v3.25.4
Financial Instruments Carried at Fair Value - Unrealized Gains or Losses on Level 3 Instruments held or in Issue at the Reporting Date (Detail) - Valuation
technique
unobservable
parameters
(Level 3) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value € 1,491 € 1,645
Unrealized gains (losses) for financial liabilities held at fair value (75) (2,135)
Total 1,416 (490)
Trading financial liabilities at fair value through profit or loss | Trading securities    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial liabilities held at fair value (1) 0
Trading financial liabilities at fair value through profit or loss | Derivatives    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial liabilities held at fair value (73) (1,930)
Trading financial liabilities at fair value through profit or loss | Other Trading    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial liabilities held at fair value (1) 0
Financial liabilities designated at fair value through profit or loss    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial liabilities held at fair value 124 (104)
Other financial liabilities at fair value    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial liabilities held at fair value (123) (102)
Trading financial assets at fair value through profit or loss | Trading securities    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value 38 113
Trading financial assets at fair value through profit or loss | Derivatives    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value 1,574 1,535
Trading financial assets at fair value through profit or loss | Other Trading    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value (218) (54)
Non-trading financial assets mandatory at fair value through profit or loss    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value 93 57
Financial assets designated at fair value through profit or loss    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value 0 0
Financial assets at fair value through other comprehensive income    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value 0 (4)
Other financial assets at fair value    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value € 5 € (3)