Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions	6 Months Ended	9 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Jul. 01, 2019	Feb. 08, 2019	Feb. 07, 2019	Dec. 31, 2018
Purchase Price Allocation:
Goodwill	$ 2,840.1	$ 2,856.2	$ 2,840.1	$ 2,856.2	$ 2,840.1				$ 773.5	$ 770.8
Orb Intelligence & coAction.com
Purchase Price Allocation:
Cash		0.5		0.5		$ 0.5
Accounts receivable		0.3		0.3		0.3
Other		0.3		0.3		0.2
Total current assets		1.1		1.1		1.0
Goodwill		10.9		10.9		10.7
Deferred tax asset		0.4		0.4		0.4
Total assets acquired		21.6		21.6		21.3
Total liabilities assumed		0.4		0.4		0.2
Total purchase price		21.2		$ 21.2		21.1
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
Lattice
Purchase Price Allocation:
Cash	0.1		0.1		0.1		$ 0.1
Accounts receivable	1.9		1.9		1.9		1.9
Other	0.7		0.7		0.7		0.7
Total current assets	2.7		2.7		2.7		2.7
Goodwill	55.2		55.2		55.2		43.0
Deferred tax asset	17.5		17.5		17.5		18.4
Other	0.5		0.5		0.5		0.7
Total assets acquired	137.8		137.8		137.8		137.9
Deferred revenue	6.5		6.5		6.5		6.5
Other liabilities	4.3		4.3		4.3		4.4
Total liabilities assumed	10.8		10.8		10.8		10.9
Total purchase price	127.0		127.0		127.0		127.0
Measurement Period Adjustments
Goodwill	12.2
Deferred tax asset	(0.9)
Other	(0.2)
Total assets acquired	(0.1)
Other liabilities	(0.1)
Total liabilities assumed	(0.1)
Total purchase price	0.0
Take Private Acquisition, Dun & Bradstreet
Business Acquisition [Line Items]
Amortization Life (years)				16 years 6 months
Purchase Price Allocation:
Cash	117.7		117.7		117.7			$ 117.7
Accounts receivable	266.1		266.1		266.1			267.8
Other	46.4		46.4		46.4			46.8
Total current assets	430.2		430.2		430.2			432.3
Goodwill	2,787.6		2,787.6		2,787.6			2,797.6
Other	34.3		34.3		34.3			34.4
Total assets acquired	9,386.3		9,386.3		9,386.3			9,333.3
Deferred revenue	397.8		397.8		397.8			398.4
Other liabilities	169.0		169.0		169.0			161.0
Total liabilities assumed	3,257.3		3,257.3		3,257.3			$ 3,247.8
Measurement Period Adjustments
Other			(0.4)
Total current assets			(2.1)
Goodwill			(10.0)		(10.0)
Other			(0.1)
Total assets acquired			53.0
Other liabilities			8.0
Total liabilities assumed			9.5
Customer relationships | Orb Intelligence & coAction.com
Business Acquisition [Line Items]
Amortization Life (years)				7 years
Purchase Price Allocation:
Intangible assets		2.4		$ 2.4		2.4
Customer relationships | Lattice
Business Acquisition [Line Items]
Amortization Life (years)				11 years
Purchase Price Allocation:
Intangible assets	14.5		14.5		14.5		25.1
Measurement Period Adjustments
Intangible assets	(10.6)
Customer relationships | Take Private Acquisition, Dun & Bradstreet
Business Acquisition [Line Items]
Amortization Life (years)				16 years 10 months 24 days
Measurement Period Adjustments
Intangible assets			(200.5)
Technology | Orb Intelligence & coAction.com
Business Acquisition [Line Items]
Amortization Life (years)				11 years
Purchase Price Allocation:
Intangible assets		$ 6.8		$ 6.8		$ 6.8
Technology | Lattice
Business Acquisition [Line Items]
Amortization Life (years)				14 years
Purchase Price Allocation:
Intangible assets	47.4		$ 47.4		$ 47.4		$ 48.0
Measurement Period Adjustments
Intangible assets	$ (0.6)