Restructuring and other (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and other	$ (171.0)	$ 338.7	$ 33.5	$ 52.2	$ 27.8	$ 7.8	$ 1.1	$ 9.2	$ 253.4	$ 45.9	$ 57.0
Employee severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other									37.2	9.8	36.2
Acquisition-related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other									7.6	21.1	2.5
Acquisition-related costs | NYX
Restructuring Cost and Reserve [Line Items]
Restructuring and other									7.7	15.1
Contingent acquisition consideration
Restructuring Cost and Reserve [Line Items]
Restructuring and other									28.7	0.0	0.0
Legal and related
Restructuring Cost and Reserve [Line Items]
Restructuring and other									152.5	0.0	0.0
Restructuring, integration and other
Restructuring Cost and Reserve [Line Items]
Restructuring and other									$ 27.4	$ 15.0	$ 18.3