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Share-based payments - Summary of Information about Awards Granted (Detail)
12 Months Ended
Dec. 31, 2025
yr
£ / shares
Dec. 31, 2024
yr
£ / shares
Dec. 31, 2023
yr
£ / shares
APP/DAP      
Information regarding option pricing models and assumptions used for grants during the year [line items]      
Weighted average share price (pence) (in dollar per share) | £ / shares £ 94.201 £ 84.818 £ 55.717
Term (years) | yr 2.9 2.2 2.3
LTIP/DAP      
Information regarding option pricing models and assumptions used for grants during the year [line items]      
Weighted average share price (pence) (in dollar per share) | £ / shares £ 92.50 £ 79.40 £ 53.18
Expected dividend yield 1.84% 2.12%  
Risk-free interest rate 3.88% 4.20% 3.85%
Volatility 21.00% 26.00%  
Term (years) | yr 2.8 3.0 3.0
LTIP/DAP | Minimum      
Information regarding option pricing models and assumptions used for grants during the year [line items]      
Expected dividend yield     2.52%
Volatility     29.00%
LTIP/DAP | Maximum      
Information regarding option pricing models and assumptions used for grants during the year [line items]      
Expected dividend yield     2.77%
Volatility     30.00%