Interim Financial Statements - Business Overview (Details) $ in Millions				1 Months Ended			3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2016 item	Jul. 27, 2016 USD ($)	Jul. 26, 2016	Oct. 31, 2016 item	Apr. 30, 2016 item	Feb. 28, 2015 item	Sep. 30, 2016 USD ($) item	Mar. 31, 2016	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) item	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Oct. 01, 2016	Jan. 31, 2016	Oct. 31, 2014
Interim Financial Statements
Total revenues | $							$ 5,152.0		$ 4,960.1	$ 15,230.7	$ 14,363.6
Ownership interest in Penske Truck Leasing Co (as a percent)	23.40%
German Automotive Dealership Group
Interim Financial Statements
Additional ownership interest acquired (as a percent)								8.00%
Ownership interest (as a percent)	68.00%						68.00%			68.00%
Nicole Group | BMW Dealership
Interim Financial Statements
Number of dealerships operated										4
Nicole Group | MINI Dealership
Interim Financial Statements
Number of dealerships operated										3
Retail Automotive Dealership
Interim Financial Statements
Total number of owned and operated franchises	349						349			349
Number of owned and operated franchises in US	163						163			163
Number of owned and operated franchises outside US	186						186			186
Minimum number of vehicles retailed and wholesaled										419,000
Minimum number of vehicle brands offered										40
Number of acquired franchises										13
Number of franchises disposed										8
Number of franchises awarded to the reporting entity										6
Retail Automotive Dealership | Subsequent event
Interim Financial Statements
Number of acquired franchises				6
Retail Automotive Dealership | Porsche Dealership | Subsequent event
Interim Financial Statements
Number of acquired franchises				3
Retail Automotive Dealership | Audi Dealership | Subsequent event
Interim Financial Statements
Number of acquired franchises				1
Retail Automotive Dealership | Land Rover Dealership | Subsequent event
Interim Financial Statements
Number of acquired franchises				1
Retail Automotive Dealership | Volvo Dealership | Subsequent event
Interim Financial Statements
Number of acquired franchises				1
Retail Automotive Dealership | Scion
Interim Financial Statements
Number of franchises disposed										17
Retail Automotive Dealership | Nicole Group
Interim Financial Statements
Ownership percentage of equity method investment														49.00%
Retail Automotive Dealership | Italian Automotive Dealership Joint Venture | Subsequent event
Interim Financial Statements
Ownership interest (as a percent)													84.00%
Retail Automotive Dealership | Dealer Group in UK
Interim Financial Statements
Number of acquired franchises										12
Retail Automotive Dealership | Dealer Group in UK | BMW Dealership
Interim Financial Statements
Number of acquired franchises										1
Retail Automotive Dealership | Dealer Group in UK | MINI Dealership
Interim Financial Statements
Number of acquired franchises										1
Retail Automotive Dealership | Dealer Group in UK | Volkswagen Dealership
Interim Financial Statements
Number of acquired franchises										7
Retail Automotive Dealership | Dealer Group in UK | Audi Dealership
Interim Financial Statements
Number of acquired franchises										1
Retail Automotive Dealership | Dealer Group in UK | Skoda Dealership
Interim Financial Statements
Number of acquired franchises										1
Retail Automotive Dealership | Dealer Group in UK | SEAT Dealership
Interim Financial Statements
Number of acquired franchises										1
Retail Commercial Truck Dealership
Interim Financial Statements
Number of operating locations										19
Number of full service retail locations operated	14						14			14
Number of retail locations acquired					5	2
Retail Commercial Truck Dealership | PTG
Interim Financial Statements
Ownership interest (as a percent)	100.00%						100.00%			100.00%		96.00%
Ownership acquired (as a percent)												5.00%
Ownership percentage of equity method investment															32.00%
Commercial Vehicle Distribution
Interim Financial Statements
Minimum number of dealership locations										70
Number of commercial vehicle dealerships										3
Automotive dealership revenues | Geographic | U.S. and Puerto Rico
Interim Financial Statements
Automotive dealership revenue (as a percent)										59.00%
Automotive dealership revenues | Geographic | Outside the U.S.
Interim Financial Statements
Automotive dealership revenue (as a percent)										41.00%
Automotive dealership revenues | Premium brands
Interim Financial Statements
Automotive dealership revenue (as a percent)										72.00%
Penske Truck Leasing Co., L.P.
Interim Financial Statements
Additional ownership interest acquired (as a percent)		14.40%
Ownership interest in Penske Truck Leasing Co (as a percent)	23.40%
Cost of acquisition | $		$ 498.5
Number of vehicles operated and maintained	240,000						240,000			240,000
Penske Truck Leasing Co., L.P. | PTL
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)	23.40%	23.40%	9.00%
Penske Corporation
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)	41.10%
Mitsui and Co
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)	20.00%
GEC
Interim Financial Statements
Ownership interest in Penske Truck Leasing Co (as a percent)	15.50%
Retail Automotive Dealership
Interim Financial Statements
Total revenues | $							$ 4,772.1		4,585.8	$ 14,121.8	13,327.5	$ 17,900.0
Retail Commercial Truck Dealership
Interim Financial Statements
Total revenues | $							266.1		268.5	782.3	703.1
Commercial Vehicle Distribution and Other
Interim Financial Statements
Total revenues | $							$ 113.8		$ 105.8	$ 326.6	$ 333.0