Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Goodwill and Other Intangible Assets - Changes in Carrying Value of Goodwill by Reportable Segment (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill	$ 1,178.2		$ 1,178.2		$ 1,260.1
Goodwill impairment charges	66.8	$ 64.0	66.8	$ 64.0
Jefferson Wells
Goodwill [Roll Forward]
Goodwill	55.5		55.5
Right Management
Goodwill [Roll Forward]
Goodwill	62.1		62.1
Germany
Goodwill [Roll Forward]
Goodwill impairment charges	66.8	$ 60.2
Americas \| United States
Goodwill [Roll Forward]
Goodwill	490.2		490.2		490.3
Americas \| United States \| Jefferson Wells
Goodwill [Roll Forward]
Goodwill	545.7		545.7		545.8
Southern Europe \| France
Goodwill [Roll Forward]
Goodwill	67.4		67.4		67.3
Southern Europe \| Italy
Goodwill [Roll Forward]
Goodwill	$ 3.8		$ 3.8		$ 4.6