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Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2021
Feb. 22, 2022
Jun. 30, 2021
Document And Entity Information      
Document Type 10-K    
Amendment Flag false    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Document Transition Report false    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Entity File Number 001-33096    
Entity Registrant Name United States Natural Gas Fund, LP    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 20-5576760    
Entity Address, Address Line One 1850 Mt. Diablo Boulevard, Suite 640    
Entity Address, City or Town Walnut Creek    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 94596    
City Area Code 510    
Local Phone Number 522-9600    
Entity Central Index Key 0001376227    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Accelerated Filer    
Entity Public Float     $ 284,942,411
Title of 12(b) Security Shares of United States Natural Gas Fund, LP    
Security Exchange Name NYSE    
Trading Symbol UNG    
Entity Common Stock, Shares Outstanding   19,384,588  
Entity Emerging Growth Company false    
Entity Small Business false    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Shell Company false    
ICFR Auditor Attestation Flag true    
Auditor Name Spicer Jeffries LLP    
Auditor Firm ID 349    
Auditor Location Denver