LOANS AND ALLOWANCE FOR CREDIT LOSSES - Schedule of Payment Defaults of Prior Modification (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Payment Deferral Only
Financing Receivable, Modified [Line Items]
Amortized Cost	$ 62,552	$ 34,338	$ 129,656	$ 62,856
All Other Modifications
Financing Receivable, Modified [Line Items]
Amortized Cost	1,046	3,025	2,161	12,006
Commercial \| C&I loans \| Payment Deferral Only
Financing Receivable, Modified [Line Items]
Amortized Cost	443	476	8,038	566
Commercial \| C&I loans \| All Other Modifications
Financing Receivable, Modified [Line Items]
Amortized Cost	5	6	42	74
Consumer \| Residential mortgages \| Payment Deferral Only
Financing Receivable, Modified [Line Items]
Amortized Cost	0	0	0	0
Consumer \| Residential mortgages \| All Other Modifications
Financing Receivable, Modified [Line Items]
Amortized Cost	0	47	196	47
Consumer \| Home equity loans and lines of credit \| Payment Deferral Only
Financing Receivable, Modified [Line Items]
Amortized Cost	0	0	0	0
Consumer \| Home equity loans and lines of credit \| All Other Modifications
Financing Receivable, Modified [Line Items]
Amortized Cost	153	84	153	84
Consumer \| RICs and auto loans \| Payment Deferral Only
Financing Receivable, Modified [Line Items]
Amortized Cost	62,109	33,862	121,618	62,290
Consumer \| RICs and auto loans \| All Other Modifications
Financing Receivable, Modified [Line Items]
Amortized Cost	$ 888	$ 2,888	$ 1,770	$ 11,801

Santander Holdings USA, Inc. 10-Q