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Cover - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2021
Feb. 22, 2022
Jun. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Document Transition Report false    
Entity File Number 001-13643    
Entity Registrant Name ONEOK, Inc.    
Entity Incorporation, State or Country Code OK    
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    
Title of 12(b) Security Common stock, par value of $0.01    
Trading Symbol OKE    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
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    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 24.4
Entity Common Stock, Shares Outstanding   446,213,285  
Documents Incorporated by Reference Portions of the definitive proxy statement to be delivered to shareholders in connection with the Annual Meeting of Shareholders to be held May 25, 2022, are incorporated by reference in Part III.    
Entity Central Index Key 0001039684    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Amendment Flag false