Restricted Cash and Other Deposits (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Special Deposits [Line Items]
Restricted Cash And Cash Equivalents	$ 3.8	$ 3.3
Cash Collateral Deposited	12.8	14.6
The Connecticut Light And Power Company [Member]
Special Deposits [Line Items]
Restricted Cash And Cash Equivalents	1.4	1.3
Public Service Company Of New Hampshire [Member]
Special Deposits [Line Items]
Restricted Cash And Cash Equivalents	$ 1.7	$ 1.7

- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

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