Floorplan Notes Payable - Schedule of Floorplan Notes Payable (Details) - Line of credit - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Revolving credit facility — floorplan notes payable
Line of Credit Facility [Line Items]
Long-term debt, gross	$ 763.7	$ 1,206.0
Long-term debt, offset	(99.7)	(106.8)
Long-term debt	664.0	1,099.1
Other non-manufacturer facilities
Line of Credit Facility [Line Items]
Long-term debt	32.6	45.3
Floorplan notes payable — credit facility and other, net
Line of Credit Facility [Line Items]
Long-term debt	696.6	1,144.4
FMCC facility
Line of Credit Facility [Line Items]
Long-term debt, gross	137.1	208.5
Long-term debt, offset	(8.1)	(4.1)
Long-term debt	129.0	204.5
Other manufacturer affiliate facilities
Line of Credit Facility [Line Items]
Long-term debt	228.7	255.4
Floorplan notes payable — manufacturer affiliates, net
Line of Credit Facility [Line Items]
Long-term debt	$ 357.7	$ 459.9