v3.24.1.1.u2
Financial risk management - Disclosure of nature and extent of risks arising from financial instruments (Details) - Currency risk - GBP (£)
£ in Millions
Mar. 31, 2024
Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic £ (43,607) £ (40,973)
Cash and cash equivalents    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 559 163
Financial investments    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 3,699 2,605
Borrowings    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (47,072) (42,985)
Pre-derivative position    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (42,814) (40,217)
Derivative effect    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (793) (756)
Trade and other receivables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 2,158 2,329
Trade and other payables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (3,715) (4,253)
Other non-current liabilities    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (458) (416)
GBP    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (21,684) (20,097)
GBP | Cash and cash equivalents    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 402 96
GBP | Financial investments    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 1,514 1,031
GBP | Borrowings    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (14,498) (14,473)
GBP | Pre-derivative position    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (12,582) (13,346)
GBP | Derivative effect    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (9,102) (6,751)
GBP | Trade and other receivables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 280 448
GBP | Trade and other payables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (1,330) (1,624)
GBP | Other non-current liabilities    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (169) (147)
Euro    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 1,040 (298)
Euro | Cash and cash equivalents    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 14
Euro | Financial investments    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Euro | Borrowings    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (11,936) (11,045)
Euro | Pre-derivative position    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (11,936) (11,031)
Euro | Derivative effect    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 12,976 10,733
Euro | Trade and other receivables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Euro | Trade and other payables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Euro | Other non-current liabilities    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
USD    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (23,221) (20,590)
USD | Cash and cash equivalents    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 157 53
USD | Financial investments    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 2,185 1,574
USD | Borrowings    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (18,938) (15,741)
USD | Pre-derivative position    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (16,596) (14,114)
USD | Derivative effect    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (6,625) (6,476)
USD | Trade and other receivables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 1,878 1,881
USD | Trade and other payables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (2,385) (2,629)
USD | Other non-current liabilities    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (289) (269)
Other    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 258 12
Other | Cash and cash equivalents    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Other | Financial investments    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Other | Borrowings    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (1,700) (1,726)
Other | Pre-derivative position    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic (1,700) (1,726)
Other | Derivative effect    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 1,958 1,738
Other | Trade and other receivables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Other | Trade and other payables    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Other | Other non-current liabilities    
Disclosure of detailed information about financial instruments [line items]    
Risk exposure associated with instruments sharing characteristic £ 0 £ 0