Fair Value - Partnership's Financial Assets and Liabilities at Fair Value (Detail) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Cash equivalents:
Total cash equivalents		$ 255	$ 193
Investments segregated under federal regulations:
Total investments segregated under federal regulations		11,393	11,327
Investment securities:
Total investment securities		1,069	1,329
Inventory securities:
Total inventory securities		88	76
Other assets:
Client fractional share ownership assets		824	680
Accounts payable, accrued expenses and other:
Client fractional share redemption obligations		824	680
Equities [Member]
Investment securities:
Total investment securities		11	8
Inventory securities:
Total inventory securities		21	20
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		5	21
Government and Agency Obligations [Member]
Investment securities:
Total investment securities		600	1,000
Inventory securities:
Total inventory securities		4	3
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		9,893	10,327
Mutual Funds [Member]
Investment securities:
Total investment securities		346	310	[1]
Inventory securities:
Total inventory securities		9	4
Municipal Obligations [Member]
Investment securities:
Total investment securities		12	11
Inventory securities:
Total inventory securities		29	28
Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		179	144
Investments segregated under federal regulations:
Total investments segregated under federal regulations		1,500	1,000
Investment securities:
Total investment securities		100
Inventory securities:
Total inventory securities		20
Money Market Funds
Cash equivalents:
Total cash equivalents		76	49
Level I [Member]
Cash equivalents:
Total cash equivalents		76	49
Investments segregated under federal regulations:
Total investments segregated under federal regulations		9,893	10,327
Investment securities:
Total investment securities		957	1,318
Inventory securities:
Total inventory securities		34	27
Other assets:
Client fractional share ownership assets		824	680
Accounts payable, accrued expenses and other:
Client fractional share redemption obligations		824	680
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities		11	8
Inventory securities:
Total inventory securities		21	20
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		600	1,000
Inventory securities:
Total inventory securities		4	3
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		9,893	10,327
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	[1]	346	310
Inventory securities:
Total inventory securities		9	4
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
Inventory securities:
Total inventory securities		0
Level I [Member] | Money Market Funds
Cash equivalents:
Total cash equivalents		76	49
Level II [Member]
Cash equivalents:
Total cash equivalents		179	144
Investments segregated under federal regulations:
Total investments segregated under federal regulations		1,500	1,000
Investment securities:
Total investment securities		112	11
Inventory securities:
Total inventory securities		54	49
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		5	21
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		0	0	[1]
Inventory securities:
Total inventory securities		0	0
Level II [Member] | Municipal Obligations [Member]
Investment securities:
Total investment securities		12	11
Inventory securities:
Total inventory securities		29	28
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents		179	144
Investments segregated under federal regulations:
Total investments segregated under federal regulations		1,500	1,000
Investment securities:
Total investment securities		100
Inventory securities:
Total inventory securities		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		0	0	[1]
Inventory securities:
Total inventory securities		0	0
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
Inventory securities:
Total inventory securities		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.