v3.26.1
Cash and Cash Equivalents - Summary of Reconciliation of Liabilities Arising from Financing Activities (Detail)
€ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2025
EUR (€)
Dec. 31, 2025
USD ($)
Dec. 31, 2024
EUR (€)
Disclosure of reconciliation of liabilities arising from financing activities [line items]      
Beginning balance € 3,013    
Ending balance 1,982   € 3,013
Cash flow hedges [member] | Subordinated borrowings - held at amortized cost [member]      
Disclosure of reconciliation of liabilities arising from financing activities [line items]      
Beginning balance 1,653   2,244
Repayment     (700)
Amortization   $ 3 5
Net exchange difference   (195) 104
Ending balance 1,461   1,653
Cash flow hedges [member] | Trust pass-through securities - held at amortized cost [member]      
Disclosure of reconciliation of liabilities arising from financing activities [line items]      
Beginning balance 113   111
Fair value hedge movements     (5)
Amortization   (1) (1)
Net exchange difference   (13) 7
Ending balance 99   113
Cash flow hedges [member] | Borrowings [member]      
Disclosure of reconciliation of liabilities arising from financing activities [line items]      
Beginning balance 3,013   2,356
Addition   700
Repayment   (209)
Amortization   2 3
Net exchange difference   (272) 162
Ending balance 1,982   3,013
Cash flow hedges [member] | Assets held to hedge Trust pass-through securities [Member]      
Disclosure of reconciliation of liabilities arising from financing activities [line items]      
Beginning balance (20)   (14)
Realized gains / (losses)     (5)
Net exchange difference   $ 2 (1)
Ending balance € (17)   € (20)