Revenues - Disaggregation of Revenues by Geography (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	$ 1,148.0	$ 895.8	$ 2,285.2	$ 1,317.7
United States [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	841.9	646.0	1,670.3	948.7
United Kingdom [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	164.9	144.7	331.2	176.7
Europe (excluding United Kingdom), Middle East and Africa [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	49.2	35.0	97.5	62.8
Asia-Pacific and Japan [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	48.4	35.4	100.0	64.4
Canada [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	27.4	22.8	54.5	41.1
Americas, excluding United States and Canada [Member]
Disaggregation Of Revenue [Line Items]
Disaggregation of revenue	$ 16.2	$ 11.9	$ 31.7	$ 24.0