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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 | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | $ (15.7) | $ 15.0 | $ (11.5)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 5.7 | (5.2) | (8.2)
Interest Rate Contracts [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (9.3) | (0.9) | 12.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.1 | 0.4 | 0.1
Foreign Exchange Contracts [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (6.4) | 15.9 | (23.9)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 4.6 | (5.6) | (8.3)
Commission Revenue [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (3.1) | 10.4 | (24.0)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 2.3 | (8.7) | (9.1)
Commission Revenue [Member] | Foreign Exchange Contracts [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (3.1) | 10.4 | (24.0)
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 2.3 | (8.7) | (9.1)
Compensation Expense [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (1.9) | 3.2 | 0.1
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.3 | 1.8 | 0.5
Compensation Expense [Member] | Foreign Exchange Contracts [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (1.9) | 3.2 | 0.1
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.3 | 1.8 | 0.5
Operating Expense [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (1.4) | 2.3 |
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.0 | 1.3 | 0.3
Operating Expense [Member] | Foreign Exchange Contracts [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (1.4) | 2.3 |
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.0 | 1.3 | 0.3
Interest Expense [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (9.3) | (0.9) | 12.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | 1.1 | 0.4 | 0.1
Interest Expense [Member] | Interest Rate Contracts [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative gains (losses) recognized in accumulated other comprehensive loss | (9.3) | (0.9) | 12.4
Derivative gains (losses) reclassified from accumulated other comprehensive loss into income (effective portion) | $ 1.1 | $ 0.4 | $ 0.1

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