CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net Income	$ 46,219	$ 78,719	$ 146,974	$ 194,303
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	516	(5,095)	939	(3,922)
Change in Unrealized Gains/Losses in Other Securities	160	149	194	144
Change in Funded Status of Pension, SERP and Other Postretirement Benefit Plans	1,759	422	3,166	1,357
Other Comprehensive Income/ (Loss)	2,435	(4,524)	4,299	(2,421)
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,441)	(3,373)	(2,870)
Comprehensive Income	46,774	72,754	147,900	189,012
The Connecticut Light And Power Company [Member]
Net Income	6,933	52,635	60,918	116,972
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	111	111	222	222
Change in Unrealized Gains/Losses in Other Securities	5	5	6	5
Other Comprehensive Income/ (Loss)	116	116	228	227
Comprehensive Income	7,049	52,751	61,146	117,199
Public Service Company Of New Hampshire [Member]
Net Income	21,232	21,665	42,494	49,129
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	291	(3,998)	581	(3,072)
Change in Unrealized Gains/Losses in Other Securities	9	8	11	8
Change in Funded Status of Pension, SERP and Other Postretirement Benefit Plans	4	0	4	0
Other Comprehensive Income/ (Loss)	304	(3,990)	596	(3,064)
Comprehensive Income	21,536	17,675	43,090	46,065
Western Massachusetts Electric Company [Member]
Net Income	11,138	8,171	25,324	18,137
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	84	(1,144)	169	(945)
Change in Unrealized Gains/Losses in Other Securities	2	2	2	2
Other Comprehensive Income/ (Loss)	86	(1,142)	171	(943)
Comprehensive Income	11,224	7,029	25,495	17,194
NSTAR Electric Company [Member]
Net Income	$ 45,482	$ 60,654	$ 49,422	$ 103,547