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Derivatives and Hedging Activity - Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions | 9 Months Ended
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Sep. 30, 2017 | Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | $ 10.2 | $ (19.4)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | (5.7) | (5.2)
Interest Rate Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (1.6) | (3.3)
Foreign Exchange Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 11.8 | (16.1)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | (5.7) | (5.2)
Commission Revenue [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 7.9 | (17.3)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | (7.6) | (5.7)
Commission Revenue [Member] | Foreign Exchange Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 7.9 | (17.3)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | (7.6) | (5.7)
Compensation Expense [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 2.3 | 0.7
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.1 | 0.3
Compensation Expense [Member] | Foreign Exchange Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 2.3 | 0.7
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.1 | 0.3
Operating Expense [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 1.6 | 0.5
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 0.8 | 0.2
Operating Expense [Member] | Foreign Exchange Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | 1.6 | 0.5
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 0.8 | 0.2
Interest Expense [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (1.6) | (3.3)
Interest Expense [Member] | Interest Rate Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | $ (1.6) | $ (3.3)

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- Definition The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4D -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959 + Details
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- Definition The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period. + References Reference 1: 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 + Details
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