Fair Value - Partnership's Financial Assets at Fair Value (Detail) - USD ($) $ in Millions	Jun. 25, 2021	Dec. 31, 2020
Cash equivalents:
Total cash equivalents	$ 149	$ 161
Investments segregated under federal regulations:
Total investments segregated under federal regulations		12,151
Investment securities:
Total investment securities	767	1,302
Inventory securities:
Total inventory securities	30	32
Equities [Member]
Investment securities:
Total investment securities	4	3
Inventory securities:
Total inventory securities	8	19
Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities	1	2
Government and Agency Obligations [Member]
Investment securities:
Total investment securities	315	971
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	12,098	12,051
Mutual Funds [Member]
Investment securities:
Total investment securities	348	327
Inventory securities:
Total inventory securities	5	1
State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	15	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	100	1
Inventory securities:
Total inventory securities	1
Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	29	41
Level I [Member]
Cash equivalents:
Total cash equivalents	29	41
Investments segregated under federal regulations:
Total investments segregated under federal regulations		12,051
Investment securities:
Total investment securities	667	1,301
Inventory securities:
Total inventory securities	13	20
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities	4	3
Inventory securities:
Total inventory securities	8	19
Level I [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities	315	971
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	12,098	12,051
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	348	327
Inventory securities:
Total inventory securities	5	1
Level I [Member] | Money Market Fund [Member]
Cash equivalents:
Total cash equivalents	29	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	100	1
Inventory securities:
Total inventory securities	17	12
Level II [Member] | Corporate Bonds and Notes [Member]
Inventory securities:
Total inventory securities	1	2
Level II [Member] | State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	15	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	100	$ 1
Inventory securities:
Total inventory securities	$ 1