Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 08, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	[1]	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Purchase Price Allocation:
Goodwill		$ 3,331.1	$ 3,318.2	$ 2,857.9		$ 2,848.8	$ 2,848.7	$ 2,841.7
Bisnode
Business Acquisition [Line Items]
Weighted Average Amortization Period (years)	13 years 7 months 6 days
Purchase Price Allocation:
Cash		29.9	29.9
Accounts receivable		61.0	61.0
Other current assets		13.1	13.1
Total current assets		104.0	104.0
Property, plant, and equipment		3.5	3.5
Goodwill		491.0	488.4
Right of use asset		27.8	26.7
Other		2.9	5.2
Total assets acquired		1,182.2	1,185.8
Accounts payable		17.5	17.5
Deferred revenue		80.6	80.6
Accrued liabilities		20.7	20.7
Short-term pension and other accrued benefits		17.1	17.1
Short-term lease liability		8.4	8.4
Other current liabilities		23.7	23.7
Total current liabilities		168.0	168.0
Long-term pension and postretirement obligations		65.4	65.4
Deferred tax liability		123.4	127.6
Long-term debt		18.8	18.2
Other liabilities		0.8	0.8
Total liabilities assumed		376.4	380.0
Total purchase price		805.8	805.8
Measurement Period Adjustment
Goodwill		2.6
Right of use asset		1.1
Other		(2.3)
Total assets acquired		(3.6)
Deferred tax liability		(4.2)
Long-term lease liability		0.6
Total liabilities assumed		(3.6)
Bisnode | Reacquired right
Business Acquisition [Line Items]
Weighted Average Amortization Period (years)	15 years
Purchase Price Allocation:
Finite-lived intangible assets acquired		270.0	271.0
Measurement Period Adjustment
Finite-lived intangible assets acquired		(1.0)
Bisnode | Database
Business Acquisition [Line Items]
Weighted Average Amortization Period (years)	12 years
Purchase Price Allocation:
Finite-lived intangible assets acquired		111.0	116.0
Measurement Period Adjustment
Finite-lived intangible assets acquired		(5.0)
Bisnode | Customer relationships
Business Acquisition [Line Items]
Weighted Average Amortization Period (years)	10 years
Purchase Price Allocation:
Finite-lived intangible assets acquired		108.0	106.0
Measurement Period Adjustment
Finite-lived intangible assets acquired		2.0
Bisnode | Technology
Business Acquisition [Line Items]
Weighted Average Amortization Period (years)	14 years
Purchase Price Allocation:
Finite-lived intangible assets acquired		64.0	$ 65.0
Measurement Period Adjustment
Finite-lived intangible assets acquired		$ (1.0)

[1] See discussion in Note 1 - Basis of Presentation for further detail regarding the elimination of the International lag reporting.