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Cover Page - shares
shares in Thousands
 9 Months Ended
Jun. 30, 2020
Aug. 04, 2020
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2020  
Document Transition Report false  
Entity Registrant Name Warner Music Group Corp.  
Entity Current Reporting Status No  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Amendment Flag false  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q3  
Entity Central Index Key 0001319161  
Current Fiscal Year End Date --09-30  
Class A Common Stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   88,550
Class B Common Stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   421,450