SECURITIES FINANCING ACTIVITIES - Schedule of Securities Loaned or Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Banking and Thrift, Other Disclosure [Abstract]
Securities sold under agreements to repurchase	$ 21,296,824	$ 16,302,948
Securities lending	212	0
Total	$ 21,297,036	$ 16,302,948

Amount, after the effects of master netting arrangements, of securities loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

- Definition

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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+ Details

Santander Holdings USA, Inc. 10-Q