Other Taxes (Details) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Excise And Sales Taxes	$ 32.0	$ 33.1	$ 70.7	$ 72.0
The Connecticut Light and Power Company [Member]
Excise And Sales Taxes	$ 28.8	$ 30.2	$ 60.2	$ 62.2

The amount of excise and sales taxes included in sales and revenues, which are then deducted as a cost of sales. Includes excise taxes, which are applied to specific types of transactions or items (such as gasoline or alcohol); and sales, use and value added taxes, which are applied to a broad class of revenue-producing transactions involving a wide range of goods and services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 1
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 06-3
-Paragraph 4

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration