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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
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss	[1]	$ 44.9	$ (26.3)	$ 82.4	$ 71.0
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(0.9)	2.0	(2.4)	0.8
Amount of Gain Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		0.6	0.9	2.3	2.3
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		$ (0.3)	$ (0.2)	$ (0.9)	$ (0.8)
Derivative Instrument, Gain (Loss) Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]		Interest Expense	Interest Expense	Interest Expense	Interest Expense
Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		$ 0.1	$ 2.9	$ 0.9	$ (2.7)
Amount of Gain Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		$ (0.1)		$ (0.1)
Derivative Instrument, Gain (Loss) Reclassified from AOCI into Income, Effective Portion, Statement of Income or Comprehensive Income [Extensible Enumeration]		Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Interest expense [Member] | Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss	[1]	$ 56.2	$ 45.5	$ 65.0	$ 181.0
Commission revenue [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss	[1]	(11.3)	(71.8)	17.4	(110.0)
Compensation expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(0.4)	(0.4)	(1.4)	(0.6)
Amount of Gain Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		0.4	0.5	1.4	1.3
Operating expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(0.3)	(0.3)	(1.0)	(0.5)
Amount of Gain Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		$ 0.3	$ 0.4	$ 1.0	$ 1.0
[1] For the three and nine-month periods ended September 30, 2023, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss was a loss of $0.1 million and a gain of $0.7 million, respectively. For the three and nine-month periods ended September 30, 2022, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss was a gain of $0.8 million and $1.3 million, respectively.

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