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Intangible Assets (Details 2) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Summary of the changes in the carrying amount of goodwill by reportable segment    
Goodwill $ 1,271.1us-gaap_Goodwill $ 1,266.3us-gaap_Goodwill
Retail Automotive    
Summary of the changes in the carrying amount of goodwill by reportable segment    
Goodwill 1,040.9us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= pag_RetailAutomotiveMember		  
Retail Commercial Truck Dealership    
Summary of the changes in the carrying amount of goodwill by reportable segment    
Goodwill 147.3us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= pag_RetailCommercialTruckDealershipMember		  
Other    
Summary of the changes in the carrying amount of goodwill by reportable segment    
Goodwill $ 82.9us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember