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

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- Definition

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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Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to excess tax benefit for share-based compensation cost.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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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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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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SHARE-BASED PAYMENTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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)	3,720,650	2,445,110
Shares outstanding (in shares)	424,119
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 56.72
Total unrecognized compensation expense	$ 22.3
Tax effect on total share-based payments (in percentage)	25.00%
Excess tax benefit	$ 1.5	$ 2.9	$ 19.1
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 56.69	$ 55.97	$ 54.67
Shares outstanding (in shares)		388,269
Weighted average shares outstanding (in dollars per share)	$ 56.57	$ 56.15
Restricted stock units available (in shares)	216,572
Restricted stock unit fully vested (in shares)	358,246
Additional restricted stock unit expected to vest (in shares)	402,913
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 56.77	$ 55.70	$ 53.64
Shares outstanding (in shares)	366,995	331,207
Weighted average shares outstanding (in dollars per share)	$ 56.17	$ 55.79
Restricted stock units available (in shares)	131,349
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 56.08
Restricted stock unit fully vested (in shares)	132,569
The Connecticut Light And Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 8.1
Period for recognition (in years)	1 year 8 months 23 days
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 8.0
Period for recognition (in years)	1 year 8 months 19 days
Public Service Company Of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 2.8
Period for recognition (in years)	1 year 8 months 19 days
Eversource
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition (in years)	1 year 8 months 23 days
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