Derivative financial instruments - The expected notional values of current hedging instruments in future years (Details) - Derivatives designated as fair value hedges - £ / shares £ / shares in Millions	Dec. 31, 2022	Dec. 31, 2021
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	80,108	58,820
Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	67,613	51,219
- Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	12,495	7,601
2022 | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	67,613
2022 | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	12,495
Later than one year and not later than two years [member] | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	63,902
Later than one year and not later than two years [member] | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	12,064
Later than two years and not later than three years [member] | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	54,595
Later than two years and not later than three years [member] | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	9,873
2025 | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	47,000
2025 | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	8,824
2026 | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	40,170
2026 | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	7,477
2027 | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	28,497
2027 | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	7,449
2028 and later | Interest rate risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	26,131
2028 and later | - Inflation risk
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]
Nominal amount	6,779