Share-Based Compensation - Allocated Share-based Compensation Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	$ 18.8	$ 6.1	$ 6.7
Total income tax benefit recognized	4.6	1.6	2.6
Cost of Services
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	2.4	2.3	2.2
Selling, General and Administrative Expenses
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	14.9	$ 3.8	4.4
Restructuring and Related Charges
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	$ 1.5		$ 0.1