SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Millions |
9 Months Ended | |
|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| NON-CASH TRANSACTIONS | ||
| Loans transferred to/(from) OREO and other repossessed assets | $ 24 | $ 21 |
| Loans transferred from/(to) LHFI (from)/to LHFS, net | 550 | 41 |
| Transfer of financial interest in a VIE - Loans | 0 | 245 |
| Transfer of financial interest in a VIE - Borrowings | 0 | 154 |
| Unsettled purchases of investment securities | 2,329 | 109 |
| Unsettled sales of investment securities | 1,469 | 0 |
| Non-cash transfer of financial assets in an off-balance sheet securitization transaction | 0 | 1,149 |
| Dividends declared and payable to shareholder | 0 | 44 |
| Exchange of Webster Series F and G preferred stock for SHUSA Series H and I preferred stock | 252 | 0 |
| Contribution from Parent Company | 9,317 | 0 |
| Proceeds from Contributions from Parent | $ 3,193 | $ 0 |