Revenues - Contract Balances (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Contract Balances
Accounts receivable, net	$ 944.4	$ 929.1
Unearned revenues	272.0	269.8
Revenue recognized from unearned revenue	174.7
Contracts in transit
Contract Balances
Accounts receivable, net	330.4	314.2
Vehicle receivables
Contract Balances
Accounts receivable, net	251.0	266.9
Manufacturer receivables
Contract Balances
Accounts receivable, net	200.9	211.3
Trade receivables
Contract Balances
Accounts receivable, net	$ 154.6	$ 129.1

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