Document and Entity Information - USD ($)
12 Months Ended
Sep. 30, 2017
Dec. 05, 2017
Mar. 31, 2017
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Trading Symbol wmg    
Entity Registrant Name Warner Music Group Corp.    
Entity Central Index Key 0001319161    
Current Fiscal Year End Date --09-30    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status No    
Entity Voluntary Filers Yes    
Entity Filer Category Non-accelerated Filer    
Entity Common Stock, Shares Outstanding   1,055  
Entity Public Float     $ 0