CONSOLIDATED STATEMENT OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Operating Activities:
Net Income	$ 886,004	$ 827,065	$ 793,689
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	665,856	614,657	610,777
Deferred Income Tax Expense (Benefit)	491,736	443,259	431,413
Pension, SERP and PBOP Expense	96,017	99,056	195,698
Pension and PBOP Contributions	(162,452)	(211,649)	(342,184)
Regulatory Over/(Under) Recoveries, Net	(163,287)	6,853	(24,276)
Amortization of Regulatory Assets/(Liabilities), Net	22,339	10,704	206,322
Amortization of Rate Reduction Bonds	0	0	42,581
Other	(91,945)	39,523	56,071
(Payments)/Refunds Related to Spent Nuclear Fuel	(297,253)	132,138
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(39,797)	(122,139)	(163,549)
Increase Decrease in Fuel, Materials and Supplies	34,112	(41,310)	(14,811)
Taxes Receivable/(Accrued)	30,282	(323,224)	(50,950)
Accounts Payable	(91,618)	144,743	(54,619)
Other Current Assets and Liabilities, Net	44,031	15,797	(22,623)
Net Cash Flows Provided by Operating Activities	1,424,025	1,635,473	1,663,539
Investing Activities:
Investments in Property, Plant and Equipment	(1,724,139)	(1,603,744)	(1,456,787)
Proceeds from Sales of Marketable Securities	799,165	488,789	627,532
Purchases of Marketable Securities	(717,114)	(491,220)	(679,784)
Other Investing Activities	(17,062)	14,380	67,816
Net Cash Flows Used in Investing Activities	(1,659,150)	(1,591,795)	(1,441,223)
Financing Activities:
Cash Dividends on Common Stock	(529,791)	(475,227)	(462,741)
Cash Dividends on Preferred Stock	(7,519)	(7,519)	(7,682)
Increase/(Decrease) in Short-Term Debt	(242,122)	285,075	(397,000)
Issuance of Long-Term Debt	1,225,000	725,000	1,680,000
Retirements of Long-Term Debt	(216,700)	(576,551)	(929,885)
Retirements of Rate Reduction Bonds	0	0	(82,139)
Other Financing Activities	(8,499)	883	(25,253)
Net Cash Flows Provided by/(Used in) Financing Activities	220,369	(48,339)	(224,700)
Net Increase/(Decrease) in Cash	(14,756)	(4,661)	(2,384)
Cash - Beginning of Year	38,703	43,364	45,748
Cash - End of Year	23,947	38,703	43,364
The Connecticut Light And Power Company [Member]
Operating Activities:
Net Income	299,360	287,754	279,412
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	215,289	188,837	177,603
Deferred Income Tax Expense (Benefit)	135,994	130,949	130,038
Pension, SERP and PBOP Expense	14,091	14,992	24,416
Regulatory Over/(Under) Recoveries, Net	(53,781)	(20,502)	28,298
Amortization of Regulatory Assets/(Liabilities), Net	12,318	59,336	4,870
Other	(36,385)	(1,342)	(3,478)
(Payments)/Refunds Related to Spent Nuclear Fuel	(242,231)	68,610
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(29,195)	(78,631)	(56,593)
Increase Decrease in Fuel, Materials and Supplies	22,810	13,063	9,997
Taxes Receivable/(Accrued)	(13,517)	(126,376)	(41,594)
Accounts Payable	(16,910)	68,891	(66,225)
Other Current Assets and Liabilities, Net	(9,514)	6,838	8,513
Net Cash Flows Provided by Operating Activities	298,329	612,419	495,257
Investing Activities:
Investments in Property, Plant and Equipment	(523,849)	(515,710)	(434,934)
Other Investing Activities	(716)	12,653	2,650
Net Cash Flows Used in Investing Activities	(524,565)	(503,057)	(432,284)
Financing Activities:
Cash Dividends on Common Stock	(196,000)	(171,200)	(151,999)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
Increase/(Decrease) in Short-Term Debt	0	0	(89,000)
Issuance of Long-Term Debt	350,000	250,000	400,000
Increase/(Decrease) in Notes Payable to Affiliate	144,000	(153,900)	(117,800)
Retirements of Long-Term Debt	(162,000)	(150,000)	(125,000)
Capital Contributions from NU Parent	105,000	120,000	40,000
Other Financing Activities	(10,504)	(3,584)	(6,379)
Net Cash Flows Provided by/(Used in) Financing Activities	224,937	(114,243)	(55,737)
Net Increase/(Decrease) in Cash	(1,299)	(4,881)	7,236
Cash - Beginning of Year	2,356	7,237	1
Cash - End of Year	1,057	2,356	7,237
NSTAR Electric Company [Member]
Operating Activities:
Net Income	344,542	303,088	268,546
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	196,770	188,693	180,298
Deferred Income Tax Expense (Benefit)	173,155	108,133	48,808
Pension, SERP and PBOP Expense	10,786	6,760	35,731
Pension Contribution	(9,886)	(120,306)	(82,000)
Regulatory Over/(Under) Recoveries, Net	(124,323)	57,696	(119,433)
Amortization of Regulatory Assets/(Liabilities), Net	(12,989)	(6,330)	230,148
Amortization of Rate Reduction Bonds	0	0	15,054
Bad Debt Expense	14,228	24,740	28,108
Other	(56,063)	(51,478)	4,428
(Payments)/Refunds Related to Spent Nuclear Fuel	783	30,193
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(35,525)	(18,853)	(45,405)
Increase Decrease in Fuel, Materials and Supplies	406	(29,943)	3,227
Taxes Receivable/(Accrued)	77,429	(122,746)	(38,003)
Accounts Payable	21,961	9,753	31,875
Accounts Payable Related Parties	11,450	115,092	(44,491)
Other Current Assets and Liabilities, Net	44,302	38,535	(6,468)
Net Cash Flows Provided by Operating Activities	657,026	533,027	510,423
Investing Activities:
Investments in Property, Plant and Equipment	(469,466)	(465,028)	(476,600)
Decrease in Restricted Cash	0	0	37,604
Other Investing Activities	0	0	400
Net Cash Flows Used in Investing Activities	(469,466)	(465,028)	(438,596)
Financing Activities:
Cash Dividends on Common Stock	(197,999)	(253,000)	(56,000)
Cash Dividends on Preferred Stock	(1,960)	(1,961)	(2,123)
Increase/(Decrease) in Short-Term Debt	(239,500)	198,500	(172,500)
Issuance of Long-Term Debt	250,000	300,000	200,000
Retirements of Long-Term Debt	(4,700)	(301,650)	(1,650)
Retirements of Rate Reduction Bonds	0	0	(43,493)
Other Financing Activities	(2,828)	(5,136)	(1,735)
Net Cash Flows Provided by/(Used in) Financing Activities	(196,987)	(63,247)	(77,501)
Net Increase/(Decrease) in Cash	(9,427)	4,752	(5,674)
Cash - Beginning of Year	12,773	8,021	13,695
Cash - End of Year	3,346	12,773	8,021
Public Service Company Of New Hampshire [Member]
Operating Activities:
Net Income	114,442	113,944	111,397
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	105,372	98,436	91,581
Deferred Income Tax Expense (Benefit)	83,776	94,813	75,693
Pension, SERP and PBOP Expense	4,580	7,197	26,846
Pension and PBOP Contributions	(982)	(2,482)	(112,964)
Regulatory Over/(Under) Recoveries, Net	41	(11,875)	(8,481)
Amortization of Regulatory Assets/(Liabilities), Net	16,276	(29,602)	(20,387)
Amortization of Rate Reduction Bonds	0	0	19,748
Other	8,677	10,095	16,079
(Payments)/Refunds Related to Spent Nuclear Fuel	979	14,453
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(4,750)	(15,576)	2,412
Increase Decrease in Fuel, Materials and Supplies	(8,729)	(19,403)	(33,391)
Taxes Receivable/(Accrued)	(23,909)	(23,857)	26,462
Accounts Payable	(22,203)	17,796	2,632
Other Current Assets and Liabilities, Net	953	(5,972)	(9,520)
Net Cash Flows Provided by Operating Activities	274,523	247,967	188,107
Investing Activities:
Investments in Property, Plant and Equipment	(308,036)	(256,159)	(186,009)
Decrease in Restricted Cash	0	(1,013)	22,040
Other Investing Activities	306	(139)	(88)
Net Cash Flows Used in Investing Activities	(307,730)	(257,311)	(164,057)
Financing Activities:
Cash Dividends on Common Stock	(106,000)	(66,000)	(68,000)
Increase/(Decrease) in Short-Term Debt	0	4,000	23,200
Issuance of Long-Term Debt	0	75,000	250,000
Increase/(Decrease) in Notes Payable to Affiliate	140,800	0	0
Retirements of Long-Term Debt	0	(50,000)	(198,235)
Retirements of Rate Reduction Bonds	0	0	(29,294)
Capital Contributions from NU Parent	0	45,000	0
Other Financing Activities	(349)	1,703	(4,084)
Net Cash Flows Provided by/(Used in) Financing Activities	34,451	9,703	(26,413)
Net Increase/(Decrease) in Cash	1,244	359	(2,363)
Cash - Beginning of Year	489	130	2,493
Cash - End of Year	1,733	489	130
Western Massachusetts Electric Company [Member]
Operating Activities:
Net Income	56,506	57,819	60,438
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	43,362	41,886	37,568
Deferred Income Tax Expense (Benefit)	39,428	34,108	87,028
Regulatory Over/(Under) Recoveries, Net	(17,501)	1,925	8,458
Amortization of Regulatory Assets/(Liabilities), Net	14,545	(6,228)	(3,206)
Amortization of Rate Reduction Bonds	0	0	7,780
Other	(6,421)	(2,005)	3,381
(Payments)/Refunds Related to Spent Nuclear Fuel	(56,784)	18,883
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(17,822)	39,872	(53,292)
Taxes Receivable/(Accrued)	(15,281)	(22,454)	19,840
Accounts Payable	(2,602)	1,269	7,456
Other Current Assets and Liabilities, Net	5,594	(11,796)	3,356
Net Cash Flows Provided by Operating Activities	43,024	153,279	178,807
Investing Activities:
Investments in Property, Plant and Equipment	(134,551)	(116,205)	(128,786)
Proceeds from Sales of Marketable Securities	186,444	73,198	70,778
Purchases of Marketable Securities	(128,861)	(73,888)	(71,390)
Other Investing Activities	0	3,200	7,401
Net Cash Flows Used in Investing Activities	(76,968)	(113,695)	(121,997)
Financing Activities:
Cash Dividends on Common Stock	(37,200)	(59,999)	(40,001)
Issuance of Long-Term Debt	0	0	80,000
Increase/(Decrease) in Notes Payable to Affiliate	122,000	21,400	(31,900)
Retirements of Long-Term Debt	(50,000)	0	(55,000)
Retirements of Rate Reduction Bonds	0	0	(9,352)
Other Financing Activities	(22)	(985)	(558)
Net Cash Flows Provided by/(Used in) Financing Activities	34,778	(39,584)	(56,811)
Net Increase/(Decrease) in Cash	834	0	(1)
Cash - Beginning of Year		0	1
Cash - End of Year	834		0
Eversource Parent [Member]
Operating Activities:
Net Income	878,485	819,546	786,007
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity In Earnings Of Subsidiaries	900,824	848,435	785,650
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	602,300	609,800	407,837
Deferred Income Tax Expense (Benefit)	16,880	7,956	15,159
Other	(22,864)	9,409	29,169
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(16,980)	88,800	14,704
Taxes Receivable/(Accrued)	(14,426)	23,178	13,295
Accounts Payable Related Parties	(134,730)	5,942	(7,058)
Other Current Assets and Liabilities, Net	6,832	14,484	(1,411)
Net Cash Flows Provided by Operating Activities	414,673	730,680	472,052
Investing Activities:
Capital Contributions To Subsidiaries	(218,500)	(437,553)	(65,400)
(Increase) Decrease In Notes Receivable From Affiliated Company	(131,650)	86,100	5,475
Other Investing Activities	12,000	0	(1,862)
Net Cash Flows Used in Investing Activities	(338,150)	(351,453)	(61,787)
Financing Activities:
Cash Dividends on Common Stock	(529,791)	(475,227)	(462,741)
Increase/(Decrease) in Short-Term Debt	(2,622)	86,575	(135,500)
Issuance of Long-Term Debt	450,000	0	750,000
Retirements of Long-Term Debt	0	0	(550,000)
Other Financing Activities	5,819	9,528	(12,418)
Net Cash Flows Provided by/(Used in) Financing Activities	(76,594)	(379,124)	(410,659)
Net Increase/(Decrease) in Cash	(71)	103	(394)
Cash - Beginning of Year	138	429
Cash - End of Year	$ 67	$ 138	$ 429