Related Party Transactions - Summary of Activity Related to Agreements with Related Party (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Related Party Transaction [Line Items]
Processing fee incurred	$ 73.1	$ 67.8	$ 135.6	$ 134.3
Earnings from equity investments	1.7	1.0	3.3	1.4
Distributions received from equity investments			4.4	6.1
LM4
Related Party Transaction [Line Items]
Processing fee incurred	$ 5.8	$ 4.7	$ 10.8	$ 9.2
Operating Cost and Expense, Related and Nonrelated Party Status [Extensible Enumeration]	us-gaap:RelatedPartyMember	us-gaap:RelatedPartyMember	us-gaap:RelatedPartyMember	us-gaap:RelatedPartyMember
Earnings from equity investments	$ 1.7	$ 1.0	$ 3.3	$ 1.4
Distributions received from equity investments	$ 1.8	$ 1.4	$ 4.4	$ 6.1

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