CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net Income	$ 209,508	$ 91,431	$ 356,482	$ 285,734
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	516	(10,678)	1,455	(14,600)
Change in Unrealized Gains/Losses in Other Securities	217	280	411	424
Change in Funded Status of Pension, SERP and Other Postretirement Benefit Plans	1,445	975	4,611	2,332
Other Comprehensive Income/ (Loss)	2,178	(9,423)	6,477	(11,844)
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,470)	(5,253)	(4,340)
Comprehensive Income	209,806	80,538	357,706	269,550
The Connecticut Light And Power Company [Member]
Net Income	74,886	66,528	135,804	183,500
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	111	111	333	333
Change in Unrealized Gains/Losses in Other Securities	8	10	14	15
Other Comprehensive Income/ (Loss)	119	121	347	348
Total Comprehensive Income	75,005	66,649	136,151	183,848
Public Service Company Of New Hampshire [Member]
Net Income	27,232	25,634	69,726	74,763
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	291	(7,478)	872	(10,550)
Change in Unrealized Gains/Losses in Other Securities	13	16	24	24
Change in Funded Status of Pension, SERP and Other Postretirement Benefit Plans	(2)	0	2	0
Other Comprehensive Income/ (Loss)	302	(7,462)	898	(10,526)
Total Comprehensive Income	27,534	18,172	70,624	64,237
Western Massachusetts Electric Company [Member]
Net Income	14,084	8,434	39,408	26,571
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Qualified Cash Flow Hedging Instruments	84	(3,248)	253	(4,193)
Change in Unrealized Gains/Losses in Other Securities	2	2	4	4
Other Comprehensive Income/ (Loss)	86	(3,246)	257	(4,189)
Total Comprehensive Income	14,170	5,188	39,665	22,382
NSTAR Electric Company [Member]
Net Income	$ 106,762	$ 99,820	$ 156,184	$ 203,367