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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, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss | [1] | $ 10.4 | $ (34.0) | $ (115.0) | $ (80.6)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings |  | (1.4) | (1.1) | (3.9) | (3.0)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing |  | 0.7 | 0.3 | 1.4 | 1.1
Interest expense [Member] | Interest Rate Contracts [Member] |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss | [1] | 3.4 | (28.0) | (104.7) | (74.7)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings |  | (0.3) | (0.3) | (0.9) | (0.9)
Commission revenue [Member] | Foreign Exchange Contracts [Member] |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss | [1] | 7.0 | (6.0) | (10.3) | (5.9)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Loss into Earnings |  | (0.4) | (0.2) | (0.9) | (0.4)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing |  | (0.1) | (0.2) | (0.4) | (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) | (0.4) | (1.2) | (1.0)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing |  | 0.4 | 0.3 | 1.0 | 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 |  | (0.3) | (0.2) | (0.9) | (0.7)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing |  | $ 0.4 | $ 0.2 | $ 0.8 | $ 0.7
[1] | For the three and nine-month periods ended September 30, 2020 and 2019, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss was a loss of $0.4 million and $0.8 million, respectively.

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