| Document and Entity Information | Oct. 31, 2024 |
| Document Information [Line Items] | |
| Document Period End Date | Oct. 31, 2024 |
| Document Type | 8-K |
| Amendment Flag | false |
| Entity Registrant Name | FLAGSTAR FINANCIAL, INC. |
| Entity Central Index Key | 0000910073 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 06-1377322 |
| Entity Address, City or Town | Hicksville, |
| Entity Address, Postal Zip Code | 11801 |
| City Area Code | 516 |
| Local Phone Number | 683-4100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity File Number | 1-31565 |
| Entity Address, Address Line One | 102 Duffy Avenue, |
| Entity Address, State or Province | NY |
| Entity Information, Former Legal or Registered Name | New York Community Bancorp, Inc. |
| Common Stock | |
| Document Information [Line Items] | |
| Security Exchange Name | NYSE |
| Title of 12(b) Security | Common stock, $0.01 par value per share |
| Trading Symbol | FLG |
| Bifurcated Option Note Unit Securities [Member] | |
| Document Information [Line Items] | |
| Security Exchange Name | NYSE |
| Title of 12(b) Security | Bifurcated Option Note Unit SecuritiESSM |
| Trading Symbol | FLG PRU |
| Fixed To Floating Rate Series A Noncumulative Perpetual Preferred Stock [Member] | |
| Document Information [Line Items] | |
| Security Exchange Name | NYSE |
| 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 |
