Lines of Credit - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
Sep. 28, 2018	Dec. 31, 2020	Dec. 31, 2019
Line Of Credit Facility [Line Items]
Line of credit facility		$ 890,000,000	$ 790,000,000
2018 Credit Facility [Member]
Line Of Credit Facility [Line Items]
Line of credit facility	$ 500,000,000	$ 500,000,000	$ 500,000,000
Maximum leverage ratio required to be maintained by partnership	35.00%	35.00%	35.00%
Required minimum partnership capital, net of reserve for anticipated withdrawals and partnership loans	$ 1,884,000,000	$ 1,884,000,000	$ 1,884,000,000
Amount outstanding under credit facility		0	0
Partnership draws against lines of credit		0	0
2018 Credit Facility [Member] \| Edward D. Jones & Co., L. P [Member]
Line Of Credit Facility [Line Items]
Minimum tangible net worth	$ 1,344,000,000	$ 1,344,000,000	$ 1,344,000,000
Minimum regulatory net capital percentage of debit items	6.00%	6.00%	6.00%
Uncommitted Secured Credit Facilities [Member]
Line Of Credit Facility [Line Items]
Line of credit facility		$ 390,000,000	$ 290,000,000
Amount outstanding under credit facility		0	0
Partnership draws against lines of credit		$ 0	$ 0

Maximum leverage ratio required to be maintained by partnership.

No definition available.

Name:	ck0000815917_MaximumLeverageRatioRequiredToBeMaintainedByPartnership
Namespace Prefix:	ck0000815917_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum regulatory net capital percentage of debit items.

+ References

No definition available.

+ Details

Name:	ck0000815917_MinimumRegulatoryNetCapitalPercentageOfDebitItems
Namespace Prefix:	ck0000815917_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum tangible net worth required to be maintained.

+ References

No definition available.

+ Details

Name:	ck0000815917_MinimumTangibleNetWorth
Namespace Prefix:	ck0000815917_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Partnership draws against lines of credit.

+ References

No definition available.

+ Details

Name:	ck0000815917_PartnershipDrawsAgainstLinesOfCredit
Namespace Prefix:	ck0000815917_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Required minimum partnership capital net of reserve for anticipated withdrawals and partnership loans.

+ References

No definition available.

+ Details

Name:	ck0000815917_RequiredMinimumPartnershipCapitalNetOfReserveForAnticipatedWithdrawalsAndPartnershipLoans
Namespace Prefix:	ck0000815917_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=ck0000815917_TwoThousandAndEighteenCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=ck0000815917_UncommittedSecuredCreditFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: