Interim Financial Statements - Assets Held For Sale, Discontinued Operations and Fair Value (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)
Combined financial information regarding entities accounted for as discontinued operations
Number of entities newly classified as held for sale \| item	0
Fair Value of Financial Instruments
Debt instrument, Carrying Value	$ 2,212.8	$ 2,216.7
3.75% senior subordinated notes due 2020
Fair Value of Financial Instruments
Interest rate (as a percent)	3.75%	3.75%
Debt instrument, Carrying Value	$ 298.2	$ 297.9
3.75% senior subordinated notes due 2020 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 299.6	$ 291.9
5.75% senior subordinated notes due 2022
Fair Value of Financial Instruments
Interest rate (as a percent)	5.75%	5.75%
Debt instrument, Carrying Value	$ 547.0	$ 546.8
5.75% senior subordinated notes due 2022 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 559.5	$ 537.6
5.375% senior subordinated notes due 2024
Fair Value of Financial Instruments
Interest rate (as a percent)	5.375%	5.375%
Debt instrument, Carrying Value	$ 297.7	$ 297.6
5.375% senior subordinated notes due 2024 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 297.8	$ 278.7
5.50% senior subordinated notes due 2026
Fair Value of Financial Instruments
Interest rate (as a percent)	5.50%	5.50%
Debt instrument, Carrying Value	$ 495.2	$ 495.1
5.50% senior subordinated notes due 2026 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	489.0	465.2
Mortgage facilities
Fair Value of Financial Instruments
Debt instrument, Carrying Value	287.3	289.6
Mortgage facilities \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 286.7	$ 290.2
Retail Automotive Franchise
Divestitures
Number of franchises disposed \| item	7
Retail Commercial Truck Location
Divestitures
Number of locations disposed \| item	1

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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