Fair Value - Partnership's Financial Assets at Fair Value (Detail) - USD ($) $ in Millions	Jun. 28, 2019	Dec. 31, 2018
Investment securities:
Total investment securities	$ 293	$ 250
Inventory securities:
Total inventory securities	59	43
Equities [Member]
Investment securities:
Total investment securities	1	2
Inventory securities:
Total inventory securities	19	16
Corporate Bonds and Notes [Member]
Investment securities:
Total investment securities	0	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	1,597	998
Mutual Funds [Member]
Investment securities:
Total investment securities	289	244
Inventory securities:
Total inventory securities	3	6
State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	30	15
Certificates of Deposit [Member]
Cash equivalents:
Cash and cash equivalents	299	298
Inventory securities:
Total inventory securities	4	3
Level I [Member]
Investment securities:
Total investment securities	293	249
Inventory securities:
Total inventory securities	22	22
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities	1	2
Inventory securities:
Total inventory securities	19	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	1,597	998
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	289	244
Inventory securities:
Total inventory securities	3	6
Level II [Member]
Investment securities:
Total investment securities	0	1
Inventory securities:
Total inventory securities	37	21
Level II [Member] | Corporate Bonds and Notes [Member]
Investment securities:
Total investment securities	0	1
Inventory securities:
Total inventory securities	3	3
Level II [Member] | State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	30	15
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Cash and cash equivalents	299	298
Inventory securities:
Total inventory securities	$ 4	$ 3