Deferred Tax - Summary of Deferred Corporate Income Tax Asset (Detail) - EUR (€) € in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Deferred Tax Assets And Liabilities [line items] | ||
| Deferred tax asset recoverable through retention of investments until recovery or maturity | € 803 | € 1,263 |
| Deferred tax asset dependent on future taxable profits | 173 | 30 |
| On December 31 | 976 | 1,293 |
| Gross carrying amount [member] | ||
| Deferred Tax Assets And Liabilities [line items] | ||
| Deferred tax asset recoverable through retention of investments until recovery or maturity | 3,823 | 6,013 |
| Deferred tax asset dependent on future taxable profits | 822 | 141 |
| On December 31 | € 4,645 | € 6,154 |