Restricted Cash and Other Deposits (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Special Deposits [Line Items]
Rate Reduction Bond Deposits		$ 69.4
Restricted Cash And Cash Equivalents	1.7	3.3
Cash Collateral Deposited	17.9	14.6
The Connecticut Light And Power Company [Member]
Special Deposits [Line Items]
Restricted Cash And Cash Equivalents	1.4	1.3
NSTAR Electric Company [Member]
Special Deposits [Line Items]
Rate Reduction Bond Deposits		42.2
Cash Collateral Deposited	9.0
Public Service Company Of New Hampshire [Member]
Special Deposits [Line Items]
Rate Reduction Bond Deposits		22.0
Restricted Cash And Cash Equivalents		1.7
Western Massachusetts Electric Company [Member]
Special Deposits [Line Items]
Rate Reduction Bond Deposits		$ 5.1