Soliciting Material Soliciting Material Written Communications Written Communications Local Phone Number Local Phone Number Class of Stock [Domain] Class of Stock [Domain] Document Information [Line Items] Document Information [Line Items] Amendment Flag Amendment Flag Entity Emerging Growth Company Entity Emerging Growth Company Entity File Number Entity File Number Security Exchange Name Security Exchange Name Entity Address, State or Province Entity Address, State or Province Entity Address, Address Line One Entity Address, Address Line One City Area Code City Area Code Cover [Abstract] Cover [Abstract] Document Period End Date Document Period End Date Document Information [Table] Document Information [Table] Pre-commencement Tender Offer Pre-commencement Tender Offer Class of Stock [Axis] Class of Stock [Axis] Entity Central Index Key Entity Central Index Key Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Legal Entity [Axis] Legal Entity [Axis] Entity Tax Identification Number Entity Tax Identification Number Entity Registrant Name Entity Registrant Name Entity [Domain] Entity [Domain] Trading Symbol Trading Symbol Southern Company Gas Southern Company Gas [Member] Southern Company Gas [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Address, City or Town Entity Address, City or Town Document Type Document Type