Effective Tax Rate Reconciliation, Percent, Tax Effect on Share-Based Payments

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Period of Graded Vesting Schedule Under Long-Term Incentive Program

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As of the balance sheet date, the number of shares into which expected to vest awards outstanding can be converted under the option plan.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

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

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- Definition

Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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EMPLOYEE BENEFITS - Share-Based Payments Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in incentive plan (up to) (in shares)	6,700,000
Shares available for issuance under incentive plan (in shares)	2,876,601	3,302,526
Shares outstanding (in shares)	379,258
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 62.99
Total unrecognized compensation expense	$ 19.3
Period for recognition	1 year 8 months 26 days
Tax effect on total share-based payments (in percentage)	26.00%
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 88.23	$ 67.91	$ 56.69
Shares outstanding (in shares)		439,293
Weighted average shares outstanding (in dollars per share)	$ 77.13	$ 63.06
Restricted stock units available (in shares)	265,020
Restricted stock unit fully vested (in shares)	294,960
Additional restricted stock unit expected to vest (in shares)	360,295
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 75.36	$ 68.33	$ 56.77
Shares outstanding (in shares)	404,698	427,894
Weighted average shares outstanding (in dollars per share)	$ 70.85	$ 60.38
Restricted stock units available (in shares)	233,426
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 55.75
Restricted stock unit fully vested (in shares)	43,107
The Connecticut Light and Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 3.6
Period for recognition	1 year 9 months
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 5.7
Period for recognition	1 year 9 months
Public Service Company of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 1.2
Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program	3 years
Board Members
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program	1 year