Document And Entity Information - shares
 6 Months Ended
Jun. 30, 2020
Jul. 20, 2020
Document Information [Line Items]    
Title of 12(b) Security Common Stock, par value $0.01 per share  
Entity Registrant Name ONE Gas, Inc.  
Entity Incorporation, State or Country Code OK  
Entity Tax Identification Number 46-3561936  
Entity Address, Address Line One 15 East Fifth Street  
Entity Address, City or Town Tulsa,  
Entity Address, State or Province OK  
Entity Address, Postal Zip Code 74103  
City Area Code (918)  
Local Phone Number 947-7000  
Entity Central Index Key 0001587732  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Shell Company false  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   52,920,531
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q2  
Document Type 10-Q  
Document Quarterly Report true  
Entity Small Business false  
Amendment Flag false  
Document Period End Date Jun. 30, 2020  
Document Transition Report false  
Entity File Number 001-36108  
Trading Symbol OGS  
Security Exchange Name NYSE  
Entity Emerging Growth Company false