Fair Value - Partnership's Financial Assets at Fair Value (Detail) - USD ($) $ in Millions	Sep. 24, 2021	Dec. 31, 2020
Cash equivalents:
Total cash equivalents	$ 161	$ 161
Investments segregated under federal regulations:
Total investments segregated under federal regulations		12,151
Investment securities:
Total investment securities	734	1,302
Inventory securities:
Total inventory securities	24	32
Equities [Member]
Investment securities:
Total investment securities	3	3
Inventory securities:
Total inventory securities	7	19
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities	2	2
Government and Agency Obligations [Member]
Investment securities:
Total investment securities	225	971
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	11,843	12,051
Mutual Funds [Member]
Investment securities:
Total investment securities	356	327
Inventory securities:
Total inventory securities	2	1
State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	12	10
Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents	120	120
Investments segregated under federal regulations:
Total investments segregated under federal regulations		100
Investment securities:
Total investment securities	150	1
Inventory securities:
Total inventory securities	1
Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	41	41
Level I [Member]
Cash equivalents:
Total cash equivalents	41	41
Investments segregated under federal regulations:
Total investments segregated under federal regulations		12,051
Investment securities:
Total investment securities	584	1,301
Inventory securities:
Total inventory securities	9	20
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities	3	3
Inventory securities:
Total inventory securities	7	19
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	225	971
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	11,843	12,051
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	356	327
Inventory securities:
Total inventory securities	2	1
Level I [Member] | State and Municipal Obligations [Member]
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
Investment securities:
Total investment securities	0	0
Inventory securities:
Total inventory securities	0
Level I [Member] | Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	41	41
Level II [Member]
Cash equivalents:
Total cash equivalents	120	120
Investments segregated under federal regulations:
Total investments segregated under federal regulations		100
Investment securities:
Total investment securities	150	1
Inventory securities:
Total inventory securities	15	12
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	2	2
Level II [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment 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
Inventory securities:
Total inventory securities	0	0
Level II [Member] | State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	12	10
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents	120	120
Investments segregated under federal regulations:
Total investments segregated under federal regulations		100
Investment securities:
Total investment securities	150	1
Inventory securities:
Total inventory securities	1
Level II [Member] | Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	$ 0	$ 0