Floorplan Notes Payable - Schedule of Floorplan Notes Payable (Details) - Line of credit - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Revolving credit facility — floorplan notes payable
Line of Credit Facility [Line Items]
Long-term debt, gross	$ 1,207.8	$ 1,206.0
Long-term debt, offset	(82.6)	(106.8)
Long-term debt	1,125.1	1,099.1
Other non-manufacturer facilities
Line of Credit Facility [Line Items]
Long-term debt	43.5	45.3
Floorplan notes payable — credit facility and other, net
Line of Credit Facility [Line Items]
Long-term debt	1,168.6	1,144.4
FMCC facility
Line of Credit Facility [Line Items]
Long-term debt, gross	235.5	208.5
Long-term debt, offset	(0.2)	(4.1)
Long-term debt	235.4	204.5
Other manufacturer affiliate facilities
Line of Credit Facility [Line Items]
Long-term debt	249.5	255.4
Floorplan notes payable — manufacturer affiliates, net
Line of Credit Facility [Line Items]
Long-term debt	$ 484.9	$ 459.9