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Marketable debt securities - Narrative (Details) - EUR (€) € in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Guarantees |  |  |
Liabilities secured by mortgage-backed bonds | € 22,624 |  |
Banco Santander, S.A. |  |  |
Guarantees |  |  |
Mortgage-backed Bonds, outstanding face value | € 22,360 |  |
Marketable debt securities |  |  |
Guarantees |  |  |
Other asset - backed securities personal loans average maturities | 5 years |  |
Other asset - backed securities SME's average maturities | 7 years |  |
Liabilities secured by mortgage-backed bonds | € 22,624 | € 22,631 | € 24,619
Marketable debt securities | Minimum |  |  |
Guarantees |  |  |
Mortgage-backed securities average maturities | 10 years |  |
Mortgage-backed bonds average maturities | 10 years |  |
Marketable debt securities | Maximum |  |  |
Guarantees |  |  |
Mortgage-backed securities loan-to-value ratio (as a percent) | 80.00% |  |
Mortgage-backed bonds loan-to-value ratio for home loans (as a percent) | 80.00% |  |
Mortgage-backed bonds loan-to-value ratio for other assets loans (as a percent) | 60.00% |  |

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