Revenue - Schedule of Partnership's Disaggregated Revenue (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 31, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Net revenue									$ 8,215	$ 7,272	$ 6,405
Net interest and dividends and other revenue									254	234	152
Net revenue	$ 2,153	$ 2,191	$ 2,083	$ 2,042	$ 1,975	$ 1,852	$ 1,882	$ 1,797	8,469	7,506	6,557
United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									8,002	7,084	6,238
Net interest and dividends and other revenue									231	221	143
Net revenue									8,233	7,305	6,381
Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									213	188	167
Net interest and dividends and other revenue									23	13	9
Net revenue									236	201	176
Asset-based Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									6,075	5,047	3,705
Asset-based Fee Revenue [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									4,214	3,341	2,120
Asset-based Fee Revenue [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,305	1,259	1,243
Asset-based Fee Revenue [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									556	447	342
Asset-based Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									5,930	4,926	3,611
Asset-based Fee Revenue [Member] | United States [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									4,156	3,299	2,093
Asset-based Fee Revenue [Member] | United States [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,218	1,180	1,176
Asset-based Fee Revenue [Member] | United States [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									556	447	342
Asset-based Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									145	121	94
Asset-based Fee Revenue [Member] | Canada [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									58	42	27
Asset-based Fee Revenue [Member] | Canada [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									87	79	67
Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									678	678	719
Account and Activity Fee Revenue [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									432	412	441
Account and Activity Fee Revenue [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									246	266	278
Account and Activity Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									664	666	707
Account and Activity Fee Revenue [Member] | United States [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									432	412	441
Account and Activity Fee Revenue [Member] | United States [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									232	254	266
Account and Activity Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									14	12	12
Account and Activity Fee Revenue [Member] | Canada [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									14	12	12
Total Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									6,753	5,725	4,424
Total Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									6,594	5,592	4,318
Total Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									159	133	106
Trade Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,462	1,547	1,981
Trade Revenue [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,320	1,407	1,778
Trade Revenue [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									142	140	203
Trade Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,408	1,492	1,920
Trade Revenue [Member] | United States [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									1,271	1,355	1,720
Trade Revenue [Member] | United States [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									137	137	200
Trade Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									54	55	61
Trade Revenue [Member] | Canada [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									49	52	58
Trade Revenue [Member] | Canada [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue									$ 5	$ 3	$ 3