.90%								28.90%
CarSense
Significant Accounting Policies
Number of retail locations acquired																		5
CarShop
Significant Accounting Policies
Number of retail locations acquired																		5
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 interest in Penske Truck Leasing Co (as a percent)																		30.00%
Ownership acquired (as a percent)	10.00%
Retail Automotive Dealership
Significant Accounting Policies
Total number of owned and operated franchises										343								343
Number of owned and operated franchises in US										155								155
Number of owned and operated franchises outside US										188								188
Number of acquired franchises																		8
Number of franchises awarded to the reporting entity																		5
Number of franchises disposed																		25
Retail Automotive Dealership | CarSense
Significant Accounting Policies
Number of retail locations acquired																		5
Retail Automotive Dealership | CarShop
Significant Accounting Policies
Number of retail locations acquired																		5
Retail Automotive Dealership | The Car People
Significant Accounting Policies
Number of retail locations acquired				4
Retail Commercial Truck Dealership | PTG
Significant Accounting Policies
Number of dealerships operated																		20
Number of full service retail locations operated																		14
Number of collision centers operated																		6
Number of retail locations acquired						2			4
Commercial Vehicle Distribution
Significant Accounting Policies
Minimum number of dealership locations																		70
Number of retail dealerships owned by the reporting entity																		8
BMW, MINI | Automotive dealership revenues
Significant Accounting Policies
Percentage of total																		23.00%
Audi/Volkswagen/Porsche/Bentley | Automotive dealership revenues
Significant Accounting Policies
Percentage of total																		24.00%
Toyota/Lexus | Automotive dealership revenues
Significant Accounting Policies
Percentage of total																		13.00%
Mercedes-Benz/Sprinter/smart | Automotive dealership revenues
Significant Accounting Policies
Percentage of total																		10.00%
Retail Automotive Dealership
Significant Accounting Policies
Total revenues | $																		$ 19,824.3	18,673.2	17,896.3
Retail Commercial Truck Dealership
Significant Accounting Policies
Total revenues | $																		1,048.0	1,000.7	944.1
Commercial Vehicle Distribution and Other
Significant Accounting Policies
Total revenues | $																		$ 514.6	444.6	444.5
New Jersey | Retail Automotive Dealership
Significant Accounting Policies
Number of acquired franchises																		2
Arizona | Retail Automotive Dealership
Significant Accounting Policies
Number of acquired franchises																		2
UK | Retail Automotive Dealership
Significant Accounting Policies
Number of acquired franchises																		2
UK | BMW, MINI and Lexus | Retail Automotive Dealership
Significant Accounting Policies
Number of franchises disposed																		5
U.S.
Significant Accounting Policies
Total revenues | $																		$ 12,487.2	$ 12,005.9	$ 11,806.9
U.S. | Smart | Retail Automotive Dealership
Significant Accounting Policies
Number of franchises disposed																		5
Germany | Retail Automotive Dealership
Significant Accounting Policies
Number of acquired franchises																		2
Puerto Rico | Retail Automotive Dealership
Significant Accounting Policies
Number of franchises disposed																		9