Stock-Based Compensation - Stock-based Compensation Expense by Award Type and Expense Category (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	$ 13.0	$ 10.7	$ 57.9	$ 56.0
Cost of services and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	6.2	4.7	23.7	22.8
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	6.7	5.7	33.8	31.4
Acquisition and integration charges
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	0.1	0.3	0.4	1.8
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	1.0	0.8	5.8	5.6
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	11.8	9.8	51.5	49.9
Common stock equivalents
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	0.2	0.1	0.6	0.5
Retirement eligible employees equity award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	$ 0.4	$ (0.3)	$ 21.8	$ 19.6