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Provisions - Litigation and other matters - Non-tax-related proceedings Narrative (Details) € in Thousands, £ in Millions, zł in Millions |  |  |  |  |  |  |  |  | 5 Months Ended | 12 Months Ended | 19 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 09, 2026 | Jul. 11, 2023 EUR (€) | Feb. 06, 2023 EUR (€) | Dec. 31, 2022 EUR (€) | Jan. 13, 2022 EUR (€) | Dec. 09, 2021 EUR (€) | Sep. 16, 2021 EUR (€) | May 29, 2020 | May 16, 2021 EUR (€) | Dec. 31, 2025 EUR (€) | Dec. 31, 2025 GBP (£) | Dec. 31, 2025 PLN (zł) | Dec. 31, 2024 EUR (€) judgement | Dec. 31, 1999 shares | Dec. 31, 1994 child | Dec. 31, 2022 EUR (€) | Dec. 31, 2025 GBP (£) | Dec. 31, 2025 PLN (zł) | Dec. 31, 2024 GBP (£) judgement | Nov. 22, 2024 EUR (€) | Apr. 25, 2024 judgement | Dec. 31, 2023 EUR (€) | Jan. 23, 2019 | Dec. 31, 2017 EUR (€)
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  | € 8,149,000 |  |  |  |  |  | € 8,355,000 |  |  | € 8,407,000 |  |  | € 8,149,000 |  |  |  |  |  | € 8,441,000 |  |
Banco Popular Espanol, S.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | € 680,000
Estimated cost of compensation to shareholders and bondholders applied to the commercial loyalty program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | € 535,000
Santander Bank Polska S.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage loans denominated in, or indexed to, CHF |  |  |  |  |  |  |  |  |  | 626,000 |  |  |  |  |  |  |  | zł 2,642.0 |  |  |  |  |  |
Santander Bank Polska S.A. | Agreement For The Sale Of Santander Bank Polska S.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of proportion of ownership interest in subsidiary | 49.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Santander Consumer Bank Polska |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage loans denominated in, or indexed to, CHF |  |  |  |  |  |  |  |  |  | 174,400 |  |  |  |  |  |  |  | 735.9 |  |  |  |  |  |
Legal case to request court judgment on the validity of the swaps |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Arbitration matter, amount claimed by entity |  |  |  |  |  |  |  |  |  | 66,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Arbitration matter, amount claimed by counterparty |  |  |  |  |  |  |  |  |  | 57,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Arbitration matter, amount to be received by entity |  |  |  |  |  |  | € 66,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Arbitration matter, amount to be received by entity, interest |  |  |  |  |  |  | € 11,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
"Planos Econmicos" |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of suspension of economic plan process |  |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
"Planos Econmicos" | Banco Santander (Brasil) S.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  |  |  |  |  |  |  | 155,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Banco Popular’s Compensation request |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal proceedings provision, possible loss, contingent liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | € 2,277,650 |  |  |  |
Tax Dividend, Cum-ex Transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individual plaintiff, CEO functions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  |  |  |  |  |  |  | 35,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Compensation sought in litigation claim |  |  |  |  |  |  |  |  | € 112,000 |  |  |  |  |  |  | 61,900 |  |  |  |  |  |  |  |
Losses on litigation settlements |  |  |  |  | € 51,400 | € 67,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in losses on litigation settlements |  |  | € 8,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on litigation settlements |  | € 9,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Individual plaintiff, CEO functions | 2018 variable remuneration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term metric achievement percentage |  |  |  | 33.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of active loans from swiss francs to PLN loans | Santander Bank Polska and Santander Consumer Bank Poland |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage loans, provision and adjustment to gross carrying amount |  |  |  |  |  |  |  |  |  | 1,391,900 |  |  |  |  |  |  |  | 5,874.3 |  |  |  |  |  |
Mortgage loans, adjustment to gross carrying amount |  |  |  |  |  |  |  |  |  | 756,300 |  |  |  |  |  |  |  | 3,191.7 |  |  |  |  |  |
Increase in adjustment to gross carrying amount, mortgage loans |  |  |  |  |  |  |  |  |  | 23,600 |  | zł 99.7 |  |  |  |  |  |  |  |  |  |  |  |
Increase through other costs associated |  |  |  |  |  |  |  |  |  | 172,400 |  | 730.5 |  |  |  |  |  |  |  |  |  |  |  |
Conversion of active loans from swiss francs to PLN loans | Santander Bank Polska S.A. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage loans, provision and adjustment to gross carrying amount |  |  |  |  |  |  |  |  |  | 1,129,400 |  |  |  |  |  |  |  | 4,766.4 |  |  |  |  |  |
Conversion of active loans from swiss francs to PLN loans | Santander Consumer Bank Polska |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage loans, provision and adjustment to gross carrying amount |  |  |  |  |  |  |  |  |  | 262,500 |  |  |  |  |  |  |  | 1,107.9 |  |  |  |  |  |
Inheritance trust | Banco Santander México, S.A., Institución de Banca Múltiple, Grupo Financiero Santander México |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of sons involved in testamentary trust | child |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |
Amount of shares to be transferred by trustee (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 36,700,000 |  |  |  |  |  |  |  |  |  |
Spanish supreme court, mortgage expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of public notary expenses and agency expenses to be paid |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% |
Percentage of the registry expenses to be paid |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |
Number of judgments rendered | judgement |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  | 2 |  | 2 |  |  |
Provision For Compensation And Associated Cost In Respect Of PPI Policies | Santander Insurance Services UK Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS | £ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | £ 515.0 |  |  |  |  |  |  |
Provision For Compensation And Associated Cost In Respect Of PPI Policies, Interest | Santander Insurance Services UK Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS | £ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 162.0 |  |  |  |  |  |  |
Other provisions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  | € 4,073,000 |  |  |  |  |  | 4,993,000 |  |  | € 5,051,000 |  |  | € 4,073,000 |  |  |  |  |  | 4,634,000 |  |
Other provisions | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  |  |  |  |  |  |  | 736,000 |  |  | 654,000 |  |  |  |  |  |  |  |  | € 373,000 |  |
Active loans, under IAS 37 | Conversion of active loans from swiss francs to PLN loans | Santander Bank Polska and Santander Consumer Bank Poland |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  |  |  |  |  |  |  | 635,600 |  |  |  |  |  |  |  | zł 2,682.6 |  |  |  |  |  |
Increase in existing provisions |  |  |  |  |  |  |  |  |  | 293,800 |  | zł 1,245.3 |  |  |  |  |  |  |  |  |  |  |  |
Financial Conduct Authority (FCA) Review of The Vehicle Finance Market | Other provisions | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of other provisions [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PROVISIONS |  |  |  |  |  |  |  |  |  | 528,100 |  |  | 353,300 |  |  |  | £ 461.0 |  | £ 293.0 |  |  |  |  |
Increase in existing provisions |  |  |  |  |  |  |  |  |  | € 214,000 | £ 183.0 |  | € 353,000 |  |  |  |  |  |  |  |  |  |  |

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