Net Capital Requirements - Partnership's Capital Figures for U.S. and Canada Broker-Dealer Subsidiaries (Detail) - USD ($) $ in Millions	Mar. 28, 2025	Dec. 31, 2024
Subsidiaries [Member]
Regulatory Capital Requirements
Net capital	$ 1,073	$ 938
Net capital in excess of the minimum required	$ 1,006	$ 873
Net capital as a percentage of aggregate debit items	32.00%	28.90%
Net capital after anticipated capital withdrawals, as a percentage of aggregate debit items	9.00%	5.20%
Canada [Member]
Regulatory Capital Requirements
Regulatory risk-adjusted capital	$ 91	$ 71
Regulatory risk-adjusted capital in excess of the minimum required	$ 90	$ 69

Capital in excess required to be held by investment industry regulatory organization of foreign country.

No definition available.

Name:	ck0000815917_CapitalInExcessRequiredToBeHeldByInvestmentIndustryRegulatoryOrganizationOfForeignCountry
Namespace Prefix:	ck0000815917_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Foreign country brokers dealers regulatory risk adjusted capital.

No definition available.

Name:	ck0000815917_ForeignCountryBrokersDealersRegulatoryRiskAdjustedCapital
Namespace Prefix:	ck0000815917_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Net capital after anticipated capital withdrawals to aggregate debit items percentage.

No definition available.

Name:	ck0000815917_NetCapitalAfterAnticipatedCapitalWithdrawalsToAggregateDebitItemsPercentage
Namespace Prefix:	ck0000815917_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Net capital to aggregate debit item percentage.

No definition available.

Name:	ck0000815917_NetCapitalToAggregateDebitItemPercentage
Namespace Prefix:	ck0000815917_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Amount of net capital in excess of minimum required net capital, calculated under Alternative Standard.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Rule 15c3-1
-Number 240
-Section 15c3-1
-Publisher SEC

Name:	srt_AlternativeExcessNetCapital
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of net capital of broker-dealer.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Rule 15c3-1
-Number 240
-Section 15c3-1
-Publisher SEC

No definition available.

Name:	srt_RegulatoryCapitalRequirementsAbstract
Namespace Prefix:	srt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_StatementGeographicalAxis=country_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: