Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Feb. 08, 2019	Dec. 31, 2018
Preliminary Purchase Price Allocation:
Goodwill	$ 2,848.0	$ 2,848.0	$ 2,850.8	$ 2,840.1	$ 2,792.6	$ 2,797.6	$ 773.5	$ 0.0
Orb Intelligence & coAction.com
Preliminary Purchase Price Allocation:
Cash	0.5	0.5	0.5
Accounts receivable	0.3	0.3	0.3
Other	0.4	0.4	0.2
Total current assets	1.2	1.2	1.0
Goodwill	10.7	10.7	10.7
Deferred tax asset	0.4	0.4	0.4
Total assets acquired	21.5	21.5	21.3
Total liabilities assumed	0.4	0.4	0.2
Total purchase price	21.1	$ 21.1	21.1
Measurement Period Adjustments
Other	0.2
Total current assets	0.2
Total assets acquired	0.2
Total liabilities assumed	0.2
Customer relationships | Orb Intelligence & coAction.com
Business Acquisition [Line Items]
Amortization Life (years)		7 years
Preliminary Purchase Price Allocation:
Intangible assets	2.4	$ 2.4	2.4
Technology | Orb Intelligence & coAction.com
Business Acquisition [Line Items]
Amortization Life (years)		11 years
Preliminary Purchase Price Allocation:
Intangible assets	$ 6.8	$ 6.8	$ 6.8