Other Income, Net (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Component Of Other Income Nonoperating [Line Items]
Other Income/(Loss), Net	$ 1,806	$ 7,334	$ 10,580	$ 17,647
The Connecticut Light And Power Company [Member]
Component Of Other Income Nonoperating [Line Items]
Other Income/(Loss), Net	447	2,058	5,747	6,663
Public Service Company Of New Hampshire [Member]
Component Of Other Income Nonoperating [Line Items]
Other Income/(Loss), Net	549	4,361	2,590	8,820
Western Massachusetts Electric Company [Member]
Component Of Other Income Nonoperating [Line Items]
Other Income/(Loss), Net	$ 188	$ 242	$ 1,280	$ 981