v3.26.1
Pensions and other post-retirement benefits - Disclosure of amounts recognised in the statement of financial position (Details) - GBP (£)
£ in Millions
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Disclosure of defined benefit plans [line items]      
Other post-employment liabilities £ (44) £ (47)  
Net defined benefit liability (asset) including restrictions on assets recognized 2,391 1,993 £ 1,814
Restrictions on asset recognised (244) (77)  
Net defined benefit asset 2,147 1,916  
Liabilities (360) (573)  
Assets 2,507 2,489  
Funded obligations      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (15,098) (16,154)  
Fair value of plan assets 17,780 18,441  
Funding surplus/(deficit) 2,682 2,287  
Unfunded obligations      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (247) (247)  
Pensions | UK      
Disclosure of defined benefit plans [line items]      
Fair value of plan assets 10,441 10,603 11,782
Other post-employment liabilities 0 0  
Net defined benefit liability (asset) including restrictions on assets recognized 1,071 1,128 1,261
Restrictions on asset recognised 0 0  
Net defined benefit asset 1,071 1,128  
Liabilities (51) (51)  
Assets 1,122 1,179  
Pensions | US      
Disclosure of defined benefit plans [line items]      
Fair value of plan assets 4,608 5,180 5,320
Other post-employment liabilities 0 0  
Net defined benefit liability (asset) including restrictions on assets recognized 413 476 408
Restrictions on asset recognised 0 0  
Net defined benefit asset 413 476  
Liabilities (186) (196)  
Assets 599 672  
Pensions | Funded obligations | UK      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (9,319) (9,424)  
Fair value of plan assets 10,441 10,603  
Funding surplus/(deficit) 1,122 1,179  
Pensions | Funded obligations | US      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (4,009) (4,508)  
Fair value of plan assets 4,608 5,180  
Funding surplus/(deficit) 599 672  
Pensions | Unfunded obligations | UK      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (51) (51)  
Pensions | Unfunded obligations | US      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (186) (196)  
Other post-retirement benefits | US      
Disclosure of defined benefit plans [line items]      
Fair value of plan assets 2,731 2,658 2,631
Other post-employment liabilities (44) (47)  
Net defined benefit liability (asset) including restrictions on assets recognized 907 389 £ 145
Restrictions on asset recognised (244) (77)  
Net defined benefit asset 663 312  
Liabilities (123) (326)  
Assets 786 638  
Other post-retirement benefits | Funded obligations | US      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations (1,770) (2,222)  
Fair value of plan assets 2,731 2,658  
Funding surplus/(deficit) 961 436  
Other post-retirement benefits | Unfunded obligations | US      
Disclosure of defined benefit plans [line items]      
Present value of funded obligations £ (10) £ 0