Net finance costs - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Finance Income And Costs [Line Items]
Tender offer	£ 1,824	£ 3,133
Tender offer accrued interest	15	43
Gains (losses) on change in fair value of derivatives	(90)	(599)	£ 473
Gain (loss) on repurchase of bonds	602	129
Transaction costs on repurchase of bonds	3	7
Interest related to adjusting tax payables	80	71	36
Losses on change in fair value of derivatives	19
Differences on exchange	(281)	(292)	431
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs
Disclosure Of Finance Income And Costs [Line Items]
Provision charged to net finance costs against non-current investments				£ 24
Provision reversal		4	17
Russia
Disclosure Of Finance Income And Costs [Line Items]
Differences on exchange			15
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Factory closure in switzerland
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables		(3)	3
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Netherlands
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables	8	16
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Brazil
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables	14
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Indonesia
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables	11
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Canada
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables	(25)
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Russia
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables		(2)
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | Interest on tax payables including FIIGLO
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables	61	60	£ 33
Adjusting items ​which ​have ​been ​adjusted ​within net finance costs | CCAA Protection
Disclosure Of Finance Income And Costs [Line Items]
Interest related to adjusting tax payables	11
Restricted cash
Disclosure Of Finance Income And Costs [Line Items]
Income on cash and cash equivalents	112	97
Derivatives
Disclosure Of Finance Income And Costs [Line Items]
Gains (losses) on change in fair value of derivatives	£ (9)	£ (151)