v3.26.1
Financial instruments - Summary of Fair value measurements using significant unobservable inputs (level 3) (Detail) - Level 3 of fair value hierarchy [member]
€ in Millions
 12 Months Ended
Dec. 31, 2025
EUR (€)
Disclosure Of Changes In Level 3 Items Of Fair Value Measurements Using Significant Unobservable Inputs [Line Items]  
Beginning balance € 32
Business combination 96
Recognized in profit or loss (12) [1]
Purchases 23
Settlements 0
Other changes 3
Ending balance 142
Unlisted Equity Securities [Member]  
Disclosure Of Changes In Level 3 Items Of Fair Value Measurements Using Significant Unobservable Inputs [Line Items]  
Beginning balance 19
Business combination 57
Recognized in profit or loss (4) [1]
Purchases 19
Settlements 0
Other changes 0
Ending balance 91
Unlisted Debt Securities [Member]  
Disclosure Of Changes In Level 3 Items Of Fair Value Measurements Using Significant Unobservable Inputs [Line Items]  
Beginning balance 0
Business combination 15
Recognized in profit or loss 0 [1]
Purchases 4
Settlements 0
Other changes 0
Ending balance 19
Other financial assets    
Disclosure Of Changes In Level 3 Items Of Fair Value Measurements Using Significant Unobservable Inputs [Line Items]  
Beginning balance 13
Business combination 24
Recognized in profit or loss (8) [1]
Purchases 0
Settlements 0
Other changes 3
Ending balance € 32
[1] Includes unrealized losses recognized in profit or loss attributable to balances held at the end of the reporting period