Revenues - Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Contract Balances
Accounts receivable	$ 1,062.8	$ 1,114.6
Unearned revenues	267.4	280.2
Contracts in transit
Contract Balances
Accounts receivable	319.8	361.9
Vehicle receivables
Contract Balances
Accounts receivable	175.8	170.6
Manufacturer receivables
Contract Balances
Accounts receivable	212.0	218.9
Trade receivables
Contract Balances
Accounts receivable	$ 334.8	$ 344.1

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479837/606-10-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-8

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479837/606-10-45-2

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant