Restructuring Costs - Schedule of Changes in Restructuring Reserve (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	$ 7.3
Severance costs	67.8
Office closure costs	22.6
Other costs	7.7
Costs paid, utilized or transferred out	(55.5)
Balance, end of period	49.9
Reportable segments | Americas
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.4
Severance costs	5.5
Office closure costs	19.6
Other costs	4.4
Costs paid, utilized or transferred out	(25.1)
Balance, end of period	4.8
Reportable segments | Southern Europe
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.7
Severance costs	16.2
Office closure costs	2.3
Other costs	2.2
Costs paid, utilized or transferred out	(15.6)
Balance, end of period	5.8
Reportable segments | Northern Europe
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	6.2
Severance costs	43.4
Office closure costs	0.2
Other costs	0.0
Costs paid, utilized or transferred out	(11.1)
Balance, end of period	38.7
Reportable segments | APME
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.0
Severance costs	2.5
Office closure costs	0.5
Other costs	1.1
Costs paid, utilized or transferred out	(3.5)
Balance, end of period	0.6
Corporate
Restructuring Cost and Reserve [Line Items]
Balance, beginning of period	0.0
Severance costs	0.2
Office closure costs	0.0
Other costs	0.0
Costs paid, utilized or transferred out	(0.2)
Balance, end of period	$ 0.0