CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net Income	$ 173,064	$ 46,219	$ 403,032	$ 146,974
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	514	516	1,030	939
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(591)	160	(772)	194
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,506	1,759	3,127	3,166
Other Comprehensive Income (Loss), Net of Tax, Total	1,429	2,435	3,385	4,299
Comprehensive Income Attributable to Noncontrolling Interests	(2,043)	(1,880)	(3,922)	(3,373)
Comprehensive Income	172,450	46,774	402,495	147,900
The Connecticut Light And Power Company [Member]
Net Income	67,857	6,933	152,865	60,918
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111	111	222	222
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(20)	5	(26)	6
Other Comprehensive Income (Loss), Net of Tax, Total	91	116	196	228
Comprehensive Income	67,948	7,049	153,061	61,146
NSTAR Electric Company [Member]
Net Income	58,031	45,482	106,153	49,422
Public Service Company Of New Hampshire [Member]
Net Income	27,194	21,232	56,189	42,494
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	291	291	582	581
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(34)	9	(45)	11
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	4	(3)	4
Other Comprehensive Income (Loss), Net of Tax, Total	257	304	534	596
Comprehensive Income	27,451	21,536	56,723	43,090
Western Massachusetts Electric Company [Member]
Net Income	16,414	11,138	35,016	25,324
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	84	84	169	169
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(6)	2	(8)	2
Other Comprehensive Income (Loss), Net of Tax, Total	78	86	161	171
Comprehensive Income	$ 16,492	$ 11,224	$ 35,177	$ 25,495