Related Party Transactions - Summary of Activity Related to Agreements with Related Party (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Processing fee incurred	$ 313.0	$ 279.6	$ 288.3
Earnings from equity investments	7.7	5.3	10.6
Distributions received from equity investments	11.4	13.0	17.4
LM4
Related Party Transaction [Line Items]
Processing fee incurred	$ 24.0	$ 20.5	$ 27.7
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Earnings from equity investments	$ 7.7	$ 5.3	$ 10.6
Distributions received from equity investments	$ 11.4	$ 13.0	$ 17.4

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