MEZZANINE AND STOCKHOLDER'S EQUITY - Schedule of Preferred Stock Activity (Details) - Preferred Stock $ in Millions	9 Months Ended
Sep. 30, 2026 USD ($)
Related Party Transaction [Line Items]
Net impact of activities on Preferred stock	$ 252
Series F and G Preferred Stock
Related Party Transaction [Line Items]
Webster preferred shares, Series F and G, acquired	252
Webster preferred shares, Series F and G, redeemed	(252)
Series H and I Preferred Stock
Related Party Transaction [Line Items]
SHUSA Preferred shares, Series H and I issued	$ 252

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

- Definition

Value of stock issued pursuant to acquisitions during the period.

+ References

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+ Details

- Definition

The increase (decrease) in stockholders' equity during the period.

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