v3.26.1
Fair Value - Carrying Values and Estimated Fair Values of Assets and Liabilities (Detail) - EUR (€)
€ in Millions
Jun. 30, 2026
Dec. 31, 2025
Debt securities - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial assets € 36 € 36
Fair value 36 36
Loans - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial assets 9,475 9,672
Fair value 8,611 8,902
Deposits with financial institutions - held at amortized cost [member] | Financial assets at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial assets 11 11
Fair value 11 11
Subordinated borrowings - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial liabilities 1,503 1,461
Total estimated fair value 1,317 1,312
Trust pass-through securities - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial liabilities 102 99
Total estimated fair value 119 118
Borrowings [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial liabilities 2,230 1,982
Total estimated fair value 2,295 2,059
Investment contracts - held at amortized cost [member] | Financial liabilities at amortised cost, category [member]    
Disclosure of carrying amount and fair value financial assets and liabilities [line items]    
Financial liabilities 13,570 12,652
Total estimated fair value € 10,152 € 9,473