Fair Values of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[1]	$ 110,272	$ 147,871
Certificates of deposit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		99	2,231
U.S. agency mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		64,861	77,688
U.S. Treasury securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		21,788	40,002
Asset-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		9,624	13,023
Corporate debt securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		12,154	12,555
Foreign government agency securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		985	969
U.S. state and municipal securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		555	638
Non-agency commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		188	450
Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		18	315
Fair Value, Recurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		12,744	14,055
Investments segregated and on deposit for regulatory purposes:		12,318	24,645
Fair Value		110,272	147,871
Other assets:		1,629	1,432
Total assets		136,963	188,003
Total accrued expenses and other liabilities		1,433	1,261
Total liabilities		1,433	1,261
Fair Value, Recurring | Money market funds
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		12,744	14,007
Fair Value, Recurring | Commercial paper
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:			48
Fair Value, Recurring | U.S. Government securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		11,368	23,645
Other assets:		2	1
Fair Value, Recurring | Certificates of deposit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		950	1,000
Fair Value		99	2,231
Fair Value, Recurring | U.S. agency mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		64,861	77,688
Fair Value, Recurring | U.S. Treasury securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		21,788	40,002
Fair Value, Recurring | Asset-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		9,624	13,023
Fair Value, Recurring | Corporate debt securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		12,154	12,555
Fair Value, Recurring | Foreign government agency securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		985	969
Fair Value, Recurring | U.S. state and municipal securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		555	638
Fair Value, Recurring | Non-agency commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		188	450
Fair Value, Recurring | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		18	315
Fair Value, Recurring | Total other securities owned at fair value
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		1,626	1,432
Fair Value, Recurring | Equity, corporate debt, and other securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		936	810
Fair Value, Recurring | Mutual funds and ETFs
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		677	596
Fair Value, Recurring | State and municipal debt obligations
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		11	25
Fair Value, Recurring | Interest rate swaps
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		3
Fair Value, Recurring | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Total accrued expenses and other liabilities		1,433	1,261
Fair Value, Recurring | Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		12,744	14,007
Investments segregated and on deposit for regulatory purposes:		0	0
Fair Value		0	0
Other assets:		1,554	1,351
Total assets		14,298	15,358
Total accrued expenses and other liabilities		1,396	1,218
Total liabilities		1,396	1,218
Fair Value, Recurring | Level 1 | Money market funds
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		12,744	14,007
Fair Value, Recurring | Level 1 | Commercial paper
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:			0
Fair Value, Recurring | Level 1 | U.S. Government securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		0	0
Other assets:		0	0
Fair Value, Recurring | Level 1 | Certificates of deposit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		0	0
Fair Value		0	0
Fair Value, Recurring | Level 1 | U.S. agency mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | U.S. Treasury securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | Asset-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | Corporate debt securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | Foreign government agency securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | U.S. state and municipal securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | Non-agency commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 1 | Total other securities owned at fair value
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		1,554	1,351
Fair Value, Recurring | Level 1 | Equity, corporate debt, and other securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		877	755
Fair Value, Recurring | Level 1 | Mutual funds and ETFs
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		677	596
Fair Value, Recurring | Level 1 | State and municipal debt obligations
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0	0
Fair Value, Recurring | Level 1 | Interest rate swaps
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0
Fair Value, Recurring | Level 1 | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Total accrued expenses and other liabilities		1,396	1,218
Fair Value, Recurring | Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		0	48
Investments segregated and on deposit for regulatory purposes:		12,318	24,645
Fair Value		110,272	147,871
Other assets:		75	81
Total assets		122,665	172,645
Total accrued expenses and other liabilities		37	43
Total liabilities		37	43
Fair Value, Recurring | Level 2 | Money market funds
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		0	0
Fair Value, Recurring | Level 2 | Commercial paper
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:			48
Fair Value, Recurring | Level 2 | U.S. Government securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		11,368	23,645
Other assets:		2	1
Fair Value, Recurring | Level 2 | Certificates of deposit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		950	1,000
Fair Value		99	2,231
Fair Value, Recurring | Level 2 | U.S. agency mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		64,861	77,688
Fair Value, Recurring | Level 2 | U.S. Treasury securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		21,788	40,002
Fair Value, Recurring | Level 2 | Asset-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		9,624	13,023
Fair Value, Recurring | Level 2 | Corporate debt securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		12,154	12,555
Fair Value, Recurring | Level 2 | Foreign government agency securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		985	969
Fair Value, Recurring | Level 2 | U.S. state and municipal securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		555	638
Fair Value, Recurring | Level 2 | Non-agency commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		188	450
Fair Value, Recurring | Level 2 | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		18	315
Fair Value, Recurring | Level 2 | Total other securities owned at fair value
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		72	81
Fair Value, Recurring | Level 2 | Equity, corporate debt, and other securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		59	55
Fair Value, Recurring | Level 2 | Mutual funds and ETFs
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0	0
Fair Value, Recurring | Level 2 | State and municipal debt obligations
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		11	25
Fair Value, Recurring | Level 2 | Interest rate swaps
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		3
Fair Value, Recurring | Level 2 | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Total accrued expenses and other liabilities		37	43
Fair Value, Recurring | Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		0	0
Investments segregated and on deposit for regulatory purposes:		0	0
Fair Value		0	0
Other assets:		0	0
Total assets		0	0
Total accrued expenses and other liabilities		0	0
Total liabilities		0	0
Fair Value, Recurring | Level 3 | Money market funds
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:		0	0
Fair Value, Recurring | Level 3 | Commercial paper
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:			0
Fair Value, Recurring | Level 3 | U.S. Government securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		0	0
Other assets:		0	0
Fair Value, Recurring | Level 3 | Certificates of deposit
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes:		0	0
Fair Value		0	0
Fair Value, Recurring | Level 3 | U.S. agency mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | U.S. Treasury securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | Asset-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | Corporate debt securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | Foreign government agency securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | U.S. state and municipal securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | Non-agency commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0	0
Fair Value, Recurring | Level 3 | Total other securities owned at fair value
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0	0
Fair Value, Recurring | Level 3 | Equity, corporate debt, and other securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0	0
Fair Value, Recurring | Level 3 | Mutual funds and ETFs
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0	0
Fair Value, Recurring | Level 3 | State and municipal debt obligations
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0	0
Fair Value, Recurring | Level 3 | Interest rate swaps
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets:		0
Fair Value, Recurring | Level 3 | Other
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Total accrued expenses and other liabilities		$ 0	$ 0

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.