DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) shares in Millions, $ in Millions			12 Months Ended
	Aug. 31, 2021 shares	Aug. 02, 2021 shares	Dec. 31, 2022 USD ($) period institution agreement segment counterparty	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Subsidiary, Sale of Stock [Line Items]
Number of operating segments | segment			1
Revenue contract term			30 days
Brokerage and transaction costs			$ 57
Advertising costs			$ 52	$ 101	$ 78
Defined contribution plan, employer matching contribution, percent of match			3.00%
Expense incurred related to defined contribution 401(k) plan			$ 14	10	3
Research and development expense			$ 381	438	$ 52
Number of service periods | period			2
Restricted cash, current			$ 1	1
Restricted cash			22	24
Securities borrowing and lending, interest revenue			(11)
Securities borrowing and lending, interest expenses incurred			$ 2
Number of financial institution counterparties | institution			2
Number of agreements with contractual term of 30 days | agreement			1
Number of fixed term agreements | agreement			2
Number of fixed term counterparties | counterparty			2
Cash sweep interest revenue			$ 68	0
Cash sweep interest expenses incurred			$ 46	0
Short-term settlement, period			30 days
Threshold period past due, writeoff			180 days
Realized and unrealized gains and losses			$ 7	$ 12
Referral program claim period			60 days
Agreement One
Subsidiary, Sale of Stock [Line Items]
Contractual term			30 days
Contractual obligation			$ 25
Agreement Two
Subsidiary, Sale of Stock [Line Items]
Contractual term			21 days
Contractual obligation			$ 35
Stock options
Subsidiary, Sale of Stock [Line Items]
Dividend yield			0.00%		0.00%
Time-Based RSUs
Subsidiary, Sale of Stock [Line Items]
Requisite service period			4 years
Market-Based RSUs
Subsidiary, Sale of Stock [Line Items]
Requisite service period			6 years
IPO | Common Class A
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares) | shares		55.0
Over-Allotment Option | Common Class A
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares) | shares	4.4