Subsidiary undertakings, joint ventures and associates - Disclosure of interests in subsidiaries (Details) |
12 Months Ended |
|---|---|
Mar. 31, 2024 | |
| Sheet Road Management Company Limited | |
| Disclosure of subsidiaries [line items] | |
| Proportion of ownership interest in subsidiary | 51.00% |
| Warwick Technology Park Management Company (No 2) Limited | |
| Disclosure of subsidiaries [line items] | |
| Proportion of ownership interest in subsidiary | 60.56% |
| New England Hydro Finance Company, Inc. | |
| Disclosure of subsidiaries [line items] | |
| Proportion of ownership interest in subsidiary | 53.704% |
| New England Hydro-Transmission Corporation | |
| Disclosure of subsidiaries [line items] | |
| Proportion of ownership interest in subsidiary | 53.704% |
| New England Hydro-Transmission Electric Company Inc. | |
| Disclosure of subsidiaries [line items] | |
| Proportion of ownership interest in subsidiary | 53.704% |
| Vermont Green Line Devco, LLC | |
| Disclosure of subsidiaries [line items] | |
| Proportion of ownership interest in subsidiary | 90.00% |