CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current Assets:
Cash	$ 50,966	$ 23,947
Receivables, Net	890,977	775,480
Unbilled Revenues	192,084	202,647
Taxes Receivable	44,171	305,359
Fuel, Materials and Supplies	359,225	336,476
Regulatory Assets Current	919,311	845,843
Prepayments and Other Current Assets	133,813	129,034
Total Current Assets	2,590,547	2,618,786
Property, Plant and Equipment, Net	20,096,693	19,892,441
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,703,486	3,737,960
Goodwill	3,519,401	3,519,401
Marketable Securities	502,948	516,478
Other Long-Term Assets	299,400	295,243
Total Deferred Debits and Other Assets	8,025,235	8,069,082
Total Assets	30,712,475	30,580,309
Current Liabilities:
Notes Payable	769,500	1,160,953
Long-Term Debt - Current Portion	378,883	228,883
Accounts Payable - Current	646,440	813,646
Obligations to Third Party Suppliers	135,978	128,564
Renewable Portfolio Standards Compliance Obligation	170,021	130,354
Regulatory Liability Current	111,414	107,759
Other Liabilities - Current	381,678	419,631
Total Current Liabilities	2,593,914	2,989,790
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	5,284,255	5,147,678
Regulatory Liabilities Long-Term	526,452	513,595
Long-Term Derivative Liabilities	344,458	337,102
Accrued Pension, SERP and PBOP	1,355,422	1,407,288
Other Long-Term Liabilities	869,220	871,499
Total Deferred Credits and Other Liabilities	8,379,807	8,277,162
Capitalization:
Long-Term Debt	9,144,687	8,805,574
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:
Common Stock	1,669,392	1,669,313
Capital Surplus, Paid In	6,243,908	6,262,368
Retained Earnings	2,900,351	2,797,355
Accumulated Other Comprehensive Loss	(65,175)	(66,844)
Treasury Stock	(309,977)	(309,977)
Common Shareholders' Equity	10,438,499	10,352,215
Total Capitalization	19,738,754	19,313,357
Total Liabilities and Capitalization	30,712,475	30,580,309
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	16,482	1,057
Receivables, Net	379,758	352,536
Accounts Receivable from Affiliated Companies	21,377	21,214
Unbilled Revenues	93,853	99,879
Taxes Receivable	4,650	137,643
Regulatory Assets Current	324,559	268,318
Materials and Supplies	48,083	43,124
Prepayments and Other Current Assets	49,753	32,234
Total Current Assets	938,515	956,005
Property, Plant and Equipment, Net	7,231,214	7,156,809
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,379,484	1,369,028
Other Long-Term Assets	113,017	111,115
Total Deferred Debits and Other Assets	1,492,501	1,480,143
Total Assets	9,662,230	9,592,957
Current Liabilities:
Notes Payable To Affiliated Companies	115,500	277,400
Long-Term Debt - Current Portion	150,000	0
Accounts Payable - Current	246,475	267,764
Accounts Payable to Affiliated Companies	59,275	66,456
Obligations to Third Party Suppliers	61,674	60,746
Regulatory Liability Current	62,999	61,155
Derivative Liabilities - Current	92,953	91,820
Other Liabilities - Current	118,697	110,631
Total Current Liabilities	907,573	935,972
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,881,725	1,820,865
Regulatory Liabilities Long-Term	77,744	74,830
Long-Term Derivative Liabilities	342,698	336,189
Accrued Pension, SERP and PBOP	267,706	271,056
Other Long-Term Liabilities	131,953	133,446
Total Deferred Credits and Other Liabilities	2,701,826	2,636,386
Capitalization:
Long-Term Debt	2,614,324	2,763,682
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	2,056,376	1,910,663
Retained Earnings	1,206,035	1,170,278
Accumulated Other Comprehensive Loss	(456)	(576)
Common Shareholders' Equity	3,322,307	3,140,717
Total Capitalization	6,052,831	6,020,599
Total Liabilities and Capitalization	9,662,230	9,592,957
NSTAR Electric Company [Member]
Current Assets:
Cash	3,504	3,346
Receivables, Net	256,760	229,936
Accounts Receivable from Affiliated Companies	2,990	4,034
Unbilled Revenues	28,596	29,464
Taxes Receivable	33,234	70,236
Fuel, Materials and Supplies	115,809	75,487
Regulatory Assets Current	361,307	348,408
Prepayments and Other Current Assets	13,957	11,448
Total Current Assets	816,157	772,359
Property, Plant and Equipment, Net	5,700,068	5,655,458
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,108,037	1,112,977
Other Long-Term Assets	58,323	62,467
Total Deferred Debits and Other Assets	1,166,360	1,175,444
Total Assets	7,682,585	7,603,261
Current Liabilities:
Notes Payable	148,500	62,500
Long-Term Debt - Current Portion	200,000	200,000
Accounts Payable - Current	189,594	228,250
Accounts Payable to Affiliated Companies	66,673	38,648
Obligations to Third Party Suppliers	62,588	56,718
Renewable Portfolio Standards Compliance Obligation	132,386	104,847
Regulatory Liability Current	4,997	3,281
Other Liabilities - Current	58,776	72,007
Total Current Liabilities	863,514	766,251
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,793,183	1,760,339
Regulatory Liabilities Long-Term	267,440	264,352
Accrued Pension, SERP and PBOP	188,974	209,153
Other Long-Term Liabilities	123,336	120,939
Total Deferred Credits and Other Liabilities	2,372,933	2,354,783
Capitalization:
Long-Term Debt	1,829,984	1,829,766
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	995,378
Retained Earnings	1,577,241	1,613,538
Accumulated Other Comprehensive Loss	535	545
Common Shareholders' Equity	2,573,154	2,609,461
Total Capitalization	4,446,138	4,482,227
Total Liabilities and Capitalization	7,682,585	7,603,261
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	3,580	1,733
Receivables, Net	89,138	77,546
Accounts Receivable from Affiliated Companies	7,667	2,352
Unbilled Revenues	36,497	38,207
Taxes Receivable	0	43,128
Fuel, Materials and Supplies	149,965	156,868
Regulatory Assets Current	101,633	104,971
Prepayments and Other Current Assets	5,963	24,302
Total Current Assets	394,443	449,107
Property, Plant and Equipment, Net	2,881,435	2,855,363
Deferred Debits and Other Assets:
Regulatory Assets Long Term	245,760	257,873
Other Long-Term Assets	34,703	34,176
Total Deferred Debits and Other Assets	280,463	292,049
Total Assets	3,556,341	3,596,519
Current Liabilities:
Notes Payable To Affiliated Companies	157,100	231,300
Accounts Payable - Current	64,717	87,925
Accounts Payable to Affiliated Companies	29,814	24,214
Regulatory Liability Current	4,723	6,898
Accrued Taxes	21,231	4,648
Other Liabilities - Current	43,132	39,273
Total Current Liabilities	320,717	394,258
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	723,110	705,894
Regulatory Liabilities Long-Term	47,930	47,851
Accrued Pension, SERP and PBOP	77,218	89,579
Other Long-Term Liabilities	50,453	50,746
Total Deferred Credits and Other Liabilities	898,711	894,070
Capitalization:
Long-Term Debt	1,071,275	1,071,017
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	760,134	748,634
Retained Earnings	511,559	494,901
Accumulated Other Comprehensive Loss	(6,055)	(6,361)
Common Shareholders' Equity	1,265,638	1,237,174
Total Capitalization	2,336,913	2,308,191
Total Liabilities and Capitalization	3,556,341	3,596,519
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	2,269	834
Receivables, Net	59,324	50,912
Accounts Receivable from Affiliated Companies	8,612	18,633
Unbilled Revenues	13,753	15,065
Taxes Receivable	6,431	33,407
Regulatory Assets Current	61,363	56,166
Prepayments and Other Current Assets	8,396	7,882
Total Current Assets	160,148	182,899
Property, Plant and Equipment, Net	1,590,524	1,575,306
Deferred Debits and Other Assets:
Regulatory Assets Long Term	131,432	135,010
Other Long-Term Assets	26,148	24,875
Total Deferred Debits and Other Assets	157,580	159,885
Total Assets	1,908,252	1,918,090
Current Liabilities:
Notes Payable To Affiliated Companies	143,500	143,400
Accounts Payable - Current	34,240	58,364
Accounts Payable to Affiliated Companies	16,740	19,896
Renewable Portfolio Standards Compliance Obligation	11,899	6,395
Regulatory Liability Current	9,760	13,122
Other Liabilities - Current	18,404	23,532
Total Current Liabilities	234,543	264,709
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	480,250	470,539
Regulatory Liabilities Long-Term	13,775	11,597
Accrued Pension, SERP and PBOP	17,897	19,515
Other Long-Term Liabilities	39,566	36,819
Total Deferred Credits and Other Liabilities	551,488	538,470
Capitalization:
Long-Term Debt	517,200	517,329
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	391,398	391,398
Retained Earnings	205,467	198,140
Accumulated Other Comprehensive Loss	(2,710)	(2,822)
Common Shareholders' Equity	605,021	597,582
Total Capitalization	1,122,221	1,114,911
Total Liabilities and Capitalization	$ 1,908,252	$ 1,918,090