v3.24.1.1.u2
Pensions and other post-retirement benefits - Disclosure of asset allocations (Details) - GBP (£)
£ in Millions
Mar. 31, 2024
Mar. 31, 2023
Mar. 31, 2022
UK | Pensions      
Disclosure of fair value of plan assets [line items]      
Equities £ 729 £ 654 £ 1,782
Property 679 883 1,124
Diversified alternatives 1,241 1,388 1,916
Buy-in/bulk annuity policies 2,060 2,126 2,784
Longevity swap (94) (88) (80)
Cash and cash equivalents 3 8 38
Other (including net current assets and liabilities) (5) 47 6
Fair value of plan assets 11,782 12,578 16,865
Repurchase agreements 2,700 3,400 6,100
Pension fund investments in employer issued securities 44 23 32
UK | Pensions | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 1,910 1,892 2,741
UK | Pensions | Government securities and liability-driven investments      
Disclosure of fair value of plan assets [line items]      
Debt instruments 5,259 5,668 6,554
UK | Pensions | Liability driven investment      
Disclosure of fair value of plan assets [line items]      
Debt instruments   4,906 5,857
UK | Pensions | Quoted      
Disclosure of fair value of plan assets [line items]      
Equities 576 475 1,458
Property 0 23 122
Diversified alternatives 669 708 1,334
Buy-in/bulk annuity policies 0 0 78
Longevity swap 0 0 0
Cash and cash equivalents 3 8 38
Other (including net current assets and liabilities) 0 59 16
Fair value of plan assets 3,158 3,927 6,573
UK | Pensions | Quoted | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 1,910 1,892 2,741
UK | Pensions | Quoted | Government securities and liability-driven investments      
Disclosure of fair value of plan assets [line items]      
Debt instruments 0 762 786
UK | Pensions | Unquoted      
Disclosure of fair value of plan assets [line items]      
Equities 153 179 324
Property 679 860 1,002
Diversified alternatives 572 680 582
Buy-in/bulk annuity policies 2,060 2,126 2,706
Longevity swap (94) (88) (80)
Cash and cash equivalents 0 0 0
Other (including net current assets and liabilities) (5) (12) (10)
Fair value of plan assets 8,624 8,651 10,292
Investments in forestry funds 288 304 283
UK | Pensions | Unquoted | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 0 0 0
UK | Pensions | Unquoted | Government securities and liability-driven investments      
Disclosure of fair value of plan assets [line items]      
Debt instruments 5,259 4,906 5,768
US | Pensions      
Disclosure of fair value of plan assets [line items]      
Equities 1,323 1,500 2,176
Property 237 299 295
Diversified alternatives 556 635 688
Cash and cash equivalents 9 16 31
Other (including net current assets and liabilities) 1 11 15
Fair value of plan assets 5,320 6,060 7,263
US | Pensions | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 2,390 2,675 3,008
US | Pensions | Government securities      
Disclosure of fair value of plan assets [line items]      
Debt instruments 804 924 1,050
US | Pensions | Quoted      
Disclosure of fair value of plan assets [line items]      
Equities 99 154 272
Property 0 0 0
Diversified alternatives 54 85 142
Cash and cash equivalents 9 16 31
Other (including net current assets and liabilities) 1 7 12
Fair value of plan assets 2,510 2,819 3,103
US | Pensions | Quoted | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 1,987 2,147 2,311
US | Pensions | Quoted | Government securities      
Disclosure of fair value of plan assets [line items]      
Debt instruments 360 410 335
US | Pensions | Unquoted      
Disclosure of fair value of plan assets [line items]      
Equities 1,224 1,346 1,904
Property 237 299 295
Diversified alternatives 502 550 546
Cash and cash equivalents 0 0 0
Other (including net current assets and liabilities) 0 4 3
Fair value of plan assets 2,810 3,241 4,160
US | Pensions | Unquoted | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 403 528 697
US | Pensions | Unquoted | Government securities      
Disclosure of fair value of plan assets [line items]      
Debt instruments 444 514 715
US | Other post-retirement benefits      
Disclosure of fair value of plan assets [line items]      
Equities 561 584 1,198
Diversified alternatives 101 109 264
Other (including net current assets and liabilities) 161 148 185
Fair value of plan assets 2,631 2,608 2,885
US | Other post-retirement benefits | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 1,397 1,334 725
US | Other post-retirement benefits | Government securities      
Disclosure of fair value of plan assets [line items]      
Debt instruments 411 433 513
US | Other post-retirement benefits | Quoted      
Disclosure of fair value of plan assets [line items]      
Equities 37 74 185
Diversified alternatives 92 100 144
Other (including net current assets and liabilities) 0 1 0
Fair value of plan assets 1,890 1,938 1,563
US | Other post-retirement benefits | Quoted | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 1,351 1,332 723
US | Other post-retirement benefits | Quoted | Government securities      
Disclosure of fair value of plan assets [line items]      
Debt instruments 410 431 511
US | Other post-retirement benefits | Unquoted      
Disclosure of fair value of plan assets [line items]      
Equities 524 510 1,013
Diversified alternatives 9 9 120
Other (including net current assets and liabilities) 161 147 185
Fair value of plan assets 741 670 1,322
US | Other post-retirement benefits | Unquoted | Corporate bonds      
Disclosure of fair value of plan assets [line items]      
Debt instruments 46 2 2
US | Other post-retirement benefits | Unquoted | Government securities      
Disclosure of fair value of plan assets [line items]      
Debt instruments £ 1 £ 2 £ 2