Interim Financial Statements - Fair Value, Assets Held For Sale, Discontinued Operations (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($) item	Dec. 31, 2018 USD ($)
Fair Value of Financial Instruments
Debt instrument, Carrying Value	$ 2,227.5	$ 2,216.7
Assets Held for Sale and Discontinued Operations
Number of entities newly classified as held for sale \| item	0
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	$ 298.5	$ 297.9
3.75% senior subordinated notes due 2020 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 299.8	$ 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	$ 547.2	$ 546.8
5.75% senior subordinated notes due 2022 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 556.8	$ 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	$ 297.8	$ 297.6
5.375% senior subordinated notes due 2024 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 304.5	$ 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	$ 495.4	$ 495.1
5.50% senior subordinated notes due 2026 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	514.9	465.2
Mortgage facilities
Fair Value of Financial Instruments
Debt instrument, Carrying Value	402.1	289.6
Mortgage facilities \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 408.1	$ 290.2
Retail Automotive Franchise \| Disposal group, not discontinued operations
Disposals
Number of franchises disposed \| item	12
Retail Commercial Truck Location \| Disposal group, not discontinued operations
Disposals
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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