Receivable from Mutual Funds, Insurance Companies, and Other - Composition of Partnership's Receivable from Mutual Funds, Insurance Companies and Other (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Brokers And Dealers [Abstract]
Deposit for Canadian retirement accounts	$ 457	$ 326
Fees from mutual funds and insurance companies	285	291	$ 278
Other receivables	76	44
Total	$ 818	$ 661

Amount due from parties in nontrade transactions, classified as other.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_OtherReceivables
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant