v3.26.1
BASIS OF PREPARATION AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
£ / shares in Units, £ in Millions, $ in Billions
6 Months Ended
Jun. 30, 2026
GBP (£)
£ / shares
Jun. 30, 2026
USD ($)
Dec. 31, 2025
GBP (£)
£ / shares
Jun. 30, 2025
GBP (£)
£ / shares
Dec. 31, 2024
GBP (£)
Disclosure of information about consolidated structured entities [line items]          
Number of major product categories 6        
Cash and cash equivalents net of bank overdrafts | £ £ 805   £ 1,303 £ 626 £ 2,207
Euro commercial paper          
Disclosure of information about consolidated structured entities [line items]          
Notional amount | £ £ 2,000        
US Dollar commercial paper          
Disclosure of information about consolidated structured entities [line items]          
Notional amount | $   $ 10.0      
Ordinary shares          
Disclosure of information about consolidated structured entities [line items]          
Nominal value per share | £ / shares £ 0.01   £ 0.01 £ 0.01  
August 2029          
Disclosure of information about consolidated structured entities [line items]          
Undrawn credit facilities | $   $ 1,750.0