Interim Financial Statements - Business Overview (Details)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2021 item	Jun. 30, 2021 USD ($) location item	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) item location	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Interim Financial Statements
Total revenues | $		$ 6,987,500,000	$ 3,651,100,000	$ 12,761,300,000	$ 8,660,200,000
Number of acquired franchises				1
PTL
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)				28.90%
KCFL
Interim Financial Statements
Number of full service dealerships added				4
Number of parts and service centers added				4
Number of collision centers added				2
Retail Automotive
Interim Financial Statements
Total number of owned and operated franchises		305		305
Number of owned and operated franchises in US		144		144
Number of owned and operated franchises outside US		161		161
Minimum number of vehicles retailed and wholesaled				294,000
Minimum number of vehicle brands offered				35
UK | Retail Automotive
Interim Financial Statements
Number of franchises disposed | $				1
Number of retail locations operated | location				12
Number of locations acquired | location		1
U.S. | Retail Automotive
Interim Financial Statements
Number of acquired franchises | $				1
Number of franchises awarded to the reporting entity | $				1
Number of retail locations operated | location				7
Number of locations acquired | location		1
Revenues | Geographic | U.S. and Puerto Rico
Interim Financial Statements
Automotive dealership revenue (as a percent)				58.00%
Revenues | Geographic | Outside the U.S.
Interim Financial Statements
Automotive dealership revenue (as a percent)				42.00%
PTL
Interim Financial Statements
Number of vehicles managed in fleet, minimum				330,000
Penske Corporation | PTL
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)				41.10%
Mitsui and Co | PTL
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)				30.00%
PTG | Retail Commercial Truck Dealership
Interim Financial Statements
Number of operating locations | location				35
Retail automotive dealership
Interim Financial Statements
Total revenues | $		$ 6,197,600,000	3,153,500,000	$ 11,404,500,000	7,570,100,000	$ 17,900,000,000
Retail automotive dealership | UK
Interim Financial Statements
Total revenues | $		2,190,600,000	837,800,000	4,044,000,000.0	2,503,200,000
Retail automotive dealership | U.S.
Interim Financial Statements
Total revenues | $		3,614,500,000	2,053,800,000	$ 6,619,300,000	4,507,700,000
Retail automotive dealership | Revenues | Premium brands
Interim Financial Statements
Automotive dealership revenue (as a percent)				71.00%
Retail commercial truck dealership
Interim Financial Statements
Total revenues | $		625,300,000	399,200,000	$ 1,060,000,000.0	890,600,000
Retail commercial truck dealership | KCFL
Interim Financial Statements
Number of full service dealerships added	4
Number of parts and service centers added	4
Number of collision centers added	2
Commercial vehicle distribution
Interim Financial Statements
Total revenues | $		$ 164,600,000	$ 98,400,000	$ 296,800,000	$ 199,500,000