Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended	11 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Feb. 08, 2019	Dec. 31, 2018
Preliminary Purchase Price Allocation:
Goodwill	$ 2,850.8	$ 2,853.9	$ 2,853.9	$ 2,840.1	$ 2,848.0	$ 2,967.4	$ 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	0.2	0.3	0.3
Total current assets	1.0	1.1	1.1
Goodwill	10.7	10.9	10.9
Deferred tax asset	0.4	0.4	0.4
Total assets acquired	21.3	21.6	21.6
Total liabilities assumed	0.2	0.4	0.4
Total purchase price	21.1	21.2	$ 21.2
Measurement Period Adjustments
Other		0.1
Total current assets		0.1
Goodwill		0.2
Total assets acquired		0.3
Total liabilities assumed		0.2
Total purchase price		0.1
Take Private Acquisition, Dun & Bradstreet
Business Acquisition [Line Items]
Amortization Life (years)			16 years 6 months
Preliminary Purchase Price Allocation:
Cash				117.7					117.7
Accounts receivable				266.1					267.8
Other				46.4					46.8
Total current assets				430.2					432.3
Goodwill				2,787.6					2,797.6
Total assets acquired				9,386.3					9,333.3
Total liabilities assumed				3,257.3					$ 3,247.8
Measurement Period Adjustments
Other				(0.4)
Total current assets				(2.1)
Goodwill	(10.0)			(10.0)
Total assets acquired				53.0
Total liabilities assumed				$ 9.5
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
Customer relationships | Take Private Acquisition, Dun & Bradstreet
Business Acquisition [Line Items]
Amortization Life (years)			16 years 10 months 24 days
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