Fair Value - Partnership's Financial Assets and Liabilities at Fair Value (Detail) - USD ($) $ in Millions		Mar. 28, 2025	Dec. 31, 2024
Cash equivalents:
Total cash equivalents		$ 205	$ 262
Investments segregated under federal regulations:
Total investments segregated under federal regulations		10,570	11,034
Securities owned:
Total investment securities		625	679
Inventory securities:
Total inventory securities		138	63
Other Assets:
Client Fractional Shares Ownership Assets		924	936
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		924	936
Equities [Member]
Securities owned:
Total investment securities		7	8
Inventory securities:
Total inventory securities		37	15
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		9	11
Government and Agency Obligations [Member]
Securities owned:
Total investment securities		201	197
Inventory securities:
Total inventory securities		4	4
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations		9,670	10,134
Mutual Funds [Member]
Securities owned:
Total investment securities	[1]	331	362
Inventory securities:
Total inventory securities		56	6
Municipal Obligations [Member]
Securities owned:
Total investment securities		11	12
Inventory securities:
Total inventory securities		27	26
Certificates of deposit [Member]
Cash equivalents:
Total cash equivalents		171	170
Investments segregated under federal regulations:
Total investments segregated under federal regulations		900	900
Securities owned:
Total investment securities		75	100
Inventory securities:
Total inventory securities		5	1
Money Market Funds [Member]
Cash equivalents:
Total cash equivalents		34	92
Level I [Member]
Cash equivalents:
Total cash equivalents		34	92
Investments segregated under federal regulations:
Total investments segregated under federal regulations		9,670	10,134
Securities owned:
Total investment securities		539	567
Inventory securities:
Total inventory securities		97	25
Other Assets:
Client Fractional Shares Ownership Assets		924	936
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		924	936
Level I [Member] | Equities [Member]
Securities owned:
Total investment securities		7	8
Inventory securities:
Total inventory securities		37	15
Level I [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Government and Agency Obligations [Member]
Securities owned:
Total investment securities		201	197
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		9,670	10,134
Level I [Member] | Mutual Funds [Member]
Securities owned:
Total investment securities	[1]	331	362
Inventory securities:
Total inventory securities		56	6
Level I [Member] | Municipal Obligations [Member]
Securities owned:
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
Securities owned:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level I [Member] | Money Market Funds [Member]
Cash equivalents:
Total cash equivalents		34	92
Level II [Member]
Cash equivalents:
Total cash equivalents		171	170
Investments segregated under federal regulations:
Total investments segregated under federal regulations		900	900
Securities owned:
Total investment securities		86	112
Inventory securities:
Total inventory securities		41	38
Other Assets:
Client Fractional Shares Ownership Assets		0	0
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		0	0
Level II [Member] | Equities [Member]
Securities owned:
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		9	11
Level II [Member] | Government and Agency Obligations [Member]
Securities owned:
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]
Securities owned:
Total investment securities	[1]	0	0
Inventory securities:
Total inventory securities		0	0
Level II [Member] | Municipal Obligations [Member]
Securities owned:
Total investment securities		11	12
Inventory securities:
Total inventory securities		27	26
Level II [Member] | Certificates of deposit [Member]
Cash equivalents:
Total cash equivalents		171	170
Investments segregated under federal regulations:
Total investments segregated under federal regulations		900	900
Securities owned:
Total investment securities		75	100
Inventory securities:
Total inventory securities		5	1
Level II [Member] | Money Market Funds [Member]
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
Securities owned:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Other Assets:
Client Fractional Shares Ownership Assets		0	0
Accounts payable, accrued expenses and other:
Client Fractional Shares Redemption Obligations		0	0
Level III [Member] | Equities [Member]
Securities owned:
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]
Securities owned:
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]
Securities owned:
Total investment securities	[1]	0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Municipal Obligations [Member]
Securities owned:
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
Securities owned:
Total investment securities		0	0
Inventory securities:
Total inventory securities		0	0
Level III [Member] | Money Market Funds [Member]
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.