Fair Value - Partnership's Financial Assets and Liabilities at Fair Value (Detail) - USD ($) $ in Millions		Dec. 31, 2024	Dec. 31, 2023
Cash equivalents:
Total cash equivalents		$ 262	$ 255
Investments segregated under federal regulations:
Total investments segregated under federal regulations		11,034	11,393
Investment securities:
Total investment securities		679	1,069
Inventory securities:
Total inventory securities		63	88
Other assets:
Client fractional share ownership assets		936	824
Accounts payable, accrued expenses and other:
Client fractional share redemption obligations		936	824
Equities [Member]
Investment securities:
Total investment securities		8	11
Inventory securities:
Total inventory securities		15	21
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		11	5
Government and Agency Obligations [Member]
Investment securities:
Total investment securities		197	600
Inventory securities:
Total inventory securities		4	4
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,134	9,893
Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	362	346
Inventory securities:
Total inventory securities		6	9	[1]
Municipal Obligations [Member]
Investment securities:
Total investment securities		12	12
Inventory securities:
Total inventory securities		26	29
Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		170	179
Investments segregated under federal regulations:
Total investments segregated under federal regulations		900	1,500
Investment securities:
Total investment securities		100	100
Inventory securities:
Total inventory securities		1	20
Money Market Funds
Cash equivalents:
Total cash equivalents		92	76
Level I [Member]
Cash equivalents:
Total cash equivalents		92	76
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,134	9,893
Investment securities:
Total investment securities		567	957
Inventory securities:
Total inventory securities		25	34
Other assets:
Client fractional share ownership assets		936	824
Accounts payable, accrued expenses and other:
Client fractional share redemption obligations		936	824
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities		8	11
Inventory securities:
Total inventory securities		15	21
Level I [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities		197	600
Inventory securities:
Total inventory securities		4	4
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,134	9,893
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	362	346
Inventory securities:
Total inventory securities		6	9	[1]
Level I [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		0	0
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Money Market Funds
Cash equivalents:
Total cash equivalents		92	76
Level II [Member]
Cash equivalents:
Total cash equivalents		170	179
Investments segregated under federal regulations:
Total investments segregated under federal regulations		900	1,500
Investment securities:
Total investment securities		112	112
Inventory securities:
Total inventory securities		38	54
Other assets:
Client fractional share ownership assets		0	0
Accounts payable, accrued expenses and other:
Client fractional share redemption obligations		0	0
Level II [Member] | Equities [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level II [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		11	5
Level II [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level II [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Level II [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	0	0
Inventory securities:
Total inventory securities		0	0	[1]
Level II [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		12	12
Inventory securities:
Total inventory securities		26	29
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		170	179
Investments segregated under federal regulations:
Total investments segregated under federal regulations		900	1,500
Investment securities:
Total investment securities		100	100
Inventory securities:
Total inventory securities		1	20
Level II [Member] | Money Market Funds
Cash equivalents:
Total cash equivalents		0	0
Level III [Member]
Cash equivalents:
Total cash equivalents		0	0
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Other assets:
Client fractional share ownership assets		0	0
Accounts payable, accrued expenses and other:
Client fractional share redemption obligations		0	0
Level III [Member] | Equities [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Level III [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	0	0
Inventory securities:
Total inventory securities		0	0	[1]
Level III [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		0	0
Investments segregated under federal regulations:
Total investments segregated under federal regulations		0	0
Investment securities:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Money Market Funds
Cash equivalents:
Total cash equivalents		$ 0	$ 0

[1] The mutual funds balance consists primarily of securities held to economically hedge future liabilities for the non-qualified deferred compensation plan. The balance also includes a security held for regulatory purposes at the Trust Co.