v3.10.0.1
Document and Entity Information - shares
9 Months Ended
Jun. 30, 2018
Jul. 31, 2018
Document Information [Line Items]    
Entity Registrant Name WGL Holdings Inc.  
Entity Central Index Key 0001103601  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Amendment Flag false  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Current Fiscal Year End Date --09-30  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   100
Washington Gas Light Company    
Document Information [Line Items]    
Entity Registrant Name Washington Gas Light Company  
Entity Central Index Key 0000104819  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Amendment Flag false  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Current Fiscal Year End Date --09-30  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   46,479,536