Restructuring and other (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and other	$ 33.5	$ 1.1	$ 85.7	$ 10.3
Employee severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other	15.8	0.0	20.9	2.7
Acquisitions and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other	(0.2)	0.8	7.6	4.2
Contingent consideration adjustment
Restructuring Cost and Reserve [Line Items]
Restructuring and other	0.0	0.0	18.0	0.0
Legal and related
Restructuring Cost and Reserve [Line Items]
Restructuring and other	10.0	0.0	26.0	0.0
Restructuring, integration and other
Restructuring Cost and Reserve [Line Items]
Restructuring and other	$ 7.9	$ 0.3	13.2	$ 3.4
NYX | Acquisitions and related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other			$ 7.7