Derivatives - Summary of Nominal Amount and Fair Value of Credit Derivatives (Detail) - EUR (€) € in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Disclosure of information about credit exposures designated as measured at fair value through profit or loss [line items] | ||
| At January 1, | € 3,851 | € 4,043 |
| At December 31, | 1,766 | 3,851 |
| At January 1, | 68 | 71 |
| Increase/(Decrease) during the year | (41) | |
| At December 31, | 27 | 68 |
| CDSs [Member] | ||
| Disclosure of information about credit exposures designated as measured at fair value through profit or loss [line items] | ||
| At January 1, | 3,851 | |
| Increase/(Decrease) during the year | (2,086) | (192) |
| At December 31, | 1,766 | 3,851 |
| At January 1, | € 68 | |
| Increase/(Decrease) during the year | (2) | |
| At December 31, | € 68 | |