Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Net restructuring costs	$ 39.8	$ 24.0
Restructuring reserve [Roll Forward]
Balance, beginning of period	15.5
Severance costs	30.8
Office closure costs and other	9.0
Costs paid, utilized or transferred out	(22.1)
Balance, end of period	33.2
Restructuring reserve transferred to current operating lease liabilities	(7.6)
Americas | United States
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.3
Balance, end of period	1.3
Southern Europe | France
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.9
Balance, end of period	0.9
Southern Europe | Italy
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.5
Balance, end of period	2.3
Reportable segments | Americas
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.3
Severance costs	3.8
Office closure costs and other	1.3
Costs paid, utilized or transferred out	(3.5)
Balance, end of period	1.9
Reportable segments | Southern Europe
Restructuring reserve [Roll Forward]
Balance, beginning of period	1.7
Severance costs	5.3
Office closure costs and other	0.1
Costs paid, utilized or transferred out	(1.1)
Balance, end of period	6.0
Reportable segments | Northern Europe
Restructuring reserve [Roll Forward]
Balance, beginning of period	13.1
Severance costs	16.5
Office closure costs and other	2.2
Costs paid, utilized or transferred out	(11.2)
Balance, end of period	20.6
Reportable segments | APME
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.0
Severance costs	3.5
Office closure costs and other	0.9
Costs paid, utilized or transferred out	(1.5)
Balance, end of period	2.9
Reportable segments | Right Management
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.4
Severance costs	0.2
Office closure costs and other	4.5
Costs paid, utilized or transferred out	(4.8)
Balance, end of period	0.3
Corporate
Restructuring reserve [Roll Forward]
Balance, beginning of period	0.0
Severance costs	1.5
Office closure costs and other	0.0
Costs paid, utilized or transferred out	0.0
Balance, end of period	$ 1.5