Purchase Price Allocation (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Jul. 17, 2014	Jun. 26, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill	$ 976.3	$ 1,021.1			$ 665.2
Fair value of non-controlling interest assumed		$ (218.8)
Web Equity Solutions [Member]
Business Acquisition [Line Items]
Current assets			$ 3.0
Property and equipment, net			2.3
Total intangible assets			54.8
Goodwill			77.6
Liabilities assumed			(7.2)
Net assets acquired			130.5
Web Equity Solutions [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Total intangible assets			0.5
Web Equity Solutions [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Total intangible assets			42.8
Web Equity Solutions [Member] | Software [Member]
Business Acquisition [Line Items]
Total intangible assets			$ 11.5
ICRA [Member]
Business Acquisition [Line Items]
Current assets				$ 25.4
Property and equipment, net				15.1
Total intangible assets				98.9
Goodwill				296.7
Other assets				56.3
Liabilities assumed				(62.7)
Fair value of non-controlling interest assumed				(218.8)
Net assets acquired				210.9
ICRA [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Total intangible assets				46.8
ICRA [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Total intangible assets				33.8
ICRA [Member] | Other Intangibles [Member]
Business Acquisition [Line Items]
Total intangible assets				$ 18.3