Discontinued Operations and Divestitures (Details) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2016 USD ($)	Feb. 28, 2015 USD ($)	Dec. 31, 2016 USD ($) entity item	Dec. 31, 2015 USD ($) entity	Dec. 31, 2014 USD ($)
Discontinued Operations and Divestitures
Number of entities newly classified as held for sale | entity			0	0
Balance Sheet information regarding entities accounted for as discontinued operations
Total assets	$ 8.3		$ 8.3	$ 12.7
Total liabilities	6.1		6.1	6.2
Held-for-sale
Combined financial information regarding entities accounted for as discontinued operations
Revenues			24.8	75.8	$ 206.8
Pre-tax loss			(1.7)	(6.7)	(31.5)
Pre-tax gain on disposal				2.9	$ 14.8
Balance Sheet information regarding entities accounted for as discontinued operations
Inventories	4.6		4.6	6.2
Other assets	3.7		3.7	6.5
Total assets	8.3		8.3	12.7
Floor plan notes payable (including non-trade)	4.8		4.8	4.3
Other liabilities	1.3		1.3	1.9
Total liabilities	$ 6.1		$ 6.1	$ 6.2
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			10
Retail Automotive Franchise | Scion
Divestitures
Number of franchises disposed | item			17
Retail Automotive Franchise | Disposed of by sale - Discontinued Operations
Divestitures
Number of franchises disposed | item			2
Retail Commercial Truck Dealership
Divestitures
Number of dealerships disposed | item			1
Retail Commercial Truck Parts Locations
Divestitures
Number of locations disposed | item			1