v3.26.1
Financial Risks - Summary of Changes in the Gross Carrying Amount / Market Value of the Financial Assets - Mortgage Loans (Detail) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance € 76,020  
Ending balance 69,293 € 76,020
Mortgages [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 10,598  
Ending balance 9,672 10,598
Mortgages [member] | Lifetime ECL not credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 60  
Ending balance 94 60
Mortgages [member] | 12-month ECL [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 10,536  
Ending balance 9,576 10,536
Mortgages [member] | Lifetime ECL credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 2  
Ending balance 2 2
Mortgages [member] | Gross carrying amount [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 10,716 10,182
Financial assets derecognized during the period other than write-offs (707) (702)
New financial assets originated or purchased 957 559
Realized gains and losses through income statement 7 4
Net exchange differences (1,268) 674
Other movements   (1)
Ending balance 9,705 10,716
Mortgages [member] | Gross carrying amount [member] | Lifetime ECL not credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 135 35
Financial assets derecognized during the period other than write-offs (45) (69)
New financial assets originated or purchased 23 76
Realized gains and losses through income statement 1 1
Net exchange differences (16) 7
Other movements   (1)
Ending balance 115 135
Mortgages [member] | Gross carrying amount [member] | 12-month ECL [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 10,574 10,147
Financial assets derecognized during the period other than write-offs (654) (633)
New financial assets originated or purchased 934 483
Realized gains and losses through income statement 5 3
Net exchange differences (1,251) 667
Other movements   (1)
Ending balance 9,588 10,574
Mortgages [member] | Gross carrying amount [member] | Lifetime ECL credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance 7  
Financial assets derecognized during the period other than write-offs (8)  
Realized gains and losses through income statement 2  
Net exchange differences (1)  
Ending balance 3 7
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 1 to Stage 2 [member] | Lifetime ECL not credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers 22 162
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 1 to Stage 2 [member] | 12-month ECL [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers (22) (162)
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 1 to Stage 3 [member] | 12-month ECL [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers   (7)
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 1 to Stage 3 [member] | Lifetime ECL credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers   7
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 2 to Stage 3 [member] | Lifetime ECL not credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers (3)  
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 2 to Stage 3 [member] | Lifetime ECL credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers 3  
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 2 to Stage 1 [member] | Lifetime ECL not credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers (2) (75)
Mortgages [member] | Gross carrying amount [member] | Transfer from Stage 2 to Stage 1 [member] | 12-month ECL [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Transfers 2 75
Mortgages [member] | Expected credit loss [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance (118)  
Ending balance (33) (118)
Mortgages [member] | Expected credit loss [member] | Lifetime ECL not credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance (75)  
Ending balance (21) (75)
Mortgages [member] | Expected credit loss [member] | 12-month ECL [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance (38)  
Ending balance (11) (38)
Mortgages [member] | Expected credit loss [member] | Lifetime ECL credit impaired [member]    
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]    
Beginning balance (5)  
Ending balance € (1) € (5)