The allowed distribution return on equity resulting from the final decision issued by the State of Connecticut's Department of Public Utility Control.

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The amount of revenue requirements approved by the State of Connecticut's Department of Public Utility Control for the current year, for the peaking generation plant in Devon.

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The amount of revenue requirements approved by the State of Connecticut's Department of Public Utility Control for the current year, for the peaking generation plant in Middletown.

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The entity's approved return on equity, as per the relevant regulatory commission.

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The ratio of debt to total capitalization (debt plus equity) resulting from the final decision issued by the State of Connecticut's Department of Public Utility Control.

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The ratio of equity to total capitalization (debt plus equity) resulting from the final decision issued by the State of Connecticut's Department of Public Utility Control.

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The cumulative amount of deposits made by the entity, through the balance sheet date, in projects to improve regional energy reliability.

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The current base return on equity (ROE) on transmission investments, as approved by the Federal Energy Regulatory Commission (the FERC).

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The amount of decoupling charge approved by the State of Connecticut's Department of Public Utility Control as of the date specified, which is to be recovered from ratepayers over a twelve month period commencing in October 2010.

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The duration (in years) of the rate plan approved by the Massachusetts Department of Public Utilities.

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The duration of the pilot program (in years) provided by the State of Connecticut's Department of Public Utility Control, for full decoupling of distribution revenues from sales.

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The expected amount of investment for ownership of specific transmission assets as they are placed in service, based on previously projected costs.

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The face amount of secured medium-term notes approved for issuance by PURA.

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Amount of long-term debt which was issued for Southern Connecticut Gas.

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- Definition

The capitalized portion of the cost to repair Tropical Storm Irene damage and restore electrical service.

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The maximum maturity (in years) of secured medium-term notes approved for issuance by PURA.

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The minimum maturity (in years) of secured medium-term notes approved for issuance by PURA.

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The maximum fixed coupon rate of secured medium-term notes approved for issuance by PURA.

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The maximum period over which the entity expects to make remaining investments.

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The minimum amount of investment for ownership of specific transmission assets as they are placed in service.

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The minimum period over which the entity expects to make remaining investments.

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Total number of customers in the entity's service area.

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Number of customers who were left without power due to Tropical Storm Irene.

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The number of inter-related transmission projects to improve regional energy reliability.

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The number of inter-related transmission projects to improve regional energy reliability, with portions sited in Connecticut.

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The number of new peaking generation plants to help address the need for power generation during the heaviest load periods.

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- Definition

The percentage of ownership in a joint venture project selected to build and operate new peaking generation plants.

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- Definition

The amount of pension and earnings sharing over-recovery credit approved by the State of Connecticut's Department of Public Utility Control as of the date specified, which is to be refunded to ratepayers over a twelve month period commencing in October 2010.

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The percentage of earnings over the allowed twelve month level, that is retained by the entity, as per the earnings sharing mechanism structure.

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The percentage of earnings over the allowed twelve month level, that is returned to customers, as per the earnings sharing mechanism structure.

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- Definition

The percentage of standard service customers with wholesale power supply agreements in place, for the second twelve month period following the end of the current fiscal year.

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- Definition

The percentage of transmission construction work in progress costs on which recovery of return is authorized, as per the Order issued by FERC.

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The allowed distribution return on equity prior to the final decision issued by the State of Connecticut's Department of Public Utility Control.

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The ratio of debt to total capitalization (debt plus equity) prior to the final decision issued by the State of Connecticut's Department of Public Utility Control.

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The ratio of equity to total capitalization (debt plus equity) prior to the final decision issued by the State of Connecticut's Department of Public Utility Control.

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Amount which may be refinanced with the proceeds of the sales of the MTN's - Southern Connecticut Gas

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Balance Type:	credit
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The amount of recoverable carrying charges to be recorded.

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The reduced base return on equity (ROE) sought by the complainants.

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The threshold percentage of another entity's costs for the Connecticut portions of the projects, by which the entity has the right to invest up to this amount, given that it is greater than the defined minimum amount.

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

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-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959

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-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44D

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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REGULATORY PROCEEDINGS (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011	Aug. 31, 2011	Sep. 01, 2010	Dec. 31, 2009
Tropical Storm Irene [Abstract]
Capitalized portion of cost to repair damage and restore electrical service	$ 4.0
Rates [Abstract]
Ownership percentage in joint venture (in hundredths)	50.00%
Tropical Storm Irene [Member] \| UI [Member]
Tropical Storm Irene [Abstract]
Number of customers without power due to Tropical Storm Irene (in customers)	158,000
Total number of customers (in customers)	325,000
Cost to repair damage and restore electrical service	20.0
United Illuminating Company (UI) [Member]
Electric Distribution and Transmission - Rates [Abstract]
Allowed distribution return on equity (in hundredths)				8.75%
Previously approved allowed distribution return on equity (in hundredths)				9.75%
Capital structure, equity ratio (in hundredths)				50.00%
Capital structure, debt ratio (in hundredths)				50.00%
Previously approved capital structure equity ratio (in hundredths)				48.00%
Previously approved capital structure debt ratio (in hundredths)				52.00%
Percentage of earnings returned to customers (in hundredths)				50.00%
Percentage of earnings retained by the entity (in hundredths)				50.00%
Duration of pilot program (in years)	2
Decoupling charge approved by PURA		1.4	1.6
Pension and earnings sharing over-recovery credit approved by the PURA			3.6
Power Supply Arrangements [Abstract]
Percentage of standard service customers with wholesale power supply agreements in place for 2013 (in hundredths)	20.00%
Collateral required to be posted if the entity's credit rating declined two ratings to fall below investment grade	12.3
Transmission Return on Equity (ROE) [Abstract]
Current base return on equity on transmission investments (in hundredths)	11.14%
Reduced base ROE sought by complainants (in hundredths)	9.20%
New England East-West Solution [Abstract]
Number of inter-related transmission projects	4
Number of inter-related transmission projects with portions sited in Connecticut	3
Percentage of transmission construction work in progress costs of which recovery of return in authorized (in hundredths)	100.00%
Minimum amount of entity's investment for ownership of specific transmission assets	60
Threshold percentage of CL&P's costs for the Connecticut portions of projects (in hundredths)	8.40%
Expected amount of investment	60
Cumulative amount of deposits	8.9
Minimum period over which remaining investments are expected to be made (in years)	3
Maximum period over which remaining investments are expected to be made (in years)	5
Rates [Abstract]
Ownership percentage in joint venture (in hundredths)	50.00%
Number of new peaking generation plants	2
Approved 2011 revenue requirements for GenConn Devon facility	36.8
Approved 2011 revenue requirements for the GenConn Middletown facility	22.6
Connecticut Natural Gas Corporation (CNG) [Member]
Rates [Abstract]
Approved return on equity (in hundredths)	9.41%
Recoverable carrying charges	2.2
The Southern Connecticut Gas Company (SCG) [Member]
Rates [Abstract]
Approved return on equity (in hundredths)	9.36%
Recoverable carrying charges	2.2
Approval for issuance of Debt [Abstract]
Face amount of secured medium-term notes approved for issuance	50
Maximum fixed coupon rate (in hundredths)	7.00%
Maturity of debt approved for issuance, minimum (in years)	1Y
Maturity of debt approved for issuance, maximum (in years)	40Y
Principal amount of maturing existing debt - Southern Connecticut Gas	30
Issued long term debt Southern Connecticut Gas	$ 50
The Berkshire Gas Company [Member]
Rates [Abstract]
Approved return on equity (in hundredths)	10.50%
Duration of approved rate plan (in years)	10Y