CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net Income	$ 229,968	$ 100,755
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	516	423
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(181)	34
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,621	1,407
Other Comprehensive Income (Loss), Net of Tax, Total	1,956	1,864
Comprehensive Income Attributable to Noncontrolling Interests	(1,879)	(1,493)
Comprehensive Income	230,045	101,126
The Connecticut Light And Power Company [Member]
Net Income	85,008	53,985
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111	111
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(6)	1
Other Comprehensive Income (Loss), Net of Tax, Total	105	112
Comprehensive Income	85,113	54,097
Public Service Company Of New Hampshire [Member]
Net Income	28,996	21,262
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	291	290
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(11)	2
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(3)
Other Comprehensive Income (Loss), Net of Tax, Total	277	292
Comprehensive Income	29,273	21,554
Western Massachusetts Electric Company [Member]
Net Income	18,603	14,186
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	85	85
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2)	0
Other Comprehensive Income (Loss), Net of Tax, Total	83	85
Comprehensive Income	18,686	14,271
NSTAR Electric Company [Member]
Net Income	$ 48,122	$ 3,940