Eversource Energy (ES) 10-Q 6 May 15 2015 Q1 Quarterly report Financial data

DOCUMENT_AND_ENTITY_INFORMATIO

DOCUMENT AND ENTITY INFORMATION (USD $)	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document And Entity [Line Items]
Entity Registrant Name	Eversource Energy
Document Period End Date	31-Mar-15
Document Type	10-Q
Entity Central Index Key	72741
Current Fiscal Year End Date	-19
Entity Common Stock, Shares Outstanding		317,647,540
Entity Public Float	$14,947,688,864
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
The Connecticut Light And Power Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	The Connecticut Light and Power Company
Entity Central Index Key	23426
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Public Service Company Of New Hampshire [Member]
Document And Entity [Line Items]
Entity Registrant Name	Public Service Company of New Hampshire
Entity Central Index Key	315256
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Western Massachusetts Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	Western Massachusetts Electric Company
Entity Central Index Key	106170
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
NSTAR Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	NSTAR Electric Company
Entity Central Index Key	13372
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current Assets:
Cash	$71,027	$38,703
Receivables, Net	1,131,434	856,346
Unbilled Revenues	229,760	211,758
Taxes Receivable	99,680	337,307
Fuel, Materials and Supplies	281,492	349,664
Regulatory Assets Current	747,349	672,493
Prepayments and Other Current Assets	231,949	226,194
Total Current Assets	2,792,691	2,692,465
Property, Plant and Equipment, Net	18,810,708	18,647,041
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,981,507	4,054,086
Goodwill	3,519,401	3,519,401
Marketable Securities	518,065	515,025
Other Long-Term Assets	329,393	349,957
Total Deferred Debits and Other Assets	8,348,366	8,438,469
Total Assets	29,951,765	29,777,975
Current Liabilities:
Notes Payable	1,003,500	956,825
Long-Term Debt - Current Portion	245,583	245,583
Accounts Payable - Current	739,324	868,231
Obligations to Third Party Suppliers	157,143	115,632
Deferred Tax Liabilities Current	218,582	160,288
Regulatory Liability Current	201,180	235,022
Other Liabilities - Current	546,470	552,800
Total Current Liabilities	3,111,782	3,134,381
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	4,574,630	4,467,473
Regulatory Liabilities Long-Term	524,940	515,144
Long-Term Derivative Liabilities	396,617	409,632
Accrued Pension, PBOP and SERP	1,605,339	1,638,558
Other Long-Term Liabilities	870,417	874,387
Total Deferred Credits and Other Liabilities	7,971,943	7,905,194
Capitalization:
Long-Term Debt	8,602,067	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	1,668,039	1,666,796
Capital Surplus, Paid In	6,241,417	6,235,834
Retained Earnings	2,569,482	2,448,661
Accumulated Other Comprehensive Loss	-72,414	-74,009
Treasury Stock	-296,119	-300,467
Common Shareholders' Equity	10,110,405	9,976,815
Total Capitalization	18,868,040	18,738,400
Total Liabilities and Capitalization	29,951,765	29,777,975
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	16,818	2,356
Receivables, Net	449,506	355,140
Accounts Receivable from Affiliated Companies	27,618	16,757
Unbilled Revenues	113,498	102,137
Taxes Receivable	0	116,148
Regulatory Assets Current	209,628	220,344
Materials and Supplies	48,135	46,664
Prepayments and Other Current Assets	51,074	37,822
Total Current Assets	916,277	897,368
Property, Plant and Equipment, Net	6,874,891	6,809,664
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,454,150	1,475,508
Other Long-Term Assets	171,085	177,568
Total Deferred Debits and Other Assets	1,625,235	1,653,076
Total Assets	9,416,403	9,360,108
Current Liabilities:
Notes Payable To Affiliated Companies	190,100	133,400
Long-Term Debt - Current Portion	162,000	162,000
Accounts Payable - Current	230,175	272,971
Accounts Payable to Affiliated Companies	67,063	65,594
Obligations to Third Party Suppliers	81,820	73,624
Regulatory Liability Current	84,127	124,722
Derivative Liabilities - Current	88,218	88,459
Other Liabilities - Current	207,843	153,420
Total Current Liabilities	1,111,346	1,074,190
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,652,415	1,642,805
Regulatory Liabilities Long-Term	82,110	81,298
Long-Term Derivative Liabilities	395,038	406,199
Accrued Pension, PBOP and SERP	272,292	273,854
Other Long-Term Liabilities	150,396	148,844
Total Deferred Credits and Other Liabilities	2,552,251	2,553,000
Capitalization:
Long-Term Debt	2,680,123	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	1,805,626	1,804,869
Retained Earnings	1,091,321	1,072,477
Accumulated Other Comprehensive Loss	-816	-931
Common Shareholders' Equity	2,956,483	2,936,767
Total Capitalization	5,752,806	5,732,918
Total Liabilities and Capitalization	9,416,403	9,360,108
NSTAR Electric Company [Member]
Current Assets:
Cash	17,897	12,773
Receivables, Net	317,410	234,481
Accounts Receivable from Affiliated Companies	8,372	40,353
Unbilled Revenues	29,228	29,741
Taxes Receivable	63,652	144,601
Fuel, Materials and Supplies	87,683	74,179
Regulatory Assets Current	309,547	198,710
Prepayments and Other Current Assets	7,885	10,815
Total Current Assets	841,674	745,653
Property, Plant and Equipment, Net	5,364,311	5,335,436
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,178,738	1,179,100
Other Long-Term Assets	55,839	73,051
Total Deferred Debits and Other Assets	1,234,577	1,252,151
Total Assets	7,440,562	7,333,240
Current Liabilities:
Notes Payable	215,500	302,000
Long-Term Debt - Current Portion	4,700	4,700
Accounts Payable - Current	233,852	217,311
Accounts Payable to Affiliated Companies	127,904	63,517
Obligations to Third Party Suppliers	63,336	34,824
Renewable Portfolio Standards Compliance Obligation	55,853	35,698
Deferred Tax Liabilities Current	111,288	55,136
Regulatory Liability Current	24,605	49,611
Other Liabilities - Current	116,128	115,991
Total Current Liabilities	953,166	878,788
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,530,972	1,527,667
Regulatory Liabilities Long-Term	268,122	262,738
Accrued Pension, PBOP and SERP	228,411	235,529
Other Long-Term Liabilities	126,006	129,279
Total Deferred Credits and Other Liabilities	2,153,511	2,155,213
Capitalization:
Long-Term Debt	1,792,717	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	1,502,528	1,468,955
Accumulated Other Comprehensive Loss	262	442
Common Shareholders' Equity	2,498,168	2,463,527
Total Capitalization	4,333,885	4,299,239
Total Liabilities and Capitalization	7,440,562	7,333,240
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	5,149	489
Receivables, Net	99,748	80,151
Accounts Receivable from Affiliated Companies	9,917	3,194
Unbilled Revenues	43,359	40,181
Taxes Receivable	31,147	14,571
Fuel, Materials and Supplies	113,566	148,139
Regulatory Assets Current	99,994	111,705
Prepayments and Other Current Assets	13,520	27,821
Total Current Assets	416,400	426,251
Property, Plant and Equipment, Net	2,666,312	2,635,844
Deferred Debits and Other Assets:
Regulatory Assets Long Term	287,203	293,115
Other Long-Term Assets	33,517	39,228
Total Deferred Debits and Other Assets	320,720	332,343
Total Assets	3,403,432	3,394,438
Current Liabilities:
Notes Payable To Affiliated Companies	82,000	90,500
Accounts Payable - Current	62,513	93,349
Accounts Payable to Affiliated Companies	42,670	33,734
Deferred Tax Liabilities Current	34,217	36,164
Regulatory Liability Current	16,102	16,044
Other Liabilities - Current	39,777	38,969
Total Current Liabilities	277,279	308,760
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	627,450	587,292
Regulatory Liabilities Long-Term	51,897	51,372
Accrued Pension, PBOP and SERP	91,847	93,243
Other Long-Term Liabilities	45,088	50,155
Total Deferred Credits and Other Liabilities	816,282	782,062
Capitalization:
Long-Term Debt	1,076,303	1,076,286
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	748,634	748,240
Retained Earnings	492,004	486,459
Accumulated Other Comprehensive Loss	-7,070	-7,369
Common Shareholders' Equity	1,233,568	1,227,330
Total Capitalization	2,309,871	2,303,616
Total Liabilities and Capitalization	3,403,432	3,394,438
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	2,045	0
Receivables, Net	72,366	51,066
Accounts Receivable from Affiliated Companies	8,726	7,851
Unbilled Revenues	18,186	15,146
Taxes Receivable	18,062	18,126
Regulatory Assets Current	66,706	51,923
Marketable Securities - Current	33,183	28,658
Prepayments and Other Current Assets	6,431	7,607
Total Current Assets	225,705	180,377
Property, Plant and Equipment, Net	1,483,895	1,461,321
Deferred Debits and Other Assets:
Regulatory Assets Long Term	137,894	146,307
Marketable Securities	25,027	29,452
Other Long-Term Assets	22,726	22,018
Total Deferred Debits and Other Assets	185,647	197,777
Total Assets	1,895,247	1,839,475
Current Liabilities:
Notes Payable To Affiliated Companies	70,500	21,400
Long-Term Debt - Current Portion	50,000	50,000
Accounts Payable - Current	40,665	53,732
Accounts Payable to Affiliated Companies	21,634	14,328
Deferred Tax Liabilities Current	24,607	18,089
Regulatory Liability Current	22,289	22,486
Other Liabilities - Current	22,958	24,080
Total Current Liabilities	252,653	204,115
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	419,043	416,822
Regulatory Liabilities Long-Term	12,673	10,835
Accrued Pension, PBOP and SERP	16,505	17,705
Other Long-Term Liabilities	34,182	33,747
Total Deferred Credits and Other Liabilities	482,403	479,109
Capitalization:
Long-Term Debt	578,239	578,471
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	391,398	391,256
Retained Earnings	182,778	178,834
Accumulated Other Comprehensive Loss	-3,090	-3,176
Common Shareholders' Equity	581,952	577,780
Total Capitalization	1,160,191	1,156,251
Total Liabilities and Capitalization	$1,895,247	$1,839,475

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating Revenues	$2,513,431	$2,290,590
Operating Expenses:
Purchased Power and Transmission	1,162,049	978,150
Operations and Maintenance	333,382	351,688
Depreciation	163,837	150,807
Amortization of Regulatory Assets/(Liabilities), Net	60,604	57,898
Energy Efficiency Programs	146,603	138,825
Taxes Other Than Income Taxes	149,481	145,533
Total Operating Expenses	2,015,956	1,822,901
Operating Income	497,475	467,689
Interest Expense:
Interest on Long-Term Debt	87,714	87,377
Other Interest	7,129	2,598
Total Interest Expense	94,843	89,975
Other Income/(Loss), Net	5,727	1,667
Income Before Income Tax Expense	408,359	379,381
Income Tax Expense	153,226	141,545
Net Income	255,133	237,836
Net Income Attributable to Noncontrolling Interests	1,879	1,879
Net Income Attributable to Controlling Interests	253,254	235,957
Basic Earnings Per Common Share	$0.80	$0.75
Diluted Earnings Per Common Share	$0.80	$0.74
Common Stock Dividends Per Share Declared	$0.42	$0.39
Weighted Average Common Shares Outstanding:
Basic	317,090,841	315,534,512
Diluted	318,491,188	316,892,119
The Connecticut Light And Power Company [Member]
Operating Revenues	804,917	734,614
Operating Expenses:
Purchased Power and Transmission	333,619	281,381
Operations and Maintenance	117,357	109,514
Depreciation	52,902	46,130
Amortization of Regulatory Assets/(Liabilities), Net	48,306	29,931
Energy Efficiency Programs	42,807	42,694
Taxes Other Than Income Taxes	68,080	66,953
Total Operating Expenses	663,071	576,603
Operating Income	141,846	158,011
Interest Expense:
Interest on Long-Term Debt	33,482	32,908
Other Interest	3,142	1,335
Total Interest Expense	36,624	34,243
Other Income/(Loss), Net	2,159	1,072
Income Before Income Tax Expense	107,381	124,840
Income Tax Expense	38,147	45,541
Net Income	69,234	79,299
NSTAR Electric Company [Member]
Operating Revenues	766,808	666,188
Operating Expenses:
Purchased Power and Transmission	401,867	319,082
Operations and Maintenance	75,824	85,924
Depreciation	48,768	46,626
Amortization of Regulatory Assets/(Liabilities), Net	-5,565	15,664
Energy Efficiency Programs	55,417	48,329
Taxes Other Than Income Taxes	30,962	32,151
Total Operating Expenses	607,273	547,776
Operating Income	159,535	118,412
Interest Expense:
Interest on Long-Term Debt	18,645	20,756
Other Interest	1,801	304
Total Interest Expense	20,446	21,060
Other Income/(Loss), Net	602	-31
Income Before Income Tax Expense	139,691	97,321
Income Tax Expense	56,130	39,234
Net Income	83,561	58,087
Public Service Company Of New Hampshire [Member]
Operating Revenues	284,847	299,833
Operating Expenses:
Purchased Power and Transmission	99,579	115,246
Operations and Maintenance	58,428	62,212
Depreciation	25,646	24,215
Amortization of Regulatory Assets/(Liabilities), Net	15,132	12,562
Energy Efficiency Programs	3,772	3,839
Taxes Other Than Income Taxes	19,079	17,715
Total Operating Expenses	221,636	235,789
Operating Income	63,211	64,044
Interest Expense:
Interest on Long-Term Debt	11,399	11,526
Other Interest	-127	445
Total Interest Expense	11,272	11,971
Other Income/(Loss), Net	382	265
Income Before Income Tax Expense	52,321	52,338
Income Tax Expense	20,276	19,700
Net Income	32,045	32,638
Western Massachusetts Electric Company [Member]
Operating Revenues	152,864	137,409
Operating Expenses:
Purchased Power and Transmission	69,661	49,431
Operations and Maintenance	19,784	22,579
Depreciation	10,375	10,321
Amortization of Regulatory Assets/(Liabilities), Net	3,927	399
Energy Efficiency Programs	11,075	11,865
Taxes Other Than Income Taxes	9,437	8,082
Total Operating Expenses	124,259	102,677
Operating Income	28,605	34,732
Interest Expense:
Interest on Long-Term Debt	6,045	6,062
Other Interest	778	-416
Total Interest Expense	6,823	5,646
Other Income/(Loss), Net	575	574
Income Before Income Tax Expense	22,357	29,660
Income Tax Expense	9,113	11,558
Net Income	$13,244	$18,102

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net Income	$255,133	$237,836
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	509	509
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	132	240
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	954	961
Other Comprehensive Income (Loss), Net of Tax, Total	1,595	1,710
Comprehensive Income Attributable to Noncontrolling Interests	-1,879	-1,879
Comprehensive Income	254,849	237,667
The Connecticut Light And Power Company [Member]
Net Income	69,234	79,299
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111	111
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	4	8
Other Comprehensive Income (Loss), Net of Tax, Total	115	119
Comprehensive Income	69,349	79,418
NSTAR Electric Company [Member]
Net Income	83,561	58,087
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	-180
Other Comprehensive Income (Loss), Net of Tax, Total	-180
Comprehensive Income	83,381
Public Service Company Of New Hampshire [Member]
Net Income	32,045	32,638
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	291	290
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	8	14
Other Comprehensive Income (Loss), Net of Tax, Total	299	304
Comprehensive Income	32,344	32,942
Western Massachusetts Electric Company [Member]
Net Income	13,244	18,102
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	85	85
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	1	2
Other Comprehensive Income (Loss), Net of Tax, Total	86	87
Comprehensive Income	$13,330	$18,189

CONSOLIDATED_STATEMENT_OF_CASH

CONSOLIDATED STATEMENT OF CASH FLOWS (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating Activities:
Net Income	$255,133	$237,836
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	163,837	150,807
Deferred Income Tax Expense (Benefit)	148,193	137,417
Pension, SERP and PBOP Expense	26,495	24,995
Pension and PBOP Contributions	-26,659	-6,622
Regulatory Over/(Under) Recoveries, Net	-110,748	872
Amortization of Regulatory Assets/(Liabilities), Net	60,604	57,898
Proceeds from DOE Damages Claim, Net	0	163,300
Other Noncash Income (Expense)	-21,617	-7,574
CYAPC and YAEC Deferred DOE Proceeds		-163,300
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	-328,299	-182,221
Increase Decrease in Fuel, Materials and Supplies	68,172	75,041
Taxes Receivable/(Accrued)	272,021	-59,840
Accounts Payable	-59,496	53,905
Other Current Assets and Liabilities	34,179	11,282
Net Cash Flows Provided by Operating Activities	481,815	493,796
Investing Activities:
Investments in Property, Plant and Equipment	-362,586	-348,691
Proceeds from Sales of Marketable Securities	114,730	128,505
Purchases of Marketable Securities	-116,735	-132,605
Other Investing Activities	66	1,637
Net Cash Flows Used in Investing Activities	-364,525	-351,154
Financing Activities:
Cash Dividends on Common Stock	-132,433	-118,460
Cash Dividends on Preferred Stock	-1,879	-1,879
Increase/(Decrease) in Short-Term Debt	-399,575	-299,500
Issuance of Long-Term Debt	450,000	400,000
Retirements of Long-Term Debt	0	-75,000
Other Financing Activities	-1,079	-2,017
Net Cash Flows Provided by/(Used in) Financing Activities	-84,966	-96,856
Net Increase/(Decrease) in Cash	32,324	45,786
Cash - Beginning of Year	38,703	43,364
Cash - End of Year	71,027	89,150
The Connecticut Light And Power Company [Member]
Operating Activities:
Net Income	69,234	79,299
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	52,902	46,130
Deferred Income Tax Expense (Benefit)	19,340	59,334
Pension, SERP and PBOP Expense, Net of Contributions	3,883	4,086
Regulatory Over/(Under) Recoveries, Net	-67,393	-40,399
Amortization of Regulatory Assets/(Liabilities), Net	48,306	29,931
Other Noncash Income (Expense)	2,322	4,536
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	-124,969	-82,833
Taxes Receivable/(Accrued)	158,163	7,015
Accounts Payable	-20,194	-2,872
Other Current Assets and Liabilities	-7,727	-8,730
Net Cash Flows Provided by Operating Activities	133,867	95,497
Investing Activities:
Investments in Property, Plant and Equipment	-127,631	-107,993
Other Investing Activities	1,981	1,027
Net Cash Flows Used in Investing Activities	-125,650	-106,966
Financing Activities:
Cash Dividends on Common Stock	-49,000	-42,800
Cash Dividends on Preferred Stock	-1,390	-1,390
Increase/(Decrease) in Notes Payable to Affiliate	56,700	64,300
Other Financing Activities	-65	-203
Net Cash Flows Provided by/(Used in) Financing Activities	6,245	19,907
Net Increase/(Decrease) in Cash	14,462	8,438
Cash - Beginning of Year	2,356	7,237
Cash - End of Year	16,818	15,675
NSTAR Electric Company [Member]
Operating Activities:
Net Income	83,561	58,087
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	8,049	6,096
Depreciation	48,768	46,626
Deferred Income Tax Expense (Benefit)	41,297	1,585
Pension, SERP and PBOP Expense, Net of Contributions	1,164	-4,908
Regulatory Over/(Under) Recoveries, Net	-103,142	6,423
Amortization of Regulatory Assets/(Liabilities), Net	-5,565	15,664
Other Noncash Income (Expense)	-21,885	-15,538
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	-90,465	-14,348
Increase Decrease in Fuel, Materials and Supplies	-13,504	-3,606
Taxes Receivable/(Accrued)	96,319	21,504
Accounts Payable	29,210	86,309
Other Current Assets and Liabilities	51,157	31,112
Accounts Payable Related Parties	96,368	-43,654
Net Cash Flows Provided by Operating Activities	221,332	191,352
Investing Activities:
Investments in Property, Plant and Equipment	-79,776	-94,957
Other Investing Activities	53	-489
Net Cash Flows Used in Investing Activities	-79,723	-95,446
Financing Activities:
Cash Dividends on Common Stock	-49,500	-253,000
Cash Dividends on Preferred Stock	-490	-490
Increase/(Decrease) in Short-Term Debt	-86,500	-103,500
Issuance of Long-Term Debt	0	300,000
Other Financing Activities	5	-4,902
Net Cash Flows Provided by/(Used in) Financing Activities	-136,485	-61,892
Net Increase/(Decrease) in Cash	5,124	34,014
Cash - Beginning of Year	12,773	8,021
Cash - End of Year	17,897	42,035
Public Service Company Of New Hampshire [Member]
Operating Activities:
Net Income	32,045	32,638
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	25,646	24,215
Deferred Income Tax Expense (Benefit)	38,767	33,667
Regulatory Over/(Under) Recoveries, Net	-288	6,827
Amortization of Regulatory Assets/(Liabilities), Net	15,132	12,562
Other Noncash Income (Expense)	2,999	4,660
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	-31,556	-14,268
Increase Decrease in Fuel, Materials and Supplies	34,572	34,326
Taxes Receivable/(Accrued)	-16,576	-30,254
Accounts Payable	-4,285	3,403
Other Current Assets and Liabilities	17,468	21,505
Net Cash Flows Provided by Operating Activities	113,924	129,281
Investing Activities:
Investments in Property, Plant and Equipment	-71,905	-61,864
Other Investing Activities	-2,277	-76
Net Cash Flows Used in Investing Activities	-74,182	-61,940
Financing Activities:
Cash Dividends on Common Stock	-26,500	-16,500
Increase/(Decrease) in Notes Payable to Affiliate	-8,500	-46,600
Other Financing Activities	-82	-87
Net Cash Flows Provided by/(Used in) Financing Activities	-35,082	-63,187
Net Increase/(Decrease) in Cash	4,660	4,154
Cash - Beginning of Year	489	130
Cash - End of Year	5,149	4,284
Western Massachusetts Electric Company [Member]
Operating Activities:
Net Income	13,244	18,102
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	10,375	10,321
Deferred Income Tax Expense (Benefit)	12,759	14,688
Regulatory Over/(Under) Recoveries, Net	-14,442	5,780
Amortization of Regulatory Assets/(Liabilities), Net	3,927	399
Other Noncash Income (Expense)	-1,197	-1,351
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	-26,298	34,905
Taxes Receivable/(Accrued)	64	-17,126
Accounts Payable	85	-10,516
Other Current Assets and Liabilities	65	-8,869
Net Cash Flows Provided by Operating Activities	-1,418	46,333
Investing Activities:
Investments in Property, Plant and Equipment	-35,899	-30,347
Proceeds from Sales of Marketable Securities	23,249	34,656
Purchases of Marketable Securities	-23,442	-34,804
Net Cash Flows Used in Investing Activities	-36,092	-30,495
Financing Activities:
Cash Dividends on Common Stock	-9,300	-49,000
Increase/(Decrease) in Notes Payable to Affiliate	49,100	37,400
Other Financing Activities	-245	-11
Net Cash Flows Provided by/(Used in) Financing Activities	39,555	-11,611
Net Increase/(Decrease) in Cash	2,045	4,227
Cash - Beginning of Year	0	0
Cash - End of Year	$2,045	$4,227

SUMMARY_OF_SIGNIFICANT_ACCOUNT

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

3 Months Ended

Mar. 31, 2015

Notes To Consolidated Financial Statements [Abstract]

Significant Accounting Policies [Text Block]

EVERSOURCE ENERGY AND SUBSIDIARIES

THE CONNECTICUT LIGHT AND POWER COMPANY

NSTAR ELECTRIC COMPANY AND SUBSIDIARY

PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE AND SUBSIDIARY

WESTERN MASSACHUSETTS ELECTRIC COMPANY

COMBINED NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (Unaudited)

Refer to the Glossary of Terms included in this combined Quarterly Report on Form 10-Q for abbreviations and acronyms used throughout the combined notes to the unaudited condensed consolidated financial statements.

1.       SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

A.       Basis of Presentation

Eversource Energy is a public utility holding company primarily engaged through its wholly owned regulated utility subsidiaries in the energy delivery business. Eversource Energy's wholly owned regulated utility subsidiaries consist of CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas. Eversource provides energy delivery service to approximately 3.6 million electric and natural gas customers through these six regulated utilities in Connecticut, Massachusetts and New Hampshire.

On April 29, 2015, the Company's name was changed from Northeast Utilities to Eversource Energy. CL&P, NSTAR Electric, PSNH and WMECO operate under the brand Eversource Energy.

The unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements."

The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the entirety of this combined Quarterly Report on Form 10-Q and the 2014 combined Annual Report on Form 10-K of Eversource, CL&P, NSTAR Electric, PSNH and WMECO, which was filed with the SEC. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly Eversource's, CL&P's, NSTAR Electric's, PSNH's and WMECO's financial position as of March 31, 2015 and December 31, 2014, and the results of operations, comprehensive income and cash flows for the three months ended March 31, 2015 and 2014. The results of operations, comprehensive income and cash flows for the three months ended March 31, 2015 and 2014 are not necessarily indicative of the results expected for a full year.

Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's, PSNH's and WMECO's combined ownership interest in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements.

Eversource's utility subsidiaries' distribution (including generation) and transmission businesses and NPT are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations, which considers the effect of regulation on the differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. See Note 2, "Regulatory Accounting," for further information.

Certain reclassifications of prior period data were made in the accompanying financial statements to conform to the current period presentation.

B.       Accounting Standards

Accounting Standards Issued but not Yet Adopted: In May 2014, the Financial Accounting Standards Board (FASB) issued ASU 2014-09, Revenue from Contracts with Customers, effective January 1, 2017, which amends existing revenue recognition guidance and is required to be applied retrospectively (either to each reporting period presented or cumulatively at the date of initial application). In April 2015, the FASB decided to propose a one-year deferral of the effective date of the ASU. Management is reviewing the requirements of the ASU. The ASU is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH and WMECO.

C.       Provision for Uncollectible Accounts

Eversource, including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at estimated net realizable value by maintaining a provision for uncollectible accounts. This provision is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. The estimate is based upon historical collection and write-off experience and management's assessment of collectability from customers. Management continuously assesses the collectability of receivables and adjusts collectability estimates based on actual experience. Receivable balances are written off against the provision for uncollectible accounts when the accounts are terminated and these balances are deemed to be uncollectible.

The PURA allows CL&P and Yankee Gas to accelerate the recovery of accounts receivable balances attributable to qualified customers under financial or medical duress (uncollectible hardship accounts receivable) outstanding for greater than 90 days. The DPU allows WMECO to also recover in rates amounts associated with certain uncollectible hardship accounts receivable. Uncollectible customer account balances, which are expected to be recovered in rates, are included in Regulatory Assets or Other Long-Term Assets.

The total provision for uncollectible accounts and for uncollectible hardship accounts, which is included in the total provision, are included in Receivables, Net on the balance sheets, and were as follows:

Total Provision for Uncollectible Accounts

Uncollectible Hardship

(Millions of Dollars)

As of March 31, 2015

As of December 31, 2014

As of March 31, 2015

As of December 31, 2014

ES

$

187.4

$

175.3

$

92.3

$

91.5

CL&P

86.6

84.3

74.5

74

NSTAR Electric

43.8

40.7

-

-

PSNH

8.1

7.7

-

-

WMECO

10.7

9.9

6.5

6.2

D.       Fair Value Measurements

Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases or normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans and nonrecurring fair value measurements of nonfinancial assets such as goodwill and AROs, and is also used to estimate the fair value of preferred stock and long-term debt.

Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available and minimizes the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and Eversource's policy is to recognize transfers between levels of the fair value hierarchy as of the end of the reporting period. The three levels of the fair value hierarchy are described below:

Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date.  Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis.

Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable.

Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products.

Determination of Fair Value: The valuation techniques and inputs used in Eversource's fair value measurements are described in Note 4, "Derivative Instruments," Note 5, "Marketable Securities," and Note 9, "Fair Value of Financial Instruments," to the financial statements.

E.       Other Income, Net

Items included within Other Income, Net on the statements of income primarily consist of investment income/(loss), interest income, AFUDC related to equity funds, and equity in earnings. Investment income/(loss) primarily relates to debt and equity securities held in trust. For further information, see Note 5, "Marketable Securities," to the financial statements.

F.       Other Taxes

Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respective customers. These gross receipts taxes are shown on a gross basis with collections in Operating Revenues and payments in Taxes Other Than Income Taxes on the statements of income as follows:

For the Three Months Ended

(Millions of Dollars)

31-Mar-15

31-Mar-14

ES

$

41.9

$

44.4

CL&P

33

35.6

Certain sales taxes are collected by Eversource's companies that serve customers in Connecticut and Massachusetts as agents for state and local governments and are recorded on a net basis with no impact on the statements of income.

G.

Supplemental Cash Flow Information

Non-cash investing activities include plant additions included in Accounts Payable as follows:

(Millions of Dollars)

As of March 31, 2015

As of March 31, 2014

ES

$

110.4

$

108.5

CL&P

42.3

36.2

NSTAR Electric

21.9

28

PSNH

21.7

14.4

WMECO

8.3

14.4

H.       Severance Benefits

For the three months ended March 31, 2015 and 2014, Eversource recorded severance benefit expense of $0.4 million and $4.3 million, respectively, in connection with ongoing post-merger integration and, in 2014, the partial outsourcing of information technology functions. As of March 31, 2015 and December 31, 2014, the severance accrual totaled $9 million and $10.4 million, respectively, and was included in Other Current Liabilities on the balance sheets.

REGULATORY_ACCOUNTING

REGULATORY ACCOUNTING	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Public Utilities Disclosure [Text Block]	2.       REGULATORY ACCOUNTING
	Eversource's Regulated companies are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations and reflect the effects of the rate-making process. The rates charged to the customers of Eversource's Regulated companies are designed to collect each company's costs to provide service, including a return on investment.
	Management believes it is probable that each of the Regulated companies will recover their respective investments in long-lived assets, including regulatory assets. If management were to determine that it could no longer apply the accounting guidance applicable to rate-regulated enterprises to any of the Regulated companies' operations, or that management could not conclude it is probable that costs would be recovered from customers in future rates, the costs would be charged to net income in the period in which the determination is made.
	Regulatory Assets: The components of regulatory assets are as follows:
		As of March 31, 2015			As of December 31, 2014
	(Millions of Dollars)	ES			ES
	Benefit Costs	$	1,976.60		$	2,016.00
	Derivative Liabilities		410.2			425.5
	Income Taxes, Net		632.1			635.3
	Storm Restoration Costs		504.8			502.8
	Goodwill-related		500.2			505.4
	Regulatory Tracker Mechanisms		434.5			350.5
	Contractual Obligations - Yankee Companies		119			123.8
	Other Regulatory Assets		151.4			167.3
	Total Regulatory Assets		4,728.80			4,726.60
	Less: Current Portion		747.3			672.5
	Total Long-Term Regulatory Assets	$	3,981.50		$	4,054.10
			As of March 31, 2015									As of December 31, 2014
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Benefit Costs		$	436.7		$	505.6	$	171.2	$	83.3	$	445.4	$	515.9	$	174.3	$	85
	Derivative Liabilities			403.3			3.5		-		-		410.9		4.5		-		-
	Income Taxes, Net			438.7			83.7		36.8		31.2		437.7		83.7		38		35.5
	Storm Restoration Costs			308.5			119.7		46.9		29.7		319.6		103.7		47.7		31.8
	Goodwill-related			-			429.5		-		-		-		433.9		-		-
	Regulatory Tracker Mechanisms			10.1			261.2		93.4		47.6		16.1		141.4		103.5		33
	Other Regulatory Assets			66.5			85		38.9		12.8		66.1		94.7		41.3		12.9
	Total Regulatory Assets			1,663.80			1,488.20		387.2		204.6		1,695.80		1,377.80		404.8		198.2
	Less: Current Portion			209.6			309.5		100		66.7		220.3		198.7		111.7		51.9
	Total Long-Term Regulatory Assets		$	1,454.20		$	1,178.70	$	287.2	$	137.9	$	1,475.50	$	1,179.10	$	293.1	$	146.3
	Regulatory Costs in Other Long-Term Assets: The Regulated companies had $49.3 million ($1.6 million for CL&P, $18.3 million for NSTAR Electric, $0.4 million for PSNH and $11.8 million for WMECO) and $60.5 million ($1.3 million for CL&P, $33.2 million for NSTAR Electric, $0.9 million for PSNH, and $11 million for WMECO) of additional regulatory costs as of March 31, 2015 and December 31, 2014, respectively, that were included in Other Long-Term Assets on the balance sheets. These amounts represent incurred costs for which recovery has not yet been specifically approved by the applicable regulatory agency. However, based on regulatory policies or past precedent on similar costs, management believes it is probable that these costs will ultimately be approved and recovered from customers in rates. The NSTAR Electric balance as of March 31, 2015 and December 31, 2014 primarily related to costs deferred in connection with the basic service bad debt adder. See Note 8E, "Commitments and Contingencies – Basic Service Bad Debt Adder," for further information.
	Regulatory Liabilities: The components of regulatory liabilities are as follows:
		As of March 31, 2015			As of December 31, 2014
	(Millions of Dollars)	ES			ES
	Cost of Removal	$	452.8		$	439.9
	Regulatory Tracker Mechanisms		183.3			192.3
	AFUDC - Transmission		67.1			67.1
	Other Regulatory Liabilities		22.9			50.8
	Total Regulatory Liabilities		726.1			750.1
	Less: Current Portion		201.2			235
	Total Long-Term Regulatory Liabilities	$	524.9		$	515.1
			As of March 31, 2015									As of December 31, 2014
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Cost of Removal		$	23.1		$	263.4	$	51.3	$	2.8	$	19.7	$	258.3	$	50.3	$	1.1
	Regulatory Tracker Mechanisms			77.5			22.5		13.9		22.2		122.6		20.7		14.2		22.3
	AFUDC - Transmission			53.3			4.7		-		9.1		53.6		4.4		-		9.1
	Other Regulatory Liabilities			12.3			2.1		2.8		0.9		10.1		28.9		2.9		0.8
	Total Regulatory Liabilities			166.2			292.7		68		35		206		312.3		67.4		33.3
	Less: Current Portion			84.1			24.6		16.1		22.3		124.7		49.6		16		22.5
	Total Long-Term Regulatory Liabilities		$	82.1		$	268.1	$	51.9	$	12.7	$	81.3	$	262.7	$	51.4	$	10.8
	2015 Regulatory Developments: As a result of the March 3, 2015 FERC order in the pending ROE complaint proceedings described in Note 8C, "Commitments and Contingencies – FERC ROE Complaints," in the first quarter of 2015, Eversource recognized a pre-tax charge to earnings (excluding interest) of $20 million, of which $12.5 million was recorded at CL&P, $2.4 million at NSTAR Electric, $1 million at PSNH, and $4.1 million at WMECO. The pre-tax charge was recorded as a regulatory liability and as a reduction of Operating Revenues.
	On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the "Settlement") as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric's energy efficiency programs for 2008 through 2011 (11 dockets in total). As a result, NSTAR Electric and NSTAR Gas will refund a combined $44.7 million to customers. The refund was recorded as a regulatory liability as of March 31, 2015 and NSTAR Electric recognized a $21.7 million pre-tax benefit in the first quarter of 2015. For further information, see Note 8D, "Commitments and Contingencies – 2014 Comprehensive Settlement Agreement."
	On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had appropriately accounted for the removal of supply-related bad debt costs from base distribution rates effective January 1, 2006. The DPU ordered NSTAR Electric and the Massachusetts Attorney General to collaborate on the reconciliation of energy-related bad debt costs through 2014. During the second quarter of 2015, NSTAR Electric expects to file with the DPU to recover from customers approximately $43 million of supply-related bad debt costs. In the first quarter of 2015, as a result of the DPU order, NSTAR Electric increased its regulatory assets and reduced Operations and Maintenance expense by $24.2 million, resulting in an increase in after-tax earnings of $14.5 million. For further information, see Note 8E, "Commitments and Contingencies – Basic Service Bad Debt Adder."

PROPERTY_PLANT_AND_ACCUMULATED

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Property Plant And Equipment Disclosure [Text Block]	3.       PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION
	The following tables summarize the investments in utility property, plant and equipment by asset category:
				As of March 31, 2015			As of December 31, 2014
	(Millions of Dollars)			ES			ES
	Distribution - Electric			$	12,539.30		$	12,495.20
	Distribution - Natural Gas				2,584.80			2,595.40
	Transmission				6,959.40			6,930.70
	Generation				1,172.20			1,170.90
	Electric and Natural Gas Utility				23,255.70			23,192.20
	Other (1)				547.9			551.3
	Property, Plant and Equipment, Gross				23,803.60			23,743.50
	Less: Accumulated Depreciation
		Electric and Natural Gas Utility			-5,842.60			-5,777.80
		Other			-232.3			-231.8
	Total Accumulated Depreciation				-6,074.90			-6,009.60
	Property, Plant and Equipment, Net				17,728.70			17,733.90
	Construction Work in Progress				1,082.00			913.1
	Total Property, Plant and Equipment, Net			$	18,810.70		$	18,647.00
	(1)       These assets are primarily comprised of building improvements, computer software, hardware and equipment and telecommunications assets at Eversource Service and Eversource's unregulated companies.
		As of March 31, 2015										As of December 31, 2014
					NSTAR									NSTAR
	(Millions of Dollars)	CL&P			Electric			PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Distribution	$	5,180.00		$	4,907.80		$	1,704.10	$	787.4	$	5,158.80	$	4,895.50	$	1,696.70	$	784.2
	Transmission		3,274.70			1,950.60			794.6		891.9		3,274.00		1,928.50		789.7		891
	Generation		-			-			1,137.80		34.4		-		-		1,136.50		34.4
	Property, Plant and Equipment, Gross		8,454.70			6,858.40			3,636.50		1,713.70		8,432.80		6,824.00		3,622.90		1,709.60
	Less: Accumulated Depreciation		-1,950.70			-1,783.60			-1,105.70		-303.3		-1,928.00		-1,761.40		-1,090.00		-297.4
	Property, Plant and Equipment, Net		6,504.00			5,074.80			2,530.80		1,410.40		6,504.80		5,062.60		2,532.90		1,412.20
	Construction Work in Progress		370.9			289.5			135.5		73.5		304.9		272.8		102.9		49.1
	Total Property, Plant and Equipment, Net	$	6,874.90		$	5,364.30		$	2,666.30	$	1,483.90	$	6,809.70	$	5,335.40	$	2,635.80	$	1,461.30
	As of March 31, 2015, PSNH had $1.1 billion in gross generation assets and Accumulated Depreciation of $497.1 million. These generation assets are the subject of a divestiture agreement in principle in a settlement Term Sheet entered into on March 11, 2015 between PSNH and key New Hampshire officials (Term Sheet) whereby, among other resolutions, PSNH has agreed to sell these assets. Upon completion of the sale, all remaining stranded costs will be recovered via bonds that will be secured by a non-bypassable charge to PSNH's customers. Consummation of the Term Sheet provisions is conditioned upon the enactment of New Hampshire legislation, completion of a final Settlement Agreement reflecting the provisions of the Term Sheet (Settlement Agreement), and NHPUC approval of the Settlement Agreement. See Note 8F, “Commitments and Contingencies – PSNH Generation Restructuring,” for further information.

DERIVATIVE_INSTRUMENTS

DERIVATIVE INSTRUMENTS	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	4.       DERIVATIVE INSTRUMENTS
	The Regulated companies purchase and procure energy and energy-related products, which are subject to price volatility, for their customers. The costs associated with supplying energy to customers are recoverable through customer rates. The Regulated companies manage the risks associated with the price volatility of energy and energy-related products through the use of derivative and nonderivative contracts.
	Many of the derivative contracts meet the definition of, and are designated as, normal and qualify for accrual accounting under the applicable accounting guidance. The costs and benefits of derivative contracts that meet the definition of normal are recognized in Operating Expenses or Operating Revenues on the statements of income, as applicable, as electricity or natural gas is delivered.
	Derivative contracts that are not designated as normal are recorded at fair value as current or long-term Derivative Assets or Derivative Liabilities on the balance sheets. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivatives, as contract settlement amounts are recovered from, or refunded to, customers in their respective energy supply rates.
	The gross fair values of derivative assets and liabilities with the same counterparty are offset and reported as net Derivative Assets or Derivative Liabilities, with current and long-term portions, on the balance sheets. The following table presents the gross fair values of contracts categorized by risk type and the net amount recorded as current or long-term derivative asset or liability:
				As of March 31, 2015									As of December 31, 2014
				Commodity Supply						Net Amount			Commodity Supply						Net Amount
				and Price Risk						Recorded as			and Price Risk							Recorded as
	(Millions of Dollars)			Management			Netting (1)			a Derivative			Management			Netting (1)			a Derivative
	Current Derivative Assets:
	Level 3:
		ES		$	16		$	-6.6		$	9.4		$	16.2		$	-6.6		$	9.6
		CL&P			16			-6.6			9.4			16.1			-6.6			9.5
		NSTAR Electric			-			-			-			0.1			-			0.1
	Long-Term Derivative Assets:
	Level 3:
		ES, CL&P		$	88.3		$	-17.8		$	70.5		$	93.5		$	-19.2		$	74.3
	Current Derivative Liabilities:
	Level 2:
		ES		$	-3.2		$	-		$	-3.2		$	-9.8		$	-		$	-9.8
	Level 3:
		ES			-90.3			-			-90.3			-90			-			-90
		CL&P			-88.2			-			-88.2			-88.5			-			-88.5
		NSTAR Electric			-2.1			-			-2.1			-1.5			-			-1.5
	Long-Term Derivative Liabilities:
	Level 2:
		ES		$	-0.2		$	-		$	-0.2		$	-0.3		$	-		$	-0.3
	Level 3:
		ES			-396.4			-			-396.4			-409.3			-			-409.3
		CL&P			-395			-			-395			-406.2			-			-406.2
		NSTAR Electric			-1.4			-			-1.4			-3.1			-			-3.1
	(1)       Amounts represent derivative assets and liabilities that Eversource elected to record net on the balance sheets. These amounts are subject to master netting agreements or similar agreements for which the right of offset exists.
	For further information on the fair value of derivative contracts, see Note 1D, "Summary of Significant Accounting Policies - Fair Value Measurements," to the financial statements.
	Derivative Contracts at Fair Value with Offsetting Regulatory Amounts
	Commodity Supply and Price Risk Management: As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of each contract allocated to CL&P and 20 percent allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020.
	NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity-related contract to purchase up to 35 MW per year through 2019.
	As of March 31, 2015 and December 31, 2014, Eversource had NYMEX financial contracts for natural gas futures in order to reduce variability associated with the purchase price of approximately 5.3 million and 8.8 million MMBtu of natural gas, respectively.
	For the three months ended March 31, 2015 and 2014, there were losses of $16.6 million and gains of $54.1 million, respectively, recorded as regulatory assets and liabilities, which reflect the current change in fair value associated with Eversource's derivative contracts.
	Credit Risk
	Certain of Eversource's derivative contracts contain credit risk contingent provisions. These provisions require Eversource to maintain investment grade credit ratings from the major rating agencies and to post collateral for contracts in a net liability position over specified credit limits. As of March 31, 2015, Eversource had approximately $3 million of derivative contracts in a net liability position that were subject to credit risk contingent provisions and would have been required to post additional collateral of approximately $3 million if ES parent's unsecured debt credit ratings had been downgraded to below investment grade. As of December 31, 2014, Eversource had approximately $10 million of derivative contracts in a net liability position that were subject to credit risk contingent provisions and would have been required to post additional collateral of approximately $10 million if ES parent's unsecured debt credit ratings had been downgraded to below investment grade.
	Fair Value Measurements of Derivative Instruments
	Derivative contracts classified as Level 2 in the fair value hierarchy relate to the financial contracts for natural gas futures. Prices are obtained from broker quotes and are based on actual market activity. The contracts are valued using NYMEX natural gas prices. Valuations of these contracts also incorporate discount rates using the yield curve approach.
	The fair value of derivative contracts classified as Level 3 utilizes significant unobservable inputs. The fair value is modeled using income techniques, such as discounted cash flow valuations adjusted for assumptions relating to exit price. Significant observable inputs for valuations of these contracts include energy and energy-related product prices in future years for which quoted prices in an active market exist. Fair value measurements categorized in Level 3 of the fair value hierarchy are prepared by individuals with expertise in valuation techniques, pricing of energy and energy-related products, and accounting requirements. The future power and capacity prices for periods that are not quoted in an active market or established at auction are based on available market data and are escalated based on estimates of inflation to address the full time period of the contract.
	Valuations of derivative contracts using a discounted cash flow methodology include assumptions regarding the timing and likelihood of scheduled payments and also reflect non-performance risk, including credit, using the default probability approach based on the counterparty's credit rating for assets and the Company's credit rating for liabilities. Valuations incorporate estimates of premiums or discounts that would be required by a market participant to arrive at an exit price, using historical market transactions adjusted for the terms of the contract.
	The following is a summary of Eversource's, including CL&P's and NSTAR Electric's, Level 3 derivative contracts and the range of the significant unobservable inputs utilized in the valuations over the duration of the contracts:
			As of March 31, 2015									As of December 31, 2014
				Range						Period Covered			Range						Period Covered
	Energy Prices:
	ES, CL&P		$	48			per MWh			2020		$	52			per MWh			2020
	Capacity Prices:
	ES		$	8.8	-	12.98		per kW-Month		2016 - 2026		$	5.3	-	12.98		per kW-Month		2016 - 2026
	CL&P		$	11.13	-	12.98		per kW-Month		2019 - 2026		$	11.08	-	12.98		per kW-Month		2018 - 2026
	NSTAR Electric		$	8.8	-	11.13		per kW-Month		2016 - 2019		$	5.3	-	11.1		per kW-Month		2016 - 2019
	Forward Reserve:
	ES, CL&P		$	5.8	-	9.5		per kW-Month		2015 - 2024		$	5.8	-	9.5		per kW-Month		2015 - 2024
	REC Prices:
	ES, NSTAR Electric		$	45	-	50	per REC			2015 - 2018		$	38	-	56	per REC			2015 - 2018
	Exit price premiums of 7 percent through 24 percent are also applied on these contracts and reflect the most recent market activity available for similar type contracts.
	Significant increases or decreases in future energy or capacity prices in isolation would decrease or increase, respectively, the fair value of the derivative liability. Any increases in the risk premiums would increase the fair value of the derivative liabilities. Changes in these fair values are recorded as a regulatory asset or liability and would not impact net income.
	Valuations using significant unobservable inputs: The following table presents changes in the Level 3 category of derivative assets and derivative liabilities measured at fair value on a recurring basis. The derivative assets and liabilities are presented on a net basis.
			For the Three Months Ended March 31,
			2015									2014
									NSTAR									NSTAR
	(Millions of Dollars)		ES			CL&P			Electric			ES			CL&P			Electric
Derivatives, Net:
Fair Value as of Beginning of Period		$	-415.4		$	-410.9		$	-4.5		$	-635.2		$	-630.6		$	-7.3
Net Realized/Unrealized Gains/(Losses) Included in Regulatory Assets and Liabilities			-12.1			-12.1			-			49.2			52			-0.1
Settlements			20.7			19.7			1			21.7			21.6			0.1
Fair Value as of End of Period		$	-406.8		$	-403.3		$	-3.5		$	-564.3		$	-557		$	-7.3

MARKETABLE_SECURITIES

MARKETABLE SECURITIES	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Marketable Securities [Text Block]	5.       MARKETABLE SECURITIES
	Eversource maintains trusts to fund certain non-qualified executive benefits and WMECO maintains a spent nuclear fuel trust to fund WMECO's prior period spent nuclear fuel liability. These trusts hold marketable securities. These trusts are not subject to regulatory oversight by state or federal agencies. In addition, CYAPC and YAEC maintain legally restricted trusts, each of which holds marketable securities, for settling the decommissioning obligations of their nuclear power plants.
	The Company elected to record mutual funds at fair value and certain other equity investments as trading securities, with the changes in fair values recorded in Other Income, Net on the statements of income. As of March 31, 2015 and December 31, 2014, the mutual funds and equity investments were classified as Level 1 in the fair value hierarchy and totaled $86.7 million and $85.1 million, respectively. For the three months ended March 31, 2015 and 2014, net gains on these securities of $1.6 million and $0.7 million, respectively, were recorded in Other Income, Net on the statements of income. Dividend income is recorded in Other Income, Net when dividends are declared. All other marketable securities are accounted for as available-for-sale.
	Available-for-Sale Securities: The following is a summary of Eversource's and WMECO's available-for-sale securities. These securities are recorded at fair value and are included in current and long-term Marketable Securities on the balance sheets.
			As of March 31, 2015												As of December 31, 2014
						Pre-Tax			Pre-Tax								Pre-Tax		Pre-Tax
			Amortized			Unrealized			Unrealized						Amortized		Unrealized		Unrealized
	(Millions of Dollars)		Cost			Gains			Losses			Fair Value			Cost		Gains		Losses		Fair Value
	ES
		Debt Securities (1)	$	318.2		$	8.2		$	-0.1		$	326.3		$	313	$	7.5	$	-0.3	$	320.2
		Equity Securities (1)		159.5			77			-			236.5			160.6		73.3		-		233.9
	WMECO
		Debt Securities (2)		58.2			-			-			58.2			58.2		-		-0.1		58.1
	Eversource's amounts include CYAPC's and YAEC's marketable securities held in nuclear decommissioning trusts of $458.3 million and $450.8 million as of March 31, 2015 and December 31, 2014, respectively, which are legally restricted and can only be used for the costs of decommissioning of the nuclear power plants owned by these companies. Unrealized gains and losses for the nuclear decommissioning trusts are recorded in Marketable Securities with the corresponding offset to Other Long-Term Liabilities on the balance sheets, with no impact on the statements of income. All of the equity securities accounted for as available-for-sale securities are held in the CYAPC and YAEC trusts.
	Unrealized gains and losses on debt securities held by WMECO are recorded in Marketable Securities with the corresponding offset to Other Long-Term Assets on the balance sheets.
	Unrealized Losses and Other-than-Temporary Impairment: There have been no significant unrealized losses, other-than-temporary impairments or credit losses for Eversource or WMECO. Factors considered in determining whether a credit loss exists include the duration and severity of the impairment, adverse conditions specifically affecting the issuer, and the payment history, ratings and rating changes of the security. For asset-backed debt securities, underlying collateral and expected future cash flows are also evaluated.
	Realized Gains and Losses: Realized gains and losses on available-for-sale securities are recorded in Other Income, Net for Eversource's benefit trust, Other Long-Term Assets for WMECO, and are offset in Other Long-Term Liabilities for CYAPC and YAEC. Eversource utilizes the specific identification basis method for the Eversource benefit trust, and the average cost basis method for the WMECO trust and the CYAPC and YAEC nuclear decommissioning trusts to compute the realized gains and losses on the sale of available-for-sale securities.
	Contractual Maturities: As of March 31, 2015, the contractual maturities of available-for-sale debt securities were as follows:
			ES						WMECO
			Amortized						Amortized
	(Millions of Dollars)		Cost			Fair Value			Cost			Fair Value
	Less than one year (1)		$	59.9		$	59.9		$	33.2		$	33.2
	One to five years			83.3			83.8			21.3			21.3
	Six to ten years			61.6			63.5			0.6			0.6
	Greater than ten years			113.4			119.1			3.1			3.1
	Total Debt Securities		$	318.2		$	326.3		$	58.2		$	58.2
	1)       Amounts in the Less than one year Eversource category include securities in the CYAPC and YAEC nuclear decommissioning trusts, which are restricted and are classified in long-term Marketable Securities on the balance sheets.
	Fair Value Measurements: The following table presents the marketable securities recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy:
					ES						WMECO
	(Millions of Dollars)				As of March 31, 2015			As of December 31, 2014			As of March 31, 2015			As of December 31, 2014
	Level 1:
		Mutual Funds and Equities			$	323.2		$	319		$	-		$	-
		Money Market Funds				32.9			24.9			10.5			4.3
	Total Level 1				$	356.1		$	343.9		$	10.5		$	4.3
	Level 2:
		U.S. Government Issued Debt Securities (Agency and Treasury)			$	46		$	51.3		$	-		$	-
		Corporate Debt Securities				157.3			49.1			14.4			14.7
		Asset-Backed Debt Securities				36.5			54.1			12.1			14.5
		Municipal Bonds				31.9			116.3			12.9			13
		Other Fixed Income Securities				21.7			24.5			8.3			11.6
	Total Level 2				$	293.4		$	295.3		$	47.7		$	53.8
	Total Marketable Securities				$	649.5		$	639.2		$	58.2		$	58.1
	U.S. government issued debt securities are valued using market approaches that incorporate transactions for the same or similar bonds and adjustments for yields and maturity dates. Corporate debt securities are valued using a market approach, utilizing recent trades of the same or similar instrument and also incorporating yield curves, credit spreads and specific bond terms and conditions. Asset-backed debt securities include collateralized mortgage obligations, commercial mortgage backed securities, and securities collateralized by auto loans, credit card loans or receivables. Asset-backed debt securities are valued using recent trades of similar instruments, prepayment assumptions, yield curves, issuance and maturity dates, and tranche information. Municipal bonds are valued using a market approach that incorporates reported trades and benchmark yields. Other fixed income securities are valued using pricing models, quoted prices of securities with similar characteristics, and discounted cash flows.

SHORT_TERM_AND_LONG_TERM_DEBT

SHORT TERM AND LONG TERM DEBT	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Debt Disclosure	6.       SHORT-TERM AND LONG-TERM DEBT
	Credit Agreements and Commercial Paper Programs: ES parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year $1.45 billion revolving credit facility that expires September 6, 2019. The revolving credit facility is used primarily to backstop ES parent's $1.45 billion commercial paper program. The commercial paper program allows ES parent to issue commercial paper as a form of short-term debt. As of March 31, 2015 and December 31, 2014, ES parent had $788 million and approximately $1.1 billion, respectively, in short-term borrowings outstanding under the ES parent commercial paper program, leaving $662 million and $348.9 million of available borrowing capacity as of March 31, 2015 and December 31, 2014, respectively. The weighted-average interest rate on these borrowings as of March 31, 2015 and December 31, 2014 was 0.53 percent and 0.43 percent, respectively, which is generally based on A2/P2 rated commercial paper. As of March 31, 2015, there were intercompany loans from ES parent of $190.1 million to CL&P, $82 million to PSNH and $70.5 million to WMECO. As of December 31, 2014, there were intercompany loans from ES parent of $133.4 million to CL&P, $90.5 million to PSNH and $21.4 million to WMECO.
	NSTAR Electric has a five-year $450 million revolving credit facility that expires September 6, 2019. This facility serves to backstop NSTAR Electric's existing $450 million commercial paper program. As of March 31, 2015 and December 31, 2014, NSTAR Electric had $215.5 million and $302 million, respectively, in short-term borrowings outstanding under its commercial paper program, leaving $234.5 million and $148 million of available borrowing capacity as of March 31, 2015 and December 31, 2014, respectively. The weighted-average interest rate on these borrowings as of March 31, 2015 and December 31, 2014 was 0.35 percent and 0.27 percent, respectively, which is generally based on A2/P1 rated commercial paper.
	Except as described below, amounts outstanding under the commercial paper programs are included in Notes Payable for Eversource and NSTAR Electric and classified in current liabilities on the balance sheets as all borrowings are outstanding for no more than 364 days at one time. Intercompany loans from ES parent to CL&P, PSNH and WMECO are included in Notes Payable to ES Parent and classified in current liabilities on the balance sheets. Intercompany loans from ES parent to CL&P, PSNH and WMECO are eliminated in consolidation in Eversource's balance sheets.
	Long-Term Debt: On January 15, 2015, ES parent issued $150 million of 1.60 percent Series G Senior Notes, due to mature in 2018 and $300 million of 3.15 percent Series H Senior Notes, due to mature in 2025. The proceeds, net of issuance costs, were used to repay short-term borrowings outstanding under the ES parent commercial paper program. As the debt issuances refinanced short-term debt, the short-term debt was classified as Long-Term Debt as of December 31, 2014.
	On April 1, 2015, CL&P repaid at maturity the $100 million 5.00 percent 2005 Series A First and Refunding Mortgage Bonds using short-term borrowings. On April 1, 2015, CL&P also redeemed the $62 million 1996A Series 1.55 percent PCRBs that were subject to mandatory tender, using short term borrowings.
	Long-Term Debt Issuance Authorization: On April 3, 2015, the DPU authorized NSTAR Gas to issue up to $100 million in long-term debt for the period through December 31, 2015.

PENSION_BENEFITS_AND_POSTRETIR

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	7.       Pension Benefits and Postretirement Benefits Other than Pensions
	As of December 31, 2014, Eversource Service sponsored two defined benefit retirement plans that covered eligible employees, including employees of CL&P, NSTAR Electric, PSNH and WMECO. Effective January 1, 2015, the two pension plans were merged into one plan, sponsored by Eversource Service. As of December 31, 2014, Eversource Service also sponsored defined benefit postretirement plans that provide certain retiree benefits, primarily medical, dental and life insurance, to retiring employees that meet certain age and service eligibility requirements, including employees of CL&P, NSTAR Electric, PSNH and WMECO. Effective January 1, 2015, the postretirement plans were merged into one plan, sponsored by Eversource Service.
	The components of net periodic benefit expense for the Pension, SERP and PBOP Plans are shown below. The net periodic benefit expense and the intercompany allocations less the capitalized portion of pension, SERP and PBOP amounts is included in Operations and Maintenance on the statements of income. Capitalized pension and PBOP amounts relate to employees working on capital projects and are included in Property, Plant and Equipment, Net. Intercompany allocations are not included in the CL&P, NSTAR Electric, PSNH and WMECO net periodic benefit expense amounts. Pension, SERP and PBOP expense reflected in the statements of cash flows for CL&P, NSTAR Electric, PSNH and WMECO does not include the intercompany allocations and the corresponding capitalized portion, as these amounts are cash settled on a short-term basis.
		Pension and SERP
		For the Three Months Ended
		31-Mar-15		31-Mar-14
	(Millions of Dollars)	ES (1)		ES
	Service Cost	$	23.2	$	22.3
	Interest Cost		56.6		56.6
	Expected Return on Plan Assets		-84.3		-77.7
	Actuarial Loss		38.9		33
	Prior Service Cost		0.9		1.1
	Total Net Periodic Benefit Expense	$	35.3	$	35.3
	Capitalized Pension Expense	$	9.6	$	9.7
		PBOP
		For the Three Months Ended
		31-Mar-15		31-Mar-14
	(Millions of Dollars)	ES (1)		ES
	Service Cost	$	4.2	$	3
	Interest Cost		11.9		12.6
	Expected Return on Plan Assets		-16.8		-15.7
	Actuarial Loss		1.8		3
	Prior Service Credit		-0.1		-0.6
	Total Net Periodic Benefit Expense	$	1	$	2.3
	Capitalized PBOP Expense	$	0.2	$	0.4
		Pension and SERP
		For the Three Months Ended March 31, 2015								For the Three Months Ended March 31, 2014
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric		PSNH (1)		WMECO		CL&P		Electric		PSNH		WMECO
	Service Cost	$	6	$	3.8	$	2.9	$	1.1	$	5.2	$	4.6	$	2.8	$	1
	Interest Cost		12.7		10.2		5.9		2.5		13.3		10.2		6.5		2.7
	Expected Return on Plan Assets		-19.7		-17.6		-10		-4.7		-19.4		-15.8		-10.2		-4.6
	Actuarial Loss		8.2		9.6		3		1.6		9.1		5.8		3.3		1.9
	Prior Service Cost		0.4		-		0.1		0.1		0.5		-		0.2		0.1
	Total Net Periodic Benefit Expense	$	7.6	$	6	$	1.9	$	0.6	$	8.7	$	4.8	$	2.6	$	1.1
	Intercompany Allocations	$	6.4	$	3.6	$	1.7	$	1.2	$	6.8	$	2.4	$	1.9	$	1.3
	Capitalized Pension Expense	$	4.3	$	2.8	$	0.8	$	0.5	$	4.9	$	1.9	$	0.9	$	0.8
		PBOP
		For the Three Months Ended March 31, 2015								For the Three Months Ended March 31, 2014
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric			PSNH (1)		WMECO	CL&P		Electric		PSNH		WMECO
	Service Cost	$	0.6	$	1.3	$	0.4	$	0.1	$	0.6	$	0.7	$	0.4	$	0.1
	Interest Cost		1.8		4.8		1		0.4		2.1		4.9		1.1		0.5
	Expected Return on Plan Assets		-2.8		-6.8		-1.5		-0.6		-2.7		-6.4		-1.4		-0.6
	Actuarial Loss/(Gain)		0.2		0.8		0.1		-		1.1		-0.1		0.5		0.1
	Prior Service Credit		-		-0.1		-		-		-		-0.5		-		-
	Total Net Periodic Benefit Expense/(Income)	$	-0.2	$	-	$	-	$	-0.1	$	1.1	$	-1.4	$	0.6	$	0.1
	Intercompany Allocations	$	0.5	$	0.3	$	0.1	$	0.1	$	1.1	$	0.1	$	0.3	$	0.2
	Capitalized PBOP Expense/(Income)	$	-	$	0.1	$	-	$	-	$	0.5	$	-0.5	$	0.2	$	0.1
	(1) Amounts exclude approximately $1 million that represented deferred regulatory assets.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Commitments and Contingencies Disclosure [Text Block]	8.       COMMITMENTS AND CONTINGENCIES
	A.       Environmental Matters
	General: Eversource, CL&P, NSTAR Electric, PSNH and WMECO are subject to environmental laws and regulations intended to mitigate or remove the effect of past operations and improve or maintain the quality of the environment. These laws and regulations require the removal or the remedy of the effect on the environment of the disposal or release of certain specified hazardous substances at current and former operating sites. Eversource, CL&P, NSTAR Electric, PSNH and WMECO have an active environmental auditing and training program and believe that they are substantially in compliance with all enacted laws and regulations.
	The number of environmental sites and reserves related to these sites for which remediation or long-term monitoring, preliminary site work or site assessment are being performed are as follows:
		As of March 31, 2015						As of December 31, 2014
					Reserve					Reserve
		Number of Sites			(in millions)			Number of Sites		(in millions)
	ES		65		$	43.6			65	$	43.3
	CL&P		16			5			16		3.8
	NSTAR Electric		14			1.7			13		1.1
	PSNH		12			3.4			13		5.2
	WMECO		4			0.6			4		0.5
	Included in the Eversource number of sites and reserve amounts above are former MGP sites that were operated several decades ago and manufactured gas from coal and other processes, which resulted in certain by-products remaining in the environment that may pose a potential risk to human health and the environment. The reserve balance related to these former MGP sites was $35.4 million and $38.8 million as of March 31, 2015 and December 31, 2014, respectively, and relates primarily to the natural gas business segment.
	B.       Guarantees and Indemnifications
	ES parent provides credit assurances on behalf of its subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, in the form of guarantees in the normal course of business.
	ES parent also issued a guaranty under which, beginning at the time the Northern Pass Transmission line goes into commercial operation, ES parent will guarantee the financial obligations of NPT under the TSA in an amount not to exceed $25 million. ES parent's obligations under the guaranty expire upon the full, final and indefeasible payment of the guaranteed obligations.
	ES parent has also guaranteed certain indemnification and other obligations as a result of the sales of former unregulated subsidiaries and the termination of an unregulated business, with maximum exposures either not specified or not material.
	Management does not anticipate a material impact to Net Income as a result of these various guarantees and indemnifications.
	The following table summarizes ES parent's guarantees of its subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, as of March 31, 2015:
						Maximum Exposure
	Company			Description		(in millions)		Expiration Dates
		Various		Surety Bonds (1)		$	54.6	2015 - 2016
		Eversource Service and Rocky River Realty Company		Lease Payments for Vehicles and Real Estate		$	13.8	2019 and 2024
	(1)       Surety bond expiration dates reflect termination dates, the majority of which will be renewed or extended. Certain surety bonds contain credit ratings triggers that would require ES parent to post collateral in the event that the unsecured debt credit ratings of Eversource are downgraded.
	C.       FERC ROE Complaints
	Beginning in 2011, three separate complaints were filed at FERC by combinations of New England state attorneys general, state regulatory commissions, consumer advocates, consumer groups, municipal parties and other parties (the "Complainants"). In the first complaint, filed in 2011, the Complainants alleged that the NETOs' base ROE of 11.14 percent that was utilized since 2006 was unjust and unreasonable, asserted that the rate was excessive due to changes in the capital markets, and sought an order to reduce it prospectively from the date of the final FERC order and for the 15-month period beginning October 1, 2011 to December 31, 2012 (the "first complaint refund period"). In the second and third complaints, filed in 2012 and 2014, the Complainants challenged the NETOs' base ROE and sought refunds for the 15-month periods beginning December 27, 2012 and July 31, 2014.
	In 2014, the FERC determined that the base ROE should be set at 10.57 percent for the first complaint refund period and that a utility's total or maximum ROE should not exceed the top of the new zone of reasonableness, which was set at 11.74 percent. The FERC ordered the NETOs to provide refunds to customers for the first complaint refund period and set the new base ROE of 10.57 percent prospectively from October 16, 2014. The NETOs and the Complainants sought rehearing from FERC. In late 2014, the NETOs made a compliance filing, which was challenged by the Complainants, and the Company began refunding amounts from the first complaint period.
	On March 3, 2015, FERC issued an order denying all issues raised on rehearing by the NETOs and Complainants in the first base ROE complaint. The FERC order upheld the base ROE of 10.57 percent for the first complaint refund period and prospectively from October 16, 2014, and upheld that the utility's total ROE (the base ROE plus any incentive adders) for the transmission assets to which the adder applies is capped at the top of the zone of reasonableness, which is currently set at 11.74 percent. As a result of clarifying information related to how the ROE cap is applied, which is contained in the order, Eversource adjusted its reserve in the first quarter of 2015 and recognized a pre-tax charge to earnings (excluding interest) of $20 million, of which $12.5 million was recorded at CL&P, $2.4 million at NSTAR Electric, $1 million at PSNH, and $4.1 million at WMECO. The pre-tax charge was recorded as a regulatory liability and as a reduction of Operating Revenues.
	D.        2014 Comprehensive Settlement Agreement
	On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the "Settlement") as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric's energy efficiency programs for 2008 through 2011 (11 dockets in total). As a result, NSTAR Electric and NSTAR Gas will refund $42.5 million and $2.2 million, respectively, to customers. The refund was recorded as a regulatory liability as of March 31, 2015 and NSTAR Electric recognized a $21.7 million pre-tax benefit in the first quarter of 2015.
	E.       Basic Service Bad Debt Adder
	In accordance with a generic 2005 DPU order, electric utilities in Massachusetts recover the energy-related portion of bad debt costs in their Basic Service rates. In February 2007, NSTAR Electric filed its 2005 through 2006 Basic Service reconciliation with the DPU proposing an adjustment related to the increase of its Basic Service bad debt charge-offs. In June 2007, the DPU approved NSTAR Electric's proposed adjustment to the Basic Service Adder but instructed NSTAR Electric to reduce distribution rates by an equal and offsetting amount. This adjustment to NSTAR Electric's distribution rates would have eliminated the fully reconciling nature of the Basic Service bad debt adder.
	In 2010, NSTAR Electric filed an appeal of the DPU's order with the SJC. NSTAR Electric took the position that it had fully removed the collection of energy-related bad debt costs from its base distribution rates effective January 1, 2006; therefore, no further adjustment to distribution rates was warranted. In 2012, the SJC vacated the DPU order and remanded the matter to the DPU for further review.
	On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had appropriately accounted for the removal of supply-related bad debt costs from base distribution rates effective January 1, 2006. The DPU ordered NSTAR Electric and the Massachusetts Attorney General to collaborate on the reconciliation of energy-related bad debt costs through 2014. During the second quarter of 2015, NSTAR Electric expects to file with the DPU to recover from customers approximately $43 million of supply-related bad debt costs. In the first quarter of 2015, as a result of the DPU order, NSTAR Electric increased its regulatory assets and reduced Operations and Maintenance expense by $24.2 million, resulting in an increase in after-tax earnings of $14.5 million.
	F.       PSNH Generation Restructuring
	On March 11, 2015, PSNH and key New Hampshire officials entered into an agreement in principle in a settlement Term Sheet. Under the Term Sheet, PSNH has agreed to pursue the divestiture of its generation assets upon NHPUC approval of a final Settlement Agreement reflecting the provisions of the Term Sheet, and PSNH will not seek a general distribution rate increase that would become effective before July 1, 2017. PSNH will contribute $5 million to create a clean energy fund, which will not be recoverable from its customers, and will record this liability and related charge upon completion of the Settlement Agreement.

FAIR_VALUE_OF_FINANCIAL_INSTRU

FAIR VALUE OF FINANCIAL INSTRUMENTS	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Fair Value Disclosures [Text Block]	9.       FAIR VALUE OF FINANCIAL INSTRUMENTS
	The following methods and assumptions were used to estimate the fair value of each of the following financial instruments:
	Preferred Stock and Long-Term Debt: The fair value of CL&P's and NSTAR Electric's preferred stock is based upon pricing models that incorporate interest rates and other market factors, valuations or trades of similar securities and cash flow projections. The fair value of long-term debt securities is based upon pricing models that incorporate quoted market prices for those issues or similar issues adjusted for market conditions, credit ratings of the respective companies and treasury benchmark yields. The fair values provided in the tables below are classified as Level 2 within the fair value hierarchy. Carrying amounts and estimated fair values are as follows:
		As of March, 31, 2015				As of December 31, 2014
		ES				ES
		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)	Amount		Value		Amount		Value
	Preferred Stock Not Subject to Mandatory Redemption	$	155.6	$	155.1	$	155.6	$	153.6
	Long-Term Debt		8,847.70		9,553.10		8,851.60		9,451.20
		As of March 31, 2015
		CL&P				NSTAR Electric				PSNH				WMECO
		Carrying		Fair		Carrying		Fair		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)	Amount		Value		Amount		Value		Amount		Value		Amount		Value
	Preferred Stock Not Subject to Mandatory Redemption	$	116.2	$	113	$	43	$	42.1	$	-	$	-	$	-	$	-
	Long-Term Debt		2,842.10		3,260.40		1,797.40		2,022.10		1,076.30		1,156.40		628.2		674.4
		As of December 31, 2014
		CL&P				NSTAR Electric				PSNH				WMECO
		Carrying		Fair		Carrying		Fair		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)	Amount		Value		Amount		Value		Amount		Value		Amount		Value
	Preferred Stock Not Subject to Mandatory Redemption	$	116.2	$	112	$	43	$	41.6	$	-	$	-	$	-	$	-
	Long-Term Debt		2,842.00		3,214.50		1,797.40		1,993.50		1,076.30		1,137.90		628.5		689.4
	Derivative Instruments: Derivative instruments are carried at fair value. For further information, see Note 4, "Derivative Instruments," to the financial statements.
	Other Financial Instruments: Investments in marketable securities are carried at fair value. For further information, see Note 5, "Marketable Securities," to the financial statements. The carrying value of other financial instruments included in current assets and current liabilities, including cash and cash equivalents and special deposits, approximates their fair value due to the short-term nature of these instruments.
	See Note 1D, "Summary of Significant Accounting Policies - Fair Value Measurements," for the fair value measurement policy and the fair value hierarchy.

ACCUMULATED_OTHER_COMPREHENSIV

ACCUMULATED OTHER COMPREHENSIVE INCOME	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Comprehensive Income Note [Text Block]	10.       ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)
	The changes in accumulated other comprehensive income/(loss) by component, net of tax, is as follows:
		For the Three Months Ended March 31, 2015								For the Three Months Ended March 31, 2014
		Qualified		Unrealized						Qualified		Unrealized
		Cash Flow		Gains on		Defined				Cash Flow		Gains on		Defined
		Hedging		Marketable		Benefit				Hedging		Marketable		Benefit
	(Millions of Dollars)	Instruments		Securities		Plans		Total		Instruments		Securities		Plans		Total
	Balance as of Beginning of Period	$	-12.4	$	0.7	$	-62.3	$	-74	$	-14.4	$	0.4	$	-32	$	-46
	OCI Before Reclassifications		-		0.1		-		0.1		-		0.2		-		0.2
	Amounts Reclassified from AOCI		0.5		-		1		1.5		0.5		-		1		1.5
	Net OCI		0.5		0.1		1		1.6		0.5		0.2		1		1.7
	Balance as of End of Period	$	-11.9	$	0.8	$	-61.3	$	-72.4	$	-13.9	$	0.6	$	-31	$	-44.3
	Eversource's qualified cash flow hedging instruments represent interest rate swap agreements on debt issuances that were settled in prior years. The settlement amount was recorded in AOCI and is being amortized into Net Income over the term of the underlying debt instrument. CL&P, PSNH and WMECO continue to amortize interest rate swaps settled in prior years from AOCI into Interest Expense over the remaining life of the associated long-term debt, which are not material to their respective financial statements. The amortization expense of actuarial gains and losses on the defined benefit plans is amortized from AOCI into Operations and Maintenance over the average future employee service period, and are reflected in amounts reclassified from AOCI. The related tax effects of the reclassification adjustments are not material to the financial statements for the three months ended March 31, 2015 and 2014.

COMMON_SHARES

COMMON SHARES	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Stock by Class [Text Block]	11.       COMMON SHARES
	The following table sets forth the ES parent common shares and the shares of common stock of CL&P, NSTAR Electric, PSNH and WMECO that were authorized and issued and the respective per share par values:
		Shares
				Authorized as of
		Per Share		March 31, 2015 and	Issued as of
		Par Value		31-Dec-14	31-Mar-15	31-Dec-14
	ES	$	5	380,000,000	333,607,844	333,359,172
	CL&P	$	10	24,500,000	6,035,205	6,035,205
	NSTAR Electric	$	1	100,000,000	100	100
	PSNH	$	1	100,000,000	301	301
	WMECO	$	25	1,072,471	434,653	434,653
	As of March 31, 2015 and December 31, 2014, there were 16,138,845 and 16,375,835 Eversource common shares held as treasury shares, respectively. As of March 31, 2015 and December 31, 2014, Eversource common shares outstanding were 317,468,999 and 316,983,337, respectively.

COMMON_SHARESHOLDERS_EQUITY_AN

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	12.       COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS
	For the three months ended March 31, 2015 and 2014, there were dividends on the preferred stock of CL&P and NSTAR Electric of $1.9 million, which were presented as Net Income Attributable to Noncontrolling Interests on the Eversource statements of income. Common Shareholders' Equity was fully attributable to the parent and Noncontrolling Interest – Preferred Stock of Subsidiaries was fully attributable to the noncontrolling interest on the Eversource balance sheets.

EARNINGS_PER_SHARE

EARNINGS PER SHARE	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Earnings Per Share [Text Block]	13.       EARNINGS PER SHARE
	Basic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is computed on the basis of the weighted average number of common shares outstanding plus the potential dilutive effect of certain share-based compensation awards as if they were converted into common shares. For the three months ended March 31, 2015 and 2014, there were no antidilutive share awards excluded from the computation.
	The following table sets forth the components of basic and diluted EPS:
			For the Three Months Ended
	(Millions of Dollars, except share information)		31-Mar-15		31-Mar-14
	Net Income Attributable to Controlling Interest		$	253.3	$	236
	Weighted Average Common Shares Outstanding:
		Basic		317,090,841		315,534,512
		Dilutive Effect		1,400,347		1,357,607
		Diluted		318,491,188		316,892,119
	Basic EPS		$	0.8	$	0.75
	Diluted EPS		$	0.8	$	0.74
	RSUs and performance shares are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. The dilutive effect of unvested RSUs and performance shares is calculated using the treasury stock method. Assumed proceeds of these units under the treasury stock method consist of the remaining compensation cost to be recognized and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the units (the difference between the market value of the average units outstanding for the period, using the average market price during the period, and the grant date market value).
	The dilutive effect of stock options to purchase common shares is also calculated using the treasury stock method. Assumed proceeds for stock options consist of cash proceeds that would be received upon exercise, and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the stock options (the difference between the market value of the average stock options outstanding for the period, using the average market price during the period, and the exercise price).

SEGMENT_INFORMATION

SEGMENT INFORMATION	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Segment Reporting Disclosure [Text Block]	14.       SEGMENT INFORMATION
	Presentation: Eversource is organized between the Electric Distribution, Electric Transmission and Natural Gas Distribution reportable segments and Other based on a combination of factors, including the characteristics of each segments' products and services, the sources of operating revenues and expenses and the regulatory environment in which each segment operates. These reportable segments represented substantially all of Eversource's total consolidated revenues for the three months ended March 31, 2015 and 2014. Revenues from the sale of electricity and natural gas primarily are derived from residential, commercial and industrial customers and are not dependent on any single customer. The Electric Distribution reportable segment includes the generation activities of PSNH and WMECO.
	The remainder of Eversource's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of ES parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of ES parent, 2) the revenues and expenses of Eversource Service, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, and 4) the results of other unregulated subsidiaries, which are not part of its core business.
	Cash flows used for investments in plant included in the segment information below are cash capital expenditures that do not include amounts incurred but not paid, cost of removal, AFUDC related to equity funds, and the capitalized portions of pension expense.
	Eversource's reportable segments are determined based upon the level at which Eversource's chief operating decision maker assesses performance and makes decisions about the allocation of company resources. Each of Eversource's subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, has one reportable segment. Eversource's operating segments and reporting units are consistent with its reportable business segments.
	Eversource's segment information is as follows:
		For the Three Months Ended March 31, 2015
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,760.10	$	507.4	$	249	$	240	$	-243.1	$	2,513.40
	Depreciation and Amortization		-159.1		-18.2		-40.4		-7.2		0.5		-224.4
	Other Operating Expenses		-1,342.80		-388.5		-74.1		-229.2		243.1		-1,791.50
	Operating Income		258.2		100.7		134.5		3.6		0.5		497.5
	Interest Expense		-47.6		-9		-27.6		-11.8		1.2		-94.8
	Other Income/(Loss), Net		2.2		-0.2		2.9		314.9		-314.1		5.7
	Net Income Attributable to Controlling Interest	$	130.6	$	55.6	$	66.6	$	312.9	$	-312.4	$	253.3
	Cash Flows Used for Investments in Plant	$	172.5	$	30	$	150	$	10.1	$	-	$	362.6
		For the Three Months Ended March 31, 2014
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,585.90	$	432.8	$	252.1	$	172.2	$	-152.4	$	2,290.60
	Depreciation and Amortization		-148.8		-17.7		-37		-7		1.8		-208.7
	Other Operating Expenses		-1,210.90		-321.4		-66.4		-165.4		149.9		-1,614.20
	Operating Income/(Loss)		226.2		93.7		148.7		-0.2		-0.7		467.7
	Interest Expense		-47.4		-8.5		-25.5		-9.6		1		-90
	Other Income, Net		1.4		0.1		1.5		294.8		-296.1		1.7
	Net Income Attributable to Controlling Interest	$	112.2	$	52.1	$	74.9	$	291.7	$	-294.9	$	236
	Cash Flows Used for Investments in Plant	$	189.4	$	28.9	$	112.2	$	18.2	$	-	$	348.7
	The following table summarizes Eversource's segmented total assets:
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	As of March 31, 2015	$	17,930.20	$	3,008.50	$	7,503.10	$	12,874.10	$	-11,364.10	$	29,951.80
	As of December 31, 2014		17,563.40		3,030.90		7,625.60		12,682.50		-11,124.40		29,778.00

SIGNIFCANT_ACCOUNTING_POLICIES

SIGNIFCANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Organization Consolidation And Presentation Of Financial Statements Disclosure Text Block	A.       Basis of Presentation
	Eversource Energy is a public utility holding company primarily engaged through its wholly owned regulated utility subsidiaries in the energy delivery business. Eversource Energy's wholly owned regulated utility subsidiaries consist of CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas. Eversource provides energy delivery service to approximately 3.6 million electric and natural gas customers through these six regulated utilities in Connecticut, Massachusetts and New Hampshire.
	On April 29, 2015, the Company's name was changed from Northeast Utilities to Eversource Energy. CL&P, NSTAR Electric, PSNH and WMECO operate under the brand Eversource Energy.
	The unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements."
	The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the entirety of this combined Quarterly Report on Form 10-Q and the 2014 combined Annual Report on Form 10-K of Eversource, CL&P, NSTAR Electric, PSNH and WMECO, which was filed with the SEC. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly Eversource's, CL&P's, NSTAR Electric's, PSNH's and WMECO's financial position as of March 31, 2015 and December 31, 2014, and the results of operations, comprehensive income and cash flows for the three months ended March 31, 2015 and 2014. The results of operations, comprehensive income and cash flows for the three months ended March 31, 2015 and 2014 are not necessarily indicative of the results expected for a full year.
	Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's, PSNH's and WMECO's combined ownership interest in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements.
	Eversource's utility subsidiaries' distribution (including generation) and transmission businesses and NPT are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations, which considers the effect of regulation on the differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. See Note 2, "Regulatory Accounting," for further information.
	Certain reclassifications of prior period data were made in the accompanying financial statements to conform to the current period presentation.
Receivables Policy Text Block	Eversource, including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at estimated net realizable value by maintaining a provision for uncollectible accounts. This provision is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. The estimate is based upon historical collection and write-off experience and management's assessment of collectability from customers. Management continuously assesses the collectability of receivables and adjusts collectability estimates based on actual experience. Receivable balances are written off against the provision for uncollectible accounts when the accounts are terminated and these balances are deemed to be uncollectible.
Derivatives Offsetting Fair Value Amounts Policy	The gross fair values of derivative assets and liabilities with the same counterparty are offset and reported as net Derivative Assets or Derivative Liabilities, with current and long-term portions, on the balance sheets.
Fair Value Of Financial Instruments Policy	Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases or normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans and nonrecurring fair value measurements of nonfinancial assets such as goodwill and AROs, and is also used to estimate the fair value of preferred stock and long-term debt.
	Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available and minimizes the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and Eversource's policy is to recognize transfers between levels of the fair value hierarchy as of the end of the reporting period. The three levels of the fair value hierarchy are described below:
	Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date.  Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis.
	Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable.
	Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products.
	Derivative contracts classified as Level 2 in the fair value hierarchy relate to the financial contracts for natural gas futures. Prices are obtained from broker quotes and are based on actual market activity. The contracts are valued using NYMEX natural gas prices. Valuations of these contracts also incorporate discount rates using the yield curve approach.
	The fair value of derivative contracts classified as Level 3 utilizes significant unobservable inputs. The fair value is modeled using income techniques, such as discounted cash flow valuations adjusted for assumptions relating to exit price. Significant observable inputs for valuations of these contracts include energy and energy-related product prices in future years for which quoted prices in an active market exist. Fair value measurements categorized in Level 3 of the fair value hierarchy are prepared by individuals with expertise in valuation techniques, pricing of energy and energy-related products, and accounting requirements. The future power and capacity prices for periods that are not quoted in an active market or established at auction are based on available market data and are escalated based on estimates of inflation to address the full time period of the contract.
	Valuations of derivative contracts using a discounted cash flow methodology include assumptions regarding the timing and likelihood of scheduled payments and also reflect non-performance risk, including credit, using the default probability approach based on the counterparty's credit rating for assets and the Company's credit rating for liabilities. Valuations incorporate estimates of premiums or discounts that would be required by a market participant to arrive at an exit price, using historical market transactions adjusted for the terms of the contract.
	The following methods and assumptions were used to estimate the fair value of each of the following financial instruments:
	Preferred Stock and Long-Term Debt: The fair value of CL&P's and NSTAR Electric's preferred stock is based upon pricing models that incorporate interest rates and other market factors, valuations or trades of similar securities and cash flow projections. The fair value of long-term debt securities is based upon pricing models that incorporate quoted market prices for those issues or similar issues adjusted for market conditions, credit ratings of the respective companies and treasury benchmark yields. The fair values provided in the tables below are classified as Level 2 within the fair value hierarchy.
Other Taxes Policy	Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respective customers. These gross receipts taxes are shown on a gross basis with collections in Operating Revenues and payments in Taxes Other Than Income Taxes on the statements of income Certain sales taxes are collected by Eversource's companies that serve customers in Connecticut and Massachusetts as agents for state and local governments and are recorded on a net basis with no impact on the statements of income.
Public Utilities Policy Text Block	Eversource's Regulated companies are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations and reflect the effects of the rate-making process. The rates charged to the customers of Eversource's Regulated companies are designed to collect each company's costs to provide service, including a return on investment.
	Management believes it is probable that each of the Regulated companies will recover their respective investments in long-lived assets, including regulatory assets. If management were to determine that it could no longer apply the accounting guidance applicable to rate-regulated enterprises to any of the Regulated companies' operations, or that management could not conclude it is probable that costs would be recovered from customers in future rates, the costs would be charged to net income in the period in which the determination is made.
Derivatives Policy Text Block	Many of the derivative contracts meet the definition of, and are designated as, normal and qualify for accrual accounting under the applicable accounting guidance. The costs and benefits of derivative contracts that meet the definition of normal are recognized in Operating Expenses or Operating Revenues on the statements of income, as applicable, as electricity or natural gas is delivered.
	Derivative contracts that are not designated as normal are recorded at fair value as current or long-term Derivative Assets or Derivative Liabilities on the balance sheets. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivatives, as contract settlement amounts are recovered from, or refunded to, customers in their respective energy supply rates.
Marketable Securities Policy	U.S. government issued debt securities are valued using market approaches that incorporate transactions for the same or similar bonds and adjustments for yields and maturity dates. Corporate debt securities are valued using a market approach, utilizing recent trades of the same or similar instrument and also incorporating yield curves, credit spreads and specific bond terms and conditions. Asset-backed debt securities include collateralized mortgage obligations, commercial mortgage backed securities, and securities collateralized by auto loans, credit card loans or receivables. Asset-backed debt securities are valued using recent trades of similar instruments, prepayment assumptions, yield curves, issuance and maturity dates, and tranche information. Municipal bonds are valued using a market approach that incorporates reported trades and benchmark yields. Other fixed income securities are valued using pricing models, quoted prices of securities with similar characteristics, and discounted cash flows.
Environmental Costs Policy	Environmental Matters
	General: Eversource, CL&P, NSTAR Electric, PSNH and WMECO are subject to environmental laws and regulations intended to mitigate or remove the effect of past operations and improve or maintain the quality of the environment. These laws and regulations require the removal or the remedy of the effect on the environment of the disposal or release of certain specified hazardous substances at current and former operating sites. Eversource, CL&P, NSTAR Electric, PSNH and WMECO have an active environmental auditing and training program and believe that they are substantially in compliance with all enacted laws and regulations.
Earnings Per Share Policy Text Block	Basic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is computed on the basis of the weighted average number of common shares outstanding plus the potential dilutive effect of certain share-based compensation awards as if they were converted into common shares.
	RSUs and performance shares are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. The dilutive effect of unvested RSUs and performance shares is calculated using the treasury stock method. Assumed proceeds of these units under the treasury stock method consist of the remaining compensation cost to be recognized and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the units (the difference between the market value of the average units outstanding for the period, using the average market price during the period, and the grant date market value).
	The dilutive effect of stock options to purchase common shares is also calculated using the treasury stock method. Assumed proceeds for stock options consist of cash proceeds that would be received upon exercise, and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the stock options (the difference between the market value of the average stock options outstanding for the period, using the average market price during the period, and the exercise price).
Segment Reporting Policy Policy Text Block	SEGMENT INFORMATION
	Presentation: Eversource is organized between the Electric Distribution, Electric Transmission and Natural Gas Distribution reportable segments and Other based on a combination of factors, including the characteristics of each segments' products and services, the sources of operating revenues and expenses and the regulatory environment in which each segment operates. These reportable segments represented substantially all of Eversource's total consolidated revenues for the three months ended March 31, 2015 and 2014. Revenues from the sale of electricity and natural gas primarily are derived from residential, commercial and industrial customers and are not dependent on any single customer. The Electric Distribution reportable segment includes the generation activities of PSNH and WMECO.
	The remainder of Eversource's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of ES parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of ES parent, 2) the revenues and expenses of Eversource Service, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, and 4) the results of other unregulated subsidiaries, which are not part of its core business.
	Cash flows used for investments in plant included in the segment information below are cash capital expenditures that do not include amounts incurred but not paid, cost of removal, AFUDC related to equity funds, and the capitalized portions of pension expense.

Provision_for_Uncollectible_Ac

Provision for Uncollectible Accounts (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Accounts Notes Loans And Financing Receivable Text Block		Total Provision for Uncollectible Accounts				Uncollectible Hardship
	(Millions of Dollars)	As of March 31, 2015		As of December 31, 2014		As of March 31, 2015		As of December 31, 2014
	ES	$	187.4	$	175.3	$	92.3	$	91.5
	CL&P		86.6		84.3		74.5		74
	NSTAR Electric		43.8		40.7		-		-
	PSNH		8.1		7.7		-		-
	WMECO		10.7		9.9		6.5		6.2

Other_Taxes_Tables

Other Taxes (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
State Of Connecticut Gross Earnings Taxes [Table Text Block]		For the Three Months Ended
	(Millions of Dollars)	31-Mar-15		31-Mar-14
	ES	$	41.9	$	44.4
	CL&P		33		35.6

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	G.	Supplemental Cash Flow Information
	Non-cash investing activities include plant additions included in Accounts Payable as follows:
	(Millions of Dollars)		As of March 31, 2015		As of March 31, 2014
	ES		$	110.4	$	108.5
	CL&P			42.3		36.2
	NSTAR Electric			21.9		28
	PSNH			21.7		14.4
	WMECO			8.3		14.4

REGULATORY_ACCOUNTING_Tables

REGULATORY ACCOUNTING (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Regulatory Assets Text Block		As of March 31, 2015			As of December 31, 2014
	(Millions of Dollars)	ES			ES
	Benefit Costs	$	1,976.60		$	2,016.00
	Derivative Liabilities		410.2			425.5
	Income Taxes, Net		632.1			635.3
	Storm Restoration Costs		504.8			502.8
	Goodwill-related		500.2			505.4
	Regulatory Tracker Mechanisms		434.5			350.5
	Contractual Obligations - Yankee Companies		119			123.8
	Other Regulatory Assets		151.4			167.3
	Total Regulatory Assets		4,728.80			4,726.60
	Less: Current Portion		747.3			672.5
	Total Long-Term Regulatory Assets	$	3,981.50		$	4,054.10
			As of March 31, 2015									As of December 31, 2014
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Benefit Costs		$	436.7		$	505.6	$	171.2	$	83.3	$	445.4	$	515.9	$	174.3	$	85
	Derivative Liabilities			403.3			3.5		-		-		410.9		4.5		-		-
	Income Taxes, Net			438.7			83.7		36.8		31.2		437.7		83.7		38		35.5
	Storm Restoration Costs			308.5			119.7		46.9		29.7		319.6		103.7		47.7		31.8
	Goodwill-related			-			429.5		-		-		-		433.9		-		-
	Regulatory Tracker Mechanisms			10.1			261.2		93.4		47.6		16.1		141.4		103.5		33
	Other Regulatory Assets			66.5			85		38.9		12.8		66.1		94.7		41.3		12.9
	Total Regulatory Assets			1,663.80			1,488.20		387.2		204.6		1,695.80		1,377.80		404.8		198.2
	Less: Current Portion			209.6			309.5		100		66.7		220.3		198.7		111.7		51.9
	Total Long-Term Regulatory Assets		$	1,454.20		$	1,178.70	$	287.2	$	137.9	$	1,475.50	$	1,179.10	$	293.1	$	146.3
Schedule Of Regulatory Liabilities Text Block		As of March 31, 2015			As of December 31, 2014
	(Millions of Dollars)	ES			ES
	Cost of Removal	$	452.8		$	439.9
	Regulatory Tracker Mechanisms		183.3			192.3
	AFUDC - Transmission		67.1			67.1
	Other Regulatory Liabilities		22.9			50.8
	Total Regulatory Liabilities		726.1			750.1
	Less: Current Portion		201.2			235
	Total Long-Term Regulatory Liabilities	$	524.9		$	515.1
			As of March 31, 2015									As of December 31, 2014
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Cost of Removal		$	23.1		$	263.4	$	51.3	$	2.8	$	19.7	$	258.3	$	50.3	$	1.1
	Regulatory Tracker Mechanisms			77.5			22.5		13.9		22.2		122.6		20.7		14.2		22.3
	AFUDC - Transmission			53.3			4.7		-		9.1		53.6		4.4		-		9.1
	Other Regulatory Liabilities			12.3			2.1		2.8		0.9		10.1		28.9		2.9		0.8
	Total Regulatory Liabilities			166.2			292.7		68		35		206		312.3		67.4		33.3
	Less: Current Portion			84.1			24.6		16.1		22.3		124.7		49.6		16		22.5
	Total Long-Term Regulatory Liabilities		$	82.1		$	268.1	$	51.9	$	12.7	$	81.3	$	262.7	$	51.4	$	10.8

PROPERTY_PLANT_AND_ACCUMULATED1

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Public Utility Property, Plant, and Equipment [Text Block]				As of March 31, 2015			As of December 31, 2014
	(Millions of Dollars)			ES			ES
	Distribution - Electric			$	12,539.30		$	12,495.20
	Distribution - Natural Gas				2,584.80			2,595.40
	Transmission				6,959.40			6,930.70
	Generation				1,172.20			1,170.90
	Electric and Natural Gas Utility				23,255.70			23,192.20
	Other (1)				547.9			551.3
	Property, Plant and Equipment, Gross				23,803.60			23,743.50
	Less: Accumulated Depreciation
		Electric and Natural Gas Utility			-5,842.60			-5,777.80
		Other			-232.3			-231.8
	Total Accumulated Depreciation				-6,074.90			-6,009.60
	Property, Plant and Equipment, Net				17,728.70			17,733.90
	Construction Work in Progress				1,082.00			913.1
	Total Property, Plant and Equipment, Net			$	18,810.70		$	18,647.00
		As of March 31, 2015										As of December 31, 2014
					NSTAR									NSTAR
	(Millions of Dollars)	CL&P			Electric			PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Distribution	$	5,180.00		$	4,907.80		$	1,704.10	$	787.4	$	5,158.80	$	4,895.50	$	1,696.70	$	784.2
	Transmission		3,274.70			1,950.60			794.6		891.9		3,274.00		1,928.50		789.7		891
	Generation		-			-			1,137.80		34.4		-		-		1,136.50		34.4
	Property, Plant and Equipment, Gross		8,454.70			6,858.40			3,636.50		1,713.70		8,432.80		6,824.00		3,622.90		1,709.60
	Less: Accumulated Depreciation		-1,950.70			-1,783.60			-1,105.70		-303.3		-1,928.00		-1,761.40		-1,090.00		-297.4
	Property, Plant and Equipment, Net		6,504.00			5,074.80			2,530.80		1,410.40		6,504.80		5,062.60		2,532.90		1,412.20
	Construction Work in Progress		370.9			289.5			135.5		73.5		304.9		272.8		102.9		49.1
	Total Property, Plant and Equipment, Net	$	6,874.90		$	5,364.30		$	2,666.30	$	1,483.90	$	6,809.70	$	5,335.40	$	2,635.80	$	1,461.30

DERIVATIVE_INSTRUMENTS_Tables

DERIVATIVE INSTRUMENTS (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Derivative Instruments In Statement Of Financial Position Fair Value Text Block
				As of March 31, 2015									As of December 31, 2014
				Commodity Supply						Net Amount			Commodity Supply						Net Amount
				and Price Risk						Recorded as			and Price Risk							Recorded as
	(Millions of Dollars)			Management			Netting (1)			a Derivative			Management			Netting (1)			a Derivative
	Current Derivative Assets:
	Level 3:
		ES		$	16		$	-6.6		$	9.4		$	16.2		$	-6.6		$	9.6
		CL&P			16			-6.6			9.4			16.1			-6.6			9.5
		NSTAR Electric			-			-			-			0.1			-			0.1
	Long-Term Derivative Assets:
	Level 3:
		ES, CL&P		$	88.3		$	-17.8		$	70.5		$	93.5		$	-19.2		$	74.3
	Current Derivative Liabilities:
	Level 2:
		ES		$	-3.2		$	-		$	-3.2		$	-9.8		$	-		$	-9.8
	Level 3:
		ES			-90.3			-			-90.3			-90			-			-90
		CL&P			-88.2			-			-88.2			-88.5			-			-88.5
		NSTAR Electric			-2.1			-			-2.1			-1.5			-			-1.5
	Long-Term Derivative Liabilities:
	Level 2:
		ES		$	-0.2		$	-		$	-0.2		$	-0.3		$	-		$	-0.3
	Level 3:
		ES			-396.4			-			-396.4			-409.3			-			-409.3
		CL&P			-395			-			-395			-406.2			-			-406.2
		NSTAR Electric			-1.4			-			-1.4			-3.1			-			-3.1
Rollforward Of Net Derivative Asset Liabilities Valued Using Unobservable Inputs [Table Text Block]			For the Three Months Ended March 31,
			2015									2014
									NSTAR									NSTAR
	(Millions of Dollars)		ES			CL&P			Electric			ES			CL&P			Electric
	Derivatives, Net:
	Fair Value as of Beginning of Period		$	-415.4		$	-410.9		$	-4.5		$	-635.2		$	-630.6		$	-7.3
	Net Realized/Unrealized Gains/(Losses) Included in Regulatory Assets and Liabilities			-12.1			-12.1			-			49.2			52			-0.1
	Settlements			20.7			19.7			1			21.7			21.6			0.1
	Fair Value as of End of Period		$	-406.8		$	-403.3		$	-3.5		$	-564.3		$	-557		$	-7.3
Fairvalueinputsliabilitiesquantitativeinformationtabletextblock			As of March 31, 2015									As of December 31, 2014
				Range						Period Covered			Range						Period Covered
	Energy Prices:
	ES, CL&P		$	48			per MWh			2020		$	52			per MWh			2020
	Capacity Prices:
	ES		$	8.8	-	12.98		per kW-Month		2016 - 2026		$	5.3	-	12.98		per kW-Month		2016 - 2026
	CL&P		$	11.13	-	12.98		per kW-Month		2019 - 2026		$	11.08	-	12.98		per kW-Month		2018 - 2026
	NSTAR Electric		$	8.8	-	11.13		per kW-Month		2016 - 2019		$	5.3	-	11.1		per kW-Month		2016 - 2019
	Forward Reserve:
	ES, CL&P		$	5.8	-	9.5		per kW-Month		2015 - 2024		$	5.8	-	9.5		per kW-Month		2015 - 2024
	REC Prices:
	ES, NSTAR Electric		$	45	-	50	per REC			2015 - 2018		$	38	-	56	per REC			2015 - 2018

MARKETABLE_SECURITIES_Tables

MARKETABLE SECURITIES (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Available For Sale Securities Reconciliation [Table TextBlock]			As of March 31, 2015												As of December 31, 2014
						Pre-Tax			Pre-Tax								Pre-Tax		Pre-Tax
			Amortized			Unrealized			Unrealized						Amortized		Unrealized		Unrealized
	(Millions of Dollars)		Cost			Gains			Losses			Fair Value			Cost		Gains		Losses		Fair Value
	ES
		Debt Securities (1)	$	318.2		$	8.2		$	-0.1		$	326.3		$	313	$	7.5	$	-0.3	$	320.2
		Equity Securities (1)		159.5			77			-			236.5			160.6		73.3		-		233.9
	WMECO
		Debt Securities (2)		58.2			-			-			58.2			58.2		-		-0.1		58.1
Investments Classified by Contractual Maturity Date [Table Text Block]			ES						WMECO
			Amortized						Amortized
	(Millions of Dollars)		Cost			Fair Value			Cost			Fair Value
	Less than one year (1)		$	59.9		$	59.9		$	33.2		$	33.2
	One to five years			83.3			83.8			21.3			21.3
	Six to ten years			61.6			63.5			0.6			0.6
	Greater than ten years			113.4			119.1			3.1			3.1
	Total Debt Securities		$	318.2		$	326.3		$	58.2		$	58.2
Fair Value Heirarchy [Table Text Block]					ES						WMECO
	(Millions of Dollars)				As of March 31, 2015			As of December 31, 2014			As of March 31, 2015			As of December 31, 2014
	Level 1:
		Mutual Funds and Equities			$	323.2		$	319		$	-		$	-
		Money Market Funds				32.9			24.9			10.5			4.3
	Total Level 1				$	356.1		$	343.9		$	10.5		$	4.3
	Level 2:
		U.S. Government Issued Debt Securities (Agency and Treasury)			$	46		$	51.3		$	-		$	-
		Corporate Debt Securities				157.3			49.1			14.4			14.7
		Asset-Backed Debt Securities				36.5			54.1			12.1			14.5
		Municipal Bonds				31.9			116.3			12.9			13
		Other Fixed Income Securities				21.7			24.5			8.3			11.6
	Total Level 2				$	293.4		$	295.3		$	47.7		$	53.8
	Total Marketable Securities				$	649.5		$	639.2		$	58.2		$	58.1

Recovered_Sheet1

Pension Benefits and Postretirement Benefits Other Than Pensions (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Net Benefit Costs [Table Text Block]		Pension and SERP
		For the Three Months Ended
		31-Mar-15		31-Mar-14
	(Millions of Dollars)	ES (1)		ES
	Service Cost	$	23.2	$	22.3
	Interest Cost		56.6		56.6
	Expected Return on Plan Assets		-84.3		-77.7
	Actuarial Loss		38.9		33
	Prior Service Cost		0.9		1.1
	Total Net Periodic Benefit Expense	$	35.3	$	35.3
	Capitalized Pension Expense	$	9.6	$	9.7
		PBOP
		For the Three Months Ended
		31-Mar-15		31-Mar-14
	(Millions of Dollars)	ES (1)		ES
	Service Cost	$	4.2	$	3
	Interest Cost		11.9		12.6
	Expected Return on Plan Assets		-16.8		-15.7
	Actuarial Loss		1.8		3
	Prior Service Credit		-0.1		-0.6
	Total Net Periodic Benefit Expense	$	1	$	2.3
	Capitalized PBOP Expense	$	0.2	$	0.4
		Pension and SERP
		For the Three Months Ended March 31, 2015								For the Three Months Ended March 31, 2014
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric		PSNH (1)		WMECO		CL&P		Electric		PSNH		WMECO
	Service Cost	$	6	$	3.8	$	2.9	$	1.1	$	5.2	$	4.6	$	2.8	$	1
	Interest Cost		12.7		10.2		5.9		2.5		13.3		10.2		6.5		2.7
	Expected Return on Plan Assets		-19.7		-17.6		-10		-4.7		-19.4		-15.8		-10.2		-4.6
	Actuarial Loss		8.2		9.6		3		1.6		9.1		5.8		3.3		1.9
	Prior Service Cost		0.4		-		0.1		0.1		0.5		-		0.2		0.1
	Total Net Periodic Benefit Expense	$	7.6	$	6	$	1.9	$	0.6	$	8.7	$	4.8	$	2.6	$	1.1
	Intercompany Allocations	$	6.4	$	3.6	$	1.7	$	1.2	$	6.8	$	2.4	$	1.9	$	1.3
	Capitalized Pension Expense	$	4.3	$	2.8	$	0.8	$	0.5	$	4.9	$	1.9	$	0.9	$	0.8
		PBOP
		For the Three Months Ended March 31, 2015								For the Three Months Ended March 31, 2014
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric			PSNH (1)		WMECO	CL&P		Electric		PSNH		WMECO
	Service Cost	$	0.6	$	1.3	$	0.4	$	0.1	$	0.6	$	0.7	$	0.4	$	0.1
	Interest Cost		1.8		4.8		1		0.4		2.1		4.9		1.1		0.5
	Expected Return on Plan Assets		-2.8		-6.8		-1.5		-0.6		-2.7		-6.4		-1.4		-0.6
	Actuarial Loss/(Gain)		0.2		0.8		0.1		-		1.1		-0.1		0.5		0.1
	Prior Service Credit		-		-0.1		-		-		-		-0.5		-		-
	Total Net Periodic Benefit Expense/(Income)	$	-0.2	$	-	$	-	$	-0.1	$	1.1	$	-1.4	$	0.6	$	0.1
	Intercompany Allocations	$	0.5	$	0.3	$	0.1	$	0.1	$	1.1	$	0.1	$	0.3	$	0.2
	Capitalized PBOP Expense/(Income)	$	-	$	0.1	$	-	$	-	$	0.5	$	-0.5	$	0.2	$	0.1
	(1) Amounts exclude approximately $1 million that represented deferred regulatory assets.

Environmental_Matters_Tables

Environmental Matters (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Environmental Loss Contingencies By Site Text Block		As of March 31, 2015				As of December 31, 2014
				Reserve				Reserve
		Number of Sites		(in millions)		Number of Sites		(in millions)
	ES		65	$	43.6		65	$	43.3
	CL&P		16		5		16		3.8
	NSTAR Electric		14		1.7		13		1.1
	PSNH		12		3.4		13		5.2
	WMECO		4		0.6		4		0.5

Guarantees_and_Indemnification

Guarantees and Indemnifications (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Guarantee Obligations Text Block				Maximum Exposure
	Company		Description	(in millions)		Expiration Dates
		Various	Surety Bonds (1)	$	54.6	2015 - 2016
		Eversource Service and Rocky River Realty Company	Lease Payments for Vehicles and Real Estate	$	13.8	2019 and 2024

FAIR_VALUE_OF_FINANCIAL_INSTRU1

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Fair Value By Balance Sheet Grouping Text Block		As of March, 31, 2015				As of December 31, 2014
		ES				ES
		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)	Amount		Value		Amount		Value
	Preferred Stock Not Subject to Mandatory Redemption	$	155.6	$	155.1	$	155.6	$	153.6
	Long-Term Debt		8,847.70		9,553.10		8,851.60		9,451.20
		As of March 31, 2015
		CL&P				NSTAR Electric				PSNH				WMECO
		Carrying		Fair		Carrying		Fair		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)	Amount		Value		Amount		Value		Amount		Value		Amount		Value
	Preferred Stock Not Subject to Mandatory Redemption	$	116.2	$	113	$	43	$	42.1	$	-	$	-	$	-	$	-
	Long-Term Debt		2,842.10		3,260.40		1,797.40		2,022.10		1,076.30		1,156.40		628.2		674.4
		As of December 31, 2014
		CL&P				NSTAR Electric				PSNH				WMECO
		Carrying		Fair		Carrying		Fair		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)	Amount		Value		Amount		Value		Amount		Value		Amount		Value
	Preferred Stock Not Subject to Mandatory Redemption	$	116.2	$	112	$	43	$	41.6	$	-	$	-	$	-	$	-
	Long-Term Debt		2,842.00		3,214.50		1,797.40		1,993.50		1,076.30		1,137.90		628.5		689.4

ACCUMULATED_OTHER_COMPREHENSIV1

ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Accumulated Other Comprehensive Income Loss Table Text Block		For the Three Months Ended March 31, 2015								For the Three Months Ended March 31, 2014
		Qualified		Unrealized						Qualified		Unrealized
		Cash Flow		Gains on		Defined				Cash Flow		Gains on		Defined
		Hedging		Marketable		Benefit				Hedging		Marketable		Benefit
	(Millions of Dollars)	Instruments		Securities		Plans		Total		Instruments		Securities		Plans		Total
	Balance as of Beginning of Period	$	-12.4	$	0.7	$	-62.3	$	-74	$	-14.4	$	0.4	$	-32	$	-46
	OCI Before Reclassifications		-		0.1		-		0.1		-		0.2		-		0.2
	Amounts Reclassified from AOCI		0.5		-		1		1.5		0.5		-		1		1.5
	Net OCI		0.5		0.1		1		1.6		0.5		0.2		1		1.7
	Balance as of End of Period	$	-11.9	$	0.8	$	-61.3	$	-72.4	$	-13.9	$	0.6	$	-31	$	-44.3

COMMON_SHARES_Tables

COMMON SHARES (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Stock by Class [Text Block]	11.       COMMON SHARES
	The following table sets forth the ES parent common shares and the shares of common stock of CL&P, NSTAR Electric, PSNH and WMECO that were authorized and issued and the respective per share par values:
		Shares
				Authorized as of
		Per Share		March 31, 2015 and	Issued as of
		Par Value		31-Dec-14	31-Mar-15	31-Dec-14
	ES	$	5	380,000,000	333,607,844	333,359,172
	CL&P	$	10	24,500,000	6,035,205	6,035,205
	NSTAR Electric	$	1	100,000,000	100	100
	PSNH	$	1	100,000,000	301	301
	WMECO	$	25	1,072,471	434,653	434,653
	As of March 31, 2015 and December 31, 2014, there were 16,138,845 and 16,375,835 Eversource common shares held as treasury shares, respectively. As of March 31, 2015 and December 31, 2014, Eversource common shares outstanding were 317,468,999 and 316,983,337, respectively.

EARNINGS_PER_SHARE_Tables

EARNINGS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Earnings Per Share Basic And Diluted [Table Text Block]			For the Three Months Ended
	(Millions of Dollars, except share information)		31-Mar-15		31-Mar-14
	Net Income Attributable to Controlling Interest		$	253.3	$	236
	Weighted Average Common Shares Outstanding:
		Basic		317,090,841		315,534,512
		Dilutive Effect		1,400,347		1,357,607
		Diluted		318,491,188		316,892,119
	Basic EPS		$	0.8	$	0.75
	Diluted EPS		$	0.8	$	0.74

SEGMENT_INFORMATION_Tables

SEGMENT INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting Information [Line Items]
Schedule Of Segment Reporting Information By Segment Text Block		For the Three Months Ended March 31, 2015
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,760.10	$	507.4	$	249	$	240	$	-243.1	$	2,513.40
	Depreciation and Amortization		-159.1		-18.2		-40.4		-7.2		0.5		-224.4
	Other Operating Expenses		-1,342.80		-388.5		-74.1		-229.2		243.1		-1,791.50
	Operating Income		258.2		100.7		134.5		3.6		0.5		497.5
	Interest Expense		-47.6		-9		-27.6		-11.8		1.2		-94.8
	Other Income/(Loss), Net		2.2		-0.2		2.9		314.9		-314.1		5.7
	Net Income Attributable to Controlling Interest	$	130.6	$	55.6	$	66.6	$	312.9	$	-312.4	$	253.3
	Cash Flows Used for Investments in Plant	$	172.5	$	30	$	150	$	10.1	$	-	$	362.6
		For the Three Months Ended March 31, 2014
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,585.90	$	432.8	$	252.1	$	172.2	$	-152.4	$	2,290.60
	Depreciation and Amortization		-148.8		-17.7		-37		-7		1.8		-208.7
	Other Operating Expenses		-1,210.90		-321.4		-66.4		-165.4		149.9		-1,614.20
	Operating Income/(Loss)		226.2		93.7		148.7		-0.2		-0.7		467.7
	Interest Expense		-47.4		-8.5		-25.5		-9.6		1		-90
	Other Income, Net		1.4		0.1		1.5		294.8		-296.1		1.7
	Net Income Attributable to Controlling Interest	$	112.2	$	52.1	$	74.9	$	291.7	$	-294.9	$	236
	Cash Flows Used for Investments in Plant	$	189.4	$	28.9	$	112.2	$	18.2	$	-	$	348.7
	The following table summarizes Eversource's segmented total assets:
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	As of March 31, 2015	$	17,930.20	$	3,008.50	$	7,503.10	$	12,874.10	$	-11,364.10	$	29,951.80
	As of December 31, 2014		17,563.40		3,030.90		7,625.60		12,682.50		-11,124.40		29,778.00

Basis_of_Presentation_Details

Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2015
Description of Consolidation of Yankee Companies	Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's, PSNH's and WMECO's combined ownership interest in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements.

Provision_for_Uncollectible_Ac1

Provision for Uncollectible Accounts (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	$187.40	$175.30
Uncollectible Hardship Accounts Receivable Reserve	92.3	91.5
The Connecticut Light And Power Company [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	86.6	84.3
Uncollectible Hardship Accounts Receivable Reserve	74.5	74
NSTAR Electric Company [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	43.8	40.7
Public Service Company Of New Hampshire [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	8.1	7.7
Western Massachusetts Electric Company [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	10.7	9.9
Uncollectible Hardship Accounts Receivable Reserve	$6.50	$6.20

Other_Taxes_Details

Other Taxes (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Excise And Sales Taxes	$41.90	$44.40
The Connecticut Light And Power Company [Member]
Excise And Sales Taxes	$33	$35.60

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Capital Expenditures Incurred But Not Yet Paid	$110.40	$108.50
The Connecticut Light And Power Company [Member]
Capital Expenditures Incurred But Not Yet Paid	42.3	36.2
NSTAR Electric Company [Member]
Capital Expenditures Incurred But Not Yet Paid	21.9	28
Public Service Company Of New Hampshire [Member]
Capital Expenditures Incurred But Not Yet Paid	21.7	14.4
Western Massachusetts Electric Company [Member]
Capital Expenditures Incurred But Not Yet Paid	$8.30	$14.40

Severance_Benefits_Details

Severance Benefits (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Notes To Consolidated Financial Statements [Abstract]
Description Of Postemployment Benefits	Severance Benefits
Postemployment Benefits Period Expense	$0.40	$4.30
Postemployment Benefits Liability Current	$9		$10.40

REGULATORY_ACCOUNTING_Details

REGULATORY ACCOUNTING (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Regulatory Asset [Line Items]
Regulatory Assets, Total	$4,728,800,000	$4,726,600,000
Regulatory Assets Current	747,349,000	672,493,000
Regulatory Assets Long Term	3,981,507,000	4,054,086,000
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	49,300,000	60,500,000
Public Utilities Disclosure Of Regulatory Matters Pending	2015 Regulatory Developments: As a result of the March 3, 2015 FERC order in the pending ROE complaint proceedings described in Note 8C, "Commitments and Contingencies – FERC ROE Complaints," in the first quarter of 2015, Eversource recognized a pre-tax charge to earnings (excluding interest) of $20 million, of which $12.5 million was recorded at CL&P, $2.4 million at NSTAR Electric, $1 million at PSNH, and $4.1 million at WMECO. The pre-tax charge was recorded as a regulatory liability and as a reduction of Operating Revenues. On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the "Settlement") as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric's energy efficiency programs for 2008 through 2011 (11 dockets in total). As a result, NSTAR Electric and NSTAR Gas will refund a combined $44.7 million to customers. The refund was recorded as a regulatory liability as of March 31, 2015 and NSTAR Electric recognized a $21.7 million pre-tax benefit in the first quarter of 2015. For further information, see Note 8D, "Commitments and Contingencies – 2014 Comprehensive Settlement Agreement." On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had appropriately accounted for the removal of supply-related bad debt costs from base distribution rates effective January 1, 2006. The DPU ordered NSTAR Electric and the Massachusetts Attorney General to collaborate on the reconciliation of energy-related bad debt costs through 2014. During the second quarter of 2015, NSTAR Electric expects to file with the DPU to recover from customers approximately $43 million of supply-related bad debt costs. In the first quarter of 2015, as a result of the DPU order, NSTAR Electric increased its regulatory assets and reduced Operations and Maintenance expense by $24.2 million, resulting in an increase in after-tax earnings of $14.5 million. For further information, see Note 8E, "Commitments and Contingencies – Basic Service Bad Debt Adder."
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	726,100,000	750,100,000
Regulatory Liability Current	201,180,000	235,022,000
Regulatory Liabilities Long-Term	524,940,000	515,144,000
Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	452,800,000	439,900,000
Regulatory Tracker Deferrals Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	183,300,000	192,300,000
AFUDC Transmission Incentive [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	67,100,000	67,100,000
Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	22,900,000	50,800,000
The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,663,800,000	1,695,800,000
Regulatory Assets Current	209,628,000	220,344,000
Regulatory Assets Long Term	1,454,150,000	1,475,508,000
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	1,600,000	1,300,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	166,200,000	206,000,000
Regulatory Liability Current	84,127,000	124,722,000
Regulatory Liabilities Long-Term	82,110,000	81,298,000
The Connecticut Light And Power Company [Member] | Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	23,100,000	19,700,000
The Connecticut Light And Power Company [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	77,500,000	122,600,000
The Connecticut Light And Power Company [Member] | AFUDC Transmission Incentive [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	53,300,000	53,600,000
The Connecticut Light And Power Company [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	12,300,000	10,100,000
NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,488,200,000	1,377,800,000
Regulatory Assets Current	309,547,000	198,710,000
Regulatory Assets Long Term	1,178,738,000	1,179,100,000
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	18,300,000	33,200,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	292,700,000	312,300,000
Regulatory Liability Current	24,605,000	49,611,000
Regulatory Liabilities Long-Term	268,122,000	262,738,000
NSTAR Electric Company [Member] | Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	263,400,000	258,300,000
NSTAR Electric Company [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	22,500,000	20,700,000
NSTAR Electric Company [Member] | AFUDC Transmission Incentive [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	4,700,000	4,400,000
NSTAR Electric Company [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	2,100,000	28,900,000
Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	387,200,000	404,800,000
Regulatory Assets Current	99,994,000	111,705,000
Regulatory Assets Long Term	287,203,000	293,115,000
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	400,000	900,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	68,000,000	67,400,000
Regulatory Liability Current	16,102,000	16,044,000
Regulatory Liabilities Long-Term	51,897,000	51,372,000
Public Service Company Of New Hampshire [Member] | Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	51,300,000	50,300,000
Public Service Company Of New Hampshire [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	13,900,000	14,200,000
Public Service Company Of New Hampshire [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	2,800,000	2,900,000
Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	204,600,000	198,200,000
Regulatory Assets Current	66,706,000	51,923,000
Regulatory Assets Long Term	137,894,000	146,307,000
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	11,800,000	11,000,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	35,000,000	33,300,000
Regulatory Liability Current	22,289,000	22,486,000
Regulatory Liabilities Long-Term	12,673,000	10,835,000
Western Massachusetts Electric Company [Member] | Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	2,800,000	1,100,000
Western Massachusetts Electric Company [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	22,200,000	22,300,000
Western Massachusetts Electric Company [Member] | AFUDC Transmission Incentive [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	9,100,000	9,100,000
Western Massachusetts Electric Company [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	900,000	800,000
Benefit Costs [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,976,600,000	2,016,000,000
Benefit Costs [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	436,700,000	445,400,000
Benefit Costs [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	505,600,000	515,900,000
Benefit Costs [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	171,200,000	174,300,000
Benefit Costs [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	83,300,000	85,000,000
Regulatory Assets Offsetting Derivative Liabilities [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	410,200,000	425,500,000
Regulatory Assets Offsetting Derivative Liabilities [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	403,300,000	410,900,000
Regulatory Assets Offsetting Derivative Liabilities [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	3,500,000	4,500,000
Regulatory Assets Offsetting Derivative Liabilities [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	0	0
Regulatory Assets Offsetting Derivative Liabilities [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	0	0
Deferred Income Tax Charges Member
Regulatory Asset [Line Items]
Regulatory Assets, Total	632,100,000	635,300,000
Deferred Income Tax Charges Member | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	438,700,000	437,700,000
Deferred Income Tax Charges Member | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	83,700,000	83,700,000
Deferred Income Tax Charges Member | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	36,800,000	38,000,000
Deferred Income Tax Charges Member | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	31,200,000	35,500,000
Storm Restoration Costs [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	504,800,000	502,800,000
Storm Restoration Costs [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	308,500,000	319,600,000
Storm Restoration Costs [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	119,700,000	103,700,000
Storm Restoration Costs [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	46,900,000	47,700,000
Storm Restoration Costs [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	29,700,000	31,800,000
Goodwill Regulatory Asset [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	500,200,000	505,400,000
Goodwill Regulatory Asset [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	429,500,000	433,900,000
Regulatory Tracker Deferrals Regulatory Assets [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	434,500,000	350,500,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	10,100,000	16,100,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	261,200,000	141,400,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	93,400,000	103,500,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	47,600,000	33,000,000
Unrecovered Contractual Obligations [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	119,000,000	123,800,000
Power Contracts Buy Out Agreements [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total
Power Contracts Buy Out Agreements [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total
Power Contracts Buy Out Agreements [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total
Other Regulatory Assets [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	151,400,000	167,300,000
Other Regulatory Assets [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	66,500,000	66,100,000
Other Regulatory Assets [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	85,000,000	94,700,000
Other Regulatory Assets [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	38,900,000	41,300,000
Other Regulatory Assets [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	$12,800,000	$12,900,000

PROPERTY_PLANT_AND_ACCUMULATED2

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	$12,539,300,000	$12,495,200,000
Public Utilities Property Plant And Equipment Distribution Natural Gas	2,584,800,000	2,595,400,000
Public Utilities Property Plant And Equipment Transmission	6,959,400,000	6,930,700,000
Public Utilities Property Plant And Equipment Generation Or Processing	1,172,200,000	1,170,900,000
Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total	23,255,700,000	23,192,200,000
Public Utilities Property Plant And Equipment Other Property Plant And Equipment	547,900,000	551,300,000
Public Utilities Property Plant And Equipment Plant In Service	23,803,600,000	23,743,500,000
Electric And Natural Gas Utility Accumulated Depreciation	-5,842,600,000	-5,777,800,000
Other Accumulated Depreciation	-232,300,000	-231,800,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-6,074,900,000	-6,009,600,000
Property Plant And Equipment Net Excluding Construction Work In Progress	17,728,700,000	17,733,900,000
Public Utilities Property Plant And Equipment Construction Work In Progress	1,082,000,000	913,100,000
Property, Plant and Equipment, Net	18,810,708,000	18,647,041,000
The Connecticut Light And Power Company [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	5,180,000,000	5,158,800,000
Public Utilities Property Plant And Equipment Transmission	3,274,700,000	3,274,000,000
Public Utilities Property Plant And Equipment Generation Or Processing	0	0
Public Utilities Property Plant And Equipment Plant In Service	8,454,700,000	8,432,800,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,950,700,000	-1,928,000,000
Property Plant And Equipment Net Excluding Construction Work In Progress	6,504,000,000	6,504,800,000
Public Utilities Property Plant And Equipment Construction Work In Progress	370,900,000	304,900,000
Property, Plant and Equipment, Net	6,874,891,000	6,809,664,000
NSTAR Electric Company [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	4,907,800,000	4,895,500,000
Public Utilities Property Plant And Equipment Transmission	1,950,600,000	1,928,500,000
Public Utilities Property Plant And Equipment Generation Or Processing	0	0
Public Utilities Property Plant And Equipment Plant In Service	6,858,400,000	6,824,000,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,783,600,000	-1,761,400,000
Property Plant And Equipment Net Excluding Construction Work In Progress	5,074,800,000	5,062,600,000
Public Utilities Property Plant And Equipment Construction Work In Progress	289,500,000	272,800,000
Property, Plant and Equipment, Net	5,364,311,000	5,335,436,000
Public Service Company Of New Hampshire [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	1,704,100,000	1,696,700,000
Public Utilities Property Plant And Equipment Transmission	794,600,000	789,700,000
Public Utilities Property Plant And Equipment Generation Or Processing	1,137,800,000	1,136,500,000
Public Utilities Property Plant And Equipment Plant In Service	3,636,500,000	3,622,900,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,105,700,000	-1,090,000,000
Property Plant And Equipment Net Excluding Construction Work In Progress	2,530,800,000	2,532,900,000
Public Utilities Property Plant And Equipment Construction Work In Progress	135,500,000	102,900,000
Property, Plant and Equipment, Net	2,666,312,000	2,635,844,000
Public Service Company Of New Hampshire [Member] | Generation Plant [Member]
Public Utility Property Plant And Equipment [Line Items]
Electric And Natural Gas Utility Accumulated Depreciation	-497,100,000
Western Massachusetts Electric Company [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	787,400,000	784,200,000
Public Utilities Property Plant And Equipment Transmission	891,900,000	891,000,000
Public Utilities Property Plant And Equipment Generation Or Processing	34,400,000	34,400,000
Public Utilities Property Plant And Equipment Plant In Service	1,713,700,000	1,709,600,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-303,300,000	-297,400,000
Property Plant And Equipment Net Excluding Construction Work In Progress	1,410,400,000	1,412,200,000
Public Utilities Property Plant And Equipment Construction Work In Progress	73,500,000	49,100,000
Property, Plant and Equipment, Net	$1,483,895,000	$1,461,321,000

DERIVATIVE_INSTURMENTS_Details

DERIVATIVE INSTURMENTS (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Derivative Instrument Detail Abstract
Derivative Liabilities, Noncurrent	($396,617,000)		($409,632,000)
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract
Description of Derivative Activity Volume	As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of each contract allocated to CL&P and 20 percent allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020. NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity-related contract to purchase up to 35 MW per year through 2019. As of March 31, 2015 and December 31, 2014, Eversource had NYMEX financial contracts for natural gas futures in order to reduce variability associated with the purchase price of approximately 5.3 million and 8.8 million MMBtu of natural gas, respectively.
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract
Derivative Instruments Gain Loss Recognized In Regulatory Asset Liability	-16,600,000	54,100,000
Derivative Credit Risk Related Contingent Features Abstract
Derivative Net Liability Position Aggregate Fair Value	-3,000,000		-10,000,000
Additional Collateral Aggregate Fair Value	3,000,000		10,000,000
The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	-88,218,000		-88,459,000
Derivative Liabilities, Noncurrent	-395,038,000		-406,199,000
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract
Description of Derivative Activity Volume	As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of each contract allocated to CL&P and 20 percent allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020.
NSTAR Electric Company [Member]
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract
Description of Derivative Activity Volume	NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity-related contract to purchase up to 35 MW per year through 2019.
Fair Value Inputs Level 2 [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	-3,200,000		-9,800,000
Derivative Liabilities, Noncurrent	-200,000		-300,000
Fair Value Inputs Level 3 [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	9,400,000		9,600,000
Derivative Liabilities - Current	-90,300,000		-90,000,000
Derivative Liabilities, Noncurrent	-396,400,000		-409,300,000
Derivative Assets Noncurrent	70,500,000		74,300,000
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsEnergyPrices	48		52
Fair Value Inputs Level 3 [Member] | MinimumMember
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	8.8		5.3
FairValueInputsRenewableEnergyCreditPrices	45		38
FairValueInputsForwardReserve	5.8		5.8
Fair Value Inputs Level 3 [Member] | MaximumMember
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	12.98		12.98
FairValueInputsRenewableEnergyCreditPrices	50		56
FairValueInputsForwardReserve	9.5		9.5
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	9,400,000		9,500,000
Derivative Liabilities - Current	-88,200,000		-88,500,000
Derivative Liabilities, Noncurrent	-395,000,000		-406,200,000
Derivative Assets Noncurrent	70,500,000		74,300,000
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsEnergyPrices	48		52
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member] | MinimumMember
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	11.13		11.08
FairValueInputsForwardReserve	5.8		5.8
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member] | MaximumMember
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	12.98		12.98
FairValueInputsForwardReserve	9.5		9.5
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	0		100,000
Derivative Liabilities - Current	-2,100,000		-1,500,000
Derivative Liabilities, Noncurrent	-1,400,000		-3,100,000
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member] | MinimumMember
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	8.8		5.3
FairValueInputsRenewableEnergyCreditPrices	45		38
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member] | MaximumMember
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	11.13		11.1
FairValueInputsRenewableEnergyCreditPrices	50		56
Amount Offset Against Derivatives [Member] | Fair Value Inputs Level 2 [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	0
Amount Offset Against Derivatives [Member] | Fair Value Inputs Level 3 [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	-6,600,000		-6,600,000
Derivative Liabilities - Current	0
Derivative Assets Noncurrent	-17,800,000		-19,200,000
Amount Offset Against Derivatives [Member] | Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	-6,600,000		-6,600,000
Derivative Assets Noncurrent	-17,800,000		-19,200,000
Commodity [Member] | Fair Value Inputs Level 2 [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	-3,200,000		-9,800,000
Derivative Liabilities, Noncurrent	-200,000		-300,000
Commodity [Member] | Fair Value Inputs Level 3 [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	16,000,000		16,200,000
Derivative Liabilities - Current	-90,300,000		-90,000,000
Derivative Liabilities, Noncurrent	-396,400,000		-409,300,000
Derivative Assets Noncurrent	88,300,000		93,500,000
Commodity [Member] | Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	16,000,000		16,100,000
Derivative Liabilities - Current	-88,200,000		-88,500,000
Derivative Liabilities, Noncurrent	-395,000,000		-406,200,000
Derivative Assets Noncurrent	88,300,000		93,500,000
Commodity [Member] | Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	0		100,000
Derivative Liabilities - Current	-2,100,000		-1,500,000
Derivative Liabilities, Noncurrent	($1,400,000)		($3,100,000)

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	($415.40)	($635.20)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	-12.1	49.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	20.7	21.7
Ending Balance	-406.8	-564.3
The Connecticut Light And Power Company [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	-410.9	-630.6
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	-12.1	52
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	19.7	21.6
Ending Balance	-403.3	-557
NSTAR Electric Company [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	-4.5	-7.3
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	0	-0.1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	1	0.1
Ending Balance	($3.50)	($7.30)

MARKETABLE_SECURITIES_Details

MARKETABLE SECURITIES (Details) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Marketable Securities, Restricted	$458.30	$450.80
Available For Sale Securities Debt Maturities Fair Value Abstract
Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value	63.5
Available For Sale Securities Debt Maturities After Ten Years Fair Value	119.1
Available For Sale Securities Debt Maturities After One Year Through Five Years Fair Value	83.8
Available For Sale Securities Debt Maturities Within One Year Fair Value	59.9
Available For Sale Securities Debt Maturities Fair Value	326.3
Available For Sale Securities Debt Maturities Amortized Cost Abstract
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	83.3
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	59.9
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost	113.4
Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost	61.6
Available For Sale Securities Debt Maturities Amortized Cost	318.2
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	649.5	639.2
TradingSecuritiesEquity	86.7	85.1
IncreaseDecreaseInTradingSecurities	1.6	0.7
Western Massachusetts Electric Company [Member]
Available For Sale Securities Debt Maturities Fair Value Abstract
Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value	0.6
Available For Sale Securities Debt Maturities After Ten Years Fair Value	3.1
Available For Sale Securities Debt Maturities After One Year Through Five Years Fair Value	21.3
Available For Sale Securities Debt Maturities Within One Year Fair Value	33.2
Available For Sale Securities Debt Maturities Fair Value	58.2
Available For Sale Securities Debt Maturities Amortized Cost Abstract
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	21.3
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	33.2
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost	3.1
Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost	0.6
Available For Sale Securities Debt Maturities Amortized Cost	58.2
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	58.2	58.1
Fair Value Inputs Level 1 Member
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	356.1	343.9
Fair Value Inputs Level 1 Member | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	10.5	4.3
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	293.4	295.3
Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	47.7	53.8
US Government Debt Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	46	51.3
US Government Debt Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	0
Corporate Bond Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	157.3	49.1
Corporate Bond Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	14.4	14.7
Asset Backed Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	36.5	54.1
Asset Backed Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	12.1	14.5
Municipal Bonds Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	31.9	116.3
Municipal Bonds Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	12.9	13
Other Debt Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	21.7	24.5
Other Debt Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	8.3	11.6
Cash And Cash Equivalents Member | Fair Value Inputs Level 1 Member
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	32.9	24.9
Cash And Cash Equivalents Member | Fair Value Inputs Level 1 Member | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	10.5	4.3
Mutual Funds [Member] | Fair Value Inputs Level 1 Member
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	323.2	319
Debt Securities
Investments, Debt and Equity Securities [Abstract]
Available For Sale Securities Fair Value Disclosure	326.3	320.2
Available-for-sale Securities, Gross Unrealized Gains	8.2	7.5
AvailableForSaleSecuritiesGrossUnrealizedLoss	-0.1	-0.3
Available For Sale Securities Amortized Cost	318.2	313
Debt Securities | Western Massachusetts Electric Company [Member]
Investments, Debt and Equity Securities [Abstract]
Available For Sale Securities Fair Value Disclosure	58.2	58.1
Available-for-sale Securities, Gross Unrealized Gains	0	0
AvailableForSaleSecuritiesGrossUnrealizedLoss	0	-0.1
Available For Sale Securities Amortized Cost	58.2	58.2
Equity Securities
Investments, Debt and Equity Securities [Abstract]
Available For Sale Securities Fair Value Disclosure	236.5	233.9
Available-for-sale Securities, Gross Unrealized Gains	77	73.3
AvailableForSaleSecuritiesGrossUnrealizedLoss	0	0
Available For Sale Securities Amortized Cost	$159.50	$160.60

SHORT_TERM_AND_LONG_TERM_DEBT_

SHORT TERM AND LONG TERM DEBT (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Line of Credit Facility, Description	Credit Agreements and Commercial Paper Programs: ES parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year $1.45 billion revolving credit facility that expires September 6, 2019. The revolving credit facility is used primarily to backstop ES parent's $1.45 billion commercial paper program. The commercial paper program allows ES parent to issue commercial paper as a form of short-term debt. As of March 31, 2015 and December 31, 2014, ES parent had $788 million and approximately $1.1 billion, respectively, in short-term borrowings outstanding under the ES parent commercial paper program, leaving $662 million and $348.9 million of available borrowing capacity as of March 31, 2015 and December 31, 2014, respectively. The weighted-average interest rate on these borrowings as of March 31, 2015 and December 31, 2014 was 0.53 percent and 0.43 percent, respectively, which is generally based on A2/P2 rated commercial paper. As of March 31, 2015, there were intercompany loans from ES parent of $190.1 million to CL&P, $82 million to PSNH and $70.5 million to WMECO. As of December 31, 2014, there were intercompany loans from ES parent of $133.4 million to CL&P, $90.5 million to PSNH and $21.4 million to WMECO. NSTAR Electric has a five-year $450 million revolving credit facility that expires September 6, 2019. This facility serves to backstop NSTAR Electric's existing $450 million commercial paper program. As of March 31, 2015 and December 31, 2014, NSTAR Electric had $215.5 million and $302 million, respectively, in short-term borrowings outstanding under its commercial paper program, leaving $234.5 million and $148 million of available borrowing capacity as of March 31, 2015 and December 31, 2014, respectively. The weighted-average interest rate on these borrowings as of March 31, 2015 and December 31, 2014 was 0.35 percent and 0.27 percent, respectively, which is generally based on A2/P1 rated commercial paper.
Notes Payable	$1,003,500,000	$956,825,000
Long Term Debt Description [Abstract]
Long-term Debt, Description	Long-Term Debt: On January 15, 2015, ES parent issued $150 million of 1.60 percent Series G Senior Notes, due to mature in 2018 and $300 million of 3.15 percent Series H Senior Notes, due to mature in 2025. The proceeds, net of issuance costs, were used to repay short-term borrowings outstanding under the ES parent commercial paper program. As the debt issuances refinanced short-term debt, the short-term debt was classified as Long-Term Debt as of December 31, 2014. On April 1, 2015, CL&P repaid at maturity the $100 million 5.00 percent 2005 Series A First and Refunding Mortgage Bonds using short-term borrowings. On April 1, 2015, CL&P also redeemed the $62 million 1996A Series 1.55 percent PCRBs that were subject to mandatory tender, using short term borrowings. Long-Term Debt Issuance Authorization: On April 3, 2015, the DPU authorized NSTAR Gas to issue up to $100 million in long-term debt for the period through December 31, 2015.
The Connecticut Light And Power Company [Member]
Line of Credit Facility [Line Items]
Notes Payable To Affiliated Companies	190,100,000	133,400,000
Long Term Debt Description [Abstract]
Long-term Debt, Description	On April 1, 2015, CL&P repaid at maturity the $100 million 5.00 percent 2005 Series A First and Refunding Mortgage Bonds using short-term borrowings. On April 1, 2015, CL&P also redeemed the $62 million 1996A Series 1.55 percent PCRBs that were subject to mandatory tender, using short term borrowings.
NSTAR Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	450,000,000
Line of Credit Facility, Remaining Borrowing Capacity	234,500,000	148,000,000
Short-term Debt, Weighted Average Interest Rate	0.35%	0.27%
Commercial Paper Borrowings	215,500,000	302,000,000
Notes Payable	215,500,000	302,000,000
Public Service Company Of New Hampshire [Member]
Line of Credit Facility [Line Items]
Notes Payable To Affiliated Companies	82,000,000	90,500,000
Western Massachusetts Electric Company [Member]
Line of Credit Facility [Line Items]
Notes Payable To Affiliated Companies	70,500,000	21,400,000
Nu Parent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,450,000,000
Line of Credit Facility, Remaining Borrowing Capacity	662,000,000	348,900,000
Short-term Debt, Weighted Average Interest Rate	0.53%	0.43%
Commercial Paper Borrowings	$788,000,000	$1,100,000,000

PENSION_BENEFITS_AND_POSTRETIR1

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, PBOP and SERP	$1,605,339,000		$1,638,558,000
Amount That Represents Deferred Regulatory Assets	1,000,000
Pension Plans Defined Benefit Member
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	23,200,000	22,300,000
Defined Benefit Plan Interest Cost	56,600,000	56,600,000
Defined Benefit Plan, Expected Return on Plan Assets	-84,300,000	-77,700,000
Defined Benefit Plan, Amortization of Gains (Losses)	38,900,000	33,000,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	900,000	1,100,000
Defined Benefit Plan Net Periodic Benefit Cost	35,300,000	35,300,000
Amount Capitalized Defined Benefit Expense	9,600,000	9,700,000
PBOP Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	4,200,000	3,000,000
Defined Benefit Plan Interest Cost	11,900,000	12,600,000
Defined Benefit Plan, Expected Return on Plan Assets	-16,800,000	-15,700,000
Defined Benefit Plan, Amortization of Gains (Losses)	1,800,000	3,000,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	-100,000	-600,000
Defined Benefit Plan Net Periodic Benefit Cost	1,000,000	2,300,000
Amount Capitalized Defined Benefit Expense	200,000	400,000
The Connecticut Light And Power Company [Member]
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, PBOP and SERP	272,292,000		273,854,000
The Connecticut Light And Power Company [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	6,000,000	5,200,000
Defined Benefit Plan Interest Cost	12,700,000	13,300,000
Defined Benefit Plan, Expected Return on Plan Assets	-19,700,000	-19,400,000
Defined Benefit Plan, Amortization of Gains (Losses)	8,200,000	9,100,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	400,000	500,000
Defined Benefit Plan Net Periodic Benefit Cost	7,600,000	8,700,000
Related Intercompany Allocationsof Defined Benefit Expense	6,400,000	6,800,000
Amount Capitalized Defined Benefit Expense	4,300,000	4,900,000
The Connecticut Light And Power Company [Member] | PBOP Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	600,000	600,000
Defined Benefit Plan Interest Cost	1,800,000	2,100,000
Defined Benefit Plan, Expected Return on Plan Assets	-2,800,000	-2,700,000
Defined Benefit Plan, Amortization of Gains (Losses)	200,000	1,100,000
Defined Benefit Plan Net Periodic Benefit Cost	-200,000	1,100,000
Related Intercompany Allocationsof Defined Benefit Expense	500,000	1,100,000
Amount Capitalized Defined Benefit Expense	0	500,000
NSTAR Electric Company [Member]
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, PBOP and SERP	228,411,000		235,529,000
NSTAR Electric Company [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	3,800,000	4,600,000
Defined Benefit Plan Interest Cost	10,200,000	10,200,000
Defined Benefit Plan, Expected Return on Plan Assets	-17,600,000	-15,800,000
Defined Benefit Plan, Amortization of Gains (Losses)	9,600,000	5,800,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	0	0
Defined Benefit Plan Net Periodic Benefit Cost	6,000,000	4,800,000
Related Intercompany Allocationsof Defined Benefit Expense	3,600,000	2,400,000
Amount Capitalized Defined Benefit Expense	2,800,000	1,900,000
NSTAR Electric Company [Member] | PBOP Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	1,300,000	700,000
Defined Benefit Plan Interest Cost	4,800,000	4,900,000
Defined Benefit Plan, Expected Return on Plan Assets	-6,800,000	-6,400,000
Defined Benefit Plan, Amortization of Gains (Losses)	800,000	-100,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	-100,000	-500,000
Defined Benefit Plan Net Periodic Benefit Cost	0	-1,400,000
Related Intercompany Allocationsof Defined Benefit Expense	300,000	100,000
Amount Capitalized Defined Benefit Expense	100,000	-500,000
Public Service Company Of New Hampshire [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Amortization Of Prior Service Cost Credit		0
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, PBOP and SERP	91,847,000		93,243,000
Amount That Represents Deferred Regulatory Assets	1,000,000
Public Service Company Of New Hampshire [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	2,900,000	2,800,000
Defined Benefit Plan Interest Cost	5,900,000	6,500,000
Defined Benefit Plan, Expected Return on Plan Assets	-10,000,000	-10,200,000
Defined Benefit Plan, Amortization of Gains (Losses)	3,000,000	3,300,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	100,000	200,000
Defined Benefit Plan Net Periodic Benefit Cost	1,900,000	2,600,000
Related Intercompany Allocationsof Defined Benefit Expense	1,700,000	1,900,000
Amount Capitalized Defined Benefit Expense	800,000	900,000
Public Service Company Of New Hampshire [Member] | PBOP Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	400,000	400,000
Defined Benefit Plan Interest Cost	1,000,000	1,100,000
Defined Benefit Plan, Expected Return on Plan Assets	-1,500,000	-1,400,000
Defined Benefit Plan, Amortization of Gains (Losses)	100,000	500,000
Defined Benefit Plan Net Periodic Benefit Cost	0	600,000
Related Intercompany Allocationsof Defined Benefit Expense	100,000	300,000
Amount Capitalized Defined Benefit Expense	0	200,000
Western Massachusetts Electric Company [Member]
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, PBOP and SERP	16,505,000		17,705,000
Western Massachusetts Electric Company [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	1,100,000	1,000,000
Defined Benefit Plan Interest Cost	2,500,000	2,700,000
Defined Benefit Plan, Expected Return on Plan Assets	-4,700,000	-4,600,000
Defined Benefit Plan, Amortization of Gains (Losses)	1,600,000	1,900,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	100,000	100,000
Defined Benefit Plan Net Periodic Benefit Cost	600,000	1,100,000
Related Intercompany Allocationsof Defined Benefit Expense	1,200,000	1,300,000
Amount Capitalized Defined Benefit Expense	500,000	800,000
Western Massachusetts Electric Company [Member] | PBOP Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	100,000	100,000
Defined Benefit Plan Interest Cost	400,000	500,000
Defined Benefit Plan, Expected Return on Plan Assets	-600,000	-600,000
Defined Benefit Plan, Amortization of Gains (Losses)	0	100,000
Defined Benefit Plan Net Periodic Benefit Cost	-100,000	100,000
Related Intercompany Allocationsof Defined Benefit Expense	100,000	200,000
Amount Capitalized Defined Benefit Expense	$0	$100,000

INCOME_TAXES_Details

INCOME TAXES (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Total Deferred Income Taxes	$148,193	$137,417
Income Tax Expense	153,226	141,545
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	408,359	379,381
Income Tax Expense	153,226	141,545
The Connecticut Light And Power Company [Member]
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Total Deferred Income Taxes	19,340	59,334
Income Tax Expense	38,147	45,541
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	107,381	124,840
Income Tax Expense	38,147	45,541
NSTAR Electric Company [Member]
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Total Deferred Income Taxes	41,297	1,585
Income Tax Expense	56,130	39,234
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	139,691	97,321
Income Tax Expense	56,130	39,234
Public Service Company Of New Hampshire [Member]
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Total Deferred Income Taxes	38,767	33,667
Income Tax Expense	20,276	19,700
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	52,321	52,338
Income Tax Expense	20,276	19,700
Western Massachusetts Electric Company [Member]
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Total Deferred Income Taxes	12,759	14,688
Income Tax Expense	9,113	11,558
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	22,357	29,660
Income Tax Expense	$9,113	$11,558

Environmental_Matters_Details

Environmental Matters (Details) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Site Contingency [Line Items]
Environmental Site Quantity	65	65
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$43.30
Ending Balance	43.6	43.3
MGP Site accrual [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Ending Balance	35.4	38.8
The Connecticut Light And Power Company [Member]
Site Contingency [Line Items]
Environmental Site Quantity	16	16
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	3.8
Ending Balance	5	3.8
NSTAR Electric Company [Member]
Site Contingency [Line Items]
Environmental Site Quantity	14	13
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	1.1
Ending Balance	1.7	1.1
Public Service Company Of New Hampshire [Member]
Site Contingency [Line Items]
Environmental Site Quantity	12	13
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	5.2
Ending Balance	3.4	5.2
Western Massachusetts Electric Company [Member]
Site Contingency [Line Items]
Environmental Site Quantity	4	4
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	0.5
Ending Balance	$0.60	$0.50

Guarantees_and_Indemnification1

Guarantees and Indemnifications (Details) (USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Guarantee Of Financial Obligations Of Npt [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	$25
Various Subsidiary Surety Bonds And Performance Guarantees Expiring Between 2015 And 2016 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	54.6
Guarantee Of Rocky River Reality And Nusco Lease Payments For Real Estate And Vehicles Expiring 2019 Through 2024 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	$13.80

Other_Contingencies_Details

Other Contingencies (Details) (FERC ROE Reserve - Incentive - First and Second Complaint [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Loss Contingencies Line Items
Loss Contingency Loss in Period	$20
The Connecticut Light And Power Company [Member]
Loss Contingencies Line Items
Loss Contingency Loss in Period	12.5
NSTAR Electric Company [Member]
Loss Contingencies Line Items
Loss Contingency Loss in Period	2.4
Public Service Company Of New Hampshire [Member]
Loss Contingencies Line Items
Loss Contingency Loss in Period	1
Western Massachusetts Electric Company [Member]
Loss Contingencies Line Items
Loss Contingency Loss in Period	$4.10

FAIR_VALUE_OF_FINANCIAL_INSTRU2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	$155,568,000	$155,568,000
Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,600,000	155,600,000
Other Long Term Debt	8,847,700,000	8,851,600,000
Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,100,000	153,600,000
Other Long Term Debt	9,553,100,000	9,451,200,000
The Connecticut Light And Power Company [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200,000	116,200,000
The Connecticut Light And Power Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200,000	116,200,000
Other Long Term Debt	2,842,100,000	2,842,000,000
The Connecticut Light And Power Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	113,000,000	112,000,000
Other Long Term Debt	3,260,400,000	3,214,500,000
NSTAR Electric Company [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000,000	43,000,000
NSTAR Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000,000	43,000,000
Other Long Term Debt	1,797,400,000	1,797,400,000
NSTAR Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	42,100,000	41,600,000
Other Long Term Debt	2,022,100,000	1,993,500,000
Public Service Company Of New Hampshire [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	1,076,300,000	1,076,300,000
Public Service Company Of New Hampshire [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	1,156,400,000	1,137,900,000
Western Massachusetts Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	628,200,000	628,500,000
Western Massachusetts Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	$674,400,000	$689,400,000

ACCUMULATED_OTHER_COMPREHENSIV2

ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	($74,009,000)	($46,000,000)
Other Comprehensive Income Before Reclassifications, Net of Tax	100,000	200,000
Reclassification From OCI, Net Of Tax	1,500,000	1,500,000
Other Comprehensive Income (Loss), Net of Tax, Total	1,595,000	1,710,000
AOCI Ending Balance	-72,414,000	-44,300,000
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	-94,843,000	-89,975,000
Income Tax Expense	-153,226,000	-141,545,000
Net Income Attributable to Controlling Interests	253,254,000	235,957,000
The Connecticut Light And Power Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	-931,000
Other Comprehensive Income (Loss), Net of Tax, Total	115,000	119,000
AOCI Ending Balance	-816,000
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	-36,624,000	-34,243,000
Income Tax Expense	-38,147,000	-45,541,000
Public Service Company Of New Hampshire [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	-7,369,000
Other Comprehensive Income (Loss), Net of Tax, Total	299,000	304,000
AOCI Ending Balance	-7,070,000
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	-11,272,000	-11,971,000
Income Tax Expense	-20,276,000	-19,700,000
Western Massachusetts Electric Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	-3,176,000
Other Comprehensive Income (Loss), Net of Tax, Total	86,000	87,000
AOCI Ending Balance	-3,090,000
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	-6,823,000	-5,646,000
Income Tax Expense	-9,113,000	-11,558,000
Qualified Cash Flow Hedging Instruments [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	-12,400,000	-14,400,000
Reclassification From OCI, Net Of Tax	500,000	500,000
Other Comprehensive Income (Loss), Net of Tax, Total	500,000	500,000
AOCI Ending Balance	-11,900,000	-13,900,000
Unrealized Gains Losses on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	700,000	400,000
Other Comprehensive Income Before Reclassifications, Net of Tax	100,000	200,000
Other Comprehensive Income (Loss), Net of Tax, Total	100,000	200,000
AOCI Ending Balance	800,000	600,000
Pension, SERP and PBOP Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance	-62,300,000	-32,000,000
Other Comprehensive Income Before Reclassifications, Net of Tax	0
Reclassification From OCI, Net Of Tax	1,000,000	1,000,000
Other Comprehensive Income (Loss), Net of Tax, Total	1,000,000	1,000,000
AOCI Ending Balance	($61,300,000)	($31,000,000)

COMMON_SHARES_Details

COMMON SHARES (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$5	$5
Common Stock Shares Authorized	380,000,000	380,000,000
Common Stock Shares Issued	333,607,844	333,359,172
Treasury Stock Shares	16,138,845	16,375,835
Common Stock, Shares, Outstanding	317,468,999	316,983,337
The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$10	$10
Common Stock Shares Authorized	24,500,000	24,500,000
Common Stock Shares Issued	6,035,205	6,035,205
NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$1	$1
Common Stock Shares Authorized	100,000,000	100,000,000
Common Stock Shares Issued	100	100
Public Service Company Of New Hampshire [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$1	$1
Common Stock Shares Authorized	100,000,000	100,000,000
Common Stock Shares Issued	301	301
Western Massachusetts Electric Company [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$25	$25
Common Stock Shares Authorized	1,072,471	1,072,471
Common Stock Shares Issued	434,653	434,653

EARNINGS_PER_SHARE_Details

EARNINGS PER SHARE (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]
Net Income Attributable to Controlling Interests	$253,254	$235,957
Basic	317,090,841	315,534,512
Weighted Average Number Diluted Shares Outstanding Adjustment	1,400,347	1,357,607
Diluted	318,491,188	316,892,119
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	0	0
Basic Earnings Per Common Share	$0.80	$0.75
Diluted Earnings Per Common Share	$0.80	$0.74

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenues	$2,513,431,000	$2,290,590,000
Operating Income	497,475,000	467,689,000
Total Interest Expense	-94,843,000	-89,975,000
Other Income/(Loss), Net	5,727,000	1,667,000
Income Tax Expense	-153,226,000	-141,545,000
Net Income	255,133,000	237,836,000
Net Income Attributable to Noncontrolling Interests	-1,879,000	-1,879,000
Net Income Attributable to Controlling Interests	253,254,000	235,957,000
Total Assets	29,951,765,000		29,777,975,000
Investments in Property, Plant and Equipment	362,586,000	348,691,000
Electric Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,760,100,000	1,585,900,000
Depreciation And Amortization	-159,100,000	-148,800,000
Operating Expenses, Other	-1,342,800,000	-1,210,900,000
Operating Income	258,200,000	226,200,000
Total Interest Expense	-47,600,000	-47,400,000
Other Income/(Loss), Net	2,200,000	1,400,000
Net Income Attributable to Controlling Interests	130,600,000	112,200,000
Total Assets	17,930,200,000		17,563,400,000
Investments in Property, Plant and Equipment	172,500,000	189,400,000
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues	507,400,000	432,800,000
Depreciation And Amortization	-18,200,000	-17,700,000
Operating Expenses, Other	-388,500,000	-321,400,000
Operating Income	100,700,000	93,700,000
Total Interest Expense	-9,000,000	-8,500,000
Other Income/(Loss), Net	-200,000	100,000
Net Income Attributable to Controlling Interests	55,600,000	52,100,000
Total Assets	3,008,500,000		3,030,900,000
Investments in Property, Plant and Equipment	30,000,000	28,900,000
Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues	249,000,000	252,100,000
Depreciation And Amortization	-40,400,000	-37,000,000
Operating Expenses, Other	-74,100,000	-66,400,000
Operating Income	134,500,000	148,700,000
Total Interest Expense	-27,600,000	-25,500,000
Other Income/(Loss), Net	2,900,000	1,500,000
Net Income Attributable to Controlling Interests	66,600,000	74,900,000
Total Assets	7,503,100,000		7,625,600,000
Investments in Property, Plant and Equipment	150,000,000	112,200,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	240,000,000	172,200,000
Depreciation And Amortization	-7,200,000	-7,000,000
Operating Expenses, Other	-229,200,000	-165,400,000
Operating Income	3,600,000	-200,000
Total Interest Expense	-11,800,000	-9,600,000
Other Income/(Loss), Net	314,900,000	294,800,000
Net Income Attributable to Controlling Interests	312,900,000	291,700,000
Total Assets	12,874,100,000		12,682,500,000
Investments in Property, Plant and Equipment	10,100,000	18,200,000
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	-243,100,000	-152,400,000
Depreciation And Amortization	500,000	1,800,000
Operating Expenses, Other	243,100,000	149,900,000
Operating Income	500,000	-700,000
Total Interest Expense	1,200,000	1,000,000
Other Income/(Loss), Net	-314,100,000	-296,100,000
Net Income Attributable to Controlling Interests	-312,400,000	-294,900,000
Total Assets	-11,364,100,000		-11,124,400,000
Investments in Property, Plant and Equipment	0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues	2,513,400,000	2,290,600,000
Depreciation And Amortization	-224,400,000	-208,700,000
Operating Expenses, Other	-1,791,500,000	-1,614,200,000
Operating Income	497,500,000	467,700,000
Total Interest Expense	-94,800,000	-90,000,000
Other Income/(Loss), Net	5,700,000	1,700,000
Net Income Attributable to Controlling Interests	253,300,000	236,000,000
Total Assets	29,951,800,000		29,778,000,000
Investments in Property, Plant and Equipment	$362,600,000	$348,700,000