v3.26.1
Financial Risks - Summary of Reconciliation of Changes in Loss Allowance - Debt Securities (Detail) - EUR (€)
€ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Impact of stage transfers on year-end ECL € 20 € (2)  
Gross carrying amount [member] | Debt securities [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance 47,446 52,247 € 52,247
Increase Through Origination Or Purchase Final 5,107   8,663
Increase Decrease Through Transfers to Disposal Financial Assets (2,928)   (8,963)
Impact of stage transfers on year-end ECL 0    
Amortizations through income statement 91   162
Unrealized gains/losses through equity (659)   1,488
Movements related to fair value hedges (1)    
Change in models 0    
Other movements (1)   (2)
Transfer to/from other headings (60)   (28)
Net exchange differences 1,332   (6,120)
Ending balance 50,328   47,446
Gross carrying amount [member] | Debt securities [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance 358 335 335
Increase Through Origination Or Purchase Final 4   4
Increase Decrease Through Transfers to Disposal Financial Assets (43)   (146)
Impact of stage transfers on year-end ECL 0    
Amortizations through income statement 1   1
Unrealized gains/losses through equity (3)   18
Movements related to fair value hedges 0    
Change in models 0    
Other movements 0   (23)
Transfer to/from other headings 0    
Net exchange differences 13   (42)
Ending balance 522   358
Gross carrying amount [member] | Debt securities [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance 46,782 51,529 51,529
Increase Through Origination Or Purchase Final 5,100   8,632
Increase Decrease Through Transfers to Disposal Financial Assets (2,842)   (8,729)
Impact of stage transfers on year-end ECL 0    
Amortizations through income statement 70   115
Unrealized gains/losses through equity (659)   1,528
Movements related to fair value hedges (1)    
Change in models 0    
Other movements (1)   7
Transfer to/from other headings (60)   (21)
Net exchange differences 1,312   (6,035)
Ending balance 49,532   46,782
Gross carrying amount [member] | Debt securities [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance [1] 306 383 383
Increase Through Origination Or Purchase Final [1] 3   27
Increase Decrease Through Transfers to Disposal Financial Assets [1] (44)   (88)
Impact of stage transfers on year-end ECL [1] 0    
Amortizations through income statement [1] 20   46
Unrealized gains/losses through equity [1] 3   (58)
Movements related to fair value hedges [1] 0    
Change in models [1] 0    
Other movements [1] 0   14
Transfer to/from other headings [1] 0   (7)
Net exchange differences [1] 8   (44)
Ending balance [1] 274   306
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 194   269
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (194)   (269)
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (12)    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 12   (12)
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] 0   12
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (5)   (24)
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0   24
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] 5   0
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 14   (36)
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] (14)   36
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0   1
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 13    
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] (13)   (1)
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 3 to Stage 1 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers     12
Gross carrying amount [member] | Debt securities [member] | Transfer from Stage 3 to Stage 1 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1]     (12)
Accumulated impairment [member] | Debt securities [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance (347) (341) (341)
Acquisition ECL (19)   (43)
Reversal Allowance Account For Credit Losses On Disposal of Financial Assets 40   73
Impact of stage transfers on year-end ECL (4)   (52)
Amortizations through income statement 0    
Unrealized gains/losses through equity 0    
Movements related to fair value hedges 0    
Change in models 46   (24)
Other movements 0    
Transfer to/from other headings 0    
Net exchange differences (8)   42
Ending balance (292)   (347)
Accumulated impairment [member] | Debt securities [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance (27) (41) (41)
Acquisition ECL (1)    
Reversal Allowance Account For Credit Losses On Disposal of Financial Assets 1   15
Impact of stage transfers on year-end ECL (5)   (10)
Amortizations through income statement 0    
Unrealized gains/losses through equity 0    
Movements related to fair value hedges 0    
Change in models (3)   3
Other movements 0    
Transfer to/from other headings 0    
Net exchange differences (1)   5
Ending balance (38)   (27)
Accumulated impairment [member] | Debt securities [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance (188) (187) (187)
Acquisition ECL (18)   (29)
Reversal Allowance Account For Credit Losses On Disposal of Financial Assets 10   30
Impact of stage transfers on year-end ECL 3   9
Amortizations through income statement 0    
Unrealized gains/losses through equity 0    
Movements related to fair value hedges 0    
Change in models 45   (26)
Other movements 0    
Transfer to/from other headings 0    
Net exchange differences (4)   23
Ending balance (154)   (188)
Accumulated impairment [member] | Debt securities [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Beginning balance [1] (131) € (112) (112)
Acquisition ECL [1] (1)   (14)
Reversal Allowance Account For Credit Losses On Disposal of Financial Assets [1] 29   28
Impact of stage transfers on year-end ECL [1] (2)   (51)
Amortizations through income statement [1] 0    
Unrealized gains/losses through equity [1] 0    
Movements related to fair value hedges [1] 0    
Change in models [1] 4   (1)
Other movements [1] 0    
Transfer to/from other headings [1] 0    
Net exchange differences [1] (3)   14
Ending balance [1] (100)   (131)
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (1)   (2)
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 1   2
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 2 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 1    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (1)    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 1 to Stage 3 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 6   1
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0   (1)
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 1 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] (6)    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (7)   4
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0   0
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 2 to Stage 3 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] 7   (4)
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member] | Lifetime ECL not credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers 0   (1)
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers (2)    
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 3 to Stage 2 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1] € 2   1
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 3 to Stage 1 [member] | 12-month ECL [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers     (9)
Accumulated impairment [member] | Debt securities [member] | Transfer from Stage 3 to Stage 1 [member] | Lifetime ECL credit impaired [member]      
Disclosure of reconciliation of changes in allowance for credit losses on receivables [line items]      
Transfers [1]     € 9
[1] Including purchased credit impaired.