Receivables and Contract Assets, Net - Financial Assets (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contracts-in-transit	$ 114.5	$ 169.9
Vehicle receivables	59.2	84.3
Total contracts-in-transit and vehicle receivables	173.7	254.1
Less: allowance for doubtful accounts	0.4	0.3
Total contracts-in-transit and vehicle receivables, net	173.3	253.8
Accounts and notes receivable
Accounts and notes receivable	156.0	227.9
Less: allowance for doubtful accounts	3.5	2.8
Accounts and notes receivable, net	152.5	225.1
Total contract assets, net	25.3	21.6
Manufacturer receivables
Accounts and notes receivable
Accounts and notes receivable	74.4	124.0
Parts and service receivables
Accounts and notes receivable
Accounts and notes receivable	45.6	57.0
F&I receivables
Accounts and notes receivable
Accounts and notes receivable	20.3	28.3
Other
Accounts and notes receivable
Accounts and notes receivable	$ 15.7	$ 18.6