Purchase Price Allocation (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Aug. 10, 2017	Dec. 31, 2016	Mar. 01, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Indemnification asset	$ 17.0		$ 16.5
Goodwill	$ 3,753.2		$ 1,023.6		$ 976.3
Gilliland Gold Young (GGY) [Member]
Business Acquisition [Line Items]
Current assets				$ 11.7
Property and equipment, net				2.0
Indemnification asset				1.5
Total intangible assets				34.1
Goodwill				59.4
Liabilities assumed				(22.2)
Net assets acquired				86.5
Gilliland Gold Young (GGY) [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Total intangible assets				3.7
Gilliland Gold Young (GGY) [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Total intangible assets				13.8
Gilliland Gold Young (GGY) [Member] | Software [Member]
Business Acquisition [Line Items]
Total intangible assets				$ 16.6
Bureau van Dijk (BvD) [Member]
Business Acquisition [Line Items]
Current assets		$ 158.4
Property and equipment, net		4.2
Total intangible assets		1,352.4
Goodwill		2,619.0
Other assets		5.9
Deferred revenue		(101.1)
Accounts payable and accrued liabilities		(48.6)
Deferred tax liabilities, net		(329.8)
Other liabilities		(118.4)
Liabilities assumed		(597.9)
Net assets acquired		3,542.0
Bureau van Dijk (BvD) [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Total intangible assets		82.3
Bureau van Dijk (BvD) [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Total intangible assets		998.7
Bureau van Dijk (BvD) [Member] | Database [Member]
Business Acquisition [Line Items]
Total intangible assets		12.9
Bureau van Dijk (BvD) [Member] | Product Technology [Member]
Business Acquisition [Line Items]
Total intangible assets		$ 258.5