Long-Term Contractual Arrangements (Details) (Public Service Company of New Hampshire [Member], Renewable Energy Contracts [Member], USD $) In Millions	Sep. 30, 2011
Public Service Company of New Hampshire [Member] \| Renewable Energy Contracts [Member]
Unrecorded Unconditional Purchase Obligation [Abstract]
Unrecorded Unconditional Purchase Obligation, Due within One Year	$ 5.1
Unrecorded Unconditional Purchase Obligation, Due within Two Years	5.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	59.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	60.7
Unrecorded Unconditional Purchase Obligation, Due within Five Years	70.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,263.1
Unrecorded Unconditional Purchase Obligation	$ 1,464.8

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The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid in more than four and within five years from the balance sheet date.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 7

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25336-109308

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid within one year of the balance sheet date.

+ References

+ Details

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid in more than three and within four years from the balance sheet date.

+ References

+ Details

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid in more than one and within two years from the balance sheet date.

+ References

+ Details

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid in more than two and within three years from the balance sheet date.

+ References

+ Details

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- Definition

The amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation as of the balance sheet date.

+ References

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- Definition

The remaining amount of the fixed and determinable portion of an unrecorded unconditional purchase obligation to be paid after five years from the balance sheet date.

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