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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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

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

Goodwill - Goodwill by Reporting Unit (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 1,297.1	$ 1,343.0	$ 1,239.9
United States
Goodwill [Line Items]
Goodwill	532.0	532.0
Germany
Goodwill [Line Items]
Goodwill	129.2	135.4
Netherlands
Goodwill [Line Items]
Goodwill	112.0	126.5
United Kingdom
Goodwill [Line Items]
Goodwill	93.7	89.2
France
Goodwill [Line Items]
Goodwill	68.9	76.3
Right Management
Goodwill [Line Items]
Goodwill	62.1	62.1
Other reporting units
Goodwill [Line Items]
Goodwill	$ 299.2	$ 321.5