Income tax expense benefit recorded due to provisions of CARES Act and U.S and Foreign tax legislation changes.

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The percentage of investment ownership.

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Represents the number of franchises disposed of by the entity during the period.

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Number of owned and operated franchises in domestic country.

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The number of retail locations operated.

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The number of stand-alone used vehicle supercenters operated in the United States and United Kingdom.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP).

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Organization and Summary of Significant Accounting Policies - Business Overview (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Significant Accounting Policies
Total revenues \| $	$ 20,443.9	$ 23,179.4	$ 22,785.1
Income tax expense benefit recorded due to provisions of CARES Act \| $	$ 11.4
Number of reportable segments	4
PTL
Significant Accounting Policies
Ownership interest in Penske Truck Leasing Co (as a percent)	28.90%
German Automotive Dealership Group
Significant Accounting Policies
Ownership interest (as a percent)	8.20%
U.S.
Significant Accounting Policies
Total revenues \| $	$ 12,105.1	13,511.8	12,607.8
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%
Retail Automotive Dealership
Significant Accounting Policies
Total number of owned and operated franchises	304
Number of owned and operated franchises in US	142
Number of owned and operated franchises outside US	162
Receivables from manufacturers \| $	$ 193.6	244.6
Number of franchises disposed	17
Number of used vehicle supercenters operated in the U.S. and U.K.	17
Retail Automotive Dealership \| UK
Significant Accounting Policies
Number of franchises disposed	13
Number of used vehicle supercenters opened	1
Retail Automotive Dealership \| U.S.
Significant Accounting Policies
Number of franchises disposed	3
Retail Automotive Dealership \| Germany
Significant Accounting Policies
Number of franchises disposed	1
Retail Automotive Dealership \| CarSense
Significant Accounting Policies
Number of retail locations operated	6
Retail Automotive Dealership \| CarShop
Significant Accounting Policies
Number of retail locations operated	11
Retail Commercial Truck Dealership \| PTG
Significant Accounting Policies
Number of operating locations	25
Audi/Volkswagen/Porsche/Bentley \| Automotive dealership revenues
Significant Accounting Policies
Percentage of total	22.00%
BMW, MINI \| Automotive dealership revenues
Significant Accounting Policies
Percentage of total	23.00%
Toyota/Lexus \| Automotive dealership revenues
Significant Accounting Policies
Percentage of total	14.00%
Retail Automotive Dealership
Significant Accounting Policies
Total revenues \| $	$ 17,928.8	20,615.8	20,849.2
Number of reportable segments	1
Retail Automotive Dealership \| UK
Significant Accounting Policies
Total revenues \| $	$ 6,344.1	7,559.4	7,961.4
Retail Automotive Dealership \| U.S.
Significant Accounting Policies
Total revenues \| $	10,270.3	11,697.6	11,504.3
Retail Commercial Truck Dealership
Significant Accounting Policies
Total revenues \| $	2,060.9	2,050.5	1,374.5
Commercial Vehicle Distribution and Other
Significant Accounting Policies
Total revenues \| $	$ 454.2	$ 513.1	$ 561.4