Interim Financial Statements (Details) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015 item	Mar. 31, 2015	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($) item	Dec. 31, 2014 USD ($)	Jul. 01, 2015	Nov. 30, 2014	Sep. 30, 2014
Interim Financial Statements.
Total revenues | $			$ 4,904.4	$ 4,370.5	$ 9,375.5	$ 8,385.7
Commercial Vehicle Distribution
Interim Financial Statements
Minimum number of dealership locations					70
Number of commercial vehicle dealerships					3
Retail Automotive Franchise
Interim Financial Statements
Minimum number of vehicle brands offered					40
Number of acquired franchises					1	2
Number of franchises disposed	2				2
Interim Financial Statements.
Total revenues | $							$ 16,600.0
Total number of owned and operated franchises	326		326		326
Number of owned and operated franchises in US	178		178		178
Number of owned and operated franchises outside US	148		148		148
Minimum number of vehicles retailed and wholesaled					255,000
Retail Commercial Truck Dealership
Interim Financial Statements
Number of acquired franchises					2
Number of operating locations					16
Ownership interest (as a percent)	91.00%		91.00%		91.00%			96.00%	91.00%
Ownership percentage of Equity Method Investment										32.00%
Number of full service retail locations operated	10		10		10
Number of full service retail locations acquired					2
Ownership acquired (as a percentage)								5.00%
Penske Truck Leasing Co., L.P.
Interim Financial Statements
Limited partnership interest (as a percent)		9.00%			9.00%
Revenues | Geographic | U.S. and Puerto Rico
Interim Financial Statements
Automotive dealership revenue (as a percent)					61.00%
Revenues | Geographic | Outside the U.S.
Interim Financial Statements
Automotive dealership revenue (as a percent)					39.00%
Revenues | Premium brands
Interim Financial Statements
Automotive dealership revenue (as a percent)					72.00%