Organization and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020 Songs
Organization And Summary Of Significant Accounting Policies [Line Items]
Date of formation of Mills Music Trust	Dec. 03, 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 2019 calendar year (the “Top 50 Songs”), together with certain copyright information with respect to each of the Top 50 Songs (the “2019 Listing”). A copy of the 2019 Listing, as provided by EMI, is included in the Trust’s annual report on Form 10-K for the fiscal year ended December 31, 2019. The 2019 Listing does not include any information regarding Copyrighted Songs for the 2020 calendar year.
2018 Listing Top 50 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated number of songs in the Catalogue	25,000
Estimated number of songs producing royalty income	1,600
Number of Copyrighted Songs in the Top 50 list	50