Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 07, 2020	Jun. 30, 2019
Document Information [Line Items]
Entity File Number	001-36108
Entity Registrant Name	ONE Gas, Inc.
Title of 12(b) Security	Common Stock, par value $0.01 per share
Entity Incorporation, State or Country Code	OK
Entity Central Index Key	0001587732
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		52,774,254
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Document Type	10-K
Document Annual Report	true
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Trading Symbol	OGS
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 4.5
Documents Incorporated by Reference [Text Block]	Portions of the definitive proxy statement to be delivered to shareholders in connection with the Annual Meeting of Shareholders to be held May 21, 2020, are incorporated by reference in Part III.