Document and Entity Information - shares
3 Months Ended
Dec. 31, 2018
Feb. 05, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Dec. 31, 2018  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Trading Symbol wmg  
Entity Registrant Name Warner Music Group Corp.  
Entity Central Index Key 0001319161  
Current Fiscal Year End Date --09-30  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   1,060