v3.26.1
Financial Instruments - fair value - Fair Value of Assets and Liabilities (Details) - GBP (£)
£ in Millions
Jun. 30, 2026
Dec. 31, 2025
Disclosure of detailed information about financial instruments [line items]    
Cash and cash equivalents £ 2,363 £ 2,694
Other investments 328 £ 334
Derivatives in designated hedge relationships | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities (10)  
Derivatives in designated hedge relationships | Level 1 | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities 0  
Derivatives in designated hedge relationships | Level 2 | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities (10)  
Derivatives in designated hedge relationships | Level 3 | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities 0  
Held at fair value through profit or loss | Contingent consideration liabilities    
Disclosure of detailed information about financial instruments [line items]    
Contingent consideration liabilities (65)  
Held at fair value through profit or loss | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities (5)  
Held at fair value through profit or loss | Level 1 | Contingent consideration liabilities    
Disclosure of detailed information about financial instruments [line items]    
Contingent consideration liabilities 0  
Held at fair value through profit or loss | Level 1 | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities 0  
Held at fair value through profit or loss | Level 2 | Contingent consideration liabilities    
Disclosure of detailed information about financial instruments [line items]    
Contingent consideration liabilities (19)  
Held at fair value through profit or loss | Level 2 | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities (5)  
Held at fair value through profit or loss | Level 3 | Contingent consideration liabilities    
Disclosure of detailed information about financial instruments [line items]    
Contingent consideration liabilities (46)  
Held at fair value through profit or loss | Level 3 | At Fair Value | Derivative liabilities    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial liabilities 0  
Derivative assets | Derivatives in designated hedge relationships | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 60  
Derivative assets | Derivatives in designated hedge relationships | Level 1 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 0  
Derivative assets | Derivatives in designated hedge relationships | Level 2 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 60  
Derivative assets | Derivatives in designated hedge relationships | Level 3 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 0  
Derivative assets | Held at fair value through profit or loss | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 2  
Derivative assets | Held at fair value through profit or loss | Level 1 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 0  
Derivative assets | Held at fair value through profit or loss | Level 2 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 2  
Derivative assets | Held at fair value through profit or loss | Level 3 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Derivative financial assets 0  
Money market funds | Held at fair value through profit or loss | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Cash and cash equivalents 432  
Money market funds | Held at fair value through profit or loss | Level 1 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Cash and cash equivalents 432  
Money market funds | Held at fair value through profit or loss | Level 2 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Cash and cash equivalents 0  
Money market funds | Held at fair value through profit or loss | Level 3 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Cash and cash equivalents 0  
Trade and other receivables | Held at fair value through other comprehensive income | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Trade and other receivables 496  
Trade and other receivables | Held at fair value through other comprehensive income | Level 1 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Trade and other receivables 0  
Trade and other receivables | Held at fair value through other comprehensive income | Level 2 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Trade and other receivables 496  
Trade and other receivables | Held at fair value through other comprehensive income | Level 3 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Trade and other receivables 0  
Other investments | Held at fair value through profit or loss | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 269  
Other investments | Held at fair value through profit or loss | Level 1 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 97  
Other investments | Held at fair value through profit or loss | Level 2 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 0  
Other investments | Held at fair value through profit or loss | Level 3 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 172  
Other investments | Held at fair value through other comprehensive income | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 59  
Other investments | Held at fair value through other comprehensive income | Level 1 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 0  
Other investments | Held at fair value through other comprehensive income | Level 2 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments 0  
Other investments | Held at fair value through other comprehensive income | Level 3 | At Fair Value    
Disclosure of detailed information about financial instruments [line items]    
Other investments £ 59