v3.26.1
Fair Value - Information about Significant Unobservable Inputs (Detail) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets € 59,574 € 65,375
Recurring fair value measurement [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 275,964 283,908
Recurring fair value measurement [member] | At fair value through other comprehensive income [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 49,757 54,715
Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Debt securities [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 47,411 52,211
Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Other investments [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets € 28 31
Level III [member] | At fair value through other comprehensive income [member] | Shares [member] | Net asset value [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Net asset value  
Level III [member] | At fair value through other comprehensive income [member] | Debt securities [member] | Broker quote [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Broker quote  
Level III [member] | At fair value through other comprehensive income [member] | Debt securities [member] | Other valuation technique [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Other  
Level III [member] | At fair value through other comprehensive income [member] | Debt securities [member] | Constant Prepayment Rate [Member] | Discounted cash flow [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Discounted cash flow  
Significant unobservable input Constant Prepayment Rate  
Level III [member] | At fair value through other comprehensive income [member] | Other investments [member] | Other valuation technique [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Other  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Shares [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Net asset value  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Shares [member] | Broker quote [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Broker quote  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Debt securities [member] | Broker quote [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Broker quote  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Debt securities [member] | Other valuation technique [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Other  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Net asset value [member] | Investment funds [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Net asset value  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Discounted cash flow [member] | Tax credit investments [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Discounted cash flow  
Significant unobservable input Discount rate  
Level III [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Other loans [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Valuation technique in assets Other  
Level III [member] | Recurring fair value measurement [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets € 5,699 6,436
Level III [member] | Recurring fair value measurement [member] | Other investments [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 4,765 5,530
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 533 799
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Shares [member] | Net asset value [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 5 0
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Debt securities [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 528 799
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Debt securities [member] | Broker quote [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 449 688
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Debt securities [member] | Other valuation technique [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 79 € 83
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Debt securities [member] | Constant Prepayment Rate [Member] | Discounted cash flow [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Range (weighted average)   21.11%
Total financial assets   € 28
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Other investments [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 1  
Level III [member] | Recurring fair value measurement [member] | At fair value through other comprehensive income [member] | Other investments [member] | Other valuation technique [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 1 0
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 164 193
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Shares [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 50 83
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Shares [member] | Broker quote [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 4 3
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Debt securities [member] | Broker quote [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 96 94
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Debt securities [member] | Other valuation technique [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 14 13
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets 4,068 4,538
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Net asset value [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets   € 3,633
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Net asset value [member] | Investment funds [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets € 3,220  
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Discounted cash flow [member] | Tax credit investments [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Range (weighted average) 6.71% 6.72%
Total financial assets € 766 € 823
Level III [member] | Recurring fair value measurement [member] | Financial assets at fair value through profit or loss, mandatorily measured at fair value, category [member] | Other investments [member] | Other loans [member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [line items]    
Total financial assets € 82 € 82