Revenues - Retail Commercial Truck Dealership (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Revenues
Total revenues	$ 5,564.4	$ 5,746.9
Retail Commercial Truck Dealership
Revenues
Total revenues	332.3	292.4
New vehicle \| Retail Commercial Truck Dealership
Revenues
Total revenues	207.4	170.4
Used vehicle \| Retail Commercial Truck Dealership
Revenues
Total revenues	24.1	26.5
Finance and insurance, net \| Retail Commercial Truck Dealership
Revenues
Total revenues	3.0	3.2
Service and parts \| Retail Commercial Truck Dealership
Revenues
Total revenues	91.5	90.4
Other \| Retail Commercial Truck Dealership
Revenues
Total revenues	$ 6.3	$ 1.9

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

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