Document and Entity Information (USD $)
9 Months Ended
Jun. 30, 2010
Jul. 31, 2010
Mar. 31, 2009
Document and Entity Information [Abstract]      
Entity Registrant Name WGL HOLDINGS INC    
Entity Central Index Key 0001103601    
Document Type 10-Q    
Document Period End Date Jun. 30, 2010    
Amendment Flag false    
Document Fiscal Year Focus 2010    
Document Fiscal Period Focus Q3    
Current Fiscal Year End Date --09-30    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 1,633,538,203
Entity Common Stock, Shares Outstanding   50,848,848