Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2024	Feb. 28, 2025	Jun. 30, 2024
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2024
Document Transition Report	false
Entity File Number	001-31565
Entity Registrant Name	FLAGSTAR FINANCIAL, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	06-1377322
Entity Address, Address Line One	102 Duffy Avenue,
Entity Address, City or Town	Hicksville,
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	11801
City Area Code	516
Local Phone Number	683-4100
Entity Well-known Seasoned Issuer	No
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
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 1.7
Entity Common Stock, Shares Outstanding		414,720,220
Documents Incorporated by Reference	Portions of the definitive Proxy Statement for the Annual Meeting of Shareholders to be held on June 4, 2025 are incorporated by reference into Part III.
Entity Central Index Key	0000910073
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Common Stock (Par Value: 0.01)
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	FLG
Security Exchange Name	NYSE
Bifurcated Option Notes Unit Securities
Document Information [Line Items]
Title of 12(b) Security	Bifurcated Option Note Unit SecuritiESSM
Trading Symbol	FLG PRU
Security Exchange Name	NYSE
Fixed-to-Floating Rate Series A Noncumulative Perpetual Preferred Stock
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares each representing a 1/40th interest in a share of Fixed-to-Floating Rate Series A Noncumulative Perpetual Preferred Stock
Trading Symbol	FLG PRA
Security Exchange Name	NYSE