Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 23, 2018
Document Information [Line Items]
Entity Registrant Name	ONE Gas, Inc.
Entity Central Index Key	0001587732
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		52,526,346
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Document Type	10-Q/A
Amendment Flag	true
Amendment Description	We filed our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018, on October 30, 2018. When filed, Exhibits 32.1 and 32.2 to our Quarterly Report on Form 10-Q reflected a clerical error identifying an incorrect periodic report in paragraph 1 of the certifications. The purpose of this Amendment No. 1 to our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018, is to re-file Exhibits 32.1 and 32.2 to reference the proper periodic report in paragraph 1 of the certifications. Except for the matter described, this Amendment No. 1 does not otherwise modify or update disclosure in, or exhibits to, our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018. Further, this Amendment No. 1 does not change any previously reported financial results, nor does it reflect events occurring subsequent to the date of the original filing of our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018.
Document Period End Date	Sep. 30, 2018