Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Intangible Assets - Information by Segment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Intangible assets
Goodwill	$ 1,760.7	$ 1,752.0
Retail Automotive Dealership
Intangible assets
Goodwill	1,519.8
Retail Commercial Truck Dealership
Intangible assets
Goodwill	162.9
Other
Intangible assets
Goodwill	78.0
Non-Automotive Investments
Intangible assets
Goodwill	$ 0.0