Segment Information - Summary of Investments (Parenthetical) (Detail) - EUR (€) € in Millions |
Jun. 30, 2026 |
Dec. 31, 2025 |
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| Disclosure Of Summarized Investment Per Segment [line items] | ||||||||
| Investments in other assets | € 27,830 | [1] | € 27,888 | [2] | ||||
| Elimination of intersegment amounts [member] | ||||||||
| Disclosure Of Summarized Investment Per Segment [line items] | ||||||||
| Investments in other assets | € (12,984) | € (13,190) | ||||||
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