Fair Value - Partnership's Financial Assets at Fair Value (Detail) - USD ($) $ in Millions	Mar. 29, 2019	Dec. 31, 2018
Investment securities:
Total investment securities	$ 270	$ 250
Inventory securities:
Total inventory securities	57	43
Equities [Member]
Investment securities:
Total investment securities	2	2
Inventory securities:
Total inventory securities	22	16
Corporate Bonds and Notes [Member]
Investment securities:
Total investment securities	1	1
Inventory securities:
Total inventory securities	3	3
Government and Agency Obligations [Member]
Investment securities:
Total investment securities	3	3
U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	1,493	998
Mutual Funds [Member]
Investment securities:
Total investment securities	264	244
Inventory securities:
Total inventory securities	2	6
State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	27	15
Certificates of Deposit [Member]
Cash equivalents:
Cash and cash equivalents	298	298
Inventory securities:
Total inventory securities	3	3
Level I [Member]
Investment securities:
Total investment securities	269	249
Inventory securities:
Total inventory securities	24	22
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities	2	2
Inventory securities:
Total inventory securities	22	16
Level I [Member] | Government and Agency Obligations [Member]
Investment securities:
Total investment securities	3	3
Level I [Member] | U.S. Treasuries [Member]
Investments segregated under federal regulations:
Total investments segregated under federal regulations	1,493	998
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	264	244
Inventory securities:
Total inventory securities	2	6
Level II [Member]
Investment securities:
Total investment securities	1	1
Inventory securities:
Total inventory securities	33	21
Level II [Member] | Corporate Bonds and Notes [Member]
Investment securities:
Total investment securities	1	1
Inventory securities:
Total inventory securities	3	3
Level II [Member] | State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	27	15
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Cash and cash equivalents	298	298
Inventory securities:
Total inventory securities	$ 3	$ 3