CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current Assets:
Cash	$ 35,781	$ 38,703
Receivables, Net	928,064	856,346
Unbilled Revenues	197,920	211,758
Taxes Receivable	12,247	337,307
Fuel, Materials and Supplies	302,225	349,664
Regulatory Assets Current	653,892	672,493
Marketable Securities - Current	119,702	124,173
Prepayments and Other Current Assets	117,857	102,021
Total Current Assets	2,367,688	2,692,465
Property, Plant and Equipment, Net	19,406,025	18,647,041
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,951,752	4,054,086
Goodwill	3,519,401	3,519,401
Marketable Securities	476,778	515,025
Other Long-Term Assets	324,382	349,957
Total Deferred Debits and Other Assets	8,272,313	8,438,469
Total Assets	30,046,026	29,777,975
Current Liabilities:
Notes Payable	1,015,500	956,825
Long-Term Debt - Current Portion	228,883	245,583
Accounts Payable - Current	610,753	868,231
Obligations to Third Party Suppliers	157,798	115,632
Regulatory Liability Current	226,061	235,022
Deferred Tax Liabilities Current	169,272	160,288
Other Liabilities - Current	563,426	552,800
Total Current Liabilities	2,971,693	3,134,381
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	4,612,828	4,467,473
Regulatory Liabilities Long-Term	517,595	515,144
Long-Term Derivative Liabilities	365,692	409,632
Accrued Pension, SERP and PBOP	1,498,346	1,638,558
Other Long-Term Liabilities	872,376	874,387
Total Deferred Credits and Other Liabilities	7,866,837	7,905,194
Capitalization:
Long-Term Debt	8,757,498	8,606,017
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:
Common Stock	1,669,313	1,666,796
Capital Surplus, Paid In	6,260,663	6,235,834
Retained Earnings	2,747,977	2,448,661
Accumulated Other Comprehensive Loss	(73,546)	(74,009)
Treasury Stock	(309,977)	(300,467)
Common Shareholders' Equity	10,294,430	9,976,815
Total Capitalization	19,207,496	18,738,400
Total Liabilities and Capitalization	30,046,026	29,777,975
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	13,407	2,356
Receivables, Net	425,955	355,140
Accounts Receivable from Affiliated Companies	28,266	16,757
Unbilled Revenues	96,301	102,137
Taxes Receivable	0	116,148
Regulatory Assets Current	243,293	220,344
Materials and Supplies	44,306	46,664
Prepaid Taxes	52,351	15,597
Prepayments and Other Current Assets	16,239	22,225
Total Current Assets	920,118	897,368
Property, Plant and Equipment, Net	7,008,603	6,809,664
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,420,974	1,475,508
Other Long-Term Assets	145,031	177,568
Total Deferred Debits and Other Assets	1,566,005	1,653,076
Total Assets	9,494,726	9,360,108
Current Liabilities:
Notes Payable To Affiliated Companies	0	133,400
Long-Term Debt - Current Portion	0	162,000
Accounts Payable - Current	207,366	272,971
Accounts Payable to Affiliated Companies	93,257	65,594
Obligations to Third Party Suppliers	75,659	73,624
Regulatory Liability Current	136,393	124,722
Accrued Taxes	47,973	4,091
Derivative Liabilities - Current	91,372	88,459
Other Liabilities - Current	124,504	149,329
Total Current Liabilities	776,524	1,074,190
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,636,831	1,642,805
Regulatory Liabilities Long-Term	76,864	81,298
Long-Term Derivative Liabilities	364,691	406,199
Accrued Pension, SERP and PBOP	284,890	273,854
Other Long-Term Liabilities	143,642	148,844
Total Deferred Credits and Other Liabilities	2,506,918	2,553,000
Capitalization:
Long-Term Debt	2,975,316	2,679,951
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200	116,200
Common Shareholders' Equity:
Common Stock	60,352	60,352
Capital Surplus, Paid In	1,910,651	1,804,869
Retained Earnings	1,149,500	1,072,477
Accumulated Other Comprehensive Loss	(735)	(931)
Common Shareholders' Equity	3,119,768	2,936,767
Total Capitalization	6,211,284	5,732,918
Total Liabilities and Capitalization	9,494,726	9,360,108
NSTAR Electric Company [Member]
Current Assets:
Cash	2,809	12,773
Receivables, Net	303,969	234,481
Accounts Receivable from Affiliated Companies	17,229	40,353
Unbilled Revenues	43,288	29,741
Taxes Receivable	0	144,601
Fuel, Materials and Supplies	52,315	74,179
Regulatory Assets Current	223,520	198,710
Prepayments and Other Current Assets	8,862	10,815
Total Current Assets	651,992	745,653
Property, Plant and Equipment, Net	5,545,082	5,335,436
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,179,996	1,179,100
Other Long-Term Assets	60,339	73,051
Total Deferred Debits and Other Assets	1,240,335	1,252,151
Total Assets	7,437,409	7,333,240
Current Liabilities:
Notes Payable	258,500	302,000
Long-Term Debt - Current Portion	200,000	4,700
Accounts Payable - Current	172,521	217,311
Accounts Payable to Affiliated Companies	25,515	63,517
Obligations to Third Party Suppliers	70,607	34,824
Renewable Portfolio Standards Compliance Obligation	67,828	35,698
Regulatory Liability Current	12,319	49,611
Accrued Taxes	66,474	4,191
Deferred Tax Liabilities Current	92,183	55,136
Other Liabilities - Current	88,905	111,800
Total Current Liabilities	1,054,852	878,788
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,546,801	1,527,667
Regulatory Liabilities Long-Term	267,342	262,738
Accrued Pension, SERP and PBOP	211,891	235,529
Other Long-Term Liabilities	122,026	129,279
Total Deferred Credits and Other Liabilities	2,148,060	2,155,213
Capitalization:
Long-Term Debt	1,592,727	1,792,712
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	43,000
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	995,378	994,130
Retained Earnings	1,603,134	1,468,955
Accumulated Other Comprehensive Loss	258	442
Common Shareholders' Equity	2,598,770	2,463,527
Total Capitalization	4,234,497	4,299,239
Total Liabilities and Capitalization	7,437,409	7,333,240
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	2,103	489
Receivables, Net	91,700	80,151
Accounts Receivable from Affiliated Companies	14,630	3,194
Unbilled Revenues	34,932	40,181
Fuel, Materials and Supplies	143,983	148,139
Regulatory Assets Current	89,513	111,705
Prepayments and Other Current Assets	22,125	42,392
Total Current Assets	398,986	426,251
Property, Plant and Equipment, Net	2,768,206	2,635,844
Deferred Debits and Other Assets:
Regulatory Assets Long Term	272,360	293,115
Other Long-Term Assets	35,075	39,228
Total Deferred Debits and Other Assets	307,435	332,343
Total Assets	3,474,627	3,394,438
Current Liabilities:
Notes Payable To Affiliated Companies	137,300	90,500
Accounts Payable - Current	76,330	93,349
Accounts Payable to Affiliated Companies	25,239	33,734
Regulatory Liability Current	11,338	16,044
Deferred Tax Liabilities Current	34,699	36,164
Other Liabilities - Current	47,589	38,969
Total Current Liabilities	332,495	308,760
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	629,055	587,292
Regulatory Liabilities Long-Term	49,680	51,372
Accrued Pension, SERP and PBOP	97,167	93,243
Other Long-Term Liabilities	48,543	50,155
Total Deferred Credits and Other Liabilities	824,445	782,062
Capitalization:
Long-Term Debt	1,076,336	1,076,286
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	748,634	748,240
Retained Earnings	499,450	486,459
Accumulated Other Comprehensive Loss	(6,733)	(7,369)
Common Shareholders' Equity	1,241,351	1,227,330
Total Capitalization	2,317,687	2,303,616
Total Liabilities and Capitalization	3,474,627	3,394,438
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	658	0
Receivables, Net	62,889	51,066
Accounts Receivable from Affiliated Companies	24,221	7,851
Unbilled Revenues	14,517	15,146
Taxes Receivable	49	18,126
Regulatory Assets Current	48,805	51,923
Marketable Securities - Current	40,459	28,658
Prepayments and Other Current Assets	6,983	7,607
Total Current Assets	198,581	180,377
Property, Plant and Equipment, Net	1,531,705	1,461,321
Deferred Debits and Other Assets:
Regulatory Assets Long Term	133,697	146,307
Marketable Securities	17,888	29,452
Other Long-Term Assets	26,709	22,018
Total Deferred Debits and Other Assets	178,294	197,777
Total Assets	1,908,580	1,839,475
Current Liabilities:
Notes Payable To Affiliated Companies	126,200	21,400
Long-Term Debt - Current Portion	0	50,000
Accounts Payable - Current	33,960	53,732
Accounts Payable to Affiliated Companies	21,496	14,328
Regulatory Liability Current	24,267	22,486
Deferred Tax Liabilities Current	13,403	18,089
Other Liabilities - Current	28,961	24,080
Total Current Liabilities	248,287	204,115
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	422,753	416,822
Regulatory Liabilities Long-Term	11,926	10,835
Accrued Pension, SERP and PBOP	18,320	17,705
Other Long-Term Liabilities	36,849	33,747
Total Deferred Credits and Other Liabilities	489,848	479,109
Capitalization:
Long-Term Debt	577,781	578,471
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	391,398	391,256
Retained Earnings	193,344	178,834
Accumulated Other Comprehensive Loss	(2,944)	(3,176)
Common Shareholders' Equity	592,664	577,780
Total Capitalization	1,170,445	1,156,251
Total Liabilities and Capitalization	$ 1,908,580	$ 1,839,475