CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Income	$ 211,380	$ 209,508	$ 614,413	$ 356,482
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	509	516	1,539	1,455
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(38)	217	(810)	411
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,611	1,445	4,738	4,611
Other Comprehensive Income (Loss), Net of Tax, Total	2,082	2,178	5,467	6,477
Comprehensive Income Attributable to Noncontrolling Interests	(1,879)	(1,880)	(5,803)	(5,253)
Comprehensive Income	211,583	209,806	614,077	357,706
The Connecticut Light And Power Company [Member]
Net Income	66,323	74,886	219,188	135,804
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111	111	333	333
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(1)	8	(27)	14
Other Comprehensive Income (Loss), Net of Tax, Total	110	119	306	347
Comprehensive Income	66,433	75,005	219,494	136,151
NSTAR Electric Company [Member]
Net Income	107,009	106,762	213,162	156,184
Public Service Company Of New Hampshire [Member]
Net Income	28,353	27,232	84,543	69,726
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	290	291	872	872
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2)	13	(47)	24
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	(2)	(3)	2
Other Comprehensive Income (Loss), Net of Tax, Total	288	302	822	898
Comprehensive Income	28,641	27,534	85,365	70,624
Western Massachusetts Electric Company [Member]
Net Income	15,025	14,084	50,041	39,408
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	85	84	254	253
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	0	2	(8)	4
Other Comprehensive Income (Loss), Net of Tax, Total	85	86	246	257
Comprehensive Income	$ 15,110	$ 14,170	$ 50,287	$ 39,665