| Document and Entity Information Document | Jan. 27, 2020 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 27, 2020 |
| Entity Registrant Name | ONEOK, Inc. |
| Entity Incorporation, State or Country Code | OK |
| Entity File Number | 001-13643 |
| Entity Tax Identification Number | 73-1520922 |
| Entity Address, Address Line One | 100 West 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 | 588-7000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, par value of $0.01 |
| Trading Symbol | OKE |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001039684 |
| Amendment Flag | false |
