Store Divestitures (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) store	Dec. 31, 2017 USD ($) store	Dec. 31, 2016 USD ($) store
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on disposal | $		$ 40.3	$ 78.2	$ 61.8
Write-downs associated with pending business divestitures | $	$ 26.2
Domestic Stores Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of businesses divested		8	2	5
Import Stores Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of businesses divested		7	4	9
Premium Luxury Stores Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of businesses divested		2
Collision Centers Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of businesses divested		1