Derivative Instruments and Hedging Activities - Net Investment Hedge Gains Recognized on Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in OCI	$ (146.0)	$ 18.8
Euro Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in OCI	$ (146.0)	9.4
Foreign Exchange Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in OCI		$ 9.4

Current period adjustment in other comprehensive income reflecting gains or losses on foreign currency transactions that are designated as, and are effective as, hedges of a net investment in a foreign entity, net of tax effect.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64808268&loc=d3e32211-110900

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration