CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net Income	$ 100,755	$ 115,584
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	423	1,173
Change in Unrealized Gains/Losses in Other Securities	34	(5)
Change in Funded Status of Pension, SERP and Other Postretirement Benefit Plans	1,407	935
Other Comprehensive Income/ (Loss)	1,864	2,103
Comprehensive Income Attributable to Noncontrolling Interests	(1,493)	(1,429)
Comprehensive Income	101,126	116,258
The Connecticut Light And Power Company [Member]
Net Income	53,985	64,337
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	111	111
Change in Unrealized Gains/Losses in Other Securities	1	0
Other Comprehensive Income/ (Loss)	112,000	111,000
Comprehensive Income	54,097	64,448
Public Service Company Of New Hampshire [Member]
Net Income	21,262	27,464
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	290	926
Change in Unrealized Gains/Losses in Other Securities	2	0
Other Comprehensive Income/ (Loss)	292,000	926,000
Comprehensive Income	21,554	28,390
Western Massachusetts Electric Company [Member]
Net Income	14,186	9,966
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	85	199
Comprehensive Income	$ 14,271	$ 10,165