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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 | 3 Months Ended | 9 Months Ended
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Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss | $ (34.0) |  | $ 4.4 | $ (80.6) |  | $ 4.2
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings | (1.1) |  | 1.1 | (3.0) |  | 4.2
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing | 0.3 |  |  | 1.1 |  |
Commission revenue [Member] | Foreign Exchange Contracts [Member] |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss | (6.0) | [1] | (3.2) | (5.9) |  | (9.3)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings | (0.2) | [1] | 0.4 | (0.4) | [1] | 1.5
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing | (0.2) |  |  | (0.6) |  |
Compensation expense [Member] |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings | (0.4) |  | 0.2 | (1.0) |  | 1.1
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing | 0.3 |  |  | 1.0 |  |
Operating expense [Member] |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings | (0.2) |  | 0.2 | (0.7) |  | 0.8
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing | 0.2 |  |  | 0.7 |  |
Interest expense [Member] | Interest Rate Contracts [Member] |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss | (28.0) |  | 7.6 | (74.7) |  | 13.5
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings | $ (0.3) |  | $ 0.3 | $ (0.9) | [1] | $ 0.8
[1] | For the three-month and nine-month periods ended September 30, 2019, the amounts excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss were losses of zero and $0.3 million, respectively.

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