Employee Benefit Plans - Schedule of Rollforward of Change in Fair Value of Level 3 Assets (Detail) - Defined Benefit Pension Plans - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Schedule Of Reconciliation Of Changes In Fair Value Of Assets And Liabilities [Line Items]
Fair value at beginning of the year	$ 427.4
Fair value at end of year	491.7	$ 427.4
Significant Unobservable Inputs (Level 3)
Schedule Of Reconciliation Of Changes In Fair Value Of Assets And Liabilities [Line Items]
Fair value at beginning of the year	230.5	236.2
Gain on assets held at end of year	11.0	4.1
Gain on assets sold during the year	0.2
Assets purchased	13.4	13.1
Assets sold	(13.8)	(13.4)
Currency exchange rate fluctuations	32.3	(9.5)
Fair value at end of year	$ 273.6	$ 230.5

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Schedule of reconciliation of changes in fair value of assets and liabilities.

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