| Cover | Jul. 07, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 7, 2021 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001587732 |
| Entity File Number | 001-36108 |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | OGS |
| Security Exchange Name | NYSE |
