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Fair value portion of asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Financial Instruments And Fair Value Measurements (Nonfinancial Assets Measured on a Nonrecurring Basis) (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill	$ 0	$ 0		$ 0	$ (318,300,000)
Equity investment	56,700,000			56,700,000
Gain/(Loss) on equity investment	3,400,000
Goodwill impairment	0	0		0	318,300,000
Franchise rights impairment	0	0		0	57,500,000
Continuing Operations [Member] \| Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	81,300,000			81,300,000		$ 25,500,000
Discontinued Operations [Member] \| Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale in discontinued operations	1,100,000			1,100,000		$ 8,000,000.0
Franchise Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Franchise rights impairment				0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill			$ (318,300,000)	0	(318,300,000)
Gain/(Loss) on franchise rights and other				0	(59,900,000)
Gain/(Loss) on equity investment				3,400,000	0
Gain/(Loss) on right-of-use assets				(100,000)	(400,000)
Gain/(Loss) on assets held and used				(1,600,000)	(5,800,000)
Goodwill impairment			318,300,000	0	318,300,000
Fair Value, Nonrecurring [Member] \| Other Intangible Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of finite-lived intangibles assets					2,400,000
Fair Value, Nonrecurring [Member] \| Franchise Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Franchise rights impairment			57,500,000
Fair Value, Nonrecurring [Member] \| Reporting Unit, Premium Luxury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill			(257,400,000)
Goodwill impairment			257,400,000
Fair Value, Nonrecurring [Member] \| Reporting Unit, Collision Centers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill			(41,600,000)
Goodwill impairment			41,600,000
Fair Value, Nonrecurring [Member] \| Reporting Unit, Parts Centers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill			(19,300,000)
Goodwill impairment			19,300,000
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0	457,500,000		0	457,500,000
Franchise rights and other	0	26,200,000		0	26,200,000
Equity investment	53,400,000	0		53,400,000	0
Right-of-use assets	0	1,400,000		0	1,400,000
Long-lived assets held and used	$ 10,400,000	$ 1,800,000		$ 10,400,000	$ 1,800,000
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Franchise rights and other			$ 24,600,000
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Weighted Average Cost of Capital [Member] \| Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.085
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.111
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.143
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Discount Rate [Member] \| Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.121
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.020
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Long-term Pretax Income Margin [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.006
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Long-term Pretax Income Margin [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.028
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Long-term Pretax Income Margin [Member] \| Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.014
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Contributory Asset Charges [Member] \| Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.042
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Contributory Asset Charges [Member] \| Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.121
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Franchise Rights [Member] \| Valuation Technique, Discounted Cash Flow [Member] \| Measurement Input, Contributory Asset Charges [Member] \| Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Franchise rights, measurement input			0.062