Business Acquisitions - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions			12 Months Ended
	Jun. 22, 2016	May 16, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Computer software			$ 8.4
Other intangible assets			13.6
Goodwill			2,329.7	$ 2,306.8	$ 2,303.8
HeavyWater and Ernst
Business Acquisition [Line Items]
Total purchase price consideration			43.4
Trade receivables			1.3
Prepaid expenses and other assets, including indefinite-lived intangible assets			2.1
Computer software			8.4
Other intangible assets			13.6
Goodwill			22.9
Total assets			48.3
Trade accounts payable and other accrued liabilities			3.1
Deferred revenues			0.9
Deferred income taxes, net			0.9
Total liabilities			4.9
Net assets			$ 43.4
eLynx
Business Acquisition [Line Items]
Total purchase price consideration		$ 115.0
Cash Acquired from Acquisition		0.6
Cash [Member] | eLynx
Business Acquisition [Line Items]
Cash paid		$ 44.0
Revolving Credit Facility | Motivity
Business Acquisition [Line Items]
Total purchase price consideration	$ 35.2