Revenue - Schedule of Partnership's Disaggregated Revenue (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 25, 2020	Jun. 26, 2020	Mar. 27, 2020	Dec. 31, 2019	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Net revenue									$ 9,894	$ 9,033	$ 8,215
Net interest and dividends and other revenue									169	336	254
Net revenue	$ 2,720	$ 2,527	$ 2,325	$ 2,491	$ 2,493	$ 2,367	$ 2,319	$ 2,190	10,063	9,369	8,469
United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									9,656	8,811	8,002
Net interest and dividends and other revenue									149	316	231
Net revenue									9,805	9,127	8,233
Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									238	222	213
Net interest and dividends and other revenue									20	20	23
Net revenue									258	242	236
Asset-based Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									7,515	6,778	6,075
Asset-based Fee Revenue [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									5,537	4,810	4,214
Asset-based Fee Revenue [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,387	1,329	1,305
Asset-based Fee Revenue [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									591	639	556
Asset-based Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									7,341	6,620	5,930
Asset-based Fee Revenue [Member] | United States [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									5,452	4,740	4,156
Asset-based Fee Revenue [Member] | United States [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,298	1,241	1,218
Asset-based Fee Revenue [Member] | United States [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									591	639	556
Asset-based Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									174	158	145
Asset-based Fee Revenue [Member] | Canada [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									85	70	58
Asset-based Fee Revenue [Member] | Canada [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									89	88	87
Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									660	674	678
Account and Activity Fee Revenue [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									424	432	432
Account and Activity Fee Revenue [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									236	242	246
Account and Activity Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									648	661	664
Account and Activity Fee Revenue [Member] | United States [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									424	432	432
Account and Activity Fee Revenue [Member] | United States [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									224	229	232
Account and Activity Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									12	13	14
Account and Activity Fee Revenue [Member] | Canada [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									12	13	14
Total Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									8,175	7,452	6,753
Total Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									7,989	7,281	6,594
Total Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									186	171	159
Trade Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,719	1,581	1,462
Trade Revenue [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,660	1,475	1,320
Trade Revenue [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									59	106	142
Trade Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,667	1,530	1,408
Trade Revenue [Member] | United States [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,611	1,428	1,271
Trade Revenue [Member] | United States [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									56	102	137
Trade Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									52	51	54
Trade Revenue [Member] | Canada [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									49	47	49
Trade Revenue [Member] | Canada [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									$ 3	$ 4	$ 5