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Financial Instruments And Fair Value Measurements (Nonfinancial Assets Measured on a Nonrecurring Basis) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill	$ 0.0	$ (318.3)
Goodwill impairment	0.0	318.3
Franchise rights impairment	0.0	57.5
Continuing Operations [Member] \| Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	56.3		$ 25.5
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	1.1		$ 8.0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain/(Loss) on goodwill	0.0	(318.3)
Gain/(Loss) on franchise rights and other	0.0	(59.9)
Gain/(Loss) on right-of-use assets	(0.1)	(0.4)
Gain/(Loss) on assets held and used	(0.9)	(5.7)
Goodwill impairment	0.0	318.3
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		2.4
Fair Value, Nonrecurring [Member] \| Franchise Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Franchise rights impairment		57.5
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		(257.4)
Goodwill impairment		257.4
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		(41.6)
Goodwill impairment		41.6
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		(19.3)
Goodwill impairment		19.3
Fair Value, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0.0	457.5
Franchise rights and other	0.0	26.2
Right-of-use assets	0.0	1.4
Long-lived assets held and used	$ 6.0	1.8
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		$ 24.6
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