Revenues - Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Contract Balances
Accounts receivable, net	$ 1,034.1	$ 929.1
Unearned revenues	275.6	269.8
Revenue recognized from unearned revenue	103.0
Contracts in transit
Contract Balances
Accounts receivable, net	348.4	314.2
Vehicle receivables
Contract Balances
Accounts receivable, net	289.2	266.9
Manufacturer receivables
Contract Balances
Accounts receivable, net	225.7	211.3
Trade receivables
Contract Balances
Accounts receivable, net	$ 156.8	$ 129.1

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