v3.26.1
Intangible Assets - Summary of Intangible Assets (Detail) - EUR (€)
€ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance € 575 € 504
Additions 13 15
Amortization through income statement (32) (30)
Acquisitions through business combinations 4 63
Other movements 0 0
Net exchange differences (40) 23
Ending balance 519 575
Gross carrying amount [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 967  
Ending balance 906 967
Accumulated amortization, depreciation and impairment losses [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance (393)  
Ending balance (387) (393)
Goodwill [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 345 291
Additions 0 0
Amortization through income statement 0 0
Acquisitions through business combinations 1 23
Other movements 0 13
Net exchange differences (34) 19
Ending balance 313 345
Goodwill [member] | Gross carrying amount [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 473  
Ending balance 426 473
Goodwill [member] | Accumulated amortization, depreciation and impairment losses [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance (128)  
Ending balance (113) (128)
Service concession rights [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 120 131
Additions 0 2
Amortization through income statement (14) (14)
Acquisitions through business combinations 0 0
Other movements 0 0
Net exchange differences (2) 1
Ending balance 105 120
Service concession rights [member] | Gross carrying amount [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 311  
Ending balance 289 311
Service concession rights [member] | Accumulated amortization, depreciation and impairment losses [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance (191)  
Ending balance (184) (191)
Software [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 51 48
Additions 12 12
Amortization through income statement (12) (11)
Acquisitions through business combinations 0 0
Other movements 0 0
Net exchange differences (1) 1
Ending balance 49 51
Software [member] | Gross carrying amount [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 85  
Ending balance 94 85
Software [member] | Accumulated amortization, depreciation and impairment losses [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance (34)  
Ending balance (45) (34)
Other [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 58 33
Additions 1 1
Amortization through income statement (6) (5)
Acquisitions through business combinations 3 40
Other movements 0 (13)
Net exchange differences (3) 2
Ending balance 52 58
Other [member] | Gross carrying amount [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance 98  
Ending balance 96 98
Other [member] | Accumulated amortization, depreciation and impairment losses [member]    
Disclosure of reconciliation of changes in intangible assets and goodwill [Line Items]    
Beginning balance (40)  
Ending balance € (44) € (40)