v3.26.1
Fair Value - Schedule of Transfers between Level 1 and Level II for Financial Assets and Liabilities Recorded at Fair Value on Recurring Basis (Detail) - Recurring fair value measurement [member] - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]    
Transfers Level I to Level II € 0 € 367
Transfers Level II to Level I 0 265
Financial assets at fair value through other comprehensive income, category [member]    
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]    
Transfers Level I to Level II 0 356
Transfers Level II to Level I 0 261
Financial assets at fair value through other comprehensive income, category [member] | Debt securities [member]    
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]    
Transfers Level I to Level II 0 308
Transfers Level II to Level I 0 261
Financial assets at fair value through other comprehensive income, category [member] | Money markets and other short term instruments [member]    
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]    
Transfers Level I to Level II 0 48
Transfers Level II to Level I 0 0
Financial assets at fair value through profit or loss [member]    
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]    
Transfers Level I to Level II 0 11
Transfers Level II to Level I 0 4
Financial assets at fair value through profit or loss [member] | Debt securities [member]    
Disclosure of transfers between level 1 and level 2 for financial assets and liabilities recorded at fair value [line items]    
Transfers Level I to Level II 0 11
Transfers Level II to Level I € 0 € 4