INVESTMENTS AND FAIR VALUE MEASUREMENT - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets
Deposits with clearing organizations	$ 1,440	$ 489
Fair Value, Recurring
Assets
Total financial assets	6,514	4,904
Liabilities
Total financial liabilities	3,618	2,530
Fair Value, Recurring \| U.S. Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	1,938	1,193
Deposits with clearing organizations	698
Fair Value, Recurring \| Foreign Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	53
Fair Value, Recurring \| Stablecoin
Assets
Other current assets	8	361
Fair Value, Recurring \| Equity securities - securities owned
Assets
Other current assets	23	15
Fair Value, Recurring \| Money market funds - escrow account
Assets
Other current assets	2	2
Fair Value, Recurring \| User-held fractional shares
Assets
Other current assets	3,618	2,530
Fair Value, Recurring \| Fractional shares repurchase obligations
Liabilities
Fractional shares repurchase obligations	3,618	2,530
Fair Value, Recurring \| Security Lending Program
Assets
Deposits with clearing organizations	697
Fair Value, Recurring \| Event Contracts
Assets
Deposits with clearing organizations	1
Fair Value, Recurring \| Time deposits
Assets
Cash equivalents		750
Fair Value, Recurring \| Money market funds
Assets
Cash equivalents	174	53
Fair Value, Recurring \| Level 1
Assets
Total financial assets	6,514	4,154
Liabilities
Total financial liabilities	3,618	2,530
Fair Value, Recurring \| Level 1 \| U.S. Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	1,938	1,193
Deposits with clearing organizations	698
Fair Value, Recurring \| Level 1 \| Foreign Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	53
Fair Value, Recurring \| Level 1 \| Stablecoin
Assets
Other current assets	8	361
Fair Value, Recurring \| Level 1 \| Equity securities - securities owned
Assets
Other current assets	23	15
Fair Value, Recurring \| Level 1 \| Money market funds - escrow account
Assets
Other current assets	2	2
Fair Value, Recurring \| Level 1 \| User-held fractional shares
Assets
Other current assets	3,618	2,530
Fair Value, Recurring \| Level 1 \| Fractional shares repurchase obligations
Liabilities
Fractional shares repurchase obligations	3,618	2,530
Fair Value, Recurring \| Level 1 \| Time deposits
Assets
Cash equivalents		0
Fair Value, Recurring \| Level 1 \| Money market funds
Assets
Cash equivalents	174	53
Fair Value, Recurring \| Level 2
Assets
Total financial assets	0	750
Liabilities
Total financial liabilities	0	0
Fair Value, Recurring \| Level 2 \| U.S. Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	0	0
Deposits with clearing organizations	0
Fair Value, Recurring \| Level 2 \| Foreign Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	0
Fair Value, Recurring \| Level 2 \| Stablecoin
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 2 \| Equity securities - securities owned
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 2 \| Money market funds - escrow account
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 2 \| User-held fractional shares
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 2 \| Fractional shares repurchase obligations
Liabilities
Fractional shares repurchase obligations	0	0
Fair Value, Recurring \| Level 2 \| Time deposits
Assets
Cash equivalents		750
Fair Value, Recurring \| Level 2 \| Money market funds
Assets
Cash equivalents	0	0
Fair Value, Recurring \| Level 3
Assets
Total financial assets	0	0
Liabilities
Total financial liabilities	0	0
Fair Value, Recurring \| Level 3 \| U.S. Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	0	0
Deposits with clearing organizations	0
Fair Value, Recurring \| Level 3 \| Foreign Treasury securities
Assets
Cash, cash equivalents, and securities segregated under federal and other regulations:	0
Fair Value, Recurring \| Level 3 \| Stablecoin
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 3 \| Equity securities - securities owned
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 3 \| Money market funds - escrow account
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 3 \| User-held fractional shares
Assets
Other current assets	0	0
Fair Value, Recurring \| Level 3 \| Fractional shares repurchase obligations
Liabilities
Fractional shares repurchase obligations	0	0
Fair Value, Recurring \| Level 3 \| Time deposits
Assets
Cash equivalents		0
Fair Value, Recurring \| Level 3 \| Money market funds
Assets
Cash equivalents	$ 0	$ 0

Cash And Securities Segregated Under Federal And Other Regulations, Fair Value

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Fair value portion of asset recognized for present right to economic benefit.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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The amount of securities on deposit with clearing organizations and other entities which provide services necessary to operations of the Company. This item would include, for instance, securities advanced as refundable collateral for securities borrowed.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of other assets.

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