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Financial Instruments And Fair Value Measurements (Nonfinancial Assets Measured on a Nonrecurring Basis) (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 USD ($) | Jun. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Mar. 31, 2020 USD ($) | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | 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 |  |
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 | 61,600,000 |  |  |  | 61,600,000 |  | $ 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
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) | (2,000,000.0) |
Gain/(Loss) on assets held and used |  |  |  |  | (3,100,000) | (6,900,000) |
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 |  |  | 0 |
Right-of-use assets | 0 |  | 5,000,000.0 |  | 0 | 5,000,000.0 |
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 |  |  |

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