v3.26.1
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
 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value € 925 € 1,572
Unrealized gains (losses) for financial liabilities held at fair value (425) (610)
Total 500 962
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 6
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 (375) (761)
Trading financial liabilities at fair value through profit or loss | Other Trading Liabilities    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial liabilities held at fair value 2 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 (34) 200
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 (19) (54)
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 191 34
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 633 1,725
Trading financial assets at fair value through profit or loss | Other trading assets    
Unrealized Gains or Losses on Level 3 Instruments [Line Items]    
Unrealized gains (losses) for financial assets held at fair value (5) (189)
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 107 (7)
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 1 0
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 € (2) € 9