Revenues - Contract Balances (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Contract Balances
Accounts receivable, net	$ 848.2	$ 960.3
Unearned revenues	276.2	262.9
Revenue recognized from unearned revenue	239.1
Contracts in transit
Contract Balances
Accounts receivable, net	258.3	291.1
Vehicle receivables
Contract Balances
Accounts receivable, net	244.9	249.8
Manufacturer receivables
Contract Balances
Accounts receivable, net	191.5	244.6
Trade receivables
Contract Balances
Accounts receivable, net	$ 143.2	$ 164.7

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