v3.26.1
Retirement benefit obligations - Plan assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of fair value of plan assets [line items]      
Market value of assets $ 640 $ 609 $ 942
Retirement benefit expense 94 95 95
Defined contributions plan expenses 81 89 84
Defined benefit plan expenses 13 6 11
Outstanding payments 0 0 0
United Kingdom      
Disclosure of fair value of plan assets [line items]      
Market value of assets 478 459 518
Defined benefit plan expenses 0 0 0
United Kingdom | Assets with a quoted market price      
Disclosure of fair value of plan assets [line items]      
Cash and cash equivalents 56 56 61
Other bonds 8 7  
Market value of assets 64 63 61
United Kingdom | Other assets      
Disclosure of fair value of plan assets [line items]      
Insurance contract 414 396 457
United States of America      
Disclosure of fair value of plan assets [line items]      
Defined benefit plan expenses 0 0 0
United States of America | Assets with a quoted market price      
Disclosure of fair value of plan assets [line items]      
Cash and cash equivalents     267
Market value of assets     267
Other Countries      
Disclosure of fair value of plan assets [line items]      
Market value of assets 162 150 157
Other Countries | Assets with a quoted market price      
Disclosure of fair value of plan assets [line items]      
Cash and cash equivalents 8 2 7
Equity securities 56 56 50
Government bonds - fixed interest 6 6 5
Corporate bonds 13 12 10
Insurance contract 19 18 23
Property 24 25 28
Other quoted securities 14 11 10
Market value of assets 140 130 133
Other Countries | Other assets      
Disclosure of fair value of plan assets [line items]      
Insurance contract $ 22 $ 20 $ 24