Revenue - Schedule of Partnership's Disaggregated Revenue (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue	$ 12,143	$ 9,894	$ 9,033
Net interest and dividends and other revenue	136	169	336
Net revenue	12,279	10,063	9,369
United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue	11,833	9,656	8,811
Net interest and dividends and other revenue	113	149	316
Net revenue	11,946	9,805	9,127
Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue	310	238	222
Net interest and dividends and other revenue	23	20	20
Net revenue	333	258	242
Total Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	10,424	8,175	7,452
Total Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue	10,169	7,989	7,281
Total Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue	255	186	171
Asset-based Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	9,737	7,515	6,778
Asset-based Fee Revenue [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	7,421	5,537	4,810
Asset-based Fee Revenue [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,676	1,387	1,329
Asset-based Fee Revenue [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	640	591	639
Asset-based Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue	9,496	7,341	6,620
Asset-based Fee Revenue [Member] | United States [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	7,293	5,452	4,740
Asset-based Fee Revenue [Member] | United States [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,563	1,298	1,241
Asset-based Fee Revenue [Member] | United States [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	640	591	639
Asset-based Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue	241	174	158
Asset-based Fee Revenue [Member] | Canada [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	128	85	70
Asset-based Fee Revenue [Member] | Canada [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	113	89	88
Asset-based Fee Revenue [Member] | Canada [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	0	0	0
Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	687	660	674
Account and Activity Fee Revenue [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	436	424	432
Account and Activity Fee Revenue [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	251	236	242
Account and Activity Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue	673	648	661
Account and Activity Fee Revenue [Member] | United States [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	436	424	432
Account and Activity Fee Revenue [Member] | United States [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	237	224	229
Account and Activity Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue	14	12	13
Account and Activity Fee Revenue [Member] | Canada [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue	0	0	0
Account and Activity Fee Revenue [Member] | Canada [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	14	12	13
Trade Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,719	1,719	1,581
Trade Revenue [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,679	1,660	1,475
Trade Revenue [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	40	59	106
Trade Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,664	1,667	1,530
Trade Revenue [Member] | United States [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	1,627	1,611	1,428
Trade Revenue [Member] | United States [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	37	56	102
Trade Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue	55	52	51
Trade Revenue [Member] | Canada [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	52	49	47
Trade Revenue [Member] | Canada [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	$ 3	$ 3	$ 4