v3.26.1
Fair value of assets and liabilities - Additional information (Details) - EUR (€)
€ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Dec. 31, 2024
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Financial assets classified as Level 3 based on quoted price € 9,800 € 10,100  
Percentage on financial asset based on unadjusted quoted price 90.40% 86.20%  
Amount of risk neutral designed financial assets € 100 € 100  
Remaining financial assets classified as level 3 using valuation techniques 900 1,500  
Financial liabilities measured at fair value 103,313 80,532  
Financial Liabilities classified as Level 3 based on unadjusted quoted price 900 600  
Financial Liabilities designed to be fully neutral in terms of market risk 100 100  
–  Trading securities      
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Transfers out of Level 2 into Level 1 of fair value hierarchy, liabilities held at end of reporting period   200  
Debt securities      
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Transfers out of Level 1 into Level 2 of fair value hierarchy, assets held at end of reporting period   300  
Transfers out of Level 2 into Level 1 of fair value hierarchy, assets held at end of reporting period   400  
Level 3      
Disclosure of fair value measurement of assets and liabilities [Line Items]      
Fair value of swap € 10,854 € 11,742 € 11,005
Percentage on financial asset based on unadjusted quoted price 79.00% 72.70%  
Financial liabilities measured at fair value € 1,076 € 802  
Remaining financial liabilities classified as level 3 using valuation techniques € 100 € 100