Derivative financial instruments - Net investment hedge (Details) - Net investment hedge € in Millions, ¥ in Millions, £ in Millions, $ in Millions, $ in Millions	12 Months Ended
Dec. 31, 2022 GBP (£) $ / £ AUD ($) € / £ JPY (¥) ¥ / £ $ / £ EUR (€) USD ($)	Dec. 31, 2021 GBP (£) $ / £ USD ($) $ / £ ¥ / £ AUD ($) JPY (¥) € / £ EUR (€)
Derivative financial instruments
Hedge ratio	1
Ineffectiveness	£ (1)	£ 2
Cross-currency swaps \| US dollar
Derivative financial instruments
Carrying amount		£ 2
Carrying amount	£ (105)
Nominal amount	1,728	596
Hedge ratio	1	1
Change in fair value of outstanding instrument	£ (109)	£ (16)
Change in fair value of hedged item	(108)	(18)
Ineffectiveness	£ (1)	£ 2
Weighted average foreign exchange rate for the year \| $ / £	1.250	1.296
Cross-currency swaps \| JPY
Derivative financial instruments
Carrying amount		£ 1
Nominal amount	1,925	1,250
Hedge ratio	1	1
Change in fair value of outstanding instrument		£ 1
Change in fair value of hedged item		£ 1
Weighted average foreign exchange rate for the year \| ¥ / £	137.071	134.326
Bonds \| Euro
Derivative financial instruments
Carrying amount	£ (510)	£ (463)
Nominal amount	577	552
Hedge ratio	1	1
Change in fair value of outstanding instrument	£ (22)	£ 28
Change in fair value of hedged item	£ (22)	£ 28
Weighted average foreign exchange rate for the year \| € / £	1.154	1.147
Term loan \| US dollar
Derivative financial instruments
Carrying amount	£ (579)
Nominal amount	700	0
Hedge ratio	1
Change in fair value of outstanding instrument	£ 60
Change in fair value of hedged item	£ 60
Weighted average foreign exchange rate for the year \| $ / £	1.152
Overdraft \| AUD
Derivative financial instruments
Carrying amount	£ (5)	£ (5)
Nominal amount	8	9
Hedge ratio	1	1
Weighted average foreign exchange rate for the year \| $ / £	1.819	1.857

The average exchange rate used by the entity. Exchange rate is the ratio of exchange for two currencies.

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The gain (loss) on the change in fair value of the hedged item used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

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The gain (loss) on the change in fair value of the hedging instrument used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

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The gain (loss) recognised in profit or loss on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness]

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The amount of a hedging instrument, recognised as an asset. [Refer: Hedging instruments [member]]

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The nominal amount of a hedging instrument. [Refer: Hedging instruments [member]]

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The hedge ratio for currencies.

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