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Interim Financial Statements - COVID-19 Disclosure (Details) $ in Millions			1 Months Ended				2 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 01, 2020 employee	Mar. 24, 2020	Jun. 30, 2020 USD ($)	May 31, 2020	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2020 employee	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) employee item	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Interim Financial Statements
Revenues								$ 3,651.1	$ 5,755.8	$ 8,660.2	$ 11,320.2
Cash			$ 159.3					$ 159.3	$ 43.8	$ 159.3	$ 43.8	$ 28.1	$ 39.4
PTL
Interim Financial Statements
Ownership interest in PTS (as a percent)										28.90%
3.75% senior subordinated notes due 2020
Interim Financial Statements
Interest rate (as a percent)			3.75%					3.75%		3.75%		3.75%
Principal amount			$ 300.0					$ 300.0		$ 300.0
Retail Automotive Dealership
Interim Financial Statements
Revenues												$ 20,600.0
COVID-19 Risk
Interim Financial Statements
Estimated capital expenditures postponed										$ 150.0
Temporary reduction in the salary for the CEO and President, percentage										100.00%
Temporary reduction in the salary for other executive officers, percentage	12.50%									25.00%
Incentive financing (as percent)						0.00%
Percentage of workforce that remains furloughed	14.00%
Reduction in number of employees \| employee										2,000
Reduction to selling, general, and administrative expenses for the amount of government assistance received								55.9
COVID-19 Risk \| PTL
Interim Financial Statements
Number of layoffs \| item										7,000
Percentage reduction in executive management pay										30.00%
COVID-19 Risk \| Minimum
Interim Financial Statements
Number of employees furloughed \| employee							15,000
COVID-19 Risk \| U.S and other
Interim Financial Statements
Government assistance								6.4
COVID-19 Risk \| UK
Interim Financial Statements
Number of employees that remain furloughed \| employee	1,950
Percentage of workforce that remains furloughed	20.00%
Government assistance								49.5
COVID-19 Risk \| UK \| Minimum
Interim Financial Statements
Percentage of employees furloughed		90.00%
COVID-19 Risk \| Used supercenters \| UK
Interim Financial Statements
Percentage decline in same store unit sales			6.00%
COVID-19 Risk \| Retail Automotive Dealership \| U.S.
Interim Financial Statements
Percentage decline in unit volume			9.00%
COVID-19 Risk \| Retail Automotive Dealership \| UK
Interim Financial Statements
Percentage increase in unit volume			9.00%
COVID-19 Risk \| Retail Automotive Dealership \| New and Used Vehicle
Interim Financial Statements
Percentage decline in same store unit sales				50.00%	71.00%
Percentage decline in revenue compared to the prior year			1.00%
COVID-19 Risk \| Retail Automotive Dealership \| New and Used Vehicle \| U.S.
Interim Financial Statements
Percentage decline in revenue compared to the prior year				26.00%	50.00%
COVID-19 Risk \| Retail Automotive Dealership \| New and Used Vehicle \| UK
Interim Financial Statements
Percentage decline in revenue compared to the prior year				85.00%	100.00%
COVID-19 Risk \| Retail Automotive Dealership \| Service and parts
Interim Financial Statements
Percentage decline in revenue compared to the prior year			3.00%	43.00%	60.00%
COVID-19 Risk \| Retail Automotive Dealership \| Service and parts \| U.S.
Interim Financial Statements
Percentage decline in revenue compared to the prior year			5.00%
COVID-19 Risk \| Retail Automotive Dealership \| Service and parts \| UK
Interim Financial Statements
Percentage decline in revenue compared to the prior year			1.00%
COVID-19 Risk \| Retail Automotive Dealership \| Used supercenters \| U.S.
Interim Financial Statements
Percentage decline in same store unit sales			20.00%
COVID-19 Risk \| Retail Commercial Truck Dealership
Interim Financial Statements
Revenues								$ 399.2
Percentage decline in unit volume								8.20%
Percentage decrease in revenue								6.50%
COVID-19 Risk \| Retail Commercial Truck Dealership \| North American Class 8 Retail
Interim Financial Statements
Percentage decline in business								51.10%
Percentage decline in same store business								40.20%
Percentage decline in same store unit sales								52.20%