Goodwill and Other Intangible Assets - Changes in Goodwill by Reportable Segment (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill [Roll Forward]
Balance, January 1, 2017	$ 1,239.9
Goodwill acquired	9.5
Currency and other impacts	42.5
Balance, June 30, 2017	1,291.9
Right Management
Goodwill [Roll Forward]
Balance, January 1, 2017	62.1
Balance, June 30, 2017	62.1
Reportable segments | Americas
Goodwill [Roll Forward]
Balance, January 1, 2017	516.4
Goodwill acquired	0.0
Currency and other impacts	1.5
Balance, June 30, 2017	517.9
Reportable segments | Americas | United States | Reportable subsegments
Goodwill [Roll Forward]
Balance, January 1, 2017	476.5
Balance, June 30, 2017	476.5
Reportable segments | Southern Europe
Goodwill [Roll Forward]
Balance, January 1, 2017	97.0
Goodwill acquired	9.4
Currency and other impacts	9.6
Balance, June 30, 2017	116.0
Reportable segments | Southern Europe | France | Reportable subsegments
Goodwill [Roll Forward]
Balance, January 1, 2017	66.8
Balance, June 30, 2017	72.6
Reportable segments | Southern Europe | Italy | Reportable subsegments
Goodwill [Roll Forward]
Balance, January 1, 2017	4.4
Balance, June 30, 2017	4.7
Reportable segments | Northern Europe
Goodwill [Roll Forward]
Balance, January 1, 2017	421.9
Goodwill acquired	0.1
Currency and other impacts	27.7
Balance, June 30, 2017	449.7
Reportable segments | APME
Goodwill [Roll Forward]
Balance, January 1, 2017	77.0
Goodwill acquired	0.0
Currency and other impacts	3.7
Balance, June 30, 2017	80.7
Reportable segments | Right Management
Goodwill [Roll Forward]
Balance, January 1, 2017	62.1
Goodwill acquired	0.0
Currency and other impacts	0.0
Balance, June 30, 2017	62.1
Corporate
Goodwill [Roll Forward]
Balance, January 1, 2017	65.5
Goodwill acquired	0.0
Currency and other impacts	0.0
Balance, June 30, 2017	65.5
Corporate | Jefferson Wells
Goodwill [Roll Forward]
Balance, June 30, 2017	$ 55.5