Revenue - Schedule of Partnership's Disaggregated Revenue (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 30, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Net revenue	$ 2,042	$ 1,797
United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,984	1,749
Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	58	48
Asset-based Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,453	1,115
Asset-based Fee Revenue [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	995	694
Asset-based Fee Revenue [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	327	316
Asset-based Fee Revenue [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	131	105
Asset-based Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,418	1,088
Asset-based Fee Revenue [Member] | United States [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	982	685
Asset-based Fee Revenue [Member] | United States [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	305	298
Asset-based Fee Revenue [Member] | United States [Member] | Other Asset-based Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	131	105
Asset-based Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	35	27
Asset-based Fee Revenue [Member] | Canada [Member] | Advisory Programs Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	13	9
Asset-based Fee Revenue [Member] | Canada [Member] | Service Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	22	18
Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	172	172
Account and Activity Fee Revenue [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	109	105
Account and Activity Fee Revenue [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	63	67
Account and Activity Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	168	169
Account and Activity Fee Revenue [Member] | United States [Member] | Shareholder Accounting Services Fees [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	109	105
Account and Activity Fee Revenue [Member] | United States [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	59	64
Account and Activity Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	4	3
Account and Activity Fee Revenue [Member] | Canada [Member] | Other Account and Activity Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	4	3
Total Fee Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,625	1,287
Total Fee Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1,586	1,257
Total Fee Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	39	30
Trade Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	364	457
Trade Revenue [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	332	415
Trade Revenue [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	32	42
Trade Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	349	442
Trade Revenue [Member] | United States [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	318	401
Trade Revenue [Member] | United States [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	31	41
Trade Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	15	15
Trade Revenue [Member] | Canada [Member] | Commissions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	14	14
Trade Revenue [Member] | Canada [Member] | Principal Transactions [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	1	1
Net Interest and Dividends Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	47	40
Net Interest and Dividends Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	45	39
Net Interest and Dividends Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	2	1
Other Revenue [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	6	13
Other Revenue [Member] | United States [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	4	11
Other Revenue [Member] | Canada [Member]
Disaggregation Of Revenue [Line Items]
Net revenue	$ 2	$ 2