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Discontinued Operations and Divestitures (Details) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Feb. 28, 2015 USD ($)	Dec. 31, 2017 USD ($) entity item	Dec. 31, 2016 USD ($) entity	Dec. 31, 2015 USD ($) entity
Discontinued Operations and Divestitures
Number of entities newly classified as held for sale \| entity			0	0	0
Balance Sheet information regarding entities accounted for as discontinued operations
Total assets	$ 8.4			$ 8.4
Total liabilities	6.1		$ 0.7	6.1
Held-for-sale
Combined financial information regarding entities accounted for as discontinued operations
Revenues			2.1	24.8	$ 75.8
Pre-tax loss			(0.4)	(1.7)	(6.7)
Pre-tax gain on disposal					$ 2.9
Balance Sheet information regarding entities accounted for as discontinued operations
Inventories	4.6			4.6
Other assets	3.8			3.8
Total assets	8.4			8.4
Floor plan notes payable (including non-trade)	4.8			4.8
Other liabilities	1.3		0.7	1.3
Total liabilities	$ 6.1		$ 0.7	$ 6.1
Disposed of by sale - Continuing Operations \| i.M. Branded
Divestitures
Ownership interest sold in previous consolidated entity (as a percent)	90.00%
Hertz car rental franchise \| Disposed of by sale - Discontinued Operations
Divestitures
Proceeds from sale of business		$ 17.8
Retail Automotive Franchise
Divestitures
Number of franchises disposed \| item			25
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			24