Acquisitions - Schedule of Business Combinations (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019
Business Acquisition [Line Items]
Cash payments, net of cash acquired	$ 269.6	$ 0.0
Goodwill	1,660.8		$ 1,500.0
Fiscal 2020 Acquisitions
Business Acquisition [Line Items]
Cash payments, net of cash acquired	211.3
Deferred payments, net	9.0
Contingent consideration liability	7.0
Aggregate purchase price	227.3
Net tangible assets acquired / (liabilities assumed)	(12.3)
Goodwill	152.0
Intangible assets	87.6
Shadow Financial
Business Acquisition [Line Items]
Cash payments, net of cash acquired	35.7
Deferred payments, net	3.0
Contingent consideration liability	0.0
Aggregate purchase price	38.7
Net tangible assets acquired / (liabilities assumed)	0.2
Goodwill	17.4
Intangible assets	21.1
Fi360
Business Acquisition [Line Items]
Cash payments, net of cash acquired	116.1
Deferred payments, net	3.5
Contingent consideration liability	0.0
Aggregate purchase price	119.6
Net tangible assets acquired / (liabilities assumed)	(13.9)
Goodwill	92.1
Intangible assets	41.5
Clear-Structure
Business Acquisition [Line Items]
Cash payments, net of cash acquired	59.5
Deferred payments, net	2.5
Contingent consideration liability	7.0
Aggregate purchase price	69.0
Net tangible assets acquired / (liabilities assumed)	1.4
Goodwill	42.6
Intangible assets	$ 25.0
Fiscal 2019 Acquisitions
Business Acquisition [Line Items]
Cash payments, net of cash acquired			354.7
Deferred payments, net			45.5
Contingent consideration liability			7.9
Aggregate purchase price			408.0
Net tangible assets acquired / (liabilities assumed)			8.3
Goodwill			239.4
Intangible assets			160.3
Rockall
Business Acquisition [Line Items]
Cash payments, net of cash acquired			34.9
Deferred payments, net			0.5
Contingent consideration liability			7.0
Aggregate purchase price			42.4
Net tangible assets acquired / (liabilities assumed)			(2.5)
Goodwill			30.7
Intangible assets			14.2
RPM
Business Acquisition [Line Items]
Cash payments, net of cash acquired			258.3
Deferred payments, net			45.0
Contingent consideration liability			0.8
Aggregate purchase price			304.1
Net tangible assets acquired / (liabilities assumed)			10.8
Goodwill			181.6
Intangible assets			111.7
TD Ameritrade*
Business Acquisition [Line Items]
Cash payments, net of cash acquired			61.5
Deferred payments, net			0.0
Contingent consideration liability			0.0
Aggregate purchase price			61.5
Net tangible assets acquired / (liabilities assumed)			0.0
Goodwill			27.1
Intangible assets			$ 34.4