CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net Income	$ 267,199	$ 237,799	$ 718,762	$ 702,319
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	534	526	1,602	1,544
Changes in Unrealized Gains/(Losses) on Marketable Securities	946	(2,803)	2,271	(3,919)
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(1,733)	764	(2,646)	2,838
Net OCI	(253)	(1,513)	1,227	463
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,879)	(5,639)	(5,639)
Comprehensive Income Attributable to Common Shareholders	265,066	234,407	714,350	697,143
The Connecticut Light And Power Company [Member]
Net Income	86,632	80,188	256,553	228,192
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	111	111	333	333
Changes in Unrealized Gains/(Losses) on Marketable Securities	33	(98)	78	(137)
Net OCI	144	13	411	196
Comprehensive Income Attributable to Common Shareholders	86,776	80,201	256,964	228,388
NSTAR Electric Company [Member]
Net Income	117,196	118,624	239,857	284,148
Other Comprehensive (Loss)/Income, Net of Tax:
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(10)	(2)	(31)	(184)
Net OCI	(10)	(2)	(31)	(184)
Comprehensive Income Attributable to Common Shareholders	117,186	118,622	239,826	283,964
Public Service Company Of New Hampshire [Member]
Net Income	38,515	32,501	105,829	92,491
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	290	291	871	872
Changes in Unrealized Gains/(Losses) on Marketable Securities	56	(169)	135	(236)
Net OCI	346	122	1,006	636
Comprehensive Income Attributable to Common Shareholders	38,861	32,623	106,835	93,127
Western Massachusetts Electric Company [Member]
Net Income	16,011	14,971	46,103	42,410
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	109	101	328	270
Changes in Unrealized Gains/(Losses) on Marketable Securities	9	(27)	22	(38)
Net OCI	118	74	350	232
Comprehensive Income Attributable to Common Shareholders	$ 16,129	$ 15,045	$ 46,453	$ 42,642