| Cover Page | 3 Months Ended |
| Mar. 31, 2021shares | |
| Cover [Abstract] | |
| Document Type | 10-Q |
| Amendment Flag | false |
| Document Period End Date | Mar. 31, 2021 |
| Document Fiscal Year Focus | 2021 |
| Document Fiscal Period Focus | Q1 |
| Entity Registrant Name | MILLS MUSIC TRUST |
| Entity Central Index Key | 0000066496 |
| Entity Address, State or Province | NY |
| Current Fiscal Year End Date | --12-31 |
| Entity Current Reporting Status | Yes |
| Entity Filer Category | Non-accelerated Filer |
| Entity Small Business | true |
| Entity Emerging Growth Company | false |
| Entity Interactive Data Current | Yes |
| Entity Shell Company | false |
| Entity Common Stock, Shares Outstanding | 277,712 |
| Statements of Cash Receipts and Disbursements - USD ($) | 3 Months Ended | |
| Mar. 31, 2021 | Mar. 31, 2020 | |
| Operating Cash Flows, Direct Method [Abstract] | ||
| Receipts from EMI | $ 280,912 | $ 259,035 |
| Undistributed Cash at Beginning of Period | 46 | 46 |
| Disbursement - Administrative Expenses | 0 | (37,517) |
| Balance Available for Distribution | 280,958 | 221,564 |
| Cash Distributions to Unit Holders | 229,797 | 221,518 |
| Undistributed Cash at End of Period | $ 51,161 | $ 46 |
| Cash Distribution per Trust Unit (based on 277,712 Trust Units outstanding) | $ 0.8275 | $ 0.7976 |
| Statements of Cash Receipts and Disbursements (Parenthetical) - USD ($) | Apr. 15, 2021 | Mar. 31, 2021 | Mar. 31, 2020 |
| Number of Trust Units Outstanding | 277,712 | 277,712 | |
| Disbursement of administrative expense | $ 0 | $ 37,517 | |
| Subsequent Event [Member] | |||
| Disbursement of administrative expense | $ 51,115 | ||
| Payment for administrative expenses | $ 51,115 |
| Organization and Summary of Significant Accounting Policies | 3 Months Ended |
| Mar. 31, 2021 | |
| Accounting Policies [Abstract] | |
| Organization and Summary of Significant Accounting Policies | NOTE 1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization and Background Mills Music Trust (the “ Trust Declaration of Trust Old Mills Contingent Portion Catalogue Asset Purchase Agreement The Contingent Portion amounts are currently payable by EMI Mills Music Inc. (“ EMI Sony/ATV HSBC Bank, USA, N.A. is the Corporate Trustee of the Trust (the “ Corporate Trustee Individual Trustees Trustees Proceeds from Contingent Portion Payments The Trust receives quarterly payments of the Contingent Portion from EMI and distributes the amounts it receives to the registered owners of Trust Certificates (the “ Unit Holders Trust Units Payments of the Contingent Portion to the Trust are based on royalty income which the Catalogue generates. The Trust does not own the Catalogue or any copyrights or other intellectual property rights and is not responsible for collecting royalties in connection with the Catalogue. As the current owner and administrator of the Catalogue, EMI is obligated under the Asset Purchase Agreement to use its best efforts to collect all royalties, domestic and foreign, in connection with the Catalogue and to remit a portion of its royalty income to the Trust as its Contingent Portion payment obligation, in accordance with the terms of the Asset Purchase Agreement. Calculation of the Contingent Portion The amount of each payment of the Contingent Portion is based on a formula set forth in the Asset Purchase Agreement. For information regarding the calculation of the Contingent Portion and a related dispute between EMI and the Trust see “Contingent Portion Payments” under Part I — Item 2, “Management’s Discussion and Analysis of Financial Condition and Results of Operations”. Cash Distributions to Unit Holders The Declaration of Trust provides for the distribution to the Unit Holders of all funds the Trust receives after payment of, or withholdings in connection with, expenses and liabilities of the Trust. See the table headed “Statement of Cash Receipts and Disbursements” for information regarding cash disbursements made to Unit Holders during the three months ended March 31, 2021 and March 31, 2020. The Copyright Catalogue The Catalogue is estimated to be composed of over 12,000 music titles (the “ Copyrighted Songs Top 50 Songs 2020 Listing annual report on Form 10-K for the fiscal year Accounting Policies EMI typically makes payments to the Trust of the Contingent Portion in March, June, September and December for the prior calendar quarter. The payments received are accounted for on a cash basis, as are expenses of the Trust. The Declaration of Trust provides for the distribution of the amounts it receives in Contingent Portion payments to the Unit Holders after payment of, or withholdings in connection with, expenses and liabilities of the Trust. The Trust’s financial statements reflect only cash transactions and do not include transactions that would be recorded in financial statements presented on the accrual basis of accounting, as contemplated by generally accepted accounting principles in the United States. The Trust does not prepare a balance sheet or a statement of cash flows. These unaudited financial statements should be read in conjunction with the financial statement and related notes in the Trust’s Annual Report on Form 10-K |
| Income Taxes | 3 Months Ended |
| Mar. 31, 2021 | |
| Income Tax Disclosure [Abstract] | |
| Income Taxes | NOTE 2. INCOME TAXES No provision for income taxes has been made since the liability thereof is that of the Unit Holders and not the Trust. |
| Governance of the Trust | 3 Months Ended |
| Mar. 31, 2021 | |
| Business Combinations [Abstract] | |
| Governance of the Trust | NOTE 3. GOVERNANCE OF THE TRUST The Trust does not have, nor does the Declaration of Trust provide for, officers, a board of directors or any employees. HSBC Bank, USA, N.A. is the Corporate Trustee of the Trust, and Lee Eastman and Michael E. Reiss are the Individual Trustees of the Trust. Pursuant to the Declaration of Trust, Trustees of the Trust serve until their removal, resignation, incapacity, or in the case of Individual Trustees, their death. On December 23, 2014, the Trust adopted a code of ethics (as defined in Item 406 of Regulation S-K under the Securities Exchange Act of 1933) applicable to the Individual Trustees and the trust officers of the Corporate Trustee. A copy of the Code of Ethics will be provided to any person without charge upon written request to the Trust at its administrative office, c/o HSBC BANK USA, N.A., Corporate Trust, Issuer Services, 452 Fifth Avenue, New York, NY. In addition, the Trust relies on the Corporate Trustee to abide by HSBC Bank, USA, N.A.’s Statement of Business Principles and Code of Ethics, which is available on the Corporate Trustee’s website at http://www.us.hsbc.com. The Trust is not a corporate entity and thus does not have an Audit Committee. The Trust has established a policy with regard to audit, audit-related and certain non-audit engagements of its independent auditors. Under this policy, the Trust annually approves certain limited, specified recurring services which may be provided by the Trust’s accountant or independent auditors. All other engagements for services to be performed by the Trust’s independent auditors must be separately pre-approved by the Trust. Joel Faden acts as Chief Financial Individual providing accounting services for the Trust. |
| Related Party Transactions | 3 Months Ended |
| Mar. 31, 2021 | |
| Related Party Transactions [Abstract] | |
| Related Party Transactions | NOTE 4. RELATED PARTY TRANSACTIONS The Trustees are paid in accordance with the Declaration of Trust, which provides that each Trustee shall receive annual compensation of $2,500, provided that such aggregate compensation to the Trustees as a group may not exceed 3% of the Contingent Portion amounts received by the Trust in any year. The Declaration of Trust also provides for the reimbursement of expenses reasonably incurred in the performance of a Trustee’s duties to the Trust, including clerical and administrative services. Accordingly, the Trustees are entitled to receive annual compensation and reimbursement for services performed for the Trust, including the Corporate Trustee’s services as the Registrar and Transfer Agent of the certificates representing the Trust Units. The Declaration of Trust also provides that if a Trustee performs unusual or extraordinary services, reasonable compensation for such services shall be paid, subject to the terms and conditions of the Declaration of Trust. Pursuant to the Declaration of Trust, disbursements were made as follows to the Trustees for the three months ended March 31, 2021 and March 31, 2020: Three Months 2021 2020 Corporate Trustee Fees $ 0 $ 625 Individual Trustee Fees 0 1,250 Transfer Agent Registrar Fees (1) 0 3,750 Totals $ 0 (2) $ 5,625 (1) These services are performed by the Corporate Trustee. (2) Corporate Trustee Fees of $625, Individual Trustee Fees of $1,250 and Transfer Agent Registrar Fees of $3,750 attributable to the three-months ended March 31, 2021 were actually paid by the Trust on April 15, 2021. The administrative office of the Trust is located at the offices of the Corporate Trustee, HSBC Bank, USA, N.A., Corporate Trust Issuer Services, 452 Fifth Avenue, New York, New York 10018. Except for fees paid to the Corporate Trustee in accordance with the Declaration of Trust, no expense is being charged or paid by the Trust for the office space and office equipment of the Corporate Trustee that is being utilized for the Trust. |
| Subsequent Events | 3 Months Ended |
| Mar. 31, 2021 | |
| Subsequent Events [Abstract] | |
| Subsequent Events | NOTE 5. SUBSEQUENT EVENTS None. |
| Organization and Summary of Significant Accounting Policies (Policies) | 3 Months Ended |
| Mar. 31, 2021 | |
| Accounting Policies [Abstract] | |
| Organization and Background | Organization and Background Mills Music Trust (the “ Trust Declaration of Trust Old Mills Contingent Portion Catalogue Asset Purchase Agreement The Contingent Portion amounts are currently payable by EMI Mills Music Inc. (“ EMI Sony/ATV HSBC Bank, USA, N.A. is the Corporate Trustee of the Trust (the “ Corporate Trustee Individual Trustees Trustees |
| Proceeds from Contingent Portion Payments | Proceeds from Contingent Portion Payments The Trust receives quarterly payments of the Contingent Portion from EMI and distributes the amounts it receives to the registered owners of Trust Certificates (the “ Unit Holders Trust Units Payments of the Contingent Portion to the Trust are based on royalty income which the Catalogue generates. The Trust does not own the Catalogue or any copyrights or other intellectual property rights and is not responsible for collecting royalties in connection with the Catalogue. As the current owner and administrator of the Catalogue, EMI is obligated under the Asset Purchase Agreement to use its best efforts to collect all royalties, domestic and foreign, in connection with the Catalogue and to remit a portion of its royalty income to the Trust as its Contingent Portion payment obligation, in accordance with the terms of the Asset Purchase Agreement. |
| Calculation of the Contingent Portion | Calculation of the Contingent Portion The amount of each payment of the Contingent Portion is based on a formula set forth in the Asset Purchase Agreement. For information regarding the calculation of the Contingent Portion and a related dispute between EMI and the Trust see “Contingent Portion Payments” under Part I — Item 2, “Management’s Discussion and Analysis of Financial Condition and Results of Operations”. |
| Cash Distributions to Unit Holders | Cash Distributions to Unit Holders The Declaration of Trust provides for the distribution to the Unit Holders of all funds the Trust receives after payment of, or withholdings in connection with, expenses and liabilities of the Trust. See the table headed “Statement of Cash Receipts and Disbursements” for information regarding cash disbursements made to Unit Holders during the three months ended March 31, 2021 and March 31, 2020. |
| The Copyright Catalogue | The Copyright Catalogue The Catalogue is estimated to be composed of over 12,000 music titles (the “ Copyrighted Songs Top 50 Songs 2020 Listing annual report on Form 10-K for the fiscal year |
| Accounting Policies | Accounting Policies EMI typically makes payments to the Trust of the Contingent Portion in March, June, September and December for the prior calendar quarter. The payments received are accounted for on a cash basis, as are expenses of the Trust. The Declaration of Trust provides for the distribution of the amounts it receives in Contingent Portion payments to the Unit Holders after payment of, or withholdings in connection with, expenses and liabilities of the Trust. The Trust’s financial statements reflect only cash transactions and do not include transactions that would be recorded in financial statements presented on the accrual basis of accounting, as contemplated by generally accepted accounting principles in the United States. The Trust does not prepare a balance sheet or a statement of cash flows. These unaudited financial statements should be read in conjunction with the financial statement and related notes in the Trust’s Annual Report on Form 10-K |
| Related Party Transactions (Tables) | 3 Months Ended |
| Mar. 31, 2021 | |
| Related Party Transactions [Abstract] | |
| Disbursements to Trustees | Pursuant to the Declaration of Trust, disbursements were made as follows to the Trustees for the three months ended March 31, 2021 and March 31, 2020: Three Months 2021 2020 Corporate Trustee Fees $ 0 $ 625 Individual Trustee Fees 0 1,250 Transfer Agent Registrar Fees (1) 0 3,750 Totals $ 0 (2) $ 5,625 (1) These services are performed by the Corporate Trustee. (2) Corporate Trustee Fees of $625, Individual Trustee Fees of $1,250 and Transfer Agent Registrar Fees of $3,750 attributable to the three-months ended March 31, 2021 were actually paid by the Trust on April 15, 2021. |
| Organization and Summary of Significant Accounting Policies - Additional Information (Detail) | 3 Months Ended |
| Mar. 31, 2021Songs | |
| Organization And Summary Of Significant Accounting Policies [Line Items] | |
| Date of formation of Mills Music Trust | Dec. 3, 1964 |
| Top 50 Songs in the Catalogue | EMI has provided the Trust with a listing of the top 50 earning songs in the Catalogue during the 2020 calendar year (the “Top 50 Songs”), together with certain copyright information with respect to each of the Top 50 Songs (the “2020 Listing”). A copy of the 2020 Listing, as provided by EMI, is included in the Trust’s annual report on Form 10-K for the fiscal year ended December 31, 2020. The 2020 Listing does not include any information regarding Copyrighted Songs for the 2021 calendar year. |
| 2020 Listing Top 50 [Member] | |
| Organization And Summary Of Significant Accounting Policies [Line Items] | |
| Estimated number of songs in the Catalogue | 12,000 |
| Estimated number of songs producing royalty income | 1,430 |
| Number of Copyrighted Songs in the Top 50 list | 50 |
| Income Taxes - Additional Information (Detail) | 3 Months Ended |
| Mar. 31, 2021USD ($) | |
| Income Tax Disclosure [Abstract] | |
| Provision for income taxes | $ 0 |
| Related Party Transactions - Additional Information (Detail) | 3 Months Ended |
| Mar. 31, 2021USD ($) | |
| Related Party Transaction [Line Items] | |
| Trustee annual compensation | $ 2,500 |
| Expense Charged Or Paid Trust For Office SpaceAnd Office Equipment | $ 0 |
| Maximum [Member] | |
| Related Party Transaction [Line Items] | |
| Aggregate compensation percentage to Trustees | 3.00% |
| Related Party Transactions - Disbursements to Trustees (Detail) - USD ($) | 3 Months Ended | |
| Mar. 31, 2021 | Mar. 31, 2020 | |
| Related Party Transaction [Line Items] | ||
| Trustee Fees and Expenses | $ 0 | $ 5,625 |
| Individual [Member] | ||
| Related Party Transaction [Line Items] | ||
| Trustee Fees and Expenses | 0 | 1,250 |
| Corporate Trustee [Member] | ||
| Related Party Transaction [Line Items] | ||
| Trustee Fees and Expenses | 0 | 625 |
| Transfer Agent Registrar Fees [Member] | ||
| Related Party Transaction [Line Items] | ||
| Trustee Fees and Expenses | $ 0 | $ 3,750 |
| Related Party Transactions - Disbursements to Trustees (Parenthetical) (Detail) - USD ($) | Apr. 15, 2021 | Mar. 31, 2021 | Mar. 31, 2020 |
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | $ 0 | $ 5,625 | |
| Individual [Member] | |||
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | 0 | 1,250 | |
| Individual [Member] | Subsequent Event [Member] | |||
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | $ 1,250 | ||
| Corporate Trustee [Member] | |||
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | 0 | 625 | |
| Corporate Trustee [Member] | Subsequent Event [Member] | |||
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | 625 | ||
| Transfer Agent Registrar Fees [Member] | |||
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | $ 0 | $ 3,750 | |
| Transfer Agent Registrar Fees [Member] | Subsequent Event [Member] | |||
| Related Party Transaction [Line Items] | |||
| Trustee Fees and Expenses | $ 3,750 |
