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Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Sep. 30, 2020	Nov. 19, 2020	Sep. 25, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-32502
Document Fiscal Year Focus	2020
Entity Registrant Name	Warner Music Group Corp.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-4271875
Entity Address, Address Line One	1633 Broadway
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10019
City Area Code	(212)
Local Phone Number	275-2000
Title of 12(b) Security	Class A Common Stock, $0.001 par value per share
Trading Symbol	WMG
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 2.4
Document Fiscal Period Focus	FY
Entity Central Index Key	0001319161
Current Fiscal Year End Date	--09-30
ICFR Auditor Attestation Flag	false
Amendment Flag	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant's Proxy Statement for the 2020 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K to the extent stated herein. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended September 25, 2020.
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		88,580,914
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		421,450,000