Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions				3 Months Ended	5 Months Ended
	Nov. 15, 2021	Nov. 05, 2021	Jan. 08, 2021	Mar. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Purchase Price Allocation:
Goodwill				$ 3,475.4	$ 3,475.4	$ 3,493.3	$ 3,318.2	$ 2,857.9
Bisnode
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 & equipment				3.5	3.5
Goodwill				495.4	495.4
Right of use assets				27.4	27.4
Other				2.9	2.9
Total assets acquired				1,186.2	1,186.2
Accounts payable				17.5	17.5
Deferred revenue				80.6	80.6
Accrued payroll				20.7	20.7
Accrued income tax and other tax liabilities				17.1	17.1
Short-term lease liability				8.6	8.6
Other current liabilities				23.7	23.7
Total current liabilities				168.2	168.2
Long-term pension and postretirement obligations				65.4	65.4
Deferred tax liability				127.8	127.8
Long-term lease liability				18.2	18.2
Other liabilities				0.8	0.8
Total liabilities assumed				380.4	380.4
Total purchase price				805.8	805.8
Bisnode | Customer relationships
Purchase Price Allocation:
Intangible assets:				108.0	108.0
Measurement Period Adjustments
Weighted average amortization period (years)			10 years
Bisnode | Technology
Purchase Price Allocation:
Intangible assets:				64.0	64.0
Measurement Period Adjustments
Weighted average amortization period (years)			14 years
Bisnode | Database
Purchase Price Allocation:
Intangible assets:				111.0	111.0
Measurement Period Adjustments
Weighted average amortization period (years)			12 years
Bisnode | Reacquired right
Purchase Price Allocation:
Intangible assets:				270.0	270.0
Measurement Period Adjustments
Weighted average amortization period (years)			15 years
Eyeota
Purchase Price Allocation:
Cash		$ 7.1		7.1	7.1
Accounts receivable		9.3		9.3	9.3
Other current assets		0.5		0.5	0.5
Total current assets		16.9		16.9	16.9
Goodwill		138.3		138.4	138.4
Total assets acquired		190.2		190.3	190.3
Deferred tax liability		5.9		5.9	5.9
Other liabilities		12.0		12.0	12.0
Total liabilities assumed		17.9		17.9	17.9
Total purchase price		$ 172.3		$ 172.4	172.4
Measurement Period Adjustments
Cash					0.0
Accounts receivable					0.0
Other					0.0
Total current assets					0.0
Goodwill					0.1
Total assets acquired					0.1
Deferred tax liability					0.0
Other liabilities					0.0
Total liabilities assumed					0.0
Total purchase price					0.1
Weighted average amortization period (years)		2 years		10 years 1 month 6 days
Eyeota | Customer relationships
Purchase Price Allocation:
Intangible assets:		$ 20.0		$ 20.0	20.0
Measurement Period Adjustments
Intangible assets:					0.0
Weighted average amortization period (years)		14 years
Eyeota | Technology
Purchase Price Allocation:
Intangible assets:		$ 14.0		14.0	14.0
Measurement Period Adjustments
Intangible assets:					0.0
Weighted average amortization period (years)		5 years
Eyeota | Trademark
Purchase Price Allocation:
Intangible assets:		$ 1.0		1.0	1.0
Measurement Period Adjustments
Intangible assets:
NetWise
Purchase Price Allocation:
Cash				2.6	2.6	2.6
Accounts receivable				2.6	2.6	2.6
Other current assets				0.4	0.4	0.4
Total current assets				5.6	5.6	5.6
Goodwill				44.8	44.8	41.9
Total assets acquired				73.9	73.9	71.0
Total liabilities assumed				3.7	3.7	1.2
Total purchase price				70.2	70.2	69.8
Measurement Period Adjustments
Cash				0.0
Accounts receivable				0.0
Other				0.0
Total current assets				0.0
Goodwill				2.9
Total assets acquired				2.9
Total liabilities assumed				2.5
Total purchase price				$ 0.4
Weighted average amortization period (years)				13 years 2 months 12 days
NetWise | Customer relationships
Purchase Price Allocation:
Intangible assets:				$ 19.8	19.8	19.8
Measurement Period Adjustments
Intangible assets:				0.0
Weighted average amortization period (years)	15 years
NetWise | Technology
Purchase Price Allocation:
Intangible assets:				1.3	1.3	1.3
Measurement Period Adjustments
Intangible assets:				0.0
Weighted average amortization period (years)	5 years
NetWise | Trademark
Purchase Price Allocation:
Intangible assets:				0.2	0.2	0.2
Measurement Period Adjustments
Intangible assets:				0.0
Weighted average amortization period (years)	2 years
NetWise | Database
Purchase Price Allocation:
Intangible assets:				2.2	$ 2.2	$ 2.2
Measurement Period Adjustments
Intangible assets:				$ 0.0
Weighted average amortization period (years)	3 years