Acquisitions - Purchase Price Allocation (Details) - USD ($) $ in Millions			6 Months Ended	8 Months Ended
	Nov. 15, 2021	Nov. 05, 2021	Jun. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Purchase Price Allocation:
Goodwill			$ 3,437.1	$ 3,437.1	$ 3,475.4	$ 3,493.3	$ 3,331.1	$ 3,318.2	$ 2,857.9
Eyeota
Purchase Price Allocation:
Cash		$ 7.1	7.1	7.1
Accounts receivable		9.3	9.3	9.3
Other		0.5	0.5	0.5
Total current assets		16.9	16.9	16.9
Goodwill		138.3	138.2	138.2
Total assets acquired		190.2	190.1	190.1
Deferred tax liability		5.9	5.9	5.9
Other liabilities		12.0	11.8	11.8
Total liabilities assumed		17.9	17.7	17.7
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				(0.2)
Total liabilities assumed				(0.2)
Total purchase price				0.1
Weighted average amortization period (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:
Weighted average amortization period (years)		2 years
NetWise
Purchase Price Allocation:
Cash			2.6	2.6		2.6
Accounts receivable			2.6	2.6		2.6
Other			0.4	0.4		0.4
Total current assets			5.6	5.6		5.6
Goodwill			45.5	45.5		41.9
Total assets acquired			74.6	74.6		71.0
Total liabilities assumed			4.4	4.4		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			3.6
Total assets acquired			3.6
Total liabilities assumed			3.2
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