Revenues - Disaggregation of Revenues by Geography (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	$ 1,173.6	$ 1,137.2
United States [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	862.0	828.3
United Kingdom [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	156.2	166.3
Europe (excluding United Kingdom), Middle East and Africa [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	63.0	48.3
Asia-Pacific and Japan [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	45.4	51.6
Canada [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	28.6	27.2
Americas, excluding United States and Canada [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	$ 18.4	$ 15.5