v3.25.4
Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2025
Feb. 04, 2026
Jun. 30, 2025
Document Information [Line Items]      
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 001-16189    
Entity Registrant Name NiSource Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 35-2108964    
Entity Address, Address Line One 801 East 86th Avenue    
Entity Address, City or Town Merrillville,    
Entity Address, State or Province IN    
Entity Address, Postal Zip Code 46410    
City Area Code (614)    
Local Phone Number 460-6000    
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 Emerging Growth Company false    
Entity Small Business false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 18,966,136,571
Entity Common Stock, Shares Outstanding   478,533,171  
Entity Central Index Key 0001111711    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Amendment Flag false    
Document Financial Statement Error Correction [Flag] false    
Documents Incorporated by Reference [Text Block]
Part III of this report incorporates by reference specific portions of the Registrant’s Notice of Annual Meeting and Proxy Statement relating to the Annual Meeting of Stockholders to be held on May 11, 2026.
    
Common Stock      
Document Information [Line Items]      
Title of 12(b) Security Common Stock, par value $0.01 per share    
Trading Symbol NI    
Security Exchange Name NYSE