v3.24.1.1.u2
Revenue - Disclosure of disaggregation of revenue by primary geographical market and major service lines (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Mar. 31, 2022
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue £ 19,070 £ 20,835 £ 17,714
Total other revenue 780 824 735
Total revenue from continuing operations 19,850 21,659 18,449
UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 2,616 1,899 2,018
Total other revenue 79 47 10
Total revenue from continuing operations 2,695 1,946 2,028
UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,785 2,028 1,464
Total other revenue 5 5 4
Total revenue from continuing operations 1,790 2,033 1,468
UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,753 4,659 3,437
Total other revenue 0 0 0
Total revenue from continuing operations 3,753 4,659 3,437
New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,867 4,374 4,496
Total other revenue 81 53 54
Total revenue from continuing operations 3,948 4,427 4,550
New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 6,008 6,953 5,525
Total other revenue 86 41 36
Total revenue from continuing operations 6,094 6,994 5,561
National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,037 922 774
Total other revenue 295 361 250
Total revenue from continuing operations 1,332 1,283 1,024
Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4 0 0
Total other revenue 234 317 381
Total revenue from continuing operations 238 317 381
UK      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 9,033 9,385 7,565
Total other revenue 30 226 238
Total revenue from continuing operations 9,063 9,611 7,803
UK | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 2,616 1,899 2,018
Total other revenue 79 47 10
UK | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,785 2,028 1,464
Total other revenue 5 5 4
UK | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,753 4,659 3,437
Total other revenue 0 0 0
UK | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
UK | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
UK | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 878 799 646
Total other revenue (76) (31) (132)
UK | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1 0 0
Total other revenue 22 205 356
US      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 10,037 11,450 10,149
Total other revenue 750 598 497
Total revenue from continuing operations 10,787 12,048 10,646
US | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
US | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
US | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
US | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,867 4,374 4,496
Total other revenue 81 53 54
US | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 6,008 6,953 5,525
Total other revenue 86 41 36
US | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 159 123 128
Total other revenue 371 392 382
US | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3 0 0
Total other revenue 212 112 25
Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4,016 3,404 3,067
Transmission | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 2,591 1,868 1,983
Transmission | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Transmission | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue (10) 126 0
Transmission | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 73 52 52
Transmission | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 493 567 405
Transmission | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 869 791 627
Transmission | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 10,998 12,638 10,919
Distribution | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Distribution | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,712 1,951 1,375
Distribution | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Distribution | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,786 4,314 4,434
Distribution | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 5,500 6,373 5,110
Distribution | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Distribution | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,763 4,533 3,418
System Operator | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,763 4,533 3,418
System Operator | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Generation      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 360 394 373
Generation | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 360 394 373
Generation | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 293 260 310
Total other revenue 420 430 362
Other | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 25 31 35
Total other revenue 79 47 10
Other | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 73 77 89
Total other revenue 5 5 4
Other | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 19
Total other revenue 0 0 0
Other | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 8 8 10
Total other revenue 81 53 54
Other | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 15 13 10
Total other revenue 86 41 36
Other | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 168 131 147
Total other revenue (65) (33) (123)
Other | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4 0 0
Total other revenue £ 234 £ 317 £ 381