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Interim Financial Statements - Assets Held For Sale, Discontinued Operations and Fair Value (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) item	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Combined financial information regarding entities accounted for as discontinued operations
Number of entities newly classified as held for sale \| item	0
Balance Sheet information regarding entities accounted for as discontinued operations
Total assets			$ 8.4
Total liabilities	$ 0.8		6.1
Fair Value of Financial Instruments
Debt instrument, Carrying Value	$ 2,037.4		$ 1,877.1
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	$ 545.3		$ 545.1
5.75% senior subordinated notes due 2022 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 564.4		$ 567.6
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	$ 296.9		$ 296.8
5.375% Senior Subordinated Notes Due 2024 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 299.3		$ 293.0
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	$ 493.9		$ 493.7
5.50% senior subordinated notes due 2026 \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	481.9		489.4
Mortgage facilities
Fair Value of Financial Instruments
Debt instrument, Carrying Value	215.0		199.9
Mortgage facilities \| Fair Value, Inputs, Level 2
Fair Value of Financial Instruments
Debt instrument, Fair Value	$ 211.4		195.6
Retail Automotive Franchise
Divestitures
Number of franchises disposed \| item	4
Retail Automotive Franchise \| Disposed of by sale - Discontinued Operations
Divestitures
Number of franchises disposed \| item	1
Retail Automotive Franchise \| Disposal group, not discontinued operations
Divestitures
Number of franchises disposed \| item	3
Retail Automotive Franchise \| Held-for-sale
Combined financial information regarding entities accounted for as discontinued operations
Revenues	$ 2.1	$ 8.4
Pre-tax loss	(0.9)
Balance Sheet information regarding entities accounted for as discontinued operations
Inventories			4.6
Other assets			3.8
Total assets			8.4
Floor plan notes payable (including non-trade)			4.8
Other liabilities	0.8		1.3
Total liabilities	$ 0.8		$ 6.1