Deferred Tax - Schedule of Loss Carryforward Period and Deferred Corporate Income Tax Assets Not Recognized (Detail) - EUR (€) € in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Deferred tax assets and liabilities [Line Items] | ||
| Gross amounts | € 1,172 | € 1,018 |
| Not recognized deferred tax asset | 388 | 364 |
| Less than 5 years [member] | ||
| Deferred tax assets and liabilities [Line Items] | ||
| Gross amounts | 18 | 41 |
| Not recognized deferred tax asset | 11 | 15 |
| Over 5 through 10 years [member] | ||
| Deferred tax assets and liabilities [Line Items] | ||
| Gross amounts | 1 | 1 |
| Not recognized deferred tax asset | 0 | 1 |
| Over 10 through 15 years [member] | ||
| Deferred tax assets and liabilities [Line Items] | ||
| Gross amounts | 0 | 0 |
| Not recognized deferred tax asset | 70 | 79 |
| Indefinitely [member] | ||
| Deferred tax assets and liabilities [Line Items] | ||
| Gross amounts | 1,153 | 976 |
| Not recognized deferred tax asset | € 307 | € 269 |