Restructuring Costs - Schedule of Changes in Restructuring Reserve (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	$ 7.3
Severance costs	37.0
Office closure and other costs	11.2
Costs paid, utilized or transferred out	(20.4)
Balance, end of period	35.1
Reportable segments | Americas
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.4
Severance costs	4.7
Office closure and other costs	8.1
Costs paid, utilized or transferred out	(8.4)
Balance, end of period	4.8
Reportable segments | Southern Europe
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.7
Severance costs	11.8
Office closure and other costs	1.3
Costs paid, utilized or transferred out	(7.0)
Balance, end of period	6.8
Reportable segments | Northern Europe
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	6.2
Severance costs	19.3
Office closure and other costs	0.2
Costs paid, utilized or transferred out	(3.4)
Balance, end of period	22.3
Reportable segments | APME
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.0
Severance costs	1.0
Office closure and other costs	1.6
Costs paid, utilized or transferred out	(1.6)
Balance, end of period	1.0
Corporate
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.0
Severance costs	0.2
Office closure and other costs	0.0
Costs paid, utilized or transferred out	0.0
Balance, end of period	$ 0.2