Fair Value - Partnership's Financial Assets at Fair Value (Detail) - USD ($) $ in Millions	Sep. 27, 2019	Dec. 31, 2018
Investment securities:
Total investment securities	$ 305	$ 250
Inventory securities:
Total inventory securities	91	43
Equities [Member]
Investment securities:
Total investment securities	2	2
Inventory securities:
Total inventory securities	33	16
Corporate Bonds and Notes [Member]
Investment securities:
Total investment securities		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	2,497	998
Mutual Funds [Member]
Investment securities:
Total investment securities	300	244
Inventory securities:
Total inventory securities	33	6
State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	18	15
Certificates of Deposit [Member]
Cash equivalents:
Cash and cash equivalents	325	298
Inventory securities:
Total inventory securities	4	3
Level I [Member]
Investment securities:
Total investment securities	305	249
Inventory securities:
Total inventory securities	66	22
Level I [Member] | Equities [Member]
Investment securities:
Total investment securities	2	2
Inventory securities:
Total inventory securities	33	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	2,497	998
Level I [Member] | Mutual Funds [Member]
Investment securities:
Total investment securities	300	244
Inventory securities:
Total inventory securities	33	6
Level II [Member]
Investment securities:
Total investment securities	0	1
Inventory securities:
Total inventory securities	25	21
Level II [Member] | Corporate Bonds and Notes [Member]
Investment securities:
Total investment securities		1
Inventory securities:
Total inventory securities	3	3
Level II [Member] | State and Municipal Obligations [Member]
Inventory securities:
Total inventory securities	18	15
Level II [Member] | Certificates of Deposit [Member]
Cash equivalents:
Cash and cash equivalents	325	298
Inventory securities:
Total inventory securities	$ 4	$ 3