Revenue - Schedule of Partnership's Disaggregated Revenue (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 25, 2020	Sep. 27, 2019	Sep. 25, 2020	Sep. 27, 2019
Disaggregation Of Revenue [Line Items]
Net revenue	$ 2,487	$ 2,296	$ 7,230	$ 6,626
Net interest and dividends and other revenue	40	71	113	250
Net revenue	2,527	2,367	7,343	6,876
United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	2,429	2,240	7,055	6,463
Net interest and dividends and other revenue	40	66	98	234
Net revenue	2,469	2,306	7,153	6,697
Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	58	56	175	163
Net interest and dividends and other revenue	0	5	15	16
Net revenue	58	61	190	179
Asset-based Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,926	1,738	5,450	4,962
Asset-based Fee Revenue [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,431	1,240	3,989	3,514
Asset-based Fee Revenue [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	353	337	1,016	980
Asset-based Fee Revenue [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	142	161	445	468
Asset-based Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,881	1,697	5,323	4,846
Asset-based Fee Revenue [Member] | United States [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,409	1,221	3,928	3,463
Asset-based Fee Revenue [Member] | United States [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	330	315	950	915
Asset-based Fee Revenue [Member] | United States [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	142	161	445	468
Asset-based Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	45	41	127	116
Asset-based Fee Revenue [Member] | Canada [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	22	19	61	51
Asset-based Fee Revenue [Member] | Canada [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	23	22	66	65
Asset-based Fee Revenue [Member] | Canada [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	0	0	0	0
Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	163	167	494	504
Account and Activity Fee Revenue [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	106	109	319	323
Account and Activity Fee Revenue [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	57	58	175	181
Account and Activity Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	160	164	485	495
Account and Activity Fee Revenue [Member] | United States [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	106	109	319	323
Account and Activity Fee Revenue [Member] | United States [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	54	55	166	172
Account and Activity Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	3	3	9	9
Account and Activity Fee Revenue [Member] | Canada [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	0	0	0	0
Account and Activity Fee Revenue [Member] | Canada [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	3	3	9	9
Total Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	2,089	1,905	5,944	5,466
Total Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	2,041	1,861	5,808	5,341
Total Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	48	44	136	125
Trade Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	398	391	1,286	1,160
Trade Revenue [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	386	371	1,241	1,077
Trade Revenue [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	12	20	45	83
Trade Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	388	379	1,247	1,122
Trade Revenue [Member] | United States [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	376	360	1,204	1,042
Trade Revenue [Member] | United States [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	12	19	43	80
Trade Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	10	12	39	38
Trade Revenue [Member] | Canada [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	10	11	37	35
Trade Revenue [Member] | Canada [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	$ 0	$ 1	$ 2	$ 3