Post balance sheet events (Details) - Major loan agreement - National Grid North America Inc. - $864.9 million, 10-year loan $ in Millions	Apr. 13, 2026 USD ($)
Disclosure of non-adjusting events after reporting period [line items]
Borrowings, term	10 years
Notional amount	$ 864.9

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
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-IssueDate 2025-01-01
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-URIDate 2025-03-27

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Period Type:	instant