Other Income, Net (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Component Of Other Income Nonoperating [Line Items]
Public Utilities Allowance For Funds Used During Construction Additions	$ 7.1	$ 6.8	$ 22.5
The Connecticut Light And Power Company [Member]
Component Of Other Income Nonoperating [Line Items]
Public Utilities Allowance For Funds Used During Construction Additions	2.9	1.9	6.0
Public Service Company Of New Hampshire [Member]
Component Of Other Income Nonoperating [Line Items]
Public Utilities Allowance For Funds Used During Construction Additions	0.2	1.9	13.2
Western Massachusetts Electric Company [Member]
Component Of Other Income Nonoperating [Line Items]
Public Utilities Allowance For Funds Used During Construction Additions	$ 1.0	$ 1.0	$ 1.0