Stock-Based Compensation - Stock-based Compensation Expense by Award Type and Expense Category (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	$ 25.1	$ 31.8
Cost of services and product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	12.1	11.3
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	13.0	20.4
Acquisition and integration charges
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	0.0	0.1
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	1.7	3.9
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	23.2	27.7
Common stock equivalents
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	0.2	0.2
Retirement eligible employees equity award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense (credit)	$ 11.6	$ 20.9