Restructuring Costs - Schedule of Changes in Restructuring Reserve (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	$ 15.5
Severance costs	32.7
Office closure costs and other	9.8
Costs paid, utilized or transferred out	(42.5)
Balance, end of period	15.5
Reportable segments | Americas
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.3
Severance costs	3.8
Office closure costs and other	1.3
Costs paid, utilized or transferred out	(4.6)
Balance, end of period	0.8
Reportable segments | Southern Europe
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	1.7
Severance costs	5.3
Office closure costs and other	0.1
Costs paid, utilized or transferred out	(4.1)
Balance, end of period	3.0
Reportable segments | Northern Europe
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	13.1
Severance costs	17.6
Office closure costs and other	2.2
Costs paid, utilized or transferred out	(23.4)
Balance, end of period	9.5
Reportable segments | APME
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.0
Severance costs	3.5
Office closure costs and other	0.9
Costs paid, utilized or transferred out	(3.8)
Balance, end of period	0.6
Reportable segments | Right Management
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.4
Severance costs	0.2
Office closure costs and other	4.5
Costs paid, utilized or transferred out	(5.0)
Balance, end of period	0.1
Corporate
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.0
Severance costs	2.3
Office closure costs and other	0.8
Costs paid, utilized or transferred out	(1.6)
Balance, end of period	$ 1.5