CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and Cash Equivalents	$ 45,763	$ 30,251
Receivables, Net	879,451	847,301
Unbilled Revenues	166,710	168,490
Fuel, Materials, Supplies and Inventory	361,779	328,721
Regulatory Assets	875,037	887,625
Prepayments and Other Current Assets	182,659	215,284
Total Current Assets	2,511,399	2,477,672
Property, Plant and Equipment, Net	21,641,898	21,350,510
Deferred Debits and Other Assets:
Regulatory Assets	3,564,700	3,638,688
Goodwill	3,519,401	3,519,401
Marketable Securities	561,585	544,642
Other Long-Term Assets	556,193	522,260
Total Deferred Debits and Other Assets	8,201,879	8,224,991
Total Assets	32,355,176	32,053,173
Current Liabilities:
Notes Payable	975,500	1,148,500
Long-Term Debt – Current Portion	773,883	773,883
Accounts Payable	745,856	884,521
Regulatory Liabilities	199,160	146,787
Other Current Liabilities	639,366	684,914
Total Current Liabilities	3,333,765	3,638,605
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	5,758,603	5,607,207
Regulatory Liabilities	692,989	702,255
Derivative Liabilities	415,795	413,676
Accrued Pension and SERP	1,077,593	1,141,514
Other Long-Term Liabilities	848,776	853,260
Total Deferred Credits and Other Liabilities	8,793,756	8,717,912
Capitalization:
Long-Term Debt	9,267,891	8,829,354
Noncontrolling Interest - Preferred Stock of Subsidiaries	155,568	155,568
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid In	6,230,608	6,250,224
Retained Earnings	3,284,108	3,175,171
Accumulated Other Comprehensive Loss	(62,141)	(65,282)
Treasury Stock	(317,771)	(317,771)
Common Stockholder's Equity	10,804,196	10,711,734
Total Capitalization	20,227,655	19,696,656
Total Liabilities and Capitalization	32,355,176	32,053,173
The Connecticut Light And Power Company [Member]
Current Assets:
Cash and Cash Equivalents	15,315	6,579
Receivables, Net	349,714	359,132
Accounts Receivable from Affiliated Companies	17,184	16,851
Unbilled Revenues	51,069	50,373
Materials, Supplies and Inventory	56,432	52,050
Regulatory Assets	370,083	335,526
Prepayments and Other Current Assets	52,406	52,670
Total Current Assets	912,203	873,181
Property, Plant and Equipment, Net	7,754,894	7,632,392
Deferred Debits and Other Assets:
Regulatory Assets	1,367,486	1,391,564
Other Long-Term Assets	140,157	137,907
Total Deferred Debits and Other Assets	1,507,643	1,529,471
Total Assets	10,174,740	10,035,044
Current Liabilities:
Notes Payable to Eversource Parent	3,400	80,100
Long-Term Debt – Current Portion	100,000	250,000
Accounts Payable	281,414	289,532
Accounts Payable to Affiliated Companies	67,250	88,075
Obligations to Third Party Suppliers	51,885	55,520
Regulatory Liabilities	58,946	47,055
Derivative Liabilities	70,739	77,765
Other Current Liabilities	127,869	120,399
Total Current Liabilities	761,503	1,008,446
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	2,037,638	1,987,661
Regulatory Liabilities	101,241	100,138
Derivative Liabilities	415,187	412,750
Accrued Pension and SERP	296,105	300,208
Other Long-Term Liabilities	123,931	123,244
Total Deferred Credits and Other Liabilities	2,974,102	2,924,001
Capitalization:
Long-Term Debt	2,813,151	2,516,010
Noncontrolling Interest - Preferred Stock of Subsidiaries	116,200	116,200
Common Shareholders' Equity:
Common Shares	60,352	60,352
Capital Surplus, Paid In	2,110,726	2,110,714
Retained Earnings	1,338,592	1,299,374
Accumulated Other Comprehensive Loss	114	(53)
Common Stockholder's Equity	3,509,784	3,470,387
Total Capitalization	6,439,135	6,102,597
Total Liabilities and Capitalization	10,174,740	10,035,044
NSTAR Electric Company [Member]
Current Assets:
Cash and Cash Equivalents	2,448	3,494
Receivables, Net	264,337	257,557
Accounts Receivable from Affiliated Companies	4,565	8,581
Unbilled Revenues	28,393	31,632
Taxes Receivable	2,884	39,738
Fuel, Materials, Supplies and Inventory	94,338	62,288
Regulatory Assets	276,476	289,400
Prepayments and Other Current Assets	17,109	14,906
Total Current Assets	690,550	707,596
Property, Plant and Equipment, Net	6,108,944	6,051,835
Deferred Debits and Other Assets:
Regulatory Assets	1,051,090	1,057,746
Prepaid PBOP	100,609	95,073
Other Long-Term Assets	63,371	60,572
Total Deferred Debits and Other Assets	1,215,070	1,213,391
Total Assets	8,014,564	7,972,822
Current Liabilities:
Notes Payable	174,500	126,500
Long-Term Debt – Current Portion	400,000	400,000
Accounts Payable	177,110	232,599
Accounts Payable to Affiliated Companies	96,924	91,532
Obligations to Third Party Suppliers	60,650	55,863
Renewable Portfolio Standards Compliance Obligations	94,800	75,571
Regulatory Liabilities	62,154	63,653
Other Current Liabilities	54,166	71,122
Total Current Liabilities	1,120,304	1,116,840
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,866,259	1,836,292
Regulatory Liabilities	390,458	391,823
Accrued Pension and SERP	99,491	111,827
Other Long-Term Liabilities	125,640	123,194
Total Deferred Credits and Other Liabilities	2,481,848	2,463,136
Capitalization:
Long-Term Debt	1,678,514	1,678,116
Noncontrolling Interest - Preferred Stock of Subsidiaries	43,000	43,000
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	1,045,378	1,045,378
Retained Earnings	1,645,156	1,625,984
Accumulated Other Comprehensive Loss	364	368
Common Stockholder's Equity	2,690,898	2,671,730
Total Capitalization	4,412,412	4,392,846
Total Liabilities and Capitalization	8,014,564	7,972,822
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash and Cash Equivalents	7,743	4,646
Receivables, Net	81,899	84,450
Accounts Receivable from Affiliated Companies	2,098	4,185
Unbilled Revenues	42,784	41,004
Fuel, Materials, Supplies and Inventory	165,725	162,354
Regulatory Assets	111,274	117,240
Prepayments and Other Current Assets	9,423	28,908
Total Current Assets	420,946	442,787
Property, Plant and Equipment, Net	3,076,608	3,039,313
Deferred Debits and Other Assets:
Regulatory Assets	243,643	245,525
Other Long-Term Assets	42,797	37,720
Total Deferred Debits and Other Assets	286,440	283,245
Total Assets	3,783,994	3,765,345
Current Liabilities:
Notes Payable to Eversource Parent	144,900	160,900
Long-Term Debt – Current Portion	70,000	70,000
Accounts Payable	70,710	85,716
Accounts Payable to Affiliated Companies	40,463	29,154
Regulatory Liabilities	17,224	12,659
Other Current Liabilities	52,771	43,253
Total Current Liabilities	396,068	401,682
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	796,118	785,385
Regulatory Liabilities	45,600	44,779
Accrued Pension and SERP	91,911	94,652
Other Long-Term Liabilities	48,435	49,442
Total Deferred Credits and Other Liabilities	982,064	974,258
Capitalization:
Long-Term Debt	1,002,305	1,002,048
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	843,134	843,134
Retained Earnings	565,098	549,286
Accumulated Other Comprehensive Loss	(4,675)	(5,063)
Common Stockholder's Equity	1,403,557	1,387,357
Total Capitalization	2,405,862	2,389,405
Total Liabilities and Capitalization	3,783,994	3,765,345
Western Massachusetts Electric Company [Member]
Current Assets:
Cash and Cash Equivalents	769	0
Receivables, Net	57,340	54,940
Accounts Receivable from Affiliated Companies	16,588	14,425
Unbilled Revenues	16,850	15,329
Fuel, Materials, Supplies and Inventory	9,911	8,618
Regulatory Assets	66,033	64,123
Prepayments and Other Current Assets	3,365	2,595
Total Current Assets	170,856	160,030
Property, Plant and Equipment, Net	1,694,818	1,678,262
Deferred Debits and Other Assets:
Regulatory Assets	123,317	127,291
Other Long-Term Assets	31,171	29,062
Total Deferred Debits and Other Assets	154,488	156,353
Total Assets	2,020,162	1,994,645
Current Liabilities:
Notes Payable to Eversource Parent	71,400	51,000
Accounts Payable	44,023	56,036
Accounts Payable to Affiliated Companies	14,837	19,478
Obligations to Third Party Suppliers	9,705	10,508
Renewable Portfolio Standards Compliance Obligations	25,110	20,383
Regulatory Liabilities	12,897	14,888
Other Current Liabilities	7,659	14,984
Total Current Liabilities	185,631	187,277
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	507,203	490,793
Regulatory Liabilities	19,119	17,227
Accrued Pension and SERP	18,660	20,390
Other Long-Term Liabilities	44,177	41,308
Total Deferred Credits and Other Liabilities	589,159	569,718
Capitalization:
Long-Term Debt	566,415	566,536
Common Shareholders' Equity:
Common Shares	10,866	10,866
Capital Surplus, Paid In	444,398	444,398
Retained Earnings	225,930	218,212
Accumulated Other Comprehensive Loss	(2,237)	(2,362)
Common Stockholder's Equity	678,957	671,114
Total Capitalization	1,245,372	1,237,650
Total Liabilities and Capitalization	$ 2,020,162	$ 1,994,645