v3.25.4
Retirement Benefit and Other Post-retirement Obligations - Summary of Remaining Average Life Expectancy in Years of Pensioner Retiring at Age 65 (Detail)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
UK [member]      
Disclosure of defined benefit plans [line items]      
Male 21 years 6 months 21 years 3 months 18 days 21 years 9 months 18 days
Female 24 years 6 months 24 years 6 months 24 years 1 month 6 days
Male 23 years 1 month 6 days 22 years 10 months 24 days 23 years 4 months 24 days
Female 26 years 2 months 12 days 26 years 2 months 12 days 25 years 9 months 18 days
US [member]      
Disclosure of defined benefit plans [line items]      
Male 20 years 9 months 18 days 20 years 8 months 12 days 20 years 8 months 12 days
Female 22 years 9 months 18 days 22 years 8 months 12 days 22 years 7 months 6 days
Male 22 years 3 months 18 days 22 years 2 months 12 days 22 years 2 months 12 days
Female 24 years 2 months 12 days 24 years 1 month 6 days 24 years 1 month 6 days