Acquisitions - Narrative (Details) customer in Thousands, $ in Millions				12 Months Ended
	Apr. 01, 2019 USD ($) country	Sep. 06, 2018 USD ($) customer	Jul. 27, 2018 USD ($)	Dec. 31, 2019 USD ($) acquisition business country	Dec. 31, 2018 USD ($) acquisition business	Dec. 31, 2017 USD ($) business	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 8,399.3	$ 6,133.1	$ 4,560.3
Goodwill, purchase accounting adjustments				74.7
Accruent
Business Acquisition [Line Items]
Total purchase price		$ 2,000.0
Revenue of prior fiscal year						200.0
Goodwill		$ 1,200.0
Number of customers served | customer		10
Gordian
Business Acquisition [Line Items]
Total purchase price			$ 778.0
Revenue of prior fiscal year						110.0
Goodwill			$ 435.0
Accruent and Gordian
Business Acquisition [Line Items]
Revenue from acquiree since acquisition date					115.0
Operating income (loss) since acquisition					(51.0)
Other
Business Acquisition [Line Items]
Total purchase price				1,207.4	44.0
Revenue of prior fiscal year					$ 191.0	35.0
Prepaid acquisition asset related to remaining Non-Principal Countries				0.0
Revenue from acquiree since acquisition date				76.0
Operating income (loss) since acquisition				(53.0)
Pretax transaction and integration related costs related costs				$ 17.0
Number of other businesses acquired | business				4	2
Goodwill				$ 772.6	$ 31.0
Tax deductible goodwill				21.0
Additional equity investment				4.0
2018 Acquisitions
Business Acquisition [Line Items]
Total purchase price					2,815.1
Prepaid acquisition asset related to remaining Non-Principal Countries					0.0
Pretax transaction and integration related costs related costs					$ 25.0
Number of other businesses acquired | acquisition					4
Goodwill					$ 1,601.2
2017 Acquisitions
Business Acquisition [Line Items]
Total purchase price						1,556.6
Revenue of prior fiscal year							$ 389.0
Prepaid acquisition asset related to remaining Non-Principal Countries						0.0
Pretax transaction and integration related costs related costs						$ 19.0
Number of other businesses acquired | business						3
Goodwill						$ 1,035.2
ASP
Business Acquisition [Line Items]
Total purchase price	$ 2,700.0			$ 2,736.5
Revenue of prior fiscal year					800.0
Number of principal countries | country	20
Number of non-principal countries | country	39
Number of principal countries closed | country				20
Number of non-principal countries closed | country				4
Percent of preliminary valuation in acquired countries				98.00%
Percent of preliminary valuation in non-principal countries				2.00%
Prepaid acquisition asset related to remaining Non-Principal Countries				$ 50.1
Revenue from acquiree since acquisition date				525.0
Operating income (loss) since acquisition				(111.0)
Post-close transaction and integration costs				230.0
Pretax transaction and integration related costs related costs				86.0	$ 42.0
Goodwill				1,420.3
Acquisitions, 2019
Business Acquisition [Line Items]
Total purchase price				3,943.9
Prepaid acquisition asset related to remaining Non-Principal Countries				50.1
Pretax transaction and integration related costs related costs				$ 102.0
Number of other businesses acquired | acquisition				5
Goodwill				$ 2,192.9