Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Summary Of Significant Accounting Policies [Line Items]
Receivables from contracts with customers	$ 301		$ 301		$ 284
Unbilled revenues	91		91		$ 63
Franchise fees and gross receipts taxes	$ 31	$ 35	$ 57	$ 63

Amount due from customers for fees and charges arising from transactions related to the entity's brokerage activities and operations.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 940
-SubTopic 310
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//940-310/tableOfContent

Name:	us-gaap_ReceivablesFromCustomers
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant