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Cover - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Feb. 13, 2026
Jun. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-40304    
Entity Registrant Name Frontier Group Holdings, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 46-3681866    
Entity Address, Address Line One 4545 Airport Way    
Entity Address, City or Town Denver    
Entity Address, State or Province CO    
Entity Address, Postal Zip Code 80239    
City Area Code 720    
Local Phone Number 374-4550    
Title of 12(b) Security Common Stock, $0.001 par value per share    
Trading Symbol ULCC    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 204
Entity Common Stock, Shares Outstanding   229,609,718  
Documents Incorporated by Reference
Portions of the registrant's definitive Proxy Statement relating to its 2026 Annual Meeting of Stockholders are incorporated by reference in Part III of this Annual Report on Form 10-K to the extent stated herein. Such Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended December 31, 2025.
    
Amendment Flag false    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001670076