The amount of an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration (or the amount is due) from the customer.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The amount of revenue from performance obligations satisfied (or partially satisfied) in previous periods. [Refer: Performance obligations [member]; Revenue from contracts with customers]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of the transaction price allocated to the performance obligations that are unsatisfied (or partially unsatisfied) as of the end of the reporting period. The transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). [Refer: Performance obligations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The useful life, measured as period of time, used for property, plant and equipment. [Refer: Property, plant and equipment]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Revenue, Remaining Performance Obligation, Expected Timing Of Satisfaction, Period

+ References

No definition available.

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Revenue - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
Revenue - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contract liabilities	£ 2,246	£ 2,006	£ 1,472
Future revenues in relation to unfulfilled performance obligations	£ 6,100	5,000	5,200
Remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue from performance obligations satisfied or partially satisfied in previous periods	£ 0	0	0
National Grid Grain LNG Limited
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 3,800	2,700	3,000
Connections \| Weighted average
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	32 years
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,900	£ 1,800	£ 1,700
Remaining performance obligation, expected timing of satisfaction, period	24 years
UK Electricity Transmission \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	40 years
UK Electricity Distribution \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	69 years
New England \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years
New York \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years