Fair Value - Partnership's Financial Assets at Fair Value (Detail) - USD ($) $ in Millions	Mar. 26, 2021	Dec. 31, 2020
Cash equivalents:
Total cash equivalents	$ 132	$ 161
Investments segregated under federal regulations:
Total investments segregated under federal regulations	13,004	12,151
Investment securities:
Total investment securities	448	1,302
Inventory securities:
Total inventory securities	27	32
Equities [Member]
Investment securities:
Total investment securities	3	3
Inventory securities:
Total inventory securities	8	19
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities	4	2
Government and Agency Obligations [Member]
Investment securities:
Total investment securities	115	971
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	12,904	12,051
Mutual Funds [Member]
Investment securities:
Total investment securities	329	327
Inventory securities:
Total inventory securities	3	1
State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	9	10
Certificates of Deposit [Member]
Cash equivalents:
Total cash equivalents	120	120
Investments segregated under federal regulations:
Total investments segregated under federal regulations	100	100
Investment securities:
Total investment securities	1	1
Inventory securities:
Total inventory securities	3
Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	12	41
Level I [Member]
Cash equivalents:
Total cash equivalents	12	41
Investments segregated under federal regulations:
Total investments segregated under federal regulations	12,904	12,051
Investment securities:
Total investment securities	447	1,301
Inventory securities:
Total inventory securities	11	20
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities	3	3
Inventory securities:
Total inventory securities	8	19
Level I [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities	115	971
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	12,904	12,051
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	329	327
Inventory securities:
Total inventory securities	3	1
Level I [Member] | Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	12	41
Level II [Member]
Cash equivalents:
Total cash equivalents	120	120
Investments segregated under federal regulations:
Total investments segregated under federal regulations	100	100
Investment securities:
Total investment securities	1	1
Inventory securities:
Total inventory securities	16	12
Level II [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities	4	2
Level II [Member] | State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	9	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	100
Investment securities:
Total investment securities	1	$ 1
Inventory securities:
Total inventory securities	$ 3