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COMMITMENTS AND CONTINGENCIES - Environmental Sites and Related Reserves (Details) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2023 USD ($) site	Sep. 30, 2022 site	Dec. 31, 2022 USD ($)
Site Contingency [Line Items]
Number of Sites | site	59	59
Reserve | $	$ 121.2		$ 122.6
CL&P
Site Contingency [Line Items]
Number of Sites | site	13	13
Reserve | $	$ 13.6		13.9
NSTAR Electric
Site Contingency [Line Items]
Number of Sites | site	10	10
Reserve | $	$ 3.4		3.4
PSNH
Site Contingency [Line Items]
Number of Sites | site	8	8
Reserve | $	$ 6.1		$ 6.1

X

- Definition

Number of environmental sites by NU Entity in the remediation or long-term monitoring phase

+ References

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- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

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