CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current Assets:
Cash	$ 38,726	$ 23,947
Receivables, Net	806,340	775,480
Unbilled Revenues	203,824	202,647
Taxes Receivable	103,926	305,359
Fuel, Materials and Supplies	292,547	336,476
Regulatory Assets Current	863,360	845,843
Prepayments and Other Current Assets	106,561	129,034
Total Current Assets	2,415,284	2,618,786
Property, Plant and Equipment, Net	20,448,475	19,892,441
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,661,578	3,737,960
Goodwill	3,519,401	3,519,401
Marketable Securities	518,750	516,478
Other Long-Term Assets	319,175	295,243
Total Deferred Debits and Other Assets	8,018,904	8,069,082
Total Assets	30,882,663	30,580,309
Current Liabilities:
Notes Payable	767,000	1,160,953
Long-Term Debt - Current Portion	178,883	228,883
Accounts Payable - Current	631,566	813,646
Obligations to Third Party Suppliers	133,943	128,564
Regulatory Liability Current	119,413	107,759
Other Liabilities - Current	472,964	549,985
Total Current Liabilities	2,303,769	2,989,790
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	5,398,926	5,147,678
Regulatory Liabilities Long-Term	527,678	513,595
Long-Term Derivative Liabilities	381,572	337,102
Accrued Pension, SERP and PBOP	1,294,548	1,407,288
Other Long-Term Liabilities	875,270	871,499
Total Deferred Credits and Other Liabilities	8,477,994	8,277,162
Capitalization:
Long-Term Debt	9,435,924	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	6,252,514	6,262,368
Retained Earnings	2,962,843	2,797,355
Accumulated Other Comprehensive Loss	(65,364)	(66,844)
Treasury Stock	(309,977)	(309,977)
Common Shareholders' Equity	10,509,408	10,352,215
Total Capitalization	20,100,900	19,313,357
Total Liabilities and Capitalization	30,882,663	30,580,309
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	9,449	1,057
Receivables, Net	370,982	352,536
Accounts Receivable from Affiliated Companies	9,703	21,214
Unbilled Revenues	99,822	99,879
Taxes Receivable	12,498	137,643
Regulatory Assets Current	312,160	268,318
Materials and Supplies	52,538	43,124
Prepayments and Other Current Assets	15,826	32,234
Total Current Assets	882,978	956,005
Property, Plant and Equipment, Net	7,336,577	7,156,809
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,368,897	1,369,028
Other Long-Term Assets	121,477	111,115
Total Deferred Debits and Other Assets	1,490,374	1,480,143
Total Assets	9,709,929	9,592,957
Current Liabilities:
Notes Payable To Affiliated Companies	93,000	277,400
Long-Term Debt - Current Portion	150,000	0
Accounts Payable - Current	219,332	267,764
Accounts Payable to Affiliated Companies	60,169	66,456
Obligations to Third Party Suppliers	61,532	60,746
Regulatory Liability Current	63,287	61,155
Derivative Liabilities - Current	91,603	91,820
Other Liabilities - Current	122,886	110,631
Total Current Liabilities	861,809	935,972
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,922,428	1,820,865
Regulatory Liabilities Long-Term	80,617	74,830
Long-Term Derivative Liabilities	380,643	336,189
Accrued Pension, SERP and PBOP	247,419	271,056
Other Long-Term Liabilities	131,883	133,446
Total Deferred Credits and Other Liabilities	2,762,990	2,636,386
Capitalization:
Long-Term Debt	2,614,878	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	2,056,389	1,910,663
Retained Earnings	1,237,620	1,170,278
Accumulated Other Comprehensive Loss	(309)	(576)
Common Shareholders' Equity	3,354,052	3,140,717
Total Capitalization	6,085,130	6,020,599
Total Liabilities and Capitalization	9,709,929	9,592,957
NSTAR Electric Company [Member]
Current Assets:
Cash	3,391	3,346
Receivables, Net	254,376	229,936
Accounts Receivable from Affiliated Companies	12,241	4,034
Unbilled Revenues	43,115	29,464
Taxes Receivable	21,564	70,236
Fuel, Materials and Supplies	40,292	75,487
Regulatory Assets Current	316,715	348,408
Prepayments and Other Current Assets	9,510	11,448
Total Current Assets	701,204	772,359
Property, Plant and Equipment, Net	5,788,659	5,655,458
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,112,099	1,112,977
Other Long-Term Assets	61,886	62,467
Total Deferred Debits and Other Assets	1,173,985	1,175,444
Total Assets	7,663,848	7,603,261
Current Liabilities:
Notes Payable	329,000	62,500
Long-Term Debt - Current Portion	0	200,000
Accounts Payable - Current	146,868	228,250
Accounts Payable to Affiliated Companies	46,174	38,648
Obligations to Third Party Suppliers	61,538	56,718
Renewable Portfolio Standards Compliance Obligation	44,239	104,847
Regulatory Liability Current	6,923	3,281
Other Liabilities - Current	58,770	72,007
Total Current Liabilities	693,512	766,251
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,809,408	1,760,339
Regulatory Liabilities Long-Term	267,809	264,352
Accrued Pension, SERP and PBOP	194,734	209,153
Other Long-Term Liabilities	124,877	120,939
Total Deferred Credits and Other Liabilities	2,396,828	2,354,783
Capitalization:
Long-Term Debt	2,077,687	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	1,456,919	1,613,538
Accumulated Other Comprehensive Loss	524	545
Common Shareholders' Equity	2,452,821	2,609,461
Total Capitalization	4,573,508	4,482,227
Total Liabilities and Capitalization	7,663,848	7,603,261
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	1,084	1,733
Receivables, Net	77,389	77,546
Accounts Receivable from Affiliated Companies	3,938	2,352
Unbilled Revenues	38,275	38,207
Taxes Receivable	8,848	43,128
Fuel, Materials and Supplies	151,475	156,868
Regulatory Assets Current	122,879	104,971
Prepayments and Other Current Assets	19,570	24,302
Total Current Assets	423,458	449,107
Property, Plant and Equipment, Net	2,925,288	2,855,363
Deferred Debits and Other Assets:
Regulatory Assets Long Term	238,612	257,873
Other Long-Term Assets	34,886	34,176
Total Deferred Debits and Other Assets	273,498	292,049
Total Assets	3,622,244	3,596,519
Current Liabilities:
Notes Payable To Affiliated Companies	120,900	231,300
Accounts Payable - Current	96,059	87,925
Accounts Payable to Affiliated Companies	21,049	24,214
Regulatory Liability Current	5,986	6,898
Other Liabilities - Current	37,264	43,921
Total Current Liabilities	281,258	394,258
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	746,785	705,894
Regulatory Liabilities Long-Term	47,283	47,851
Accrued Pension, SERP and PBOP	75,721	89,579
Other Long-Term Liabilities	50,318	50,746
Total Deferred Credits and Other Liabilities	920,107	894,070
Capitalization:
Long-Term Debt	1,071,532	1,071,017
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	831,634	748,634
Retained Earnings	523,414	494,901
Accumulated Other Comprehensive Loss	(5,701)	(6,361)
Common Shareholders' Equity	1,349,347	1,237,174
Total Capitalization	2,420,879	2,308,191
Total Liabilities and Capitalization	3,622,244	3,596,519
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	1,421	834
Receivables, Net	54,685	50,912
Accounts Receivable from Affiliated Companies	9,139	18,633
Unbilled Revenues	13,928	15,065
Taxes Receivable	422	33,407
Regulatory Assets Current	57,660	56,166
Prepayments and Other Current Assets	8,598	7,882
Total Current Assets	145,853	182,899
Property, Plant and Equipment, Net	1,616,305	1,575,306
Deferred Debits and Other Assets:
Regulatory Assets Long Term	124,804	135,010
Other Long-Term Assets	27,625	24,875
Total Deferred Debits and Other Assets	152,429	159,885
Total Assets	1,914,587	1,918,090
Current Liabilities:
Notes Payable To Affiliated Companies	53,700	143,400
Accounts Payable - Current	32,783	58,364
Accounts Payable to Affiliated Companies	19,935	19,896
Obligations to Third Party Suppliers	10,336	9,654
Renewable Portfolio Standards Compliance Obligation	11,251	6,395
Regulatory Liability Current	11,256	13,122
Other Liabilities - Current	11,556	13,878
Total Current Liabilities	150,817	264,709
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	487,389	470,539
Regulatory Liabilities Long-Term	13,280	11,597
Accrued Pension, SERP and PBOP	12,135	19,515
Other Long-Term Liabilities	40,175	36,819
Total Deferred Credits and Other Liabilities	552,979	538,470
Capitalization:
Long-Term Debt	566,885	517,329
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	426,398	391,398
Retained Earnings	209,232	198,140
Accumulated Other Comprehensive Loss	(2,590)	(2,822)
Common Shareholders' Equity	643,906	597,582
Total Capitalization	1,210,791	1,114,911
Total Liabilities and Capitalization	$ 1,914,587	$ 1,918,090