Goodwill and Other Intangible Assets - Changes in Goodwill by Reportable Segment (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Goodwill [Roll Forward]
Balance, December 31, 2018	$ 1,297.1
Goodwill acquired	0.4
Currency and other impacts	(3.9)
Balance, March 31, 2019	1,293.6
Jefferson Wells
Goodwill [Roll Forward]
Balance, March 31, 2019	55.5
Americas | United States
Goodwill [Roll Forward]
Balance, December 31, 2018	476.5
Balance, March 31, 2019	476.5
Southern Europe | France
Goodwill [Roll Forward]
Balance, December 31, 2018	68.9
Balance, March 31, 2019	67.4
Southern Europe | Italy
Goodwill [Roll Forward]
Balance, December 31, 2018	4.8
Balance, March 31, 2019	4.6
Reportable segments | Americas
Goodwill [Roll Forward]
Balance, December 31, 2018	519.9
Goodwill acquired	0.4
Currency and other impacts	0.8
Balance, March 31, 2019	521.1
Reportable segments | Southern Europe
Goodwill [Roll Forward]
Balance, December 31, 2018	112.2
Goodwill acquired	0.0
Currency and other impacts	(1.9)
Balance, March 31, 2019	110.3
Reportable segments | Northern Europe
Goodwill [Roll Forward]
Balance, December 31, 2018	435.4
Goodwill acquired	0.0
Currency and other impacts	(2.8)
Balance, March 31, 2019	432.6
Reportable segments | APME
Goodwill [Roll Forward]
Balance, December 31, 2018	102.0
Goodwill acquired	0.0
Currency and other impacts	0.0
Balance, March 31, 2019	102.0
Reportable segments | Right Management
Goodwill [Roll Forward]
Balance, December 31, 2018	62.1
Goodwill acquired	0.0
Currency and other impacts	0.0
Balance, March 31, 2019	62.1
Corporate
Goodwill [Roll Forward]
Balance, December 31, 2018	65.5
Goodwill acquired	0.0
Currency and other impacts	0.0
Balance, March 31, 2019	$ 65.5