Revenue - Schedule of Partnership's Disaggregated Revenue (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation Of Revenue [Line Items]
Net revenue									$ 9,033	$ 8,215	$ 7,272
Net interest and dividends and other revenue									336	254	234
Net revenue	$ 2,493	$ 2,367	$ 2,319	$ 2,190	$ 2,153	$ 2,191	$ 2,083	$ 2,042	9,369	8,469	7,506
United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									8,811	8,002	7,084
Net interest and dividends and other revenue									316	231	221
Net revenue									9,127	8,233	7,305
Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									222	213	188
Net interest and dividends and other revenue									20	23	13
Net revenue									242	236	201
Asset-based Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									6,778	6,075	5,047
Asset-based Fee Revenue [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									4,810	4,214	3,341
Asset-based Fee Revenue [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,329	1,305	1,259
Asset-based Fee Revenue [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									639	556	447
Asset-based Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									6,620	5,930	4,926
Asset-based Fee Revenue [Member] | United States [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									4,740	4,156	3,299
Asset-based Fee Revenue [Member] | United States [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,241	1,218	1,180
Asset-based Fee Revenue [Member] | United States [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									639	556	447
Asset-based Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									158	145	121
Asset-based Fee Revenue [Member] | Canada [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									70	58	42
Asset-based Fee Revenue [Member] | Canada [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									88	87	79
Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									674	678	678
Account and Activity Fee Revenue [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									432	432	412
Account and Activity Fee Revenue [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									242	246	266
Account and Activity Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									661	664	666
Account and Activity Fee Revenue [Member] | United States [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									432	432	412
Account and Activity Fee Revenue [Member] | United States [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									229	232	254
Account and Activity Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									13	14	12
Account and Activity Fee Revenue [Member] | Canada [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									13	14	12
Total Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									7,452	6,753	5,725
Total Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									7,281	6,594	5,592
Total Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									171	159	133
Trade Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,581	1,462	1,547
Trade Revenue [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,475	1,320	1,407
Trade Revenue [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									106	142	140
Trade Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,530	1,408	1,492
Trade Revenue [Member] | United States [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,428	1,271	1,355
Trade Revenue [Member] | United States [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									102	137	137
Trade Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									51	54	55
Trade Revenue [Member] | Canada [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									47	49	52
Trade Revenue [Member] | Canada [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									$ 4	$ 5	$ 3