Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 21, 2019
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		52,737,473
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Document Type	10-Q
Document Quarterly Report	true
Entity Small Business	false
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-36108
Trading Symbol	OGS
Security Exchange Name	NYSE
Entity Emerging Growth Company	false