v3.26.1
Fair Value - Carrying Values and Estimated Fair Values of Assets and Liabilities (Detail) - EUR (€)
€ in Millions
Dec. 31, 2025
Dec. 31, 2024
Disclosure of fair value financial assets and liabilities [line items]    
Financial assets € 69,293 € 76,020
Fair value 59,574 65,375
Debt securities - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial assets 36
Fair value 36
Loans - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial assets 9,672 10,598
Fair value 8,902 9,380
Deposits with financial institutions - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial assets 11
Fair value 11
Subordinated borrowings - held at amortized cost [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 1,312 1,490
Subordinated borrowings - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial liabilities 1,653
Total estimated fair value 1,490
Trust pass-through securities - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial liabilities 113
Total estimated fair value 133
Borrowings [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial liabilities 1,982 3,013
Total estimated fair value 2,059 3,076
Investment contracts - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Financial liabilities 12,592
Total estimated fair value 9,432
Level I [member] | Debt securities - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 36
Level I [member] | Loans - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 0 0
Level I [member] | Deposits with financial institutions - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 11
Level I [member] | Subordinated borrowings - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 763
Level I [member] | Trust pass-through securities - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 0 0
Level I [member] | Borrowings [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 837 867
Level I [member] | Investment contracts - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 0 0
Level II [member] | Debt securities - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 0 0
Level II [member] | Loans - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 1 1
Level II [member] | Deposits with financial institutions - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 0 0
Level II [member] | Subordinated borrowings - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 620 727
Level II [member] | Trust pass-through securities - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 118 133
Level II [member] | Borrowings [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 1,221 2,209
Level II [member] | Investment contracts - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 0 0
Level III [member] | Debt securities - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 0 0
Level III [member] | Loans - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 8,901 9,379
Level III [member] | Deposits with financial institutions - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Fair value 0 0
Level III [member] | Subordinated borrowings - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 0 0
Level III [member] | Trust pass-through securities - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 0 0
Level III [member] | Borrowings [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value 0 0
Level III [member] | Investment contracts - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of fair value financial assets and liabilities [line items]    
Total estimated fair value € 9,473 € 9,432