CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net Income	$ 400,513	$ 394,107	$ 335,592
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	(14,177)	200	200
Change in Unrealized Gains/Losses in Other Securities	506	402	(976)
Change in Funded Status of Pension, SERP and Other Postretirement Benefit Plans	(13,645)	(505)	(5,426)
Other Comprehensive Income/ (Loss)	(27,316)	97	(6,202)
Comprehensive Income Attributable to Noncontrolling Interests	(5,820)	(6,158)	(5,559)
Comprehensive Income	367,377	388,046	323,831
The Connecticut Light And Power Company [Member]
Net Income	250,164	244,143	216,316
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	445	444	445
Change in Unrealized Gains/Losses in Other Securities	17	14	(30)
Other Comprehensive Income/ (Loss)	462	458	415
Comprehensive Income	250,626	244,601	216,731
Public Service Company Of New Hampshire [Member]
Net Income	100,267	90,067	65,570
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	(10,260)	87	87
Change in Unrealized Gains/Losses in Other Securities	29	24	(50)
Other Comprehensive Income/ (Loss)	(10,231)	111	37
Comprehensive Income	90,036	90,178	65,607
Western Massachusetts Electric Company [Member]
Net Income	43,054	23,090	26,196
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	(4,108)	(79)	(79)
Change in Unrealized Gains/Losses in Other Securities	5	4	(119)
Other Comprehensive Income/ (Loss)	(4,103)	(75)	(198)
Comprehensive Income	$ 38,951	$ 23,015	$ 25,998