Eversource Energy (ES) 10-K25 Feb 142013 FY Annual reportFinancial data

Company Profile

DOCUMENT_AND_ENTITY_INFORMATIO

DOCUMENT AND ENTITY INFORMATION (USD $)	12 Months Ended
DOCUMENT AND ENTITY INFORMATION (USD $)	Dec. 31, 2013	Jan. 31, 2014	Jun. 30, 2013
Document And Entity [Line Items]	'	'	'
Entity Registrant Name	'NORTHEAST UTILITIES	'	'
Document Period End Date	31-Dec-13	'	'
Document Type	'10-K	'	'
Entity Central Index Key	'0000072741	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Common Stock, Shares Outstanding	'	315,434,940	'
Entity Public Float	'	'	$13,224,337,788
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	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
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	'0000023426	'	'
Current Fiscal Year End Date	'--12-31	'	'
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	'0000315256	'	'
Current Fiscal Year End Date	'--12-31	'	'
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	'0000106170	'	'
Current Fiscal Year End Date	'--12-31	'	'
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	'0000013372	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Non-accelerated Filer	'	'

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Current Assets:	'	'
Cash	$43,364	$45,748
Receivables, Net	765,391	792,822
Unbilled Revenues	224,982	216,040
Fuel, Materials and Supplies	303,233	267,713
Regulatory Assets Current	535,791	705,025
Prepayments and Other Current Assets	214,288	199,947
Total Current Assets	2,087,049	2,227,295
Property, Plant and Equipment, Net	17,576,186	16,605,010
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	3,758,694	5,132,411
Goodwill	3,519,401	3,519,401
Marketable Securities	488,515	400,329
Derivative Assets Noncurrent	74,155	90,612
Other Long-Term Assets	291,537	327,766
Total Deferred Debits and Other Assets	8,132,302	9,470,519
Total Assets	27,795,537	28,302,824
Current Liabilities:	'	'
Notes Payable to Banks	1,093,000	1,120,196
Long-Term Debt - Current Portion	533,346	763,338
Accounts Payable - Current	742,251	764,350
Regulatory Liability Current	204,278	134,115
Other Liabilities - Current	702,776	861,691
Total Current Liabilities	3,275,651	3,643,690
Rate Reduction Bonds	0	82,139
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	4,029,026	3,463,347
Regulatory Liabilities Long-Term	502,984	540,162
Long-Term Derivative Liabilities	624,050	882,654
Accrued Pension, PBOP and SERP	896,844	2,130,497
Other Long-Term Liabilities	923,053	967,561
Total Deferred Credits and Other Liabilities	6,975,957	7,984,221
Capitalization:	'	'
Long-Term Debt	7,776,833	7,200,156
Noncontrolling Interest in Consolidated Subsidiary:	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:	'	'
Common Stock	1,665,351	1,662,547
Capital Surplus, Paid In	6,192,765	6,183,267
Retained Earnings	2,125,980	1,802,714
Accumulated Other Comprehensive Loss	-46,031	-72,854
Treasury Stock	-326,537	-338,624
Common Shareholders' Equity	9,611,528	9,237,050
Total Capitalization	17,543,929	16,592,774
Total Liabilities and Capitalization	27,795,537	28,302,824
The Connecticut Light And Power Company [Member]	'	'
Current Assets:	'	'
Cash	7,237	1
Receivables, Net	319,670	284,787
Accounts Receivable from Affiliated Companies	13,777	6,641
Unbilled Revenues	92,401	85,353
Regulatory Assets Current	150,943	185,858
Materials and Supplies	54,606	64,603
Prepayments and Other Current Assets	53,082	26,413
Total Current Assets	691,716	653,656
Property, Plant and Equipment, Net	6,451,259	6,152,959
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	1,663,147	2,158,363
Derivative Assets Noncurrent	71,384	90,612
Other Long-Term Assets	102,996	86,498
Total Deferred Debits and Other Assets	1,837,527	2,335,473
Total Assets	8,980,502	9,142,088
Current Liabilities:	'	'
Notes Payable To Affiliated Companies	287,300	99,296
Long-Term Debt - Current Portion	150,000	125,000
Accounts Payable - Current	201,047	262,857
Accounts Payable to Affiliated Companies	56,531	52,326
Obligations to Third Party Suppliers	73,914	67,344
Accrued Taxes	37,186	60,109
Regulatory Liability Current	93,961	32,119
Derivative Liabilities - Current	92,233	96,931
Other Liabilities - Current	97,530	125,662
Total Current Liabilities	1,089,702	921,644
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	1,510,586	1,336,105
Regulatory Liabilities Long-Term	93,757	124,319
Long-Term Derivative Liabilities	617,072	865,571
Accrued Pension, PBOP and SERP	95,895	304,696
Other Long-Term Liabilities	163,588	197,434
Total Deferred Credits and Other Liabilities	2,480,898	2,828,125
Capitalization:	'	'
Long-Term Debt	2,591,208	2,737,790
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	1,682,047	1,640,149
Retained Earnings	961,482	839,628
Accumulated Other Comprehensive Loss	-1,387	-1,800
Common Shareholders' Equity	2,702,494	2,538,329
Total Capitalization	5,409,902	5,392,319
Total Liabilities and Capitalization	8,980,502	9,142,088
NSTAR Electric Company [Member]	'	'
Current Assets:	'	'
Cash	8,021	13,695
Receivables, Net	209,711	202,025
Accounts Receivable from Affiliated Companies	27,264	160,176
Unbilled Revenues	41,368	41,377
Regulatory Assets Current	204,144	347,081
Materials and Supplies	44,236	26,754
Prepayments and Other Current Assets	36,710	1,332
Total Current Assets	571,454	792,440
Property, Plant and Equipment, Net	5,043,887	4,735,297
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	1,235,156	1,444,870
Other Long-Term Assets	60,624	87,382
Total Deferred Debits and Other Assets	1,295,780	1,532,252
Total Assets	6,911,121	7,059,989
Current Liabilities:	'	'
Notes Payable to Banks	103,500	276,000
Long-Term Debt - Current Portion	301,650	1,650
Accounts Payable - Current	207,559	168,611
Accounts Payable to Affiliated Companies	75,707	247,061
Deferred Tax Liabilities Current	50,128	104,668
Regulatory Liability Current	53,958	47,539
Other Liabilities - Current	118,410	144,433
Total Current Liabilities	910,912	989,962
Rate Reduction Bonds	0	43,493
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	1,466,835	1,321,026
Regulatory Liabilities Long-Term	253,108	244,224
Accrued Pension, PBOP and SERP	118,010	360,932
Other Long-Term Liabilities	142,214	183,190
DueToRelatedPartiesNoncurrent	64,172	70,221
Total Deferred Credits and Other Liabilities	2,044,339	2,179,593
Capitalization:	'	'
Long-Term Debt	1,499,417	1,600,911
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	992,625	992,625
Retained Earnings	1,420,828	1,210,405
Common Shareholders' Equity	2,413,453	2,203,030
Total Capitalization	3,955,870	3,846,941
Total Liabilities and Capitalization	6,911,121	7,059,989
Public Service Company Of New Hampshire [Member]	'	'
Current Assets:	'	'
Cash	130	2,493
Receivables, Net	76,331	87,164
Accounts Receivable from Affiliated Companies	90	723
Unbilled Revenues	38,344	39,982
Taxes Receivable	2,180	17,177
Fuel, Materials and Supplies	128,736	95,345
Regulatory Assets Current	92,194	62,882
Prepayments and Other Current Assets	21,920	22,205
Total Current Assets	359,925	327,971
Property, Plant and Equipment, Net	2,467,556	2,352,515
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	219,346	351,059
Other Long-Term Assets	39,891	83,052
Total Deferred Debits and Other Assets	259,237	434,111
Total Assets	3,086,718	3,114,597
Current Liabilities:	'	'
Notes Payable To Affiliated Companies	86,500	63,300
Long-Term Debt - Current Portion	50,000	'
Accounts Payable - Current	82,920	62,864
Accounts Payable to Affiliated Companies	22,040	21,337
Deferred Tax Liabilities Current	28,596	10,364
Regulatory Liability Current	20,643	23,002
Other Liabilities - Current	42,811	40,586
Renewable Portfolio Standards Compliance Obligation	8,918	17,383
Total Current Liabilities	342,428	238,836
Rate Reduction Bonds	0	29,294
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	500,166	441,577
Regulatory Liabilities Long-Term	51,723	52,418
Accrued Pension, PBOP and SERP	15,272	33,981
Other Long-Term Liabilities	46,247	47,896
Total Deferred Credits and Other Liabilities	613,408	762,020
DefinedBenefitPensionPlanLiabilitiesNoncurrent	'	186,148
Capitalization:	'	'
Long-Term Debt	999,006	997,932
Common Shareholders' Equity:	'	'
Common Stock	0	0
Capital Surplus, Paid In	701,911	701,052
Retained Earnings	438,515	395,118
Accumulated Other Comprehensive Loss	-8,550	-9,655
Common Shareholders' Equity	1,131,876	1,086,515
Total Capitalization	2,130,882	2,084,447
Total Liabilities and Capitalization	3,086,718	3,114,597
Western Massachusetts Electric Company [Member]	'	'
Current Assets:	'	'
Cash	0	1
Receivables, Net	49,018	47,297
Accounts Receivable from Affiliated Companies	47,607	164
Unbilled Revenues	16,562	16,192
Taxes Receivable	432	15,513
Regulatory Assets Current	43,024	42,370
Marketable Securities - Current	26,628	27,352
Prepayments and Other Current Assets	10,479	7,963
Total Current Assets	193,750	156,852
Property, Plant and Equipment, Net	1,381,060	1,290,498
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	146,088	221,752
Marketable Securities	31,243	30,342
Other Long-Term Assets	40,679	23,625
Total Deferred Debits and Other Assets	218,010	275,719
Total Assets	1,792,820	1,723,069
Current Liabilities:	'	'
Notes Payable To Affiliated Companies	0	31,900
Long-Term Debt - Current Portion	0	55,000
Accounts Payable - Current	62,961	68,141
Accounts Payable to Affiliated Companies	9,230	7,103
Accrued Interest	7,525	8,304
Deferred Tax Liabilities Current	13,098	8,404
Regulatory Liability Current	19,858	21,037
Other Liabilities - Current	20,629	15,754
CounterPartyDeposit	7,688	751
Total Current Liabilities	140,989	216,394
Rate Reduction Bonds	0	9,352
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	396,933	303,111
Regulatory Liabilities Long-Term	13,873	9,686
Accrued Pension, PBOP and SERP	3,911	11,884
Other Long-Term Liabilities	28,619	40,148
Total Deferred Credits and Other Liabilities	443,336	389,044
DefinedBenefitPensionPlanLiabilitiesNoncurrent	'	24,215
Capitalization:	'	'
Long-Term Debt	629,389	550,270
Common Shareholders' Equity:	'	'
Common Stock	10,866	10,866
Capital Surplus, Paid In	390,743	390,412
Retained Earnings	181,014	160,577
Accumulated Other Comprehensive Loss	-3,517	-3,846
Common Shareholders' Equity	579,106	558,009
Total Capitalization	1,208,495	1,108,279
Total Liabilities and Capitalization	$1,792,820	$1,723,069

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Revenues	$7,301,204	$6,273,787	$4,465,657
Operating Expenses:	'	'	'
Purchased Power and Transmission	2,482,954	2,084,364	1,657,914
Operations and Maintenance	1,514,986	1,583,070	1,095,358
Depreciation	610,777	519,010	302,192
Amortization of Regulatory Assets/(Liabilities), Net	206,322	79,762	91,080
Amortization of Rate Reduction Bonds	42,581	142,019	69,912
Energy Efficiency Programs	401,919	313,149	131,415
Taxes Other Than Income Taxes	512,230	434,207	323,610
Total Operating Expenses	5,771,769	5,155,581	3,671,481
Operating Income	1,529,435	1,118,206	794,176
Interest Expense:	'	'	'
Interest on Long-Term Debt	340,970	316,987	231,630
Interest on Rate Reduction Bonds	422	6,168	8,611
Other Interest	-2,693	6,790	10,184
Total Interest Expense	338,699	329,945	250,425
Other Income/(Loss), Net	29,894	19,742	27,715
Income Before Income Tax Expense	1,220,630	808,003	571,466
Income Tax Expense	426,941	274,926	170,953
Net Income	793,689	533,077	400,513
Net Income Attributable to Noncontrolling Interests	7,682	7,132	5,820
Net Income Attributable to Controlling Interests	786,007	525,945	394,693
Diluted Earnings Per Common Share	$2.49	$1.89	$2.22
Basic Earnings Per Common Share	$2.49	$1.90	$2.22
Weighted Average Common Shares Outstanding:	'	'	'
Basic	315,311,387	277,209,819	177,410,167
Diluted	316,211,160	277,993,631	177,804,568
The Connecticut Light And Power Company [Member]	'	'	'
Operating Revenues	2,442,341	2,407,449	2,548,387
Operating Expenses:	'	'	'
Purchased Power and Transmission	872,769	858,231	982,514
Operations and Maintenance	523,247	635,733	580,736
Depreciation	177,603	166,853	157,747
Amortization of Regulatory Assets/(Liabilities), Net	4,870	14,372	61,025
Energy Efficiency Programs	89,858	89,299	90,297
Taxes Other Than Income Taxes	234,418	215,972	212,885
Total Operating Expenses	1,902,765	1,980,460	2,085,204
Operating Income	539,576	426,989	463,183
Interest Expense:	'	'	'
Interest on Long-Term Debt	130,620	124,894	131,918
Other Interest	3,030	8,233	809
Total Interest Expense	133,650	133,127	132,727
Other Income/(Loss), Net	15,149	10,300	9,741
Income Before Income Tax Expense	421,075	304,162	340,197
Income Tax Expense	141,663	94,437	90,033
Net Income	279,412	209,725	250,164
NSTAR Electric Company [Member]	'	'	'
Operating Revenues	2,493,479	2,300,997	2,403,053
Operating Expenses:	'	'	'
Purchased Power and Transmission	849,149	788,252	905,226
Operations and Maintenance	376,360	431,802	387,533
Depreciation	180,298	171,070	163,368
Amortization of Regulatory Assets/(Liabilities), Net	230,148	117,682	82,979
Amortization of Rate Reduction Bonds	15,054	90,322	90,322
Energy Efficiency Programs	206,536	201,234	175,747
Taxes Other Than Income Taxes	127,778	119,219	111,705
Total Operating Expenses	1,985,323	1,919,581	1,916,880
Operating Income	508,156	381,416	486,173
Interest Expense:	'	'	'
Interest on Long-Term Debt	79,088	87,100	90,040
Interest on Rate Reduction Bonds	399	3,585	7,226
Other Interest	-9,104	-20,631	-27,839
Total Interest Expense	70,383	70,054	69,427
Other Income/(Loss), Net	3,639	2,846	1,434
Income Before Income Tax Expense	441,412	314,208	418,180
Income Tax Expense	172,866	123,966	165,686
Net Income	268,546	190,242	252,494
Public Service Company Of New Hampshire [Member]	'	'	'
Operating Revenues	935,402	988,013	1,013,003
Operating Expenses:	'	'	'
Purchased Power and Transmission	269,754	319,253	327,905
Operations and Maintenance	267,797	263,234	278,153
Depreciation	91,581	87,602	76,167
Amortization of Regulatory Assets/(Liabilities), Net	-20,387	-24,086	25,383
Amortization of Rate Reduction Bonds	19,748	56,645	53,389
Energy Efficiency Programs	14,494	14,245	12,917
Taxes Other Than Income Taxes	67,196	66,025	58,985
Total Operating Expenses	710,183	782,918	832,899
Operating Income	225,219	205,095	180,104
Interest Expense:	'	'	'
Interest on Long-Term Debt	44,370	46,228	36,832
Interest on Rate Reduction Bonds	-154	2,687	6,276
Other Interest	1,960	1,313	1,039
Total Interest Expense	46,176	50,228	44,147
Other Income/(Loss), Net	3,455	3,008	14,255
Income Before Income Tax Expense	182,498	157,875	150,212
Income Tax Expense	71,101	60,993	49,945
Net Income	111,397	96,882	100,267
Western Massachusetts Electric Company [Member]	'	'	'
Operating Revenues	472,724	441,164	417,315
Operating Expenses:	'	'	'
Purchased Power and Transmission	147,059	136,086	161,480
Operations and Maintenance	96,194	97,031	80,241
Depreciation	37,568	29,971	26,455
Amortization of Regulatory Assets/(Liabilities), Net	-3,206	410	4,492
Amortization of Rate Reduction Bonds	7,780	17,632	16,523
Energy Efficiency Programs	39,524	27,802	21,804
Taxes Other Than Income Taxes	28,458	21,458	17,957
Total Operating Expenses	353,377	330,390	328,952
Operating Income	119,347	110,774	88,363
Interest Expense:	'	'	'
Interest on Long-Term Debt	23,625	23,462	20,023
Interest on Rate Reduction Bonds	177	1,229	2,335
Other Interest	1,049	1,943	1,254
Total Interest Expense	24,851	26,634	23,612
Other Income/(Loss), Net	3,310	2,503	1,489
Income Before Income Tax Expense	97,806	86,643	66,240
Income Tax Expense	37,368	32,140	23,186
Net Income	$60,438	$54,503	$43,054

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Income	$793,689	$533,077	$400,513
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,049	1,971	-14,177
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-940	217	506
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	25,714	-4,356	-13,645
Other Comprehensive Income (Loss), Net of Tax, Total	26,823	-2,168	-27,316
Comprehensive Income Attributable to Noncontrolling Interests	-7,682	-7,132	-5,820
Comprehensive Income	812,830	523,777	367,377
The Connecticut Light And Power Company [Member]	'	'	'
Net Income	279,412	209,725	250,164
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	444	444	445
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-31	7	17
Other Comprehensive Income (Loss), Net of Tax, Total	413	451	462
Comprehensive Income	279,825	210,176	250,626
NSTAR Electric Company [Member]	'	'	'
Net Income	268,546	190,242	252,494
Public Service Company Of New Hampshire [Member]	'	'	'
Net Income	111,397	96,882	100,267
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	1,162	1,162	-10,260
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-54	13	29
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	-3	2	0
Other Comprehensive Income (Loss), Net of Tax, Total	1,105	1,177	-10,231
Comprehensive Income	112,502	98,059	90,036
Western Massachusetts Electric Company [Member]	'	'	'
Net Income	60,438	54,503	43,054
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	338	338	-4,108
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-9	2	5
Other Comprehensive Income (Loss), Net of Tax, Total	329	340	-4,103
Comprehensive Income	$60,767	$54,843	$38,951

CONSOLIDATED_STATEMENT_OF_CASH

CONSOLIDATED STATEMENT OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities:	'	'	'
Net Income	$793,689	$533,077	$400,513
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'
Depreciation	610,777	519,010	302,192
Deferred Income Tax Expense (Benefit)	431,413	292,000	196,761
Pension and PBOP Expense, Net of PBOP Contributions	195,698	218,540	133,000
Pension and Other Postretirement Benefit Contributions	-342,184	-295,028	-191,101
Regulatory (Underrecoveries)/Overrecoveries, Net	-24,276	-259,853	-70,863
Amortization of Regulatory Assets/(Liabilities), Net	206,322	79,762	91,080
Amortization of Rate Reduction Bonds	42,581	142,019	69,912
Other Noncash Income (Expense)	56,071	42,852	-48,772
Changes in Current Assets and Liabilities:	'	'	'
Receivables and Unbilled Revenues, Net	-163,549	-20,214	17,570
Inventory	-14,811	34,321	-11,033
Taxes Receivable/(Accrued)	-50,950	-5,450	49,642
Change in Accounts Payable	-54,619	-128,339	18,916
Other Current Assets and Liabilities	-22,623	8,532	12,569
Net Cash Flows Provided by Operating Activities	1,663,539	1,161,229	970,386
Investing Activities:	'	'	'
Investments in Property, Plant and Equipment	-1,456,787	-1,472,272	-1,076,730
Proceeds from Sales of Marketable Securities	627,532	317,294	149,441
Purchases of Marketable Securities	-679,784	-348,629	-151,972
Other Investing Activities	67,816	35,683	60,674
Net Cash Flows Used in Investing Activities	-1,441,223	-1,467,924	-1,018,587
Financing Activities:	'	'	'
Cash Dividends on Common Stock	-462,741	-375,047	-194,555
Cash Dividends on Preferred Stock	-7,682	-7,029	-5,559
Increase/(Decrease) in Short-Term Debt	-397,000	825,000	50,000
Issuance of Long-Term Debt	1,680,000	850,000	627,500
Retirements of Long-Term Debt	-929,885	-839,136	-369,586
Retirements of Rate Reduction Bonds	-82,139	-114,433	-69,312
Other Financing Activities	-25,253	6,529	-7,123
Net Cash Flows Provided by/(Used in) Financing Activities	-224,700	345,884	31,365
Net Increase/(Decrease) in Cash	-2,384	39,189	-16,836
Cash - Beginning of Year	45,748	6,559	23,395
Cash - End of Year	43,364	45,748	6,559
The Connecticut Light And Power Company [Member]	'	'	'
Operating Activities:	'	'	'
Net Income	279,412	209,725	250,164
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'
Depreciation	177,603	166,853	157,747
Deferred Income Tax Expense (Benefit)	130,038	140,993	112,620
Pension and PBOP Expense, Net of PBOP Contributions	24,416	24,062	10,664
Regulatory (Underrecoveries)/Overrecoveries, Net	28,298	-100,505	-82,502
Amortization of Regulatory Assets/(Liabilities), Net	4,870	14,372	61,025
Other Noncash Income (Expense)	-3,478	-28,952	-33,713
Changes in Current Assets and Liabilities:	'	'	'
Receivables and Unbilled Revenues, Net	-56,593	-7,741	14,610
Inventory	9,997	-4,573	-2,206
Taxes Receivable/(Accrued)	-41,594	15,702	2,719
Change in Accounts Payable	-66,225	-190,240	8,864
Other Current Assets and Liabilities	8,513	-27,803	13,291
Net Cash Flows Provided by Operating Activities	495,257	211,893	513,283
Investing Activities:	'	'	'
Investments in Property, Plant and Equipment	-434,934	-449,137	-424,865
Proceeds From Sale Of Property Plant And Equipment	0	'	46,841
Other Investing Activities	2,650	32,009	16,001
Net Cash Flows Used in Investing Activities	-432,284	-417,128	-362,023
Financing Activities:	'	'	'
Cash Dividends on Common Stock	-151,999	-100,486	-243,218
Cash Dividends on Preferred Stock	-5,559	-5,559	-5,559
Increase/(Decrease) in Short-Term Debt	-89,000	58,000	31,000
Issuance of Long-Term Debt	400,000	'	245,500
Increase/(Decrease) in Notes Payable to Affiliate	-117,800	346,575	52,300
Retirements of Long-Term Debt	-125,000	-116,400	-245,500
Capital Contributions from NU Parent	40,000	25,000	6,748
Other Financing Activities	-6,379	-1,895	-2,292
Net Cash Flows Provided by/(Used in) Financing Activities	-55,737	205,235	-161,021
Net Increase/(Decrease) in Cash	7,236	'	-9,761
Cash - Beginning of Year	1	1	9,762
Cash - End of Year	7,237	1	1
NSTAR Electric Company [Member]	'	'	'
Operating Activities:	'	'	'
Net Income	268,546	190,242	252,494
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'
Bad Debt Expense	28,108	40,301	22,582
Depreciation	180,298	171,070	163,368
Deferred Income Tax Expense (Benefit)	48,808	4,264	72,006
Pension and PBOP Expense, Net of PBOP Contributions	35,731	66,010	54,704
Pension Contribution	-82,000	-25,000	-125,000
Regulatory (Underrecoveries)/Overrecoveries, Net	-119,433	-16,129	68,353
Amortization of Regulatory Assets/(Liabilities), Net	230,148	117,682	82,979
Amortization of Rate Reduction Bonds	15,054	90,322	90,322
Other Noncash Income (Expense)	4,428	-32,048	539
Changes in Current Assets and Liabilities:	'	'	'
Receivables and Unbilled Revenues, Net	-45,405	-10,496	-26,041
Inventory	3,227	1,813	-12,968
Taxes Receivable/(Accrued)	-38,003	29,899	149,889
Change in Accounts Payable	31,875	2,662	-53,939
Other Current Assets and Liabilities	-6,468	22,568	14,272
IncreaseDecreaseInAccountsPayableRelatedParties	-44,491	-61,879	-7,232
Net Cash Flows Provided by Operating Activities	510,423	591,281	746,328
Investing Activities:	'	'	'
Investments in Property, Plant and Equipment	-476,600	-414,089	-390,427
DecreaseInRestrictedCash	37,604	3,060	-2,732
Other Investing Activities	400	400	6,095
Net Cash Flows Used in Investing Activities	-438,596	-410,629	-387,064
Financing Activities:	'	'	'
Cash Dividends on Common Stock	-56,000	-217,000	-169,900
Cash Dividends on Preferred Stock	-2,123	-1,960	-1,960
Increase/(Decrease) in Short-Term Debt	-172,500	134,500	-86,000
Issuance of Long-Term Debt	200,000	400,000	0
Retirements of Long-Term Debt	-1,650	-401,650	-16,650
Retirements of Rate Reduction Bonds	-43,493	-84,367	-84,346
Other Financing Activities	-1,735	-5,853	0
Net Cash Flows Provided by/(Used in) Financing Activities	-77,501	-176,330	-358,856
Net Increase/(Decrease) in Cash	-5,674	4,322	408
Cash - Beginning of Year	13,695	9,373	8,965
Cash - End of Year	8,021	13,695	9,373
Public Service Company Of New Hampshire [Member]	'	'	'
Operating Activities:	'	'	'
Net Income	111,397	96,882	100,267
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'
Depreciation	91,581	87,602	76,167
Deferred Income Tax Expense (Benefit)	75,693	58,552	75,628
Pension and PBOP Expense, Net of PBOP Contributions	26,846	26,312	27,298
Pension and Other Postretirement Benefit Contributions	-112,964	-96,880	-121,178
Regulatory (Underrecoveries)/Overrecoveries, Net	-8,481	-183	6,079
Amortization of Regulatory Assets/(Liabilities), Net	-20,387	-24,086	25,383
Amortization of Rate Reduction Bonds	19,748	56,645	53,389
Changes in Derivative Assets and Liabilities	0	0	-18,072
Other Noncash Income (Expense)	16,079	11,205	-13,923
Changes in Current Assets and Liabilities:	'	'	'
Receivables and Unbilled Revenues, Net	2,412	-84	7,833
Inventory	-33,391	25,897	-9,873
Taxes Receivable/(Accrued)	26,462	-9,752	5,139
Change in Accounts Payable	2,632	-15,248	-4,517
Other Current Assets and Liabilities	-9,520	13,436	-4,915
Net Cash Flows Provided by Operating Activities	188,107	230,298	204,705
Investing Activities:	'	'	'
Investments in Property, Plant and Equipment	-186,009	-203,902	-241,772
(Increase) Decrease In Notes Receivable From Affiliated Company	'	55,900	-55,900
DecreaseInRestrictedCash	22,040	4,200	2,223
Other Investing Activities	-88	-135	-134
Net Cash Flows Used in Investing Activities	-164,057	-143,937	-295,583
Financing Activities:	'	'	'
Cash Dividends on Common Stock	-68,000	-90,674	-58,828
Increase/(Decrease) in Short-Term Debt	23,200	0	-30,000
Issuance of Long-Term Debt	250,000	0	282,000
Increase/(Decrease) in Notes Payable to Affiliate	0	63,300	-47,900
Retirements of Long-Term Debt	-198,235	0	-119,800
Retirements of Rate Reduction Bonds	-29,294	-56,074	-52,879
Capital Contributions from NU Parent	0	0	120,030
Other Financing Activities	-4,084	-476	-4,248
Net Cash Flows Provided by/(Used in) Financing Activities	-26,413	-83,924	88,375
Net Increase/(Decrease) in Cash	-2,363	2,437	-2,503
Cash - Beginning of Year	2,493	56	2,559
Cash - End of Year	130	2,493	56
Western Massachusetts Electric Company [Member]	'	'	'
Operating Activities:	'	'	'
Net Income	60,438	54,503	43,054
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'
Depreciation	37,568	29,971	26,455
Deferred Income Tax Expense (Benefit)	87,028	53,942	23,056
Regulatory (Underrecoveries)/Overrecoveries, Net	8,458	-19,152	3,328
Amortization of Regulatory Assets/(Liabilities), Net	-3,206	410	4,492
Amortization of Rate Reduction Bonds	7,780	17,632	16,523
Changes in Derivative Assets and Liabilities	0	0	-6,859
Other Noncash Income (Expense)	3,381	-3,954	-586
Changes in Current Assets and Liabilities:	'	'	'
Receivables and Unbilled Revenues, Net	-53,292	-8,896	-7,263
Inventory	865	-2,882	331
Taxes Receivable/(Accrued)	19,840	-8,311	5,084
Change in Accounts Payable	7,456	-19,297	12,956
Other Current Assets and Liabilities	2,491	581	3,824
Net Cash Flows Provided by Operating Activities	178,807	94,547	124,395
Investing Activities:	'	'	'
Investments in Property, Plant and Equipment	-128,786	-264,175	-237,996
Proceeds from Sales of Marketable Securities	70,778	79,769	125,157
Purchases of Marketable Securities	-71,390	-80,529	-125,453
(Increase) Decrease In Notes Receivable From Affiliated Company	0	11,000	-11,000
Other Investing Activities	7,401	-28	-1,919
Net Cash Flows Used in Investing Activities	-121,997	-253,963	-251,211
Financing Activities:	'	'	'
Cash Dividends on Common Stock	-40,001	-9,432	-26,305
Issuance of Long-Term Debt	80,000	150,000	100,000
Increase/(Decrease) in Notes Payable to Affiliate	-31,900	31,900	-20,400
Retirements of Long-Term Debt	-55,000	-53,800	0
Retirements of Rate Reduction Bonds	-9,352	-17,540	-16,433
Capital Contributions from NU Parent	0	50,000	91,812
Other Financing Activities	-558	8,288	-1,858
Net Cash Flows Provided by/(Used in) Financing Activities	-56,811	159,416	126,816
Net Increase/(Decrease) in Cash	-1	0	0
Cash - Beginning of Year	1	1	1
Cash - End of Year	$0	$1	$1

CONSOLIDATED_STATEMENTS_OF_COM1

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS EQUITY (USD $)

12 Months Ended

In Thousands, except Share data, unless otherwise specified

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Common Stock [Member]

Additional Paid-in Capital [Member]

Retained Earnings [Member]

Accumulated Other Comprehensive Income (Loss) [Member]

Treasury Stock [Member]

Stockholders Equity Total Member

Common Shareholders Equity [Member]

The Connecticut Light And Power Company [Member]

NSTAR Electric Company [Member]

Public Service Company Of New Hampshire [Member]

Western Massachusetts Electric Company [Member]

Common Stock [Member]

Additional Paid-in Capital [Member]

Retained Earnings [Member]

Accumulated Other Comprehensive Income (Loss) [Member]

Common Shareholders Equity [Member]

Common Stock [Member]

Additional Paid-in Capital [Member]

Retained Earnings [Member]

Common Shareholders Equity [Member]

Common Stock [Member]

Additional Paid-in Capital [Member]

Retained Earnings [Member]

Accumulated Other Comprehensive Income (Loss) [Member]

Common Shareholders Equity [Member]

Common Stock [Member]

Additional Paid-in Capital [Member]

Retained Earnings [Member]

Accumulated Other Comprehensive Income (Loss) [Member]

Common Shareholders Equity [Member]

Common Stock, Shares, Outstanding

315,273,559

314,053,634

177,158,692

176,448,081

6,035,205

100

301

434,653

Common Stock, Value, Outstanding

$1,665,351

$1,662,547

$980,264

$978,909

$6,192,765

$6,183,267

$1,797,884

$1,777,592

$2,125,980

$1,802,714

$1,651,875

$1,452,777

($46,031)

($72,854)

($70,686)

($43,370)

($326,537)

($338,624)

($346,667)

($354,732)

$9,611,528

$9,237,050

$4,012,670

$3,811,176

$60,352

$1,682,047

$1,640,149

$1,613,503

$1,605,275

$961,482

$839,628

$735,948

$734,561

($1,387)

($1,800)

($2,251)

($2,713)

$2,702,494

$2,538,329

$2,407,552

$2,397,475

$992,625

$1,420,828

$1,210,405

$1,239,123

$1,158,489

$2,413,453

$2,203,030

$2,231,748

$2,151,114

$701,911

$701,052

$700,285

$579,577

$438,515

$395,118

$388,910

$347,471

($8,550)

($9,655)

($10,832)

($601)

$1,131,876

$1,086,515

$1,078,363

$926,447

$10,866

$390,743

$390,412

$340,115

$248,044

$181,014

$160,577

$115,506

$98,757

($3,517)

($3,846)

($4,186)

($83)

$579,106

$558,009

$462,301

$357,584

Net Income

533,077

793,689

533,077

400,513

793,689

533,077

400,513

279,412

209,725

250,164

279,412

209,725

250,164

268,546

190,242

252,494

268,546

190,242

252,494

111,397

96,882

100,267

111,397

96,882

100,267

60,438

54,503

43,054

60,438

54,503

43,054

Dividends on Common Shares

-462,741

-375,527

-195,595

-462,741

-375,527

-195,595

-151,999

-100,486

-243,218

-151,999

-100,486

-243,218

-56,000

-217,000

-169,900

-56,000

-217,000

-169,900

-68,000

-90,674

-58,828

-68,000

-90,674

-58,828

-40,001

-9,432

-26,305

-40,001

-9,432

-26,305

Issuance of Common Shares

2,804

2,040

1,355

8,274

11,287

4,496

11,078

13,327

5,851

Stock Issued During Period, Shares, New Issues

560,848

408,018

271,030

Dividends, Preferred Stock

-7,682

-7,029

-5,559

-7,682

-7,029

-5,559

-2,123

-1,960

-2,123

-1,960

Stock Issued During Period, Value, Employee Stock Ownership Plan

1,847

1,595

1,429

1,847

1,595

1,429

859

767

678

859

767

678

331

297

259

331

297

259

Long-Term Incentive Plan Activity

-10,748

-3,897

7,359

-10,748

-3,897

7,359

Other Comprehensive Income (Loss), Net of Tax

-2,168

26,823

-2,168

-27,316

26,823

-2,168

-27,316

413

451

462

413

451

462

1,105

1,177

-10,231

1,105

1,177

-10,231

329

340

-4,103

329

340

-4,103

Stock Issued During Period, Value, Treasury Stock Reissued

17,381

8,454

7,048

12,087

8,043

8,065

29,468

16,497

15,113

Stock Issued During Period, Shares, Treasury Stock Reissued

659,077

438,329

439,581

Payments of Stock Issuance Costs

Net Income Attributable to Noncontrolling Interests

7,132

-103

-261

-103

-261

Capital Contributions from NU Parent

40,000

25,000

6,748

40,000

25,000

6,748

120,030

50,000

91,812

50,000

91,812

SharesIssuedInConnectionWithNstarMerger

136,048,595

SharesIssuedValueInConectionWithNstarMerger

680,243

4,358,027

5,038,270

OtherChangesInShareholdersEquity

-5,409

8,574

1,389

-5,409

8,574

1,389

OtherEquityImpactsOfMergerWithNstar

$2,938

$421

$3,359

SUMMARY_OF_SIGNIFICANT_ACCOUNT

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Significant Accounting Policies [Text Block]	'
	NORTHEAST UTILITIES 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 FINANCIAL STATEMENTS

	Refer to the Glossary of Terms included in this combined Annual Report on Form 10-K for abbreviations and acronyms used throughout the combined notes to the financial statements.

	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

	A. About NU, CL&P, NSTAR Electric, PSNH and WMECO
	NU Consolidated: NU is a public utility holding company primarily engaged through its wholly owned regulated utility subsidiaries in the energy delivery business. On April 10, 2012, NU acquired NSTAR and its subsidiaries. NU's wholly owned regulated utility subsidiaries consist of CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas. NU 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. See Note 2, "Merger of NU and NSTAR," for further information regarding the merger.

	NU, CL&P, NSTAR Electric, PSNH and WMECO are reporting companies under the Securities Exchange Act of 1934. NU is a public utility holding company under the Public Utility Holding Company Act of 2005. Arrangements among the regulated electric companies and other NU companies, outside agencies and other utilities covering interconnections, interchange of electric power and sales of utility property are subject to regulation by the FERC. The Regulated companies are subject to regulation of rates, accounting and other matters by the FERC and/or applicable state regulatory commissions (the PURA for CL&P and Yankee Gas, the DPU for NSTAR Electric, WMECO and NSTAR Gas, and the NHPUC for PSNH).

	Regulated Companies: CL&P, NSTAR Electric, PSNH and WMECO furnish franchised retail electric service in Connecticut, Massachusetts and New Hampshire. NSTAR Gas is engaged in the distribution and sale of natural gas to customers within central and eastern Massachusetts. Yankee Gas owns and operates Connecticut's largest natural gas distribution system. CL&P, NSTAR Electric, PSNH and WMECO's results include the operations of their respective distribution and transmission businesses. PSNH and WMECO's distribution results include the operations of their respective generation businesses. NU also has a regulated subsidiary, NPT, which was formed to construct, own and operate the Northern Pass line, a new HVDC transmission line from Québec to New Hampshire that will interconnect with a new HVDC transmission line being developed by a transmission subsidiary of HQ.

	Other: NUSCO, RRR, Renewable Properties, Inc., a wholly-owned subsidiary of NUTV, and Properties, Inc., a wholly-owned subsidiary of PSNH, provide support services to NU, including its regulated companies. Harbor Electric Energy Company, a wholly-owned subsidiary of NSTAR Electric, provides distribution service and ongoing support to its only customer, the Massachusetts Water Resources Authority. Hopkinton, a subsidiary of NU, provides natural gas liquefaction and storage services to NSTAR Gas. As of December 31, 2013, NU Enterprises' primary business consisted of NGS' operation and maintenance agreements, E.S. Boulos Company, an electrical contractor based in Maine, and NSTAR Communications, Inc., an unregulated telecommunications subsidiary.

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

	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.

	NU's consolidated financial information includes NSTAR and its subsidiaries' results of operations beginning April 10, 2012. The information disclosed for NSTAR Electric represents its results of operations for each of the years ended December 31, 2013, 2012 and 2011 presented on a comparable basis. NU did not apply "push-down accounting" to NSTAR Electric, whereby the adjustments of assets and liabilities to fair value and the resultant goodwill would be shown on the financial statements of the acquired subsidiary.

	NU consolidates CYAPC and YAEC as 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 NU financial statements. For CL&P, NSTAR Electric, PSNH and WMECO, the investments in CYAPC and YAEC continue to be accounted for under the equity method. See Note 1J, "Summary of Significant Accounting Policies – Equity Method Investments," for further information.

	NU's utility subsidiaries are subject to the application of accounting guidance for entities with rate-regulated operations that considers the effect of regulation resulting from differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. NU's utility subsidiaries' energy delivery business is subject to rate-regulation that is based on cost recovery and meets the criteria for application of rate-regulated accounting. See Note 3, "Regulatory Accounting," for further information.

	Certain reclassifications of prior year data were made in the accompanying balance sheets for NU, NSTAR Electric, PSNH and WMECO and the statements of cash flows for all companies presented. These reclassifications were made to conform to the current year presentation.

	In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by NU or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of NU. The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on the balance sheets of NU, CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Board of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric.

	C. Accounting Standards
	Recently Adopted Accounting Standards: In the first quarter of 2013, NU, CL&P, NSTAR Electric, PSNH and WMECO, adopted the following Financial Accounting Standards Board's (FASB) final Accounting Standards Updates (ASU) relating to additional disclosure requirements:

	Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income (AOCI): The ASU does not change existing guidance on which items should be reclassified out of AOCI but requires additional disclosures about the components of AOCI and the amount of reclassification adjustments to be presented in one location in the footnotes. The ASU was effective beginning in the first quarter of 2013 and was applied prospectively. For further information, see Note 15, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The ASU did not affect the calculation of net income, comprehensive income or EPS and did not have an impact on financial position, results of operations or cash flows.

	Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities: Clarifies the scope of the offsetting disclosure requirements under GAAP and applies to derivative instruments. The ASU was effective beginning in the first quarter of 2013 with retrospective application. For further information, see Note 5, "Derivative Instruments," to the financial statements. The ASU did not have an impact on financial position, results of operations or cash flows.

	Accounting Standards Issued but not Yet Adopted: In July 2013, the FASB issued a final ASU effective January 1, 2014, requiring presentation of certain unrecognized tax benefits as reductions to deferred tax assets. The ASU is required to be implemented prospectively on January 1, 2014. Implementation of this guidance will have an immaterial impact on the balance sheets and no impact on the results of operations or cash flows.

	D. Cash and Cash Equivalents
	Cash and cash equivalents include cash on hand and short-term cash investments that are highly liquid in nature and have original maturities of three months or less. At the end of each reporting period, any overdraft amounts are reclassified from Cash and Cash Equivalents to Accounts Payable on the balance sheets.
	E. Provision for Uncollectible Accounts
	NU, including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at net realizable value by maintaining a provision for uncollectible amounts. This provision is determined based upon a variety of factors, including applying an estimated uncollectible account percentage to each receivable aging category, based upon historical collection and write-off experience and management's assessment of collectibility from individual customers. Management assesses the collectibility of receivables, and if circumstances change, collectibility estimates are adjusted accordingly. 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. As of December 31, 2013, CL&P, WMECO and Yankee Gas had uncollectible hardship accounts receivable reserves in the amount of $67.3 million, $5.5 million and $8.4 million, respectively, with the corresponding under recovery of bad debt expense recorded as Regulatory Assets or Other Long-Term Assets as these amounts are probable of recovery. As of December 31, 2012, these amounts totaled $65.2 million, $4.7 million and $6.4 million, respectively. These amounts are reflected in the total provision for uncollectible accounts in the table below.

	The provision for uncollectible accounts, which is included in Receivables, Net on the balance sheets, was as follows:
			As of December 31,
	(Millions of Dollars)		2013			2012
	NU		$	171.3		$	165.5
	CL&P			82			77.6
	NSTAR Electric			41.7			44.1
	PSNH			7.4			6.8
	WMECO			10			8.5

	F. Fuel, Materials and Supplies and Allowance Inventory
	Fuel, Materials and Supplies include natural gas, coal, biomass and oil inventories as well as materials purchased primarily for construction or operation and maintenance purposes. Natural gas, coal, biomass and oil inventories are valued at their respective weighted average cost. Materials and supplies are valued at the lower of average cost or market.

As of December 31, 2013, NU had $139.5 million ($74.2 million at PSNH) of fuel and $163.7 million ($54.5 million at PSNH) of materials and supplies. As of December 31, 2012, NU had $109 million ($39.6 million at PSNH) of fuel and $158.7 million ($55.7 million at PSNH) of materials and supplies.

PSNH is subject to federal and state laws and regulations that regulate emissions of air pollutants, including SO2, CO2, and NOx related to its regulated generation units, and uses SO2, CO2, and NOx emissions allowances. At the end of each compliance period, PSNH is required to relinquish SO2, CO2, and NOx emissions allowances corresponding to the actual respective emissions emitted by its generating units over the compliance period. SO2 and NOx emissions allowances are obtained through an annual allocation from the federal and state regulators that are granted at no cost and through purchases from third parties. CO2 emissions allowances are acquired through auctions and through purchases from third parties.

SO2, CO2, and NOx emissions allowances are recorded within Fuel, Materials and Supplies and are classified on the balance sheet as short-term or long-term depending on the period in which they are expected to be utilized against actual emissions. As of December 31, 2013 and 2012, PSNH had $0.2 million and $0.4 million, respectively, of short-term SO2, CO2, and NOx emissions allowances classified as Fuel, Materials and Supplies and $19.4 million and $19.4 million, respectively, of long-term SO2 and CO2 emissions allowances classified as Other Long-Term Assets on the balance sheets.

SO2, CO2, and NOx emissions allowances are charged to expense based on their weighted average cost as they are utilized against emissions volumes at PSNH's generating units. PSNH recorded expenses of $0.3 million, $0.4 million and $5.1 million for the years ended December 31, 2013, 2012, and 2011, respectively, which were included in Purchased Power, Fuel and Transmission on the statements of income. These costs or benefits are recovered from or refunded to customers through energy supply revenues. For the year ended December 31, 2013, PSNH received $6.8 million in proceeds from the auction of allowances, resulting in a net benefit of $6.5 million.

G. Restricted Cash and Other Deposits
As of December 31, 2013, NU and CL&P had $1.7 million and $1.4 million, respectively, of restricted cash relating to amounts held in escrow, which were included in Prepayments and Other Current Assets on the balance sheets. As of December 31, 2012, these amounts were $3.3 million, $1.3 million and $1.7 million for NU, CL&P and PSNH, respectively.

As of December 31, 2013 and 2012, NU had $17.9 million ($9 million of which related to NSTAR Electric) and $14.6 million, respectively, of cash collateral posted not subject to master netting agreements, primarily with ISO-NE, which were included in Prepayments and Other Current Assets on the balance sheets.

As of December 31, 2012, NU, NSTAR Electric, PSNH and WMECO had $69.4 million, $42.2 million, $22 million and $5.1 million, respectively, on deposit related to subsidiaries used for the payment of RRBs. As of December 31, 2013, there were no deposits related to these RRB subsidiaries as NSTAR Electric, PSNH and WMECO made their final payments in the first half of 2013 and these deposit balances were fully utilized.
H. 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 investment valuations used to calculate the funded status of pension and PBOP plans and nonrecurring fair value measurements of nonfinancial assets such as goodwill and AROs.

Fair Value Hierarchy: In measuring fair value, NU 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. NU evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and NU'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 NU's fair value measurements are described in Note 2, "Merger of NU and NSTAR," Note 5, "Derivative Instruments," Note 6, "Marketable Securities," Note 7, "Asset Retirement Obligations," and Note 14, "Fair Value of Financial Instruments," to the financial statements.

I. Derivative Accounting
Many of the Regulated companies' contracts for the purchase and sale of energy or energy-related products are derivatives. The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts, as costs are recovered from, or refunded to, customers in future rates.

The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of the normal exception, and determination of the fair value of derivative contracts. All of these judgments can have a significant impact on the financial statements.

The judgment applied in the election of the normal exception (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then the normal exception and accrual accounting is terminated and fair value accounting is applied prospectively.

The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. Changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.

For further information regarding derivative contracts, see Note 5, "Derivative Instruments," to the financial statements.

J. Equity Method Investments
Regional Decommissioned Nuclear Companies: CL&P, NSTAR Electric, PSNH and WMECO own common stock in three regional nuclear generation companies (CYAPC, YAEC and MYAPC, collectively referred to as the Yankee Companies), each of which owned a single nuclear generating facility that has been decommissioned. Upon consummation of the merger with NSTAR, NSTAR Electric's ownership interests in CYAPC and YAEC combined with CL&P's, PSNH's and WMECO's respective ownership interests in CYAPC and YAEC totaled greater than 50 percent, requiring NU to consolidate CYAPC and YAEC beginning April 10, 2012. The investments in CYAPC and YAEC had previously been accounted for under the equity method of accounting by NU. For CL&P, NSTAR Electric, PSNH and WMECO, the investment in CYAPC and YAEC, as well as MYAPC, continues to be accounted for under the equity method. At the NU consolidated level, intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation.

Ownership interests in the Yankee Companies as of December 31, 2013 and 2012 were as follows:
(Percent)	CYAPC			YAEC			MYAPC
CL&P	34.5			24.5			12
NSTAR Electric	14			14			4
PSNH	5			7			5
WMECO	9.5			7			3
The total carrying values of CL&P's, NSTAR Electric's, PSNH's and WMECO's ownership interests in CYAPC, YAEC and MYAPC, which are included in Other Long-Term Assets on their respective balance sheets, were as follows:
	As of December 31,
(Millions of Dollars)	2013			2012
CL&P	$	1.2		$	1.4
NSTAR Electric		0.5			0.6
PSNH		0.3			0.3
WMECO		0.3			0.4
For further information on the Yankee Companies, see Note 12C, "Commitments and Contingencies - Contractual Obligations - Yankee Companies," to the financial statements.

Other Investments: As of December 31, 2013 and 2012, NU had a 37.2 percent (14.5 percent of which related to NSTAR Electric) equity ownership interest in two companies that transmit electricity imported from the Hydro-Québec system in Canada. These investments are accounted for under the equity method of accounting. NU's investment totaled $5.1 million and $6 million as of December 31, 2013 and 2012, respectively, and NSTAR Electric's investment totaled $2 million and $2.3 million as of December 31, 2013 and 2012, respectively. As of December 31, 2013 and 2012, NU also had an equity ownership interest of $9.8 million and $6.8 million in an energy investment fund, respectively.

Equity investments are included in Other Long-Term Assets on the balance sheets and net earnings related to these equity investments are included in Other Income, Net on the statements of income.

K. Revenues
Regulated Companies: The Regulated companies' retail revenues are based on rates approved by their respective state regulatory commissions. In general, rates can only be changed through formal proceedings with the state regulatory commissions. The Regulated companies' rates are designed to recover the costs to provide service to their customers, including a return on investment. The Regulated companies also utilize regulatory commission-approved tracking mechanisms to recover certain costs on a fully-reconciling basis. These tracking mechanisms require rates to be changed periodically, with overcollections refunded to customers or undercollections collected from customers in future periods. WMECO has a revenue decoupling mechanism to recover a pre-established level of baseline distribution delivery service revenues per year, independent of actual customer usage. Such decoupling mechanisms effectively break the relationship between kWhs consumed by customers and revenues recognized.

Energy purchases are recorded in Purchased Power, Fuel, and Transmission, and sales of energy associated with these purchases are recorded in Operating Revenues.

Regulated Companies' Unbilled Revenues: Because customers are billed throughout the month based on pre-determined cycles rather than on a calendar month basis, an estimate of electricity or natural gas delivered to customers for which the customers have not yet been billed is calculated as of the balance sheet date. Unbilled revenues are included in Operating Revenues on the statements of income and are assets on the balance sheets. Actual amounts billed to customers when meter readings become available may vary from the estimated amount.

The Regulated companies estimate unbilled sales monthly using the daily load cycle method. The daily load cycle method allocates billed sales to the current calendar month based on the daily load for each billing cycle. The billed sales are subtracted from total month load, net of delivery losses, to estimate unbilled sales. Unbilled revenues are estimated by first allocating unbilled sales to the respective customer classes, then applying an estimated rate by customer class to those sales.

Regulated Companies' Transmission Revenues - Wholesale Rates: Wholesale transmission revenues are recovered through FERC approved formula rates. Wholesale transmission revenues for CL&P, NSTAR Electric, PSNH, and WMECO are collected under the ISO New England Inc. Transmission, Markets and Services Tariff (ISO-NE Tariff). The ISO-NE Tariff includes Regional Network Service (RNS) and Schedule 21 - NU rate schedules that recover the costs of transmission and other transmission-related services for CL&P, PSNH and WMECO and Schedule 21 - NSTAR rate schedules that recover costs of transmission and other transmission-related services for NSTAR Electric. The RNS rate, administered by ISO-NE and billed to all New England transmission load, including CL&P, NSTAR Electric, PSNH and WMECO's distribution businesses, is reset on June 1st of each year and recovers the revenue requirements associated with transmission facilities that benefit the entire New England region. Schedule 21 - NU and Schedule 21 - NSTAR rates, administered by NU, recovers the remainder of the transmission revenue requirements. The Schedule 21 - NU rate is reset on January 1st and June 1st of each year, while the Schedule 21 - NSTAR rate is reset on June 1st of each year. The Schedule 21 - NU and Schedule 21 - NSTAR rate calculations recover total transmission revenue requirements net of revenues received from other sources (i.e., RNS, rentals, etc.), thereby ensuring that NU recovers all of CL&P's, NSTAR Electric's, PSNH's and WMECO's regional and local transmission revenue requirements in accordance with the ISO-NE Tariff. RNS, Schedule 21 - NU and Schedule 21 - NSTAR rates provide for the annual reconciliation and recovery or refund of estimated costs to actual costs. The financial impacts of differences between actual and estimated costs are deferred for future recovery from, or refunded to, transmission customers.

Regulated Companies' Transmission Revenues - Retail Rates: A significant portion of the NU transmission segment revenue comes from ISO-NE charges to the distribution businesses of CL&P, NSTAR Electric, PSNH and WMECO, each of which recovers these costs through rates charged to their retail customers. CL&P, NSTAR Electric, PSNH and WMECO each have a retail transmission cost tracking mechanism as part of their rates, which allows the electric distribution companies to charge their retail customers for transmission costs on a timely basis.

L. Operating Expenses
Costs related to fuel and natural gas included in Purchased Power, Fuel and Transmission on the statements of income were as follows:
	For the Years Ended December 31,
(Millions of Dollars)	2013			2012			2011
NU- Natural Gas and Fuel⁽¹⁾	$	466.5		$	346.8		$	307.9
PSNH - Fuel		104.8			103.4			115.9

(1) NSTAR Gas natural gas costs were included in NU beginning April 10, 2012.
M. Allowance for Funds Used During Construction
AFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the Regulated companies' utility plant. The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Other Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income. AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense.
NU		For the Years Ended December 31,
(Millions of Dollars, except percentages)		2013			2012 ⁽¹⁾			2011
AFUDC:
	Borrowed Funds	$	4.1		$	5.3		$	11.8
	Equity Funds		7.1			6.8			22.5
Total		$	11.2		$	12.1		$	34.3
Average AFUDC Rate			2.70%			3.70%			7.30%

(1) NSTAR amounts were included in NU beginning April 10, 2012.
		For the Years Ended December 31,
		2013											2012								2011
(Millions of Dollars,					NSTAR										NSTAR								NSTAR
except percentages)		CL&P			Electric			PSNH			WMECO		CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
AFUDC:
	Borrowed Funds	$	2.2		$	0.5		$	0.5		$	0.5	$	2.5	$	0.3	$	1.6	$	0.5	$	3.3	$	0.2	$	7.1	$	0.5
	Equity Funds		2.9			-			0.2			1		1.9		-		1.9		1		6		-		13.2		1
Total		$	5.1		$	0.5		$	0.7		$	1.5	$	4.4	$	0.3	$	3.5	$	1.5	$	9.3	$	0.2	$	20.3	$	1.5
Average AFUDC Rate			3.70%			0.50%			1.10%			6.10%		3.60%		0.40%		5.90%		6.80%		8.30%		0.30%		7.10%		7.40%
The Regulated companies' average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings as well as a company's capitalization (preferred stock, long-term debt and common equity). The average rate is applied to average eligible CWIP amounts to calculate AFUDC.

N. 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 related to the NU supplemental benefit trust. For further information, see Note 6, "Marketable Securities," to the financial statements. For further information on AFUDC related to equity funds, see Note 1M, "Summary of Significant Accounting Policies – Allowance for Funds Used During Construction," to the financial statements. For further information on equity in earnings, see Note 1J, "Summary of Significant Accounting Policies – Equity Method Investments," to the financial statements.

O. 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 Years Ended December 31,
(Millions of Dollars)	2013			2012			2011
NU	$	144.1		$	135		$	137.8
CL&P		128.2			120.7			121.6
Certain sales taxes are also collected by NU'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.
P.			Supplemental Cash Flow Information

NU				As of and For the Years Ended December 31,
(Millions of Dollars)				2013			2012 ⁽¹⁾			2011
Cash Paid/(Received) During the Year for:
	Interest, Net of Amounts Capitalized			$	343.3		$	356.5		$	256.3
	Income Taxes				50			-12.8			-76.6
Non-Cash Investing Activities:
	Plant Additions Included in Accounts Payable (As of)				193.1			160.6			168.5

(1) NSTAR amounts were included in NU beginning April 10, 2012.
		As of and For the Years Ended December 31,
		2013											2012								2011
					NSTAR										NSTAR								NSTAR
(Millions of Dollars)		CL&P			Electric			PSNH			WMECO		CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
Cash Paid/(Received) During
	the Year for:
	Interest, Net of Amounts
	Capitalized	$	131.6		$	75.8		$	43.3		$	25.8	$	129.4	$	94.6	$	49.8	$	25.8	$	136.6	$	96.1	$	49.3	$	22.1
	Income Taxes		55			163.4			-30.1			-69		-42		88.1		14.7		-8.4		-27.5		-62.2		-29		-4.9
Non-Cash Investing Activities:
	Plant Additions Included in
	Accounts Payable (As of)		51.4			57			34.9			19.5		42.8		50		16.8		30		32.7		34.3		51.1		61.3
The merger of NU with NSTAR on April 10, 2012 represented a significant non-cash transaction. Refer to Note 2, "Merger of NU and NSTAR," for further information on the purchase price of NSTAR.

Q. Related Parties
NUSCO, NU's service company, provides centralized accounting, administrative, engineering, financial, information technology, legal, operational, planning, purchasing, and other services to NU's companies. RRR, Renewable Properties, Inc. and Properties, Inc., three other NU subsidiaries, construct, acquire or lease some of the property and facilities used by NU's companies.

As of both December 31, 2013 and 2012, CL&P, PSNH and WMECO had long-term receivables from NUSCO in the amounts of $25 million, $3.8 million and $5.5 million, respectively, which were included in Other Long-Term Assets on the balance sheets. These amounts related to the funding of investments held in trust by NUSCO in connection with certain postretirement benefits for CL&P, PSNH and WMECO employees and have been eliminated in consolidation on the NU financial statements.

NSTAR Electric's balance sheets included $64.2 million and $70.2 million in Payable to Affiliated Companies as of December 31, 2013 and 2012, respectively. These amounts related to payments received from affiliates as a result of NSTAR Electric's role as the acting sponsor of the NSTAR Pension Plan.

Included in the CL&P, NSTAR Electric, PSNH and WMECO balance sheets as of December 31, 2013 and 2012 were Accounts Receivable from Affiliated Companies and Accounts Payable to Affiliated Companies relating to transactions between CL&P, NSTAR Electric, PSNH and WMECO and other subsidiaries that are wholly owned by NU. These amounts have been eliminated in consolidation on the NU financial statements.

R. Severance Benefits
During 2013, NU recorded severance benefit expenses of $9.7 million in connection with the partial outsourcing of information technology functions made as part of ongoing post-merger integration. As of December 31, 2013, the severance accrual totaled $14.7 million and was included in Other Current Liabilities on the balance sheet.

MERGER_OF_NU_AND_NSTAR

MERGER OF NU AND NSTAR	12 Months Ended
MERGER OF NU AND NSTAR	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Business Combination Disclosure	'
	2. MERGER OF NU AND NSTAR

	On April 10, 2012, NU acquired 100 percent of the outstanding common shares of NSTAR. Pursuant to the terms and conditions of the Agreement and Plan of Merger, as amended, (the "Merger Agreement,") NSTAR and its subsidiaries became wholly-owned subsidiaries of NU.

	NSTAR was a holding company engaged through its subsidiaries in the energy delivery business serving electric and natural gas distribution customers in Massachusetts. As part of the merger, NSTAR shareholders received 1.312 NU common shares for each NSTAR common share owned (the "exchange ratio") as of the acquisition date. The exchange ratio was structured to result in a no-premium merger based on the average closing share price of each company's common shares for the 20 trading days preceding the announcement of the merger in October 2010. NU issued approximately 136 million common shares to the NSTAR shareholders as a result of the merger.

	Purchase Price: Pursuant to the merger, all of the NSTAR common shares were exchanged at the fixed exchange ratio of 1.312 NU common shares for each NSTAR common share. The total consideration transferred in the merger was based on the closing price of NU common shares on April 9, 2012, the day prior to the date the merger was completed, and was calculated as follows:
	NSTAR common shares outstanding as of April 9, 2012 (in thousands)*			103,696
	Exchange ratio			1.312
	NU common shares issued for NSTAR common shares outstanding (in thousands)			136,049
	Closing price of NU common shares on April 9, 2012		$	36.79
	Value of common shares issued (in millions)		$	5,005
	Fair value of NU replacement stock-based compensation awards related to
		pre-merger service (in millions)		33
	Total purchase price (in millions)		$	5,038
	* Included 109 thousand shares related to NSTAR stock-based compensation awards that vested immediately prior to the merger.

	Certain of NSTAR's stock-based compensation awards, including deferred shares, performance shares and all outstanding stock options, were replaced with NU awards using the exchange ratio upon consummation of the merger. In accordance with accounting guidance for business combinations, the portion of the fair value of these awards attributable to service provided prior to the merger was included in the purchase price as it represented consideration transferred in the merger. See Note 10D, "Employee Benefits – Share-Based Payments," for further information.

	Purchase Price Allocation: The allocation of the total purchase price to the estimated fair values of the assets acquired and liabilities assumed was determined based on the accounting guidance for fair value measurements, which defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The allocation of the total purchase price included adjustments to record the fair value of NSTAR's unregulated telecommunications business, regulatory assets not earning a return, lease agreements, long-term debt and the preferred stock of NSTAR Electric. The fair values of NSTAR's assets and liabilities were determined based on significant estimates and assumptions, including Level 3 inputs, that were judgmental in nature. These estimates and assumptions included the timing and amounts of projected future cash flows and discount rates reflecting risk inherent in future cash flows.

	In accordance with accounting guidance for business combinations, the excess of the purchase price over the estimated fair values of the assets acquired and liabilities assumed was recognized as goodwill. The allocation of the purchase price was as follows:
	(Millions of Dollars)
	Current Assets	$	739
	Property Plant and Equipment, Net		5,155
	Goodwill		3,232
	Other Long-Term Assets, excluding Goodwill		2,103
	Current Liabilities		-1,330
	Long-Term Liabilities		-2,723
	Long-Term Debt and Other Long-Term Obligations		-2,099
	Noncontrolling Interest		-39
	Total Purchase Price	$	5,038
	The goodwill from the merger with NSTAR of $3.2 billion was allocated to NU's reporting units based on their estimated fair values. NU's reporting units consist of Electric Distribution, Electric Transmission and Natural Gas Distribution. See the "Goodwill" section below for the allocation of goodwill to each reporting unit.

	Pro Forma Financial Information: The following unaudited pro forma financial information reflects the pro forma combined results of operations of NU and NSTAR and reflects the amortization of purchase price adjustments assuming the merger had taken place on January 1, 2011. The unaudited pro forma financial information has been presented for illustrative purposes only and is not necessarily indicative of the consolidated results of operations that would have been achieved or the future consolidated results of operations of NU.
		For the Years Ended December 31,
	(Pro forma amounts in millions, except per share amounts)	2012			2011
	Operating Revenues	$	7,004		$	7,361
	Net Income Attributable to Controlling Interest		630			689
	Basic EPS		2			2.2
	Diluted EPS		1.99			2.19
	Pro forma net income does not include potential cost savings associated with the merger. Pro forma net income also excludes certain non-recurring merger costs and costs related to the Connecticut and Massachusetts merger settlement agreements described below, with the following aggregate after-tax impacts:

			For the Years Ended December 31,
	(Millions of Dollars)		2012			2011
	Transaction and Other Costs		$	32		$	19
	Settlement Agreement Impacts			60			-
	Total After-Tax Non-Recurring Costs Excluded from
		Pro Forma Net Income Attributable to Controlling Interest	$	92		$	19
	Regulatory Approvals: On February 15, 2012, NU and NSTAR reached comprehensive merger settlement agreements with the Massachusetts Attorney General and the DOER. The Attorney General settlement agreement covered a variety of rate-making and rate design issues, including a base distribution rate freeze through 2015 for NSTAR Electric, NSTAR Gas and WMECO and $15 million, $3 million and $3 million in the form of rate credits to their respective customers. The settlement agreement reached with the DOER covered the same rate-making and rate design issues as the Attorney General's settlement agreement, as well as a variety of matters impacting the advancement of Massachusetts clean energy policy established by the Green Communities Act and Global Warming Solutions Act. On April 4, 2012, the DPU approved the settlement agreements and the merger of NU and NSTAR.

	On March 13, 2012, NU and NSTAR reached a comprehensive merger settlement agreement with both the Connecticut Attorney General and the Connecticut Office of Consumer Counsel. The settlement agreement covered a variety of matters, including a $25 million rate credit to CL&P customers, a CL&P base distribution rate freeze until December 1, 2014, and the establishment of a $15 million fund for energy efficiency and other initiatives to be disbursed at the direction of the DEEP. In the agreement, CL&P agreed to forego rate recovery of $40 million of the deferred storm restoration costs associated with restoration activities following Tropical Storm Irene and the October 2011 snowstorm. On April 2, 2012, the PURA approved the settlement agreement and the merger of NU and NSTAR.

	The pre-tax financial impacts of the Connecticut and Massachusetts merger settlement agreements that were recognized in 2012 by NU, CL&P, NSTAR Electric, and WMECO are summarized as follows:
	(Millions of Dollars)	NU			CL&P			NSTAR Electric			WMECO
	Customer Rate Credits	$	46		$	25		$	15		$	3
	Storm Costs Deferral Reduction		40			40			-			-
	Establishment of Energy Efficiency Fund		15			-			-			-
	Total Pre-Tax Settlement Agreement Impacts	$	101		$	65		$	15		$	3
	Goodwill: In accordance with the accounting standards, goodwill is not subject to amortization. However, goodwill is subject to fair value-based rules for measuring impairment, and resulting write-downs, if any, are charged to Operating Expenses. These accounting standards require that goodwill be reviewed at least annually for impairment and whenever facts or circumstances indicate that there may be an impairment. NU uses October 1st as the annual goodwill impairment testing date.

	On April 10, 2012, upon consummation of the merger with NSTAR, NU recorded approximately $3.2 billion of goodwill. With the completion of the merger, NU reviewed its management structure and determined that the reporting units for the purpose of testing goodwill for impairment are Electric Distribution, Electric Transmission and Natural Gas Distribution. NU's reporting units are consistent with the operating segments underlying the reportable segments identified in Note 21, "Segment Information," to the financial statements. Accordingly, the goodwill resulting from the merger was allocated to the Electric Distribution, Electric Transmission and Natural Gas Distribution reporting units based on the estimated fair values of the reporting units as of the merger date.

Prior to the merger with NSTAR, the only reporting unit that maintained goodwill was the Natural Gas Distribution reportable segment related to the acquisition of the parent of Yankee Gas in 2000. This goodwill was recorded at Yankee Gas. The goodwill balance at Yankee Gas as of December 31, 2013 and 2012 was $0.3 billion.

NU completed its annual goodwill impairment test for each of its reporting units as of October 1, 2013 and determined that no impairment exists. There were no events subsequent to October 1, 2013 that indicated impairment of goodwill.

The allocation of goodwill to NU's reporting units was as follows:
(Billions of Dollars)			Electric			Electric			Natural Gas
			Distribution			Transmission			Distribution			Total
Balance as of December 31, 2011			$	0		$	0		$	0.3		$	0.3
	Merger with NSTAR			2.5			0.6			0.1			3.2
Balance as of December 31, 2012			$	2.5		$	0.6		$	0.4		$	3.5

There were no changes to the goodwill balance or the allocation of goodwill for the year ended December 31, 2013.

REGULATORY_ACCOUNTING

REGULATORY ACCOUNTING	12 Months Ended
REGULATORY ACCOUNTING	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Public Utilities Disclosure [Text Block]	'
	3. REGULATORY ACCOUNTING

	The rates charged to the customers of NU's Regulated companies are designed to collect each company's costs to provide service, including a return on investment. Therefore, the accounting policies of the Regulated companies reflect the application of accounting guidance for entities with rate-regulated operations and reflect the effects of the rate-making process.

	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:
	NU	As of December 31,
	(Millions of Dollars)	2013			2012
	Benefit Costs	$	1,240.20		$	2,452.10
	Derivative Liabilities		638			885.6
	Goodwill		525.9			537.6
	Storm Restoration Costs		589.6			547.7
	Income Taxes, Net		626.2			516.2
	Securitized Assets		-			232.6
	Contractual Obligations - Yankee Companies		154.2			217.6
	Buy Out Agreements for Power Contracts		70.2			92.9
	Regulatory Tracker Mechanisms		323.4			190.1
	Other Regulatory Assets		126.8			165
	Total Regulatory Assets		4,294.50			5,837.40
	Less: Current Portion		535.8			705
	Total Long-Term Regulatory Assets	$	3,758.70		$	5,132.40
			As of December 31,
			2013												2012
						NSTAR												NSTAR
	(Millions of Dollars)		CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO
	Benefit Costs		$	297.7		$	496.7		$	100.6		$	57.3		$	563.2		$	781.2		$	223.7		$	116
	Derivative Liabilities			630.4			7.7			-			-			866.2			14.9			-			3
	Goodwill			-			451.5			-			-			-			461.5			-			-
	Storm Restoration Costs			397.8			109.3			43.7			38.8			413.9			55.8			34.5			43.5
	Income Taxes, Net			415.5			84			40.3			43.7			367.5			47.1			36.2			31
	Securitized Assets			-			-			-			-			-			205.1			19.7			7.8
	Contractual Obligations -
		Yankee Companies		19.8			6.2			-			4.5			64			22.8			-			14.9
	Buy Out Agreements for Power Contracts			-			64.7			5.5			-			-			85.9			7			-
	Regulatory Tracker Mechanisms			8			169.5			83.3			32.6			12.2			71.4			49.3			31.9
	Other Regulatory Assets			44.8			49.7			38.1			12.2			57.3			46.3			43.6			16.1
	Total Regulatory Assets			1,814.00			1,439.30			311.5			189.1			2,344.30			1,792.00			414			264.2
	Less: Current Portion			150.9			204.1			92.2			43			185.9			347.1			62.9			42.4
	Total Long-Term Regulatory Assets		$	1,663.10		$	1,235.20		$	219.3		$	146.1		$	2,158.40		$	1,444.90		$	351.1		$	221.8
	Regulatory Costs in Other Long-Term Assets: The Regulated companies had $65.1 million ($7.3 million for CL&P, $33.4 million for NSTAR Electric, and $10.1 million for WMECO) and $69.9 million ($3.9 million for CL&P, $25.4 million for NSTAR Electric, $35.7 million for PSNH, and $1.4 million for WMECO) of additional regulatory costs as of December 31, 2013 and 2012, 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 PSNH balance as of December 31, 2012 primarily related to storm restoration costs incurred for Tropical Storm Irene, the October 2011 snowstorm and Storm Sandy that met the NHPUC criteria for cost deferral and recovery. Refer to the "Storm Restoration Costs" section in this Note for further discussion. The NSTAR Electric balance as of December 31, 2013 and 2012 primarily related to costs deferred in connection with the basic service bad debt adder. See Note 12G, "Commitments and Contingencies – Basic Service Bad Debt Adder," for further information.

	Equity Return on Regulatory Assets: For rate-making purposes, the Regulated companies recover the carrying cost related to their regulatory assets. For certain regulatory assets, the carrying cost recovered includes an equity return component. This equity return, which is not recorded on the balance sheets, totaled $1.9 million and $2.5 million for CL&P and $33.1 million and $21.8 million for PSNH as of December 31, 2013 and 2012, respectively. These carrying costs will be recovered from customers in future rates.

	Regulatory Assets - The following provides further information about regulatory assets:

	Benefit Costs: NU's Pension, SERP and PBOP Plans are accounted for in accordance with accounting guidance on defined benefit pension and other postretirement plans. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of a charge to Accumulated Other Comprehensive Income/(Loss) to reflect the liability that is recognized for the funded status of the pension and other postretirement plans and is remeasured annually. Regulatory accounting was also applied to the portions of NU's service company costs that support the Regulated companies, as these amounts are also recoverable. CL&P, NSTAR Electric, PSNH and WMECO do not collect carrying charges on these benefit costs regulatory assets.

	CL&P, NSTAR Electric, PSNH and WMECO recover benefit costs related to their distribution and transmission operations from customers in rates as allowed by their applicable regulatory commissions. NSTAR Electric and WMECO each recover their qualified pension and postretirement expenses related to distribution operations through rate reconciling mechanisms that fully track the change in net pension and postretirement expenses each year. NSTAR Electric earns a carrying charge on the excess cumulative benefit plan trust fund contributions it has made over what it has cumulatively recognized as net periodic benefit expense, net of deferred income taxes. As of December 31, 2013 and 2012, these balances were $379.9 million and $366.8 million of the total benefit costs regulatory asset, respectively.

	Derivative Liabilities: Regulatory assets recorded as an offset to derivative liabilities relate to the fair value of contracts used to purchase energy and energy-related products that will be recovered from customers in future rates. See Note 5, "Derivative Instruments," to the financial statements for further information. These assets are excluded from rate base and are being recovered as the actual settlements occur over the duration of the contracts.

	Goodwill: The goodwill regulatory asset originated from the transaction that created NSTAR in 1999. This regulatory asset is currently being amortized and recovered from customers in rates without a carrying charge over a 40-year period (as of December 31, 2013, there were 26 years of amortization remaining).

	Storm Restoration Costs: The storm restoration cost deferrals relate to costs incurred at CL&P, NSTAR Electric, PSNH and WMECO that each company expects to recover from customers. A storm must meet certain criteria to be declared a major storm with the criteria specific to each state jurisdiction and utility company as follows:


	Connecticut - qualifying storm restoration costs must exceed $5 million for a storm to be declared a major storm;
	Massachusetts - qualifying storm restoration costs must exceed $1 million for NSTAR Electric and $300,000 for WMECO and an emergency response plan must be initiated for a storm to be declared a major storm; and
	New Hampshire - For a storm to be declared a major storm: (1) at least 10 percent of customers must be without power with at least 200 concurrent locations requiring repairs (trouble spots), or (2) at least 300 concurrent trouble spots must be reported.


Once a storm is declared major, all qualifying expenses prudently incurred during storm restoration efforts are deferred and recovered from customers.

In addition to storm restoration costs, PSNH is allowed recovery of prudently incurred storm pre-staging costs in accordance with NHPUC regulation.

In 2013, 2012 and 2011, CL&P, NSTAR Electric, PSNH and WMECO experienced significant storms, including Tropical Storm Irene, the October 2011 snowstorm, Storm Sandy, and the February 2013 blizzard. As a result of these storm events, each Company suffered extensive damage to its distribution and transmission systems resulting in customer outages, which required the incurrence of costs to repair damage and restore customer service. The storm restoration cost regulatory asset balance at CL&P, NSTAR Electric, PSNH and WMECO reflects costs incurred for major storm events. Management believes the storm restoration costs were prudent and meet the criteria for specific cost recovery in Connecticut, Massachusetts and New Hampshire and as a result, are probable of recovery.

Storm Filings: Each electric utility is seeking recovery of its deferred storm restoration costs through its applicable regulatory recovery process.

On February 3, 2014, the PURA issued a draft decision on CL&P's request to recover storm restoration costs associated with five major storms, all of which occurred in 2011 and 2012. In its draft decision, the PURA approved recovery of $365 million of deferred storm restoration costs and ordered CL&P to capitalize approximately $18 million of the deferred storm restoration costs as utility plant, which will be included in depreciation expense in future rate proceedings. PURA will allow recovery of the $365 million with carrying charges in CL&P's distribution rates over a six-year period beginning December 1, 2014. The remaining costs were either disallowed or are probable of recovery in future rates and did not have a material impact on CL&P's financial position, results of operations or cash flows.

On December 30, 2013, the DPU approved NSTAR Electric's request to recover storm restoration costs, plus carrying costs, related to Tropical Storm Irene and the October 2011 snowstorm. The DPU approved recovery of $34.2 million of the $38 million requested costs. NSTAR Electric will recover these costs, plus carrying costs, in its distribution rates over a five-year period beginning on January 1, 2014.

On June 27, 2013, the NHPUC approved an increase to PSNH's distribution rates effective July 1, 2013, which included a $5 million increase to the current level of funding for the major storm cost reserve. The major storm cost reserve is used to offset the storm restoration cost regulatory asset.

On August 30, 2013, WMECO submitted its 2013 Annual SRRCA filing to begin recovering the restoration costs associated with the October 2011 snowstorm and Storm Sandy. On December 20, 2013, the DPU approved the 2013 Annual SRRCA filing for effect on January 1, 2014, subject to further review and reconciliation.

Income Taxes, Net: The tax effect of temporary book-tax differences (differences between the periods in which transactions affect income in the financial statements and the periods in which they affect the determination of taxable income, including those differences relating to uncertain tax positions) is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and accounting guidance for income taxes. Differences in income taxes between the accounting guidance and the rate-making treatment of the applicable regulatory commissions are recorded as regulatory assets. As these assets are offset by deferred income tax liabilities, no carrying charge is collected. For further information regarding income taxes, see Note 11, "Income Taxes," to the financial statements.

Securitized Assets: NSTAR Electric's securitized regulatory asset balance primarily included costs related to purchase power contract divestitures and certain costs related to NSTAR Electric's former generation business that were recovered with a return through the transition charge and amounted to $186.1 million as of December 31, 2012. These costs were fully recovered from customers in 2013.

The securitized regulatory asset balance as of December 31, 2012 also included proceeds received from the issuance of RRBs at NSTAR Electric, PSNH and WMECO that were used to buy out or buy down purchase power contracts. The collateralized amounts reflected as securitized regulatory assets for NSTAR Electric, PSNH and WMECO as of December 31, 2012 were $14.1 million, $19.7 million and $7.8 million, respectively. As of December 31, 2013, NSTAR Electric's, PSNH's and WMECO's RRBs were fully redeemed and the related regulatory assets were fully recovered from customers.

Contractual Obligations - Yankee Companies: CL&P, NSTAR Electric, PSNH and WMECO are responsible for their proportionate share of the remaining costs of the CYAPC, YAEC and MYAPC nuclear facilities, including decommissioning. A portion of these amounts was recorded as a regulatory asset. Amounts for CL&P are earning a return and are being recovered through the CTA. Amounts for NSTAR Electric and WMECO are being recovered without a return through the transition charge. Amounts for PSNH were fully recovered in 2006. As a result of NU's consolidation of CYAPC and YAEC, NU's regulatory asset balance also includes the regulatory assets of CYAPC and YAEC, which totalled $129.8 million and $214 million as of December 31, 2013 and 2012, respectively. At the NU consolidated level, intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation.

Buy Out Agreements for Power Contracts: NSTAR Electric's balance represents the contract termination liability related to certain purchase power contract buy out agreements that were executed in 2004. The contracts' termination payments occur through September 2016 and are collected from customers through NSTAR Electric's transition charge over the same period. Therefore, NSTAR Electric does not earn a return on this regulatory asset. PSNH's balance represents payments associated with the termination of various power purchase contracts that were recorded as regulatory assets and are amortized over the remaining life of the contracts.

Regulatory Tracker Mechanisms: The Regulated companies' approved rates are designed to recover their incurred costs to provide service to customers. The Regulated companies are permitted to recover certain of their costs on a fully-reconciling basis through regulatory commission-approved tracking mechanisms. The difference between the costs incurred (or the rate recovery allowed) and the actual revenues is recorded as regulatory assets (for undercollections) or regulatory liabilities (for overcollections) to be included in future customer rates each year. Carrying charges are recorded on all material regulatory tracker mechanisms.

CL&P, NSTAR Electric, PSNH and WMECO each recover the costs associated with the procurement of energy, transmission related costs from FERC-approved transmission tariffs, energy efficiency programs, low income assistance programs, and restructuring and stranded costs as a result of deregulation, on a fully reconciling basis. Energy procurement costs at PSNH include the costs related to its generating stations.

WMECO's distribution revenue is decoupled from its customer sales volume. WMECO reconciles its annual base distribution rate recovery to a pre-established level of baseline distribution delivery service revenue. Any difference between the allowed level of distribution revenue and the actual amount incurred in a calendar year is adjusted through rates in the following year.

Other Regulatory Assets: Other Regulatory Assets primarily include asset retirement obligations, environmental remediation costs, losses associated with the reacquisition or redemption of long-term debt and various other items, partially offset by purchase price adjustments recorded as Regulatory Assets in connection with the merger with NSTAR. The ARO costs associated with the depreciation of the Regulated companies' ARO assets and accretion of the ARO liabilities are recorded as regulatory assets. For CL&P, NSTAR Electric and WMECO, ARO assets, regulatory assets and liabilities offset and are excluded from rate base. PSNH's ARO assets, regulatory assets and liabilities are included in rate base; these costs are being recovered over the life of the underlying property, plant and equipment.

Regulatory Liabilities: The components of regulatory liabilities are as follows:
NU	As of December 31,
(Millions of Dollars)	2013			2012
Cost of Removal	$	435.1		$	440.8
Regulatory Tracker Mechanisms		151.2			95.1
AFUDC - Transmission		68.1			70
Other Regulatory Liabilities		52.9			68.4
Total Regulatory Liabilities		707.3			674.3
Less: Current Portion		204.3			134.1
Total Long-Term Regulatory Liabilities	$	503		$	540.2
		As of December 31,
		2013												2012
					NSTAR												NSTAR
(Millions of Dollars)		CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO
Cost of Removal		$	29.1		$	250		$	49.7		$	-		$	44.2		$	240.3		$	51.2		$	-
Regulatory Tracker Mechanisms			95.6			21.9			21.6			21.1			39.1			14.4			20.4			19
AFUDC - Transmission			54.7			4.1			-			9.3			56.6			4.1			-			9.3
Other Regulatory Liabilities			8.4			31.1			1			3.4			16.5			32.9			3.8			2.4
Total Regulatory Liabilities			187.8			307.1			72.3			33.8			156.4			291.7			75.4			30.7
Less: Current Portion			94			54			20.6			19.9			32.1			47.5			23			21
Total Long-Term Regulatory Liabilities		$	93.8		$	253.1		$	51.7		$	13.9		$	124.3		$	244.2		$	52.4		$	9.7
Cost of Removal: NU's Regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. The estimated cost to remove utility assets from service is recognized as a component of depreciation expense and the cumulative amounts collected from customers but not yet expended is recognized as a regulatory liability. Expended costs that exceed amounts collected from customers are recognized as regulatory assets, as they are probable of recovery in future rates.

AFUDC - Transmission: AFUDC was recorded by CL&P and WMECO for their NEEWS projects through May 31, 2011, all of which was reserved as a regulatory liability to reflect rate base recovery for 100 percent of the CWIP as a result of FERC-approved transmission incentives. Effective June 1, 2011, FERC approved changes to the ISO-NE Tariff in order to include 100 percent of the NEEWS CWIP in regional rate base. As a result, CL&P and WMECO no longer record AFUDC on NEEWS CWIP. NSTAR Electric recorded AFUDC on reliability-related projects over $5 million through December 31, 2013, 50 percent of which was recorded as a regulatory liability to reflect rate base recovery for 50 percent of the CWIP as a result of FERC-approved transmission incentives.

Other Regulatory Liabilities: Other Regulatory Liabilities primarily includes amounts that are subject to various rate reconciling mechanisms that, as of each period end date, would result in refunds to customers.

PROPERTY_PLANT_AND_ACCUMULATED

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION	12 Months Ended
PROPERTY, PLANT AND ACCUMULATED DEPRECIATION	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Property Plant And Equipment Disclosure [Text Block]	'
	4. PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION

	Utility property, plant and equipment is recorded at original cost. Original cost includes materials, labor, construction overhead and AFUDC for regulated property. The cost of repairs and maintenance, including planned major maintenance activities, is charged to Operating Expenses as incurred.

	The following tables summarize the investments in utility property, plant and equipment by asset category:

	NU			As of December 31,
	(Millions of Dollars)			2013			2012
	Distribution - Electric			$	11,950.20		$	11,438.20
	Distribution - Natural Gas				2,425.90			2,274.20
	Transmission				6,412.50			5,541.10
	Generation				1,152.30			1,146.60
	Electric and Natural Gas Utility				21,940.90			20,400.10
	Other⁽¹⁾				508.7			429.3
	Property, Plant and Equipment, Gross				22,449.60			20,829.40
	Less: Accumulated Depreciation
		Electric and Natural Gas Utility			-5,387.00			-5,065.10
		Other			-196.2			-171.5
	Total Accumulated Depreciation				-5,583.20			-5,236.60
	Property, Plant and Equipment, Net				16,866.40			15,592.80
	Construction Work in Progress				709.8			1,012.20
	Total Property, Plant and Equipment, Net			$	17,576.20		$	16,605.00
	(1) These assets represent unregulated property and are primarily comprised of building improvements at RRR, software, hardware and equipment at NUSCO and telecommunications assets at NSTAR Communications, Inc.
		As of December 31,
		2013												2012
					NSTAR												NSTAR
	(Millions of Dollars)	CL&P			Electric			PSNH			WMECO			CL&P			Electric		PSNH		WMECO
	Distribution	$	4,930.70		$	4,694.70		$	1,608.20		$	756.6		$	4,691.30		$	4,539.90	$	1,520.10	$	724.2
	Transmission		3,071.90			1,772.30			695.7			826.4			2,796.10			1,529.70		599.2		583.7
	Generation		-			-			1,131.20			21.1			-			-		1,125.50		21.1
	Property, Plant and
	Equipment, Gross		8,002.60			6,467.00			3,435.10			1,604.10			7,487.40			6,069.60		3,244.80		1,329.00
	Less: Accumulated Depreciation		-1,804.10			-1,631.30			-1,021.80			-271.5			-1,698.10			-1,540.10		-954		-252.1
	Property, Plant and Equipment, Net		6,198.50			4,835.70			2,413.30			1,332.60			5,789.30			4,529.50		2,290.80		1,076.90
	Construction Work in Progress		252.8			208.2			54.3			48.5			363.7			205.8		61.7		213.6
	Total Property, Plant and
	Equipment, Net	$	6,451.30		$	5,043.90		$	2,467.60		$	1,381.10		$	6,153.00		$	4,735.30	$	2,352.50	$	1,290.50
	Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution). The composite rates are subject to approval by the appropriate state regulatory agency. The composite rates include a cost of removal component, which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability. Depreciation rates are applied to property from the time it is placed in service.

	Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation. The actual incurred removal costs are applied against the related regulatory liability.

	The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows:
	(Percent)	2013			2012			2011
	NU		2.8			2.5			2.6
	CL&P		2.5			2.5			2.4
	NSTAR Electric		2.9			2.8			3
	PSNH		3			3			2.9
	WMECO		2.9			3.3			2.9
	The following table summarizes average useful lives of depreciable assets:

			Average Depreciable Life
	(Years)		NU			CL&P			NSTAR Electric			PSNH			WMECO
	Distribution			36.1			42			32.9			32.7			29.8
	Transmission			43			39.6			47.2			42.3			49.5
	Generation			32.2			-			-			32.4			25
	Other			14.6			-			-			-			-

DERIVATIVE_INSTRUMENTS

DERIVATIVE INSTRUMENTS	12 Months Ended
DERIVATIVE INSTRUMENTS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Derivative Instruments and Hedging Activities Disclosure [Text Block]	'
	5. DERIVATIVE INSTRUMENTS

	The Regulated companies purchase and procure energy and energy-related products for their customers, which are subject to price volatility. 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 costs are recovered from, or refunded to, customers in their respective energy supply rates. For NU's unregulated wholesale marketing contracts that expired on December 31, 2013, changes in fair values of derivatives were included in Net Income.

	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. Cash collateral posted or collected under master netting agreements is recorded as an offset to the derivative asset or liability. The following tables present 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 December 31, 2013
			Commodity Supply and						Net Amount Recorded as
	(Millions of Dollars)		Price Risk Management			Netting ⁽¹⁾			Derivative Asset/(Liability)
	Current Derivative Assets:
	Level 2:
		Other⁽¹⁾	$	1.9		$	-0.3		$	1.6
	Level 3:
		CL&P⁽¹⁾		17.1			-9.8			7.3
		NSTAR Electric		1.2			-			1.2
		WMECO		0.1			-			0.1
	Total Current Derivative Assets		$	20.3		$	-10.1		$	10.2

	Long-Term Derivative Assets:
	Level 2:
		Other	$	0.2		$	-		$	0.2
	Level 3:
		CL&P⁽¹⁾		113.6			-42.2			71.4
		WMECO		2.6			-			2.6
	Total Long-Term Derivative Assets		$	116.4		$	-42.2		$	74.2

	Current Derivative Liabilities:
	Level 3:
		CL&P	$	-92.2		$	-		$	-92.2
		NSTAR Electric		-1.5			-			-1.5
	Total Current Derivative Liabilities		$	-93.7		$	-		$	-93.7

	Long-Term Derivative Liabilities:
	Level 3:
		CL&P	$	-617.1		$	-		$	-617.1
		NSTAR Electric		-7			-			-7
	Total Long-Term Derivative Liabilities		$	-624.1		$	-		$	-624.1
			As of December 31, 2012
			Commodity Supply and						Net Amount Recorded as
	(Millions of Dollars)		Price Risk Management			Netting⁽¹⁾			Derivative Asset/(Liability)
	Current Derivative Assets:
	Level 2:
		Other	$	0.2		$	0		$	0.2
	Level 3:
		CL&P ⁽¹⁾		17.7			-12			5.7
		Other		5.5			-			5.5
	Total Current Derivative Assets		$	23.4		$	-12		$	11.4

	Long-Term Derivative Assets:
	Level 3:
		CL&P ⁽¹⁾	$	159.7		$	-69.1		$	90.6
	Total Long-Term Derivative Assets		$	159.7		$	-69.1		$	90.6

	Current Derivative Liabilities:
	Level 2:
		Other ^{(1) (2)}	$	-19.9		$	0.6		$	-19.3
	Level 3:
		CL&P		-96.9			-			-96.9
		NSTAR Electric		-1			-			-1
	Total Current Derivative Liabilities		$	-117.8		$	0.6		$	-117.2

Long-Term Derivative Liabilities:
Level 2:
	Other	$	-0.2		$	-		$	-0.2
Level 3:
	CL&P		-865.6			-			-865.6
	NSTAR Electric		-13.9			-			-13.9
	WMECO		-3			-			-3
Total Long-Term Derivative Liabilities		$	-882.7		$	-		$	-882.7
(1) Amounts represent derivative assets and liabilities that NU 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.

(2) As of December 31, 2012, NU had $4.1 million of cash posted related to these contracts, which was not offset against the derivative liability and is recorded as Prepayments and Other Current Assets on the balance sheets.

The business activities that result in the recognition of derivative assets also create exposure to various counterparties. As of December 31, 2013, NU and CL&P's derivative assets were exposed to counterparty credit risk. Of the total derivative assets, $80 million and $79 million, respectively, were contracted with investment grade entities.

For further information on the fair value of derivative contracts, see Note 1H, "Summary of Significant Accounting Policies - Fair Value Measurements," and Note 1I, "Summary of Significant Accounting Policies - Derivative Accounting," to the financial statements.

Derivatives Not Designated as Hedges
Commodity Supply and Price Risk Management: As required by regulation, CL&P has capacity-related contracts with generation facilities. These contracts and similar UI contracts have an expected capacity of 787 MW. 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 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 forward 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.

WMECO has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2029 with a facility that has not yet achieved commercial operation.

As of December 31, 2013 and 2012, NU had NYMEX future contracts in order to reduce variability associated with the purchase price of approximately 9.1 million and 11.5 million MMBtu of natural gas, respectively.

As of December 31, 2012, NU had approximately 24 thousand MWh of supply volumes remaining in its unregulated wholesale portfolio when expected sales were compared with supply contracts. These contracts expired on December 31, 2013.

The following table presents the current change in fair value, primarily recovered through rates from customers, associated with NU's derivative contracts not designated as hedges:

Location of Amounts				Amounts Recognized on Derivatives
Recognized on Derivatives				For the Years Ended December 31,
(Millions of Dollars)				2013			2012			2011
NU
Balance Sheet:
	Regulatory Assets and Liabilities			$	160.6		$	-29		$	-162
Statement of Income:
	Purchased Power, Fuel and Transmission				1			-0.7			0.5
Credit Risk
Certain of NU's derivative contracts contain credit risk contingent features. These features require NU 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 December 31, 2013, there were no derivative contracts in a net liability position that were subject to credit risk contingent features. As of December 31, 2012, NU had $15.3 million of derivative contracts in a net liability position that were subject to credit risk contingent features and would have been required to post additional collateral of $17.4 million if NU parent's unsecured debt credit ratings had been downgraded to below investment grade.
Fair Value Measurements of Derivative Instruments
Valuation of Derivative Instruments: Derivative contracts classified as Level 2 in the fair value hierarchy relate to the financial contracts for natural gas futures and forward contracts to purchase energy. Prices are obtained from broker quotes and are based on actual market activity. The contracts are valued using the mid-point of the bid-ask spread. 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 NU's, including CL&P's, NSTAR Electric's and WMECO'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 December 31, 2013									As of December 31, 2012
		Range						Period Covered			Range				Period Covered
Energy Prices:
NU	$	49	-		77	per MWh		2018-2029		$	43	-	90	per MWh	2018 - 2028
CL&P	$	56	-		58	per MWh		2018-2029		$	50	-	55	per MWh	2018 - 2020
WMECO	$	49	-		77	per MWh		2018-2029		$	43	-	90	per MWh	2018 - 2028

Capacity Prices:
NU	$	5.07	-		11.82	per kW-Month		2017-2029		$	1.4	-	10.53	per kW-Month	2016 - 2028
CL&P	$	5.07	-		10.42	per kW-Month		2017-2026		$	1.4	-	9.83	per kW-Month	2016 - 2026
NSTAR Electric	$	5.07	-		7.38	per kW-Month		2017-2019		$	1.4	-	3.39	per kW-Month	2016 - 2019
WMECO	$	5.07	-		11.82	per kW-Month		2017-2029		$	1.4	-	10.53	per kW-Month	2016 - 2028

Forward Reserve:
NU, CL&P	$	3.3	-		3.3	per kW-Month		2014-2024		$	0.35	-	0.9	per kW-Month	2013 - 2024

REC Prices:
NU	$	36	-		87	per REC		2014-2029		$	25	-	85	per REC	2013 - 2028
NSTAR Electric	$	36	-		70	per REC		2014-2018		$	25	-	71	per REC	2013 - 2018
WMECO	$	36	-		87	per REC		2014-2029		$	25	-	85	per REC	2013 - 2028
Exit price premiums of 10 percent through 32 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 tables present changes for the years ended December 31, 2013 and 2012 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. The fair value in 2012 reflects a transfer of remaining unregulated wholesale marketing sourcing contracts that had previously been presented as a portfolio along with the unregulated wholesale marketing sales contract as Level 3 under the highest and best use valuation premise. These contracts, which expired on December 31, 2013, were classified within Level 2 of the fair value hierarchy as of December 31, 2012
(Millions of Dollars)		NU ⁽¹⁾			CL&P			NSTAR Electric			WMECO
Derivatives, Net:
Fair Value as of January 1, 2012		$	-962.2		$	-931.6		$	-3.4		$	-7.3
Liabilities Assumed due to Merger with NSTAR			-5.4			-			-			-
Transfer to Level 2			32.2			-			-			-
Net Realized/Unrealized Gains/(Losses) Included in:
	Net Income ⁽²⁾		10.9			-			-			-
	Regulatory Assets and Liabilities		-29.2			-21.6			-15.2			4.3
Settlements			75.1			87			3.7			-
Fair Value as of December 31, 2012		$	-878.6		$	-866.2		$	-14.9		$	-3
Net Realized/Unrealized Gains/(Losses) Included in:
	Net Income ⁽²⁾		10.9			-			-			-
	Regulatory Assets and Liabilities		158.3			148.9			3.5			5.7
Settlements			74.2			86.7			4.1			-
Fair Value as of December 31, 2013		$	-635.2		$	-630.6		$	-7.3		$	2.7

NSTAR Electric amounts were included in NU beginning April 10, 2012.



The Net Income impact for the years ended December 31, 2013 and 2012 related to the unregulated wholesale marketing sales contract that was offset by the gains/(losses) on the unregulated sourcing contracts classified as Level 2 in the fair value hierarchy, resulting in a total net gain of $1 million and net loss of $0.7 million, respectively.

MARKETABLE_SECURITIES

MARKETABLE SECURITIES	12 Months Ended
MARKETABLE SECURITIES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Marketable Securities [Text Block]	'
	6. MARKETABLE SECURITIES

	NU maintains a supplemental benefit trust to fund certain non-qualified executive retirement benefit obligations and WMECO maintains a spent nuclear fuel trust to fund WMECO's prior period spent nuclear fuel liability, each of which 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 elects to record mutual funds purchased by the NU supplemental benefit trust at fair value. As such, any change in fair value of these mutual funds is reflected in Net Income. These mutual funds, classified as Level 1 in the fair value hierarchy, totaled $57.2 million and $47 million as of December 31, 2013 and 2012, respectively, and were included in Prepayments and Other Current Assets on the accompanying balance sheets. Net gains on these securities of $10.2 million and $5.9 million and net losses of $1.1 million for the years ended December 31, 2013, 2012 and 2011, respectively, were recorded in Other Income, Net on the statements of income. Dividend income is recorded in Other Income, Net on the statements of income 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 NU's available-for-sale securities held in the NU supplemental benefit trust, WMECO's spent nuclear fuel trust and CYAPC's and YAEC's nuclear decommissioning trusts. These securities are recorded at fair value and included in current and long-term Marketable Securities on the balance sheets.
			As of December 31, 2013
						Pre-Tax			Pre-Tax
			Amortized			Unrealized			Unrealized
	(Millions of Dollars)		Cost			Gains⁽¹⁾			Losses⁽¹⁾			Fair Value
	NU
		Debt Securities⁽²⁾	$	299.2		$	2.5		$	-2.1		$	299.6
		Equity Securities⁽²⁾		163.6			60.5			-			224.1

	WMECO
		Debt Securities		57.9			-			-			57.9

			As of December 31, 2012
						Pre-Tax			Pre-Tax
			Amortized			Unrealized			Unrealized
	(Millions of Dollars)		Cost			Gains⁽¹⁾			Losses⁽¹⁾			Fair Value
	NU
		Debt Securities⁽²⁾	$	266.6		$	13.3		$	-0.1		$	279.8
		Equity Securities⁽²⁾		145.5			20			-			165.5

	WMECO
		Debt Securities		57.7			0.1			-0.1			57.7

	Unrealized gains and losses on debt securities for the NU supplemental benefit trust and WMECO spent nuclear fuel trust are recorded in AOCI and Other Long-Term Assets, respectively, on the balance sheets.


	(2) NU's amounts include CYAPC's and YAEC's marketable securities held in nuclear decommissioning trusts of $424 million and $340.4 million as of December 31, 2013 and 2012, respectively, the majority of which are legally restricted and can only be used for the decommissioning of the nuclear power plants owned by these companies. In the first quarter of 2013, CYAPC and YAEC received cash from the DOE related to the litigation of storage costs for spent nuclear fuel, which was invested in the nuclear decommissioning trusts. Unrealized gains and losses for the nuclear decommissioning trusts are offset in Other Long-Term Liabilities on the balance sheets, with no impact on the statement of income. All of the equity securities accounted for as available-for-sale securities are held in these trusts.

	Unrealized Losses and Other-than-Temporary Impairment: There have been no significant unrealized losses, other-than-temporary impairments or credit losses for the NU supplemental benefit trust, the WMECO spent nuclear fuel trust, and the trusts held by CYAPC and YAEC. 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 the NU supplemental benefit trust, Other Long-Term Assets for the WMECO spent nuclear fuel trust, and offset in Other Long-Term Liabilities for CYAPC and YAEC. NU utilizes the specific identification basis method for the NU supplemental benefit trust securities and the average cost basis method for the WMECO spent nuclear fuel 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 December 31, 2013, the contractual maturities of available-for-sale debt securities are as follows:

			NU						WMECO
			Amortized						Amortized
	(Millions of Dollars)		Cost			Fair Value			Cost			Fair Value
	Less than one year⁽¹⁾		$	72.4		$	72.3		$	26.5		$	26.6
	One to five years			62.1			62.7			25.6			25.5
	Six to ten years			59.4			59.3			1.7			1.7
	Greater than ten years			105.3			105.3			4.1			4.1
	Total Debt Securities		$	299.2		$	299.6		$	57.9		$	57.9
	(1) Amounts in the Less than one year NU 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:
					NU						WMECO
					As of December 31,						As of December 31,
	(Millions of Dollars)				2013			2012			2013			2012
	Level 1:
		Mutual Funds and Equities			$	281.3		$	212.5		$	-		$	-
		Money Market Funds				32.9			40.2			10.9			5.2
	Total Level 1				$	314.2		$	252.7		$	10.9		$	5.2
	Level 2:
		U.S. Government Issued Debt Securities
			(Agency and Treasury)		$	61.4		$	69.9		$	6.8		$	18.7
		Corporate Debt Securities				53.6			33			15.1			7
		Asset-Backed Debt Securities				30.4			28.5			9			10.9
	Municipal Bonds				105.5			93.8			11.2			11.6
	Other Fixed Income Securities				15.8			14.4			4.9			4.3
Total Level 2				$	266.7		$	239.6		$	47		$	52.5
Total Marketable Securities				$	580.9		$	492.3		$	57.9		$	57.7
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.

ASSET_RETIREMENT_OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	12 Months Ended
ASSET RETIREMENT OBLIGATIONS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Asset Retirement Obligation Disclosure [Text Block]	'
	7. ASSET RETIREMENT OBLIGATIONS

	In accordance with accounting guidance for conditional AROs, NU, including CL&P, NSTAR Electric, PSNH and WMECO, recognizes a liability for the fair value of an ARO on the obligation date if the liability's fair value can be reasonably estimated and is conditional on a future event. Settlement dates and future costs are reasonably estimated when sufficient information becomes available. Management has identified various categories of AROs, primarily certain assets containing asbestos and hazardous contamination and has performed fair value calculations, reflecting expected probabilities for settlement scenarios.

	The fair value of an ARO is recorded as a liability in Other Long-Term Liabilities with a corresponding amount included in Property, Plant and Equipment, Net on the balance sheets. As the Regulated companies are rate-regulated on a cost-of-service basis, these companies apply regulatory accounting guidance and the costs associated with the Regulated companies' AROs are included in Regulatory Assets. The ARO assets are depreciated, and the ARO liabilities are accreted over the estimated life of the obligation with corresponding credits recorded as accumulated depreciation and ARO liabilities, respectively. Both the depreciation and accretion were recorded as increases to Regulatory Assets on the balance sheets. For further information, see Note 3, "Regulatory Accounting," to the financial statements.
	A reconciliation of the beginning and ending carrying amounts of ARO liabilities are as follows:
	NU			As of December 31,
	(Millions of Dollars)			2013		2012
	Balance as of Beginning of Year			$	412.2	$	56.2
	Liability Assumed Upon Consolidation of CYAPC and YAEC				-		284.2
	Liability Assumed Upon Merger With NSTAR				-		35.9
	Liabilities Incurred During the Year				0.1		1.5
	Liabilities Settled During the Year				-13.8		-7.2
	Accretion				23.8		20.2
	Revisions in Estimated Cash Flows				2.6		21.4
	Balance as of End of Year			$	424.9	$	412.2

		As of December 31,
		2013								2012
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Balance as of Beginning of Year	$	33.6	$	31.4	$	18.4	$	4.3	$	32.2	$	27.5	$	17	$	4
	Liabilities Incurred During the Year		-		-		-		-		-		-		0.3		-
	Liabilities Settled During the Year		-0.7		-0.1		-		-		-0.9		-1		-		-
	Accretion		2.2		1.5		1.2		0.3		2		1.5		1.1		0.3
	Revisions in Estimated Cash Flows		-0.1		-		-0.1		-0.1		0.3		3.4		-		-
	Balance as of End of Year	$	35	$	32.8	$	19.5	$	4.5	$	33.6	$	31.4	$	18.4	$	4.3
	The Liability Assumed Upon Consolidation of CYAPC and YAEC represents the CYAPC and YAEC ARO fair value as of the merger date. The fair value of the ARO for CYAPC and YAEC includes uncertainties of the fuel off-load dates related to the DOE's timing of performance regarding its obligation to dispose of the spent nuclear fuel and high level waste. The incremental asset recorded as an offset to the ARO was fully depreciated since the plants have no remaining useful life. Any changes in the assumptions used to calculate the fair value of the ARO are recorded as an offset to the related regulatory asset. The assets held in the decommissioning trust are restricted for settling the asset retirement obligation and all other decommissioning obligations. For further information on the assets held in trust to support this obligation, see Note 6, “Marketable Securities,” to the financial statements

SHORT_TERM_DEBT

SHORT TERM DEBT	12 Months Ended
SHORT TERM DEBT	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Short Term Debt Text Block	'
	8. SHORT-TERM DEBT

	Limits: The amount of short-term borrowings that may be incurred by CL&P, NSTAR Electric and WMECO is subject to periodic approval by the FERC. On July 31, 2013, the FERC granted authorization to allow CL&P and WMECO to incur total short-term borrowings up to a maximum of $600 million and $300 million, respectively, effective January 1, 2014 through December 31, 2015. On May 16, 2012, the FERC granted authorization to allow NSTAR Electric to issue total short-term debt securities in an aggregate principal amount not to exceed $655 million outstanding at any one time, effective October 23, 2012 through October 23, 2014. As a result of the NHPUC having jurisdiction over PSNH's short-term debt, PSNH is not currently required to obtain FERC approval for its short-term borrowings.

	PSNH is authorized by regulation of the NHPUC to incur short-term borrowings up to 10 percent of net fixed plant plus an additional $60 million until further ordered by the NHPUC. As of December 31, 2013, PSNH's short-term debt authorization under the 10 percent of net fixed plant test plus $60 million totaled approximately $293 million.

	CL&P's certificate of incorporation contains preferred stock provisions restricting the amount of unsecured debt that CL&P may incur, including limiting unsecured indebtedness with a maturity of less than 10 years to 10 percent of total capitalization. In November 2003, CL&P obtained from its preferred stockholders a waiver of such 10 percent limit for a ten-year period expiring in March 2014, provided that all unsecured indebtedness does not exceed 20 percent of total capitalization. As of December 31, 2013, CL&P had $776.9 million of unsecured debt capacity available under this authorization.

	Yankee Gas and NSTAR Gas are not required to obtain approval from any state or federal authority to incur short-term debt.

	Credit Agreements and Commercial Paper Programs: NU parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year revolving credit facility. The revolving credit facility is to be used primarily to backstop the commercial paper program at NU, which commenced July 25, 2012. The commercial paper program allows NU parent to issue commercial paper as a form of short-term debt. On September 6, 2013, the $1.15 billion revolving credit facility dated July 25, 2012 was amended to increase the aggregate principal amount available thereunder by $300 million to $1.45 billion, to extend the expiration date from July 25, 2017 to September 6, 2018, and to increase CL&P's borrowing sublimit from $300 million to $600 million. PSNH and WMECO each have borrowing sublimits of $300 million. On September 6, 2013, NU parent's $1.15 billion commercial paper program was increased by $300 million to $1.45 billion.

	NSTAR Electric has a five-year $450 million revolving credit facility. This facility serves to backstop NSTAR Electric's existing $450 million commercial paper program. On September 6, 2013, NSTAR Electric amended its revolving credit facility dated July 25, 2012 to extend the expiration date from July 25, 2017 to September 6, 2018.

	On September 6, 2013, the CL&P five-year $300 million revolving credit facility was terminated. As of December 31, 2012, CL&P had $89 million in borrowings outstanding under this credit agreement with a weighted average interest rate of 3.325 percent.

	As of December 31, 2013 and 2012, NU had approximately $1.01 billion and $1.15 billion, respectively, in short-term borrowings outstanding under the commercial paper program, leaving $435.5 million of available borrowing capacity as of December 31, 2013. The weighted-average interest rate on these borrowings as of December 31, 2013 and 2012 was 0.24 percent and 0.46 percent, respectively, which is generally based on money market rates. As of December 31, 2013 and 2012, NSTAR Electric had $103.5 million and $276 million, respectively, in short-term borrowings outstanding under its commercial paper program, leaving $346.5 million and $174 million of available borrowing capacity as of December 31, 2013 and 2012, respectively. The weighted-average interest rate on these borrowings as of December 31, 2013 and 2012 was 0.13 percent and 0.31 percent, respectively, which is generally based on money market rates.

	Amounts outstanding under the commercial paper programs for NU and NSTAR Electric are generally included in Notes Payable and classified in current liabilities on the balance sheets as all borrowings are outstanding for no more than 364 days at one time. On January 2, 2014, Yankee Gas issued $100 million of Series L First Mortgage Bonds. A portion of the proceeds was used to pay short-term borrowings outstanding under the NU commercial paper program. As a result and in accordance with applicable accounting guidance, $25 million of the NU commercial paper program borrowings have been classified as Long-Term Debt as of December 31, 2013.

	As of December 31, 2013 and 2012, there were intercompany loans from NU of $287.3 million and $405.1 million to CL&P, $86.5 million and $63.3 million to PSNH, and zero and $31.9 million to WMECO, respectively. Intercompany loans from NU to CL&P, PSNH and WMECO are included in Notes Payable to Affiliated Companies and generally classified in current liabilities on the CL&P, PSNH and WMECO balance sheets. On January 15, 2013, CL&P issued $400 million of Series A First and Refunding Mortgage Bonds. The proceeds, net of issuance costs, were used to pay short-term borrowings outstanding under the CL&P credit agreement of $89 million and the NU commercial paper program of $305.8 million. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on the balance sheet as of December 31, 2012.

	Intercompany loans from NU to CL&P, PSNH and WMECO are eliminated in consolidation in NU's balance sheets.

	Under the credit facilities, NU and its subsidiaries must comply with certain financial and non-financial covenants, including a consolidated debt to total capitalization ratio. As of December 31, 2013 and 2012, NU and its subsidiaries were in compliance with these covenants. If NU or its subsidiaries were not in compliance with these covenants, an event of default would occur requiring all outstanding borrowings by such borrower to be repaid and additional borrowings by such borrower would not be permitted under its respective credit facility.

	Working Capital: Each of NU, CL&P, NSTAR Electric, PSNH and WMECO use its available capital resources to fund its respective construction expenditures, meet debt requirements, pay operating costs, including storm-related costs, pay dividends and fund other corporate obligations, such as pension contributions. The current growth in NU's transmission construction expenditures utilizes a significant amount of cash for projects that have a long-term return on investment and recovery period. In addition, NU's Regulated companies recover its electric and natural gas distribution construction expenditures as the related project costs are depreciated over the life of the assets. This impacts the timing of the revenue stream designed to fully recover the total investment plus a return on the equity portion of the cost and related financing costs. These factors have resulted in current liabilities exceeding current assets by approximately $1.2 billion, $398 million and $339 million at NU, CL&P and NSTAR Electric, respectively, as of December 31, 2013.

	As of December 31, 2013, $501.7 million of NU's obligations classified as current liabilities relates to long-term debt that will be paid in the next 12 months, consisting of $150 million for CL&P, $301.7 million for NSTAR Electric and $50 million for PSNH. In addition, $31.7 million relates to the amortization of the purchase accounting fair value adjustment that will be amortized in the next twelve months. NU, with its strong credit ratings, has several options available in the financial markets to repay or refinance these maturities with the issuance of new long-term debt. NU, CL&P, NSTAR Electric, PSNH and WMECO will reduce their short-term borrowings with cash received from operating cash flows or with the issuance of new long-term debt, determined considering capital requirements and maintenance of NU's credit rating and profile. Management expects the future operating cash flows of NU, CL&P, NSTAR Electric, PSNH and WMECO, along with the access to financial markets, will be sufficient to meet any future operating requirements and capital investment forecasted opportunities.

LONGTERM_DEBT

LONG-TERM DEBT	12 Months Ended
LONG-TERM DEBT	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Long-term Debt [Text Block]	'
	9. LONG-TERM DEBT

	Details of long-term debt outstanding are as follows:

		CL&P		As of December 31,
		(Millions of Dollars)		2013			2012
		First Mortgage Bonds:
			7.875% 1994 Series D due 2024	$	139.8		$	139.8
			4.800% 2004 Series A due 2014		150			150
			5.750% 2004 Series B due 2034		130			130
			5.000% 2005 Series A due 2015		100			100
			5.625% 2005 Series B due 2035		100			100
			6.350% 2006 Series A due 2036		250			250
			5.375% 2007 Series A due 2017		150			150
			5.750% 2007 Series B due 2037		150			150
			5.750% 2007 Series C due 2017		100			100
			6.375% 2007 Series D due 2037		100			100
			5.650% 2008 Series A due 2018		300			300
			5.500% 2009 Series A due 2019		250			250
			2.500% 2013 Series A due 2023⁽¹⁾		400			-
		Total First Mortgage Bonds			2,319.80			1,919.80
		Pollution Control Notes:
			4.375% Fixed Rate Tax Exempt due 2028		120.5			120.5
			1.25% Fixed Rate Tax Exempt due 2028⁽²⁾		-			125
			1.55% Fixed Rate Tax Exempt due 2031⁽²⁾		62			62
		Total Pollution Control Notes			182.5			307.5
		Total First Mortgage Bonds and Pollution Control Notes			2,502.30			2,227.30
		Fees and Interest due for Spent Nuclear Fuel Disposal Costs			244.4			244.3
		CL&P Commercial Paper and Revolver Borrowings⁽¹⁾			-			394.8
		Less Amounts due Within One Year			-150			-125
		Unamortized Premiums and Discounts, Net			-5.5			-3.6
		CL&P Long-Term Debt		$	2,591.20		$	2,737.80

		NSTAR Electric		As of December 31,
		(Millions of Dollars)		2013			2012
		Debentures:
			4.875% due 2014	$	300		$	300
			5.75% due 2036		200			200
			5.625% due 2017		400			400
			5.50% due 2040		300			300
			2.375% due 2022		400			400
			Variable Rate due 2016⁽³⁾		200			-
		Total Debentures			1,800.00			1,600.00
		Bonds:
			7.375% Tax Exempt Sewage Facility Revenue Bonds, due 2015		6.4			8
		Less Amounts due Within One Year			-301.7			-1.7
		Unamortized Premiums and Discounts, Net			-5.3			-5.4
		NSTAR Electric Long-Term Debt		$	1,499.40		$	1,600.90

		PSNH		As of December 31,
		(Millions of Dollars)		2013			2012
		First Mortgage Bonds:
			5.25% 2004 Series L due 2014	$	50		$	50
			5.60% 2005 Series M due 2035		50			50
			6.15% 2007 Series N due 2017		70			70
			6.00% 2008 Series O due 2018		110			110
			4.50% 2009 Series P due 2019		150			150
			4.05% 2011 Series Q due 2021		122			122
			3.20% 2011 Series R due 2021		160			160
			3.50% 2013 Series S due 2023⁽⁴⁾		250			-
		Total First Mortgage Bonds			962			712
		Pollution Control Revenue Bonds:
			4.75% - 5.45% Tax Exempt Series B and C due 2021⁽⁴⁾		-			198.2
		Adjustable Rate Series A due 2021		89.3			89.3
	Total Pollution Control Revenue Bonds			89.3			287.5
	Less Amounts due Within One Year			-50			-
	Unamortized Premiums and Discounts, Net			-2.3			-1.6
	PSNH Long-Term Debt		$	999		$	997.9

	WMECO		As of December 31,
	(Millions of Dollars)		2013			2012
	Other Notes:
		5.00% Senior Notes Series A, due 2013⁽⁵⁾	$	-		$	55
		5.90% Senior Notes Series B, due 2034		50			50
		5.24% Senior Notes Series C, due 2015		50			50
		6.70% Senior Notes Series D, due 2037		40			40
		5.10% Senior Notes Series E, due 2020		95			95
		3.50% Senior Notes Series F, due 2021		250			250
		3.88% Senior Notes Series G, due 2023⁽⁵⁾		80			-
	Total Other Notes			565			540
	Fees and Interest due for Spent Nuclear Fuel Disposal Costs			57.3			57.3
	Less Amounts due Within One Year⁽⁵⁾			-			-55
	Unamortized Premiums and Discounts, Net			7.1			8
	WMECO Long-Term Debt		$	629.4		$	550.3

	OTHER		As of December 31,
	(Millions of Dollars)		2013				2012
	Yankee Gas - First Mortgage Bonds:
		8.48% Series B due 2022	$	20		$	20
		4.80% Series G due 2014⁽⁶⁾		75			75
		5.26% Series H due 2019		50			50
		5.35% Series I due 2035		50			50
		6.90% Series J due 2018		100			100
		4.87% Series K due 2020		50			50
	Total First Mortgage Bonds			345			345
	Unamortized Premium			0.7			0.8
	Yankee Gas Long-Term Debt			345.7			345.8

	NSTAR Gas - First Mortgage Bonds:
		9.95% Series J due 2020		25			25
		7.11% Series K due 2033		35			35
		7.04% Series M due 2017		25			25
		4.46% Series N due 2020		125			125
	NSTAR Gas Long-Term Debt			210			210

	Other - Notes and Debentures:
		5.65% Senior Notes Series C due 2013 (NU Parent)⁽⁷⁾		-			250
		Variable Rate Senior Notes Series D due 2013 (NU Parent)⁽⁷⁾		-			300
		1.45% Senior Notes Series E due 2018 (NU Parent)⁽⁷⁾		300			-
		2.80% Senior Notes Series F due 2023 (NU Parent)⁽⁷⁾		450			-
		4.50% Debentures due 2019 (NU Parent)		350			350
		NU Commercial Paper Borrowings⁽⁶⁾		25			-
		Spent Nuclear Fuel Obligation (CYAPC)		179.4			179.3
	Total Other Long-Term Debt			1,304.40			1,079.30
	Fair Value Adjustment⁽⁸⁾			230.7			259.9
	Less Amounts due Within One Year			-			-550
	Less Fair Value Adjustment - Current Portion⁽⁸⁾			-31.7			-31.7
	Unamortized Premiums and Discounts, Net			-1.3			-
	Total NU Long-Term Debt		$	7,776.80		$	7,200.20

On January 15, 2013, CL&P issued $400 million of 2.50 percent Series A First and Refunding Mortgage Bonds with a maturity date of January 15, 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings outstanding under the CL&P credit agreement of $89 million and the NU commercial paper program of $305.8 million. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on the balance sheet as of December 31, 2012.



In April 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. The PCRBs, which mature on May 1, 2031, carry a coupon rate of 1.55 percent during the current three-year fixed rate period and are subject to mandatory tender for purchase on April 1, 2015. On September 3, 2013, CL&P redeemed at par $125 million of 1.25 percent Series B 2011 PCRBs, which were subject to mandatory tender for purchase, using short-term debt.



On May 17, 2013, NSTAR Electric issued $200 million of three-year floating rate debentures due in May 2016. The proceeds, net of issuance costs, were used to repay commercial paper borrowings and for general corporate purposes. The debentures have a coupon rate reset quarterly based on 3-month LIBOR plus a credit spread of 0.24 percent. The interest rate as of December 31, 2013 was 0.478 percent.



On May 1, 2013, PSNH redeemed at par approximately $109 million of the 2001 Series C PCRBs that were due to mature in 2021 using short-term debt. On November 14, 2013, PSNH issued $250 million of 3.50 percent Series S First Mortgage Bonds due in 2023. On December 23, 2013, PSNH redeemed approximately $89 million of the Series B PCRBs that were due to mature in 2021. The proceeds of the Series S issuance were used to repay the short term debt used to redeem the $109 million 2001 Series C PCRBs and to redeem the $89 million Series B PCRBs and pay the associated call premium. The remaining proceeds of the offering were used to refinance short-term debt.



On September 1, 2013, WMECO repaid at maturity the $55 million Series A Senior Notes using short-term debt. On November 15, 2013, WMECO issued $80 million of 3.88 percent Series G Senior Notes due in 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings and for other working capital purposes.



On January 2, 2014, Yankee Gas issued $100 million of 4.82 percent Series L First Mortgage Bonds due to mature in 2044. The proceeds, net of issuance costs, were used to repay the Series G $75 million First Mortgage Bonds that matured on January 1, 2014 and to pay $25 million in short-term borrowings. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on NU's balance sheet as of December 31, 2013.



On May 13, 2013, NU parent issued $750 million of Senior Notes, consisting of $300 million of 1.45 percent Series E Senior Notes due to mature in 2018 and $450 million of 2.80 percent Series F Senior Notes due to mature in 2023. The proceeds, net of issuance costs, were used to repay the NU parent $250 million Series C Senior Notes at a coupon rate of 5.65 percent that matured on June 1, 2013 and the NU parent $300 million floating rate Series D Senior Notes that matured on September 20, 2013. The remaining net proceeds were used to repay commercial paper program borrowings and for working capital purposes.



Amount relates to the purchase price adjustment required to record the NSTAR long-term debt at fair value on the date of the merger.


Long-term debt maturities, mandatory tender payments and cash sinking fund requirements on debt outstanding for the years 2014 through 2018 and thereafter are shown below. These amounts exclude fees and interest due for spent nuclear fuel disposal costs, net unamortized premiums and discounts, and other fair value adjustments as of December 31, 2013:
(Millions of Dollars)	NU			CL&P			NSTAR Electric		PSNH		WMECO
2014	$	576.7		$	150		$	301.7	$	50	$	-
2015		216.7			162			4.7		-		50
2016		200			-			200		-		-
2017		745			250			400		70		-
2018		810			300			-		110		-
Thereafter		5,031.60			1,640.30			900		821.3		515
Total	$	7,580.00		$	2,502.30		$	1,806.40	$	1,051.30	$	565
The utility plant of CL&P, PSNH, Yankee Gas and NSTAR Gas is subject to the lien of each company's respective first mortgage bond indenture. The NSTAR Electric, WMECO and NU Parent debt is unsecured.

CL&P's obligation to repay each series of PCRBs is secured by first mortgage bonds. Each such series of first mortgage bonds contains similar terms and provisions as the applicable series of PCRBs. If CL&P fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. CL&P's $62 million tax-exempt PCRBs, which is subject to mandatory tender for purchase on April 1, 2015, cannot be redeemed prior to its tender date. CL&P's $120.5 million tax-exempt PCRBs will be subject to redemption at par on or after September 1, 2021. All other long-term debt securities are subject to make-whole provisions.

PSNH's obligation to repay the PCRBs is secured by first mortgage bonds and bond insurance. The first mortgage bonds contain similar terms and provisions as the PCRBs. If PSNH fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. The PSNH Series A tax-exempt PCRBs are currently callable at 100 percent of par. The PCRBs bear interest at a rate that is periodically set pursuant to auctions. PSNH is not obligated to purchase these PCRBs, which mature in 2021, from the remarketing agent. The interest rate as of December 31, 2013 was 0.088 percent.

The long-term debt agreements provide that NU and certain of its subsidiaries must comply with certain covenants as are customarily included in such agreements, including a minimum equity requirement for NSTAR Gas. Under the minimum equity requirement, the outstanding long-term debt of NSTAR Gas must not exceed equity.

Yankee Gas has certain long-term debt agreements that contain cross-default provisions applicable to all of Yankee Gas' outstanding first mortgage bond series. The cross-default provisions on Yankee Gas' Series B Bonds would be triggered if Yankee Gas were to default on a payment due on indebtedness in excess of $2 million. The cross-default provisions on all other series of Yankee Gas' first mortgage bonds would be triggered if Yankee Gas were to default in a payment due on indebtedness in excess of $10 million. No other debt issuances contain cross-default provisions as of December 31, 2013.

Spent Nuclear Fuel Obligation: Under the Nuclear Waste Policy Act of 1982, CL&P and WMECO must pay the DOE for the costs of disposal of spent nuclear fuel and high-level radioactive waste for the period prior to the sale of their ownership shares in the Millstone nuclear power stations.

The DOE is responsible for the selection and development of repositories for, and the disposal of, spent nuclear fuel and high-level radioactive waste. For nuclear fuel used to generate electricity prior to April 7, 1983 (Prior Period Spent Nuclear Fuel) for CL&P and WMECO, an accrual has been recorded for the full liability, and payment must be made by CL&P and WMECO to the DOE prior to the first delivery of spent fuel to the DOE. After the sale of Millstone, CL&P and WMECO remained responsible for their share of the disposal costs associated with the Prior Period Spent Nuclear Fuel. Until such payment to the DOE is made, the outstanding liability will continue to accrue interest at the 3-month Treasury bill yield rate. In addition, as a result of consolidating CYAPC, NU has consolidated $179.4 million in additional spent nuclear fuel obligations, including interest, as of December 31, 2013. Fees due to the DOE for the disposal of CL&P's and WMECO's Prior Period Spent Nuclear Fuel and CYAPC's spent nuclear fuel obligation include accumulated interest costs of $350.3 million and $350 million ($177.9 million and $177.8 million for CL&P and $41.7 million and $41.7 million for WMECO) as of December 31, 2013 and 2012, respectively.

WMECO and CYAPC maintain trusts to fund amounts due to the DOE for the disposal of spent nuclear fuel. For further information on these trusts, see Note 6, "Marketable Securities," to the financial statements.

PENSION_BENEFITS_AND_POSTRETIR

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS	12 Months Ended
	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Pension and Other Postretirement Benefits Disclosure [Text Block]	'
	10. EMPLOYEE BENEFITS

	A. Pension Benefits and Postretirement Benefits Other Than Pensions
	NUSCO sponsors a defined benefit retirement plan that covers most employees, including CL&P, PSNH, and WMECO employees, hired before 2006 (or as negotiated, for bargaining unit employees), referred to as the NUSCO Pension Plan. NSTAR Electric acts as plan sponsor for a defined benefit retirement plan that covers most employees of NSTAR Electric and certain affiliates, hired before October 1, 2012, or as negotiated by bargaining unit employees, referred to as the NSTAR Pension Plan. Both plans are subject to the provisions of ERISA, as amended by the PPA of 2006. NUSCO also maintains non-qualified defined benefit retirement plans (herein collectively referred to as the SERP Plans), which provide benefits in excess of Internal Revenue Code limitations to eligible current and retired participants.

	NUSCO also sponsors defined benefit postretirement plans that provide certain retiree health care benefits, primarily medical and dental, and life insurance benefits to retiring employees that meet certain age and service eligibility requirements (NUSCO PBOP Plans and NSTAR PBOP Plan). Under certain circumstances, eligible retirees are required to contribute to the costs of postretirement benefits. The benefits provided under the NUSCO and NSTAR PBOP Plans are not vested and the Company has the right to modify any benefit provision subject to applicable laws at that time.

	The funded status of the Pension, SERP and PBOP Plans is calculated based on the difference between the benefit obligation and the fair value of plan assets and is recorded on the balance sheets as an asset or a liability. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of an adjustment to Accumulated Other Comprehensive Income/(Loss). Regulatory accounting was also applied to the portions of the NUSCO costs that support the Regulated companies, as these costs are also recovered from customers. Adjustments to the Pension and PBOP funded status for the unregulated companies are recorded on an after-tax basis to Accumulated Other Comprehensive Income/(Loss). For further information, see Note 3, "Regulatory Accounting," and Note 15, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The SERP Plans do not have plan assets.

	For the NUSCO Pension and PBOP Plans, the expected return on plan assets is calculated by applying the assumed rate of return to a four-year rolling average of plan asset fair values, which reduces year-to-year volatility. This calculation recognizes investment gains or losses over a four-year period from the years in which they occur. Investment gains or losses for this purpose are the difference between the calculated expected return and the actual return. As investment gains and losses are reflected in the average plan asset fair values, they are subject to amortization with other unrecognized actuarial gains or losses. For the NSTAR Pension and PBOP Plans, the entire difference between the actual return and calculated expected return on plan assets is reflected as a component of unrecognized actuarial gain or loss. Unrecognized actuarial gains or losses are amortized as a component of Pension and PBOP expense over the estimated average future employee service period.

	Pension and SERP Plans: The funded status of each of the plans is recorded on the respective acting sponsor's balance sheet: NUSCO (NUSCO Pension, NUSCO SERP and NSTAR SERP) and NSTAR Electric (NSTAR Pension). The NUSCO plans are accounted for under the multiple-employer approach while the NSTAR plans are accounted for under the multi-employer approach. Accordingly, the balance sheet of NSTAR Electric reflects the full funded status of the NSTAR Pension Plan.

	The following tables provide information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status:
			Pension and SERP
	NU		As of December 31,
	(Millions of Dollars)		2013			2012 ⁽¹⁾
	Change in Benefit Obligation
	Benefit Obligation as of Beginning of Year		$	-5,022.80		$	-3,098.90
	Liabilities Assumed from Merger with NSTAR			-			-1,409.70
	Service Cost			-102.3			-84.3
	Interest Cost			-206.7			-198.3
	Actuarial Gain/(Loss)			433.6			-429.7
	Benefits Paid - Pension			216.6			187.7
	Benefits Paid - SERP			5.1			4.2
	SERP Curtailment			-			6.2
	Benefit Obligation as of End of Year		$	-4,676.50		$	-5,022.80
	Change in Pension Plan Assets
	Fair Value of Plan Assets as of Beginning of Year		$	3,411.30		$	2,005.90
	Assets Assumed from Merger with NSTAR			-			984.7
	Employer Contributions			284.7			222.4
	Actual Return on Plan Assets			506.5			386
	Benefits Paid			-216.6			-187.7
	Fair Value of Plan Assets as of End of Year		$	3,985.90		$	3,411.30
	Funded Status as of December 31^st		$	-690.6		$	-1,611.50
			Pension and SERP
			As of December 31, 2013												As of December 31, 2012
						NSTAR												NSTAR
	(Millions of Dollars)		CL&P			Electric ⁽²⁾			PSNH			WMECO			CL&P			Electric ⁽²⁾			PSNH			WMECO
	Change in Benefit Obligation
	Benefit Obligation as of Beginning of Year		$	-1,178.00		$	-1,430.00		$	-576		$	-243.1		$	-1,043.80		$	-1,346.20		$	-497.9		$	-215.8
	Service Cost			-24.9			-33.1			-13.1			-4.7			-21.8			-30.3			-11.8			-4.1
	Interest Cost			-48.3			-58			-23.6			-10			-51.2			-58.9			-24.4			-10.5
	Actuarial Gain/(Loss)			110.7			96.6			62.4			22.4			-117.4			-63.6			-61.3			-24
	Benefits Paid - Pension			56.6			71.2			21.1			11.5			55.9			69			19.7			11.3
	Benefits Paid - SERP			0.5			-			0.2			-			0.3			-			-			-
	SERP Curtailment			-			-			-			-			-			-			-0.3			-
	Benefit Obligation as of End of Year		$	-1,083.40		$	-1,353.30		$	-529		$	-223.9		$	-1,178.00		$	-1,430.00		$	-576		$	-243.1
	Change in Pension Plan Assets
	Fair Value of Plan Assets as of Beginning of Year		$	937.6		$	1,069.10		$	386.6		$	218.5		$	869.6		$	988.5		$	279.7		$	202
	Employer Contributions			-			82			108.3			-			-			25			87.7			-
	Actual Return on Plan Assets			135.3			155.4			54.8			33.4			123.9			124.6			38.9			27.8
	Benefits Paid			-56.6			-71.2			-21.1			-11.5			-55.9			-69			-19.7			-11.3
	Fair Value of Plan Assets as of End of Year		$	1,016.30		$	1,235.30		$	528.6		$	240.4		$	937.6		$	1,069.10		$	386.6		$	218.5
	Funded Status as of December 31^st		$	-67.1		$	-118		$	-0.4		$	16.5		$	-240.4		$	-360.9		$	-189.4		$	-24.6

	(1) NSTAR amounts were included in NU beginning April 10, 2012.

	(2) NSTAR Electric amounts do not include benefit obligations of the NSTAR SERP Plan.

	As of December 31, 2013, prepaid pension assets of $3 million and $17 million for PSNH and WMECO, respectively, were included in Other Long-term Assets on their accompanying balance sheets. Pension and SERP benefits funded status includes the current portion of the SERP liability, which is included in Other Current Liabilities on the accompanying balance sheets.

	Although NU maintains marketable securities in a supplemental benefit trust, the plan itself does not contain any assets. See Note 6, "Marketable Securities," to the financial statements.
The accumulated benefit obligation for the Pension and SERP Plans is as follows:

		Pension and SERP
		As of December 31,
(Millions of Dollars)		2013			2012
NU		$	4,538.80		$	4,622.10
CL&P			1,058.00			1,061.80
NSTAR Electric ⁽¹⁾			1,280.60			1,353.10
PSNH			520.1			515.9
WMECO			220.6			221.3

-1	NSTAR Electric amounts do not include the accumulated benefit obligation for the SERP Plan.

The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status:
		Pension and SERP
		As of December 31,
		2013			2012
NUSCO Pension and SERP Plans
Discount Rate		5.03	%		4.24	%
Compensation/Progression Rate		3.5	%		3.5	%

NSTAR Pension and SERP Plans
Discount Rate		4.85	%		4.13	%
Compensation/Progression Rate		4	%		4	%
Pension and SERP Expense: For the NUSCO Plans, NU allocates net periodic pension expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. Benefit payments to participants and contributions are also tracked for each subsidiary. The actual investment return in the trust each year is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the NSTAR Pension Plan, the net periodic pension expense recorded at NSTAR Electric represents the full cost of the plan and then a portion of the costs are allocated to affiliated companies based on participant demographic data. The components of net periodic benefit expense, for which the total expense less capitalized amounts is included in Operations and Maintenance on the statements of income, the portion of pension amounts capitalized related to employees working on capital projects, which is included in Property, Plant and Equipment, Net on the balance sheets, and intercompany allocations not included in the net periodic benefit expense amounts for the Pension and SERP Plans are as follows:
		Pension and SERP
		For the Year Ended December 31, 2013
								NSTAR
(Millions of Dollars)		NU			CL&P			Electric⁽²⁾			PSNH			WMECO
Service Cost		$	102.3		$	24.9		$	33.1		$	13.1		$	4.7
Interest Cost			206.7			48.3			58			23.6			10
Expected Return on Plan Assets			-278.1			-73.8			-84.4			-35.4			-17.4
Actuarial Loss			210.5			55.9			58.1			21.6			11.8
Prior Service Cost/(Credit)			4			1.8			-0.3			0.7			0.4
Total Net Periodic Benefit Expense		$	245.4		$	57.1		$	64.5		$	23.6		$	9.5
Related Intercompany Allocations			N/A		$	44.9		$	-8.4		$	10.5		$	8
Capitalized Pension Expense		$	73.2		$	28		$	28.9		$	7.3		$	5.2

		Pension and SERP
		For the Year Ended December 31, 2012 ⁽¹⁾
								NSTAR
(Millions of Dollars)		NU			CL&P			Electric⁽²⁾			PSNH			WMECO
Service Cost		$	84.3		$	21.8		$	30.3		$	11.8		$	4.1
Interest Cost			198.3			51.2			58.9			24.4			10.5
Expected Return on Plan Assets			-220.9			-70.6			-65.6			-28.2			-16.4
Actuarial Loss			172.4			49.6			63.1			16.2			10.7
Prior Service Cost/(Credit)			7.9			3.6			-0.6			1.5			0.8
Total Net Periodic Benefit Expense		$	242		$	55.6		$	86.1		$	25.7		$	9.7
Curtailments and Settlements		$	2.2		$	-		$	-		$	-		$	-
Related Intercompany Allocations			N/A		$	42.8		$	-12.3		$	10.1		$	8.1
Capitalized Pension Expense		$	70.6		$	26.8		$	30.7		$	7.9		$	5.1

		Pension and SERP
		For the Year Ended December 31, 2011
								NSTAR
(Millions of Dollars)		NU			CL&P			Electric⁽²⁾			PSNH			WMECO
Service Cost		$	55.4		$	19.5		$	26		$	10.6		$	3.9
Interest Cost			153.3			51.9			61			24.4			10.7
Expected Return on Plan Assets			-170.8			-76.6			-71.4			-19.8			-17.7
Actuarial Loss			84.2			33.4			48.6			10.7			7.1
Prior Service Cost/(Credit)			9.7			4.2			-0.7			1.8			0.9
Total Net Periodic Benefit Expense		$	131.8		$	32.4		$	63.5		$	27.7		$	4.9
Related Intercompany Allocations			N/A		$	34.1		$	-10.2		$	7.6		$	6.2
Capitalized Pension Expense		$	29.7		$	16.6		$	19.8		$	7.6		$	2.7

-1	NSTAR Electric amounts were included in NU beginning April 10, 2012.
-2	NSTAR Electric's allocated expense associated with the NSTAR SERP was $3.2 million, $3.6 million and $4.4 million for the years ended December 31, 2013, 2012 and 2011, respectively, and are not included in the NSTAR Electric amounts in the tables above.
The following actuarial assumptions were used to calculate Pension and SERP expense amounts:
		Pension and SERP
		For the Years Ended December 31,
NUSCO Pension and SERP Plans		2013			2012			2011
Discount Rate		4.24	%		5.03	%		5.57	%
Expected Long-Term Rate of Return		8.25	%		8.25	%		8.25	%
Compensation/Progression Rate		3.5	%		3.5	%		3.5	%

NSTAR Pension and SERP Plans
Discount Rate		4.13	%		4.52	%		5.3	%
Expected Long-Term Rate of Return		8.25	%		7.3	%		8	%
Compensation/Progression Rate		4	%		4	%		4	%

The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income (OCI) as well as amounts in Regulatory Assets and OCI reclassified as net periodic benefit expense during the years presented:

		Amounts Reclassified To/From
		Regulatory Assets						OCI
(Millions of Dollars)		For the Years Ended December 31,
NU Pension and SERP Plans⁽¹⁾		2013			2012			2013			2012
Actuarial (Gains)/Losses Arising During the Year		$	-635.2		$	245.7		$	-28.9		$	19.1
Actuarial Losses Reclassified as Net Periodic Benefit Expense			-201.2			-164.6			-9.4			-7.8
Prior Service Cost Reclassified as Net Periodic Benefit Expense			-3.8			-7.7			-0.2			-0.2

(1) The NU amounts include the NSTAR Pension and SERP Plans beginning April 10, 2012.

The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2013 and 2012, and the amounts that are expected to be recognized as components in 2014:

			Regulatory Assets as of						Expected			AOCI as of					Expected
(Millions of Dollars)		December 31,							2014		December 31,						2014
NU Pension and SERP Plans		2013			2012			Expense			2013			2012			Expense
Actuarial Loss		$	1,137.40		$	1,973.80		$	126.2		$	43.2		$	81.5		$	5.6
Prior Service Cost			17.4			21.2			4.2			1			1.2			0.2
As of December 31, 2013 and 2012, NSTAR Electric had $497.9 million and $724 million, respectively, of unrecognized actuarial losses included in Regulatory Assets that have not been recognized as components of net periodic benefit expense. For the years ended December 31, 2013 and 2012, NSTAR Electric reclassified $58.1 million and $62.8 million, respectively, of actuarial losses and $0.3 million and $0.6 million, respectively, of prior service credit as net periodic benefit expense. Actuarial gains of $168 million and actuarial losses of $4.6 million, respectively, arose during 2013 and 2012, respectively.

PBOP Plans: The NUSCO Plans are accounted for under the multiple-employer approach while the NSTAR Plan is accounted for under the multi-employer approach. Accordingly, the funded status of the NUSCO PBOP Plans is allocated to its subsidiaries, including CL&P, PSNH and WMECO, while the NSTAR PBOP Plan is not reflected on the SEC registrant NSTAR Electric's balance sheet.

NU annually funds postretirement costs through tax deductible contributions to external trusts.

The following tables provide information on PBOP Plan benefit obligations, fair values of plan assets, and funded status:
		PBOP
		As of December 31,
		2013												2012
(Millions of Dollars)		NU			CL&P			PSNH			WMECO			NU ⁽¹⁾			CL&P			PSNH			WMECO
Change in Benefit Obligation
Benefit Obligation as of Beginning of Year		$	-1,233.30		$	-196.8		$	-100.2		$	-42.5		$	-520.9		$	-198.9		$	-99.2		$	-42.9
Liabilities Assumed from Merger with NSTAR			-			-			-			-			-770.6			-			-			-
Service Cost			-16.9			-3.4			-2.3			-0.7			-15.7			-3			-2			-0.6
Interest Cost			-47.2			-7.9			-4			-1.7			-49			-9.2			-4.6			-2
Actuarial Gain			200.9			13.3			7.2			3.3			70.9			1.2			0.3			0.1
Federal Subsidy on Benefits Paid			-			-			-			-			-6.2			-1.7			-0.6			-0.3
Benefits Paid			58.5			14.4			5.8			2.9			58.2			14.8			5.9			3.2
Benefit Obligation as of End of Year		$	-1,038.00		$	-180.4		$	-93.5		$	-38.7		$	-1,233.30		$	-196.8		$	-100.2		$	-42.5
Change in Plan Assets
Fair Value of Plan Assets as of Beginning of Year		$	709.1		$	132.2		$	69.5		$	31		$	285.4		$	112.2		$	58.7		$	27.1
Assets Assumed from Merger with NSTAR			-			-			-			-			330.4			-			-			-
Actual Return on Plan Assets			118.3			24.8			13.4			6			78.8			15			7.5			3.5
Employer Contributions			57.6			8.7			4.7			1.2			72.7			19.8			9.2			3.6
Benefits Paid			-58.5			-14.4			-5.8			-2.9			-58.2			-14.8			-5.9			-3.2
Fair Value of Plan Assets as of End of Year		$	826.5		$	151.3		$	81.8		$	35.3		$	709.1		$	132.2		$	69.5		$	31
Funded Status as of December 31^st		$	-211.5		$	-29.1		$	-11.7		$	-3.4		$	-524.2		$	-64.6		$	-30.7		$	-11.5

-1	NU results include NSTAR PBOP Plan activity beginning April 10, 2012.
The following actuarial assumptions were used in calculating the PBOP Plans' year end funded status:

			PBOP
			As of December 31,
			2013			2012
NUSCO PBOP Plans
Discount Rate			4.78	%		4.04	%
Health Care Cost Trend Rate			7	%		7	%

NSTAR PBOP Plan
Discount Rate			5.1	%		4.35	%
Health Care Cost Trend Rate			7	%		7.1	%
PBOP Expense: For the NUSCO Plans, NU allocates net periodic postretirement benefits expense to certain subsidiaries based on the actual participant demographic data for each subsidiary's participants. Benefit payments to participants and contributions are also tracked for each subsidiary. The actual investment return in the trust is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the NSTAR Plan, NU allocates the net periodic postretirement expenses to certain subsidiaries based on actual participant demographic data for each of its subsidiaries. The net periodic postretirement expense allocated to NSTAR Electric was $4.6 million, $34.1 million, and $26 million for the years ended December 31, 2013, 2012 and 2011, respectively.

The components of net periodic benefit expense, for which the total expense less capitalized amounts is included in Operations and Maintenance on the statements of income, the portion of PBOP amounts capitalized related to employees working on capital projects, which is included in Property, Plant and Equipment, Net on the balance sheets, and intercompany allocations not included in the net periodic benefit expense amounts for the PBOP Plans are as follows
			PBOP
		For the Years Ended December 31,
		2013												2012												2011
(Millions of Dollars)		NU			CL&P			PSNH			WMECO			NU ⁽¹⁾			CL&P			PSNH			WMECO			NU		CL&P		PSNH		WMECO
Service Cost		$	16.9		$	3.4		$	2.3		$	0.7		$	15.7		$	3		$	2		$	0.6		$	9.2	$	2.9	$	1.9	$	0.6
Interest Cost			47.2			7.9			4			1.7			49			9.2			4.6			2			25.7		10		4.8		2.2
Expected Return
	on Plan Assets		-55.4			-10.1			-5.2			-2.3			-39.2			-9.1			-4.6			-2.1			-21.6		-8.7		-4.3		-2
Actuarial Loss			26			7.4			3.6			1.1			36			7.5			3.6			1.2			19		7.2		3.2		1.1
Prior Service
	Cost/(Credit)		-2.1			-			-			-			-1.4			-			-			-			-0.3		-		-		-
Net Transition
	Obligation Cost ⁽²⁾		-			-			-			-			12.2			6.1			2.5			1.3			11.6		6.2		2.5		1.3
Total Net Periodic Benefit Expense		$	32.6		$	8.6		$	4.7		$	1.2		$	72.3		$	16.7		$	8.1		$	3		$	43.6	$	17.6	$	8.1	$	3.2
Related Intercompany Allocations			N/A		$	7.1		$	1.6		$	1.3			N/A		$	7.9		$	2		$	1.5			N/A	$	8.2	$	2	$	1.5
Capitalized PBOP Expense		$	8.8		$	3.9		$	1.3		$	0.6		$	26.6		$	8.2		$	2.3		$	1.6		$	12.7	$	8.7	$	2.2	$	1.5

-1	NU results include NSTAR PBOP Plan activity beginning April 10, 2012.
-2	The PBOP Plans' transition obligation costs were fully amortized in 2013.
The following actuarial assumptions were used to calculate PBOP expense amounts:

			PBOP
			For the Years Ended December 31,
			2013			2012			2011
NUSCO PBOP Plans
Discount Rate			4.04	%		4.84	%		5.28	%
Expected Long-Term Rate of Return			8.25	%		8.25	%		8.25	%

NSTAR PBOP Plan
Discount Rate			4.35	%		4.58	%		N/A
Expected Long-Term Rate of Return			8.25	%		7.3	%		N/A
The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts in Regulatory Assets and OCI reclassified as net periodic benefit (expense)/income during the years presented:

		Amounts Reclassified To/From
	Regulatory Assets						OCI
(Millions of Dollars)	For the Years Ended December 31,
NU PBOP Plans ⁽¹⁾	2013			2012			2013			2012
Actuarial Gains Arising During the Year	$	-262		$	-108.6		$	-1.9		$	-1.8
Actuarial Losses Reclassified as Net Periodic Benefit Expense		-24.9			-34.9			-1.1			-1.1
Prior Service Credit Reclassified as Net Periodic Benefit Income		2.1			1.4			-			-
Transition Obligation Reclassified as Net Periodic Benefit Expense		-			-11.9			-			-0.2

(1) The NU amounts include the NSTAR PBOP Plan beginning April 10, 2012.

The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2013 and 2012, and the amounts that are expected to be recognized as components in 2014:

		Regulatory Assets as of					Expected				AOCI as of					Expected
(Millions of Dollars)	December 31,						2014				December 31,					2014
NU PBOP Plans	2013			2012			Expense			2013			2012			Expense
Actuarial Loss	$	89.2		$	376.1		$	11.4		$	6.2		$	9.2		$	0.7
Prior Service Credit		-4.6			-6.7			-2.8			-			-			-

The health care cost trend rate assumption used to calculate the 2013 PBOP expense amounts was 7 percent for the NUSCO PBOP Plan, subsequently decreasing by 50 basis points per year to an ultimate rate of 5 percent in 2017, and 7.10 percent for the NSTAR PBOP Plan, subsequently decreasing to an ultimate rate of 4.5 percent in 2024. As of December 31, 2013, the health care cost trend rate assumption used to determine the NUSCO and NSTAR PBOP Plans' year end funded status is 7 percent, subsequently decreasing to an ultimate rate of 4.5 percent in 2024.

Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. The effect of changing the assumed health care cost trend rate by one percentage point for the year ended December 31, 2013 would have the following effects:
(Millions of Dollars)	One Percentage			One Percentage
NU PBOP Plans	Point Increase			Point Decrease
Effect on Postretirement Benefit Obligation	$	85.8		$	-70.4
Effect on Total Service and Interest Cost Components		7.1			-5.5
Estimated Future Benefit Payments: The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans:

(Millions of Dollars)	Pension
NU	and SERP			PBOP
2014	$	263.3		$	61.6
2015		273.3			63.3
2016		282.9			64.5
2017		287.4			65.6
2018		299.4			66.6
2019-2023		1,617.00			344.4

NSTAR Pension Plan
2014	$	88			N/A
2015		90.6			N/A
2016		88.4			N/A
2017		88.5			N/A
2018		90			N/A
2019-2023		449.2			N/A
Contributions: NU's policy is to annually fund the NUSCO and NSTAR Pension Plans in an amount at least equal to an amount that will satisfy federal requirements. NU contributed $202.7 million to the NUSCO Pension Plan in 2013, of which $108.3 million was contributed by PSNH. NSTAR Electric contributed $82 million to the NSTAR Pension Plan in 2013. Based on the current status of the NUSCO Pension Plan, NU expects to make a contribution of $68.6 million in 2014. NSTAR Electric expects to make a contribution of $3 million in 2014 to the NSTAR Pension Plan.
For the PBOP Plans, it is NU's policy to annually fund the NUSCO PBOP Plans in an amount equal to the PBOP Plans' postretirement benefit cost, excluding curtailment and termination benefits, and the NSTAR PBOP Plan in an amount that approximates annual benefit payments. NU contributed $57.6 million to the PBOP Plans in 2013 and expects to make $39.7 million in contributions in 2014.

Fair Value of Pension and PBOP Plan Assets: Pension and PBOP funds are held in external trusts. Trust assets, including accumulated earnings, must be used exclusively for Pension and PBOP payments. NU's investment strategy for its Pension and PBOP Plans is to maximize the long-term rates of return on these plans' assets within an acceptable level of risk. The investment strategy for each asset category includes a diversification of asset types, fund strategies and fund managers and establishes target asset allocations that are routinely reviewed and periodically rebalanced. In 2013 and 2012, PBOP assets were comprised of specific assets within the defined benefit pension plan trust (401(h) assets) as well as assets held in the PBOP Plans. The investment policy and strategy of the 401(h) assets is consistent with those of the defined benefit pension plans, which are detailed below. NU's expected long-term rates of return on Pension and PBOP Plan assets are based on these target asset allocation assumptions and related expected long-term rates of return. In developing its expected long-term rate of return assumptions for the Pension and PBOP Plans, NU evaluated input from consultants, as well as long-term inflation assumptions and historical returns. For the year ended December 31, 2013, management has assumed long-term rates of return of 8.25 percent for the Pension and PBOP Plan assets. These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows:
		As of December 31,
		2013				2012
		NUSCO and NSTAR Pension				NUSCO Pension
		and Tax-Exempt PBOP Plans⁽¹⁾				and PBOP Plans				NSTAR Pension Plan				NSTAR PBOP Plan
		Target		Assumed		Target		Assumed		Target		Assumed		Target		Assumed
		Asset		Rate		Asset		Rate		Asset		Rate		Asset		Rate
		Allocation		of Return		Allocation		of Return		Allocation		of Return		Allocation		of Return
Equity Securities:
	United States	24%		9%		24%		9%		25%		8.30%		25%		8.30%
	International	10%		9%		13%		9%		13%		8.60%		20%		8.60%
	Emerging Markets	6%		10%		3%		10%		5%		8.80%		5%		8.80%
	Private Equity	10%		13%		12%		13%		-		-		-		-
Debt Securities:
	Fixed Income	15%		5%		20%		5%		21%		4.60%		30%		4.60%
	High Yield Fixed Income	9%		7.50%		3.50%		7.50%		9%		6.50%		-		-
	Emerging Markets Debt	6%		7.50%		3.50%		7.50%		4%		6.40%		-		-
Real Estate and Other Assets		9%		7.50%		8%		7.50%		10%		7.90%		10%		7.90%
Hedge Funds		11%		7%		13%		7%		13%		8.40%		10%		8.40%


The Taxable PBOP Plans have a target asset allocation of 70 percent equity securities and 30 percent fixed income securities.


The following table presents, by asset category, the Pension and PBOP Plan assets recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy:
			NU Pension Plans
			Fair Value Measurements as of December 31,
	(Millions of Dollars)		2013												2012
	Asset Category:		Level 1			Level 2			Level 3			Total			Level 1			Level 2			Level 3			Total
	Equity Securities:
		United States ⁽¹⁾	$	294.6		$	597.7		$	194		$	1,086.30		$	336.5		$	302.8		$	270.6		$	909.9
		International ⁽¹⁾		32.2			362.6			61.5			456.3			42			362.6			52.1			456.7
		Emerging Markets⁽¹⁾		-			211.8			-			211.8			-			135.3			-			135.3
		Private Equity		96.4			-			300.3			396.7			26.7			-			267.9			294.6
	Fixed Income⁽²⁾			11.6			605.1			589.5			1,206.20			54.9			629.2			315.1			999.2
	Real Estate and Other Assets			-			88.2			288.5			376.7			-			78.9			235.4			314.3
	Hedge Funds			-			-			416.9			416.9			-			-			418.9			418.9
	Total Master Trust Assets		$	434.8		$	1,865.40		$	1,850.70		$	4,150.90		$	460.1		$	1,508.80		$	1,560.00		$	3,528.90
		Less: 401(h) PBOP Assets⁽³⁾											-165												-117.6
	Total Pension Assets											$	3,985.90											$	3,411.30

			NSTAR Pension Plan
			Fair Value Measurements as of December 31,
	(Millions of Dollars)		2013												2012
	Asset Category:		Level 1			Level 2			Level 3			Total			Level 1			Level 2			Level 3			Total
	Equity Securities:
		United States ⁽¹⁾	$	87.7		$	177.9		$	57.8		$	323.4		$	96.7		$	246.4		$	-		$	343.1
		International⁽¹⁾		9.6			108			18.3			135.9			-			98.3			52.1			150.4
		Emerging Markets⁽¹⁾		-			63.1			-			63.1			-			55.9			-			55.9
		Private Equity		28.7			-			89.4			118.1
	Fixed Income⁽²⁾			3.4			180			175.4			358.8			54.9			292.5			-			347.4
	Real Estate and Other Assets			-			26.3			85.6			111.9			-			-			127.2			127.2
	Hedge Funds			-			-			124.1			124.1			-			-			122.7			122.7
	Total Master Trust Assets		$	129.4		$	555.3		$	550.6		$	1,235.30		$	151.6		$	693.1		$	302		$	1,146.70
		Less: 401(h) PBOP Assets⁽³⁾																							-77.6
	Total Pension Assets																							$	1,069.10

			NU PBOP Plans
			Fair Value Measurements as of December 31,
	(Millions of Dollars)		2013												2012
	Asset Category:		Level 1			Level 2			Level 3			Total			Level 1			Level 2			Level 3			Total
	Cash and Cash Equivalents		$	11.1		$	-		$	-		$	11.1		$	9.7		$	-		$	-		$	9.7
	Equity Securities:
		United States⁽¹⁾		67			120.6			69.1			256.7			116.3			57.7			36.3			210.3
		International⁽¹⁾		28.1			42.8			-			70.9			68			29.7			-			97.7
		Emerging Markets⁽¹⁾		15.2			13.4			-			28.6			7.7			14			-			21.7
		Private Equity		-			-			17.9			17.9			-			-			11.3			11.3
	Fixed Income ⁽²⁾			-			119.7			51.5			171.2			-			137.7			32.1			169.8
	Real Estate and Other Assets			-			14.2			33.9			48.1			-			4.7			26.7			31.4
	Hedge Funds			-			-			57			57			-			-			39.6			39.6
	Total		$	121.4		$	310.7		$	229.4		$	661.5		$	201.7		$	243.8		$	146		$	591.5
		Add: 401(h) PBOP Assets⁽³⁾											165												117.6
	Total PBOP Assets											$	826.5											$	709.1

United States, International and Emerging Markets equity securities classified as Level 2 include investments in commingled funds. Level 3 investments include hedge funds that are overlayed with equity index swaps and futures contracts and funds invested in equities that have redemption restrictions.
Fixed Income investments classified as Level 3 investments include fixed income funds that invest in a variety of opportunistic fixed income strategies, and hedge funds that are overlayed with fixed income futures.
The assets of the Pension Plans include a 401(h) account that has been allocated to provide health and welfare postretirement benefits under the PBOP Plans.


Effective January 1, 2013, the NSTAR Pension Plan assets were transferred into the NUSCO Pension Plan master trust. The, NUSCO Pension Plan is entitled to approximately 66 percent of each asset category in the master trust, the NSTAR Pension Plan is entitled to approximately 30 percent of each asset category in the master trust and the 401(h) plans are entitled to approximately four percent of each asset category in the master trust.

CL&P, PSNH and WMECO participate in the NUSCO Pension and PBOP Plans. Each company participating in the plans is allocated a portion of the total plan assets. As of December 31, 2013 and 2012, the NUSCO Pension Plan had total assets of $2,750.4 million and $2,342.6 million, respectively. CL&P's, PSNH's and WMECO's portion of these total Pension Plan assets was 37 percent, 19 percent and 9 percent, respectively, as of December 31, 2013, and 40 percent, 17 percent and 9 percent, respectively, as of December 31, 2012. The NUSCO PBOP Plans had total assets of $391 million and $334.9 million as of December 31, 2013 and 2012, respectively. CL&P's, PSNH's and WMECO's portion of these total PBOP Plan assets was 39 percent, 21 percent and 9 percent, respectively, as of December 31, 2013 and 2012.

The Company values assets based on observable inputs when available. Equity securities, exchange traded funds and futures contracts classified as Level 1 in the fair value hierarchy are priced based on the closing price on the primary exchange as of the balance sheet date. Commingled funds included in Level 2 equity securities are recorded at the net asset value provided by the asset manager, which is based on the market prices of the underlying equity securities. Swaps are valued using pricing models that incorporate interest rates and equity and fixed income index closing prices to determine a net present value of the cash flows. Fixed income securities, such as government issued securities, corporate bonds and high yield bond funds, are included in Level 2 and are valued using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The pricing models utilize observable inputs such as recent trades for the same or similar instruments, yield curves, discount margins and bond structures. Hedge funds and investments in opportunistic fixed income funds are recorded at net asset value based on the values of the underlying assets. The assets in the hedge funds and opportunistic fixed income funds are valued using observable inputs and are classified as Level 3 within the fair value hierarchy due to redemption restrictions. Private Equity investments and Real Estate and Other Assets are valued using the net asset value provided by the partnerships, which are based on discounted cash flows of the underlying investments, real estate appraisals or public market comparables of the underlying investments. These investments are classified as Level 3 due to redemption restrictions.

Fair Value Measurements Using Significant Unobservable Inputs (Level 3): The following tables present changes in the Level 3 category of Pension and PBOP Plan assets for the years ended December 31, 2013 and 2012. The NSTAR Pension Plan table reflects the change in asset categories on January 1, 2013 as a result of the transfer of assets into the NUSCO Pension Plan master trust.
		NU Pension Plans
		United												Real Estate
		States						Private			Fixed			and Other			Hedge
(Millions of Dollars)		Equity			International			Equity			Income			Assets			Funds			Total
Balance as of January 1, 2012		$	259.4		$	-		$	255.1		$	276.2		$	71.8		$	240		$	1,102.50
Assets Assumed from Merger with NSTAR			-			41.4			-			-			111			126.6			279
Actual Return/(Loss) on Plan Assets:
	Relating to Assets Still Held as of Year End		11.2			10.7			17			42.1			5.7			21.8			108.5
	Relating to Assets Distributed During the Year		-			-			15			0.7			7.6			-0.3			23
Purchases, Sales and Settlements			-			-			-19.2			-3.9			39.3			30.8			47
Balance as of December 31, 2012		$	270.6		$	52.1		$	267.9		$	315.1		$	235.4		$	418.9	0	$	1,560.00
Transfer Between Categories			-			-			-			32.5			-			-32.5			-
Actual Return/(Loss) on Plan Assets:
	Relating to Assets Still Held as of Year End		11.2			9.4			15.4			55.3			12.9			33.4			137.6
	Relating to Assets Distributed During the Year		12.2			-			13.7			-1			6.2			-			31.1
Purchases, Sales and Settlements			-100			-			3.3			187.6			34			-2.9			122
Balance as of December 31, 2013		$	194		$	61.5		$	300.3		$	589.5		$	288.5		$	416.9		$	1,850.70

		NU PBOP Plans
		United									Real Estate
		States			Private			Fixed			and Other				Hedge
(Millions of Dollars)		Equity			Equity			Income			Assets				Funds			Total
Balance as of January 1, 2012		$	10.7		$	5.1		$	26		$	2.5		$	16.1		$	60.4
Assets Assumed from Merger with NSTAR			19.7			-			-			18.4			21.4			59.5
Actual Return on Plan Assets:
	Relating to Assets Still Held as of Year End		5.9			1.6			4			3			2.1			16.6
Purchases, Sales and Settlements			-			4.6			2.1			2.8			-			9.5
Balance as of December 31, 2012		$	36.3		$	11.3		$	32.1		$	26.7		$	39.6		$	146
Actual Return/(Loss) on Plan Assets:												-
	Relating to Assets Still Held as of Year End		20.8			1.5			4.1			3.9			5.4			35.7
	Relating to Assets Distributed During the Year		-			0.2			-			-0.1			-			0.1
Purchases, Sales and Settlements			12			4.9			15.3			3.4			12			47.6
Balance as of December 31, 2013		$	69.1		$	17.9		$	51.5		$	33.9		$	57		$	229.4

		NSTAR Pension Plan
		United												Real Estate
		States							Private		Fixed			and Other				Hedge
(Millions of Dollars)		Equity			International				Equity		Income			Assets				Funds			Total
Balance as of January 1, 2012		$	-		$	41.4		$	-		$	-		$	111		$	126.6		$	279
Actual Return/(Loss) on Plan Assets:
	Relating to Assets Still Held as of Year End		-			10.7			-			-			9.9			5.6			26.2
	Relating to Assets Distributed During the Year		-			-			-			-			-			-0.3			-0.3
Purchases, Sales and Settlements			-			-			-			-			6.3			-9.2			-2.9
Balance as of December 31, 2012		$	-		$	52.1		$	-		$	-		$	127.2		$	122.7		$	302
Transfer of Assets into NUSCO Pension Plan Trust			80.5			-36.6		$	79.7			93.8			-57.1			2			162.3
Transfer Between Categories			-			-			-			9.7			-			-9.7			-
Actual Return/(Loss) on Plan Assets:
	Relating to Assets Still Held as of Year End		3.5			2.8			4.6			16.4			3.5			9.9			40.7
	Relating to Assets Distributed During the Year		3.6			-			4.2			-0.3			1.8			-			9.3
Purchases, Sales and Settlements			-29.8			-			0.9			55.8			10.2			-0.8			36.3
Balance as of December 31, 2013		$	57.8		$	18.3		$	89.4		$	175.4		$	85.6		$	124.1		$	550.6

DEFINED_CONTRIBUTION_PLANS

DEFINED CONTRIBUTION PLANS	12 Months Ended
DEFINED CONTRIBUTION PLANS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Compensation and Employee Benefit Plans [Text Block]	'
	B. Defined Contribution Plans
	As of December 31, 2013, NU maintained two defined contribution plans on behalf of eligible participants. The NUSCO 401(k) Plan covered eligible employees, including CL&P, PSNH, WMECO, and effective in 2012, certain newly-hired NSTAR employees. The NSTAR Savings Plan covered eligible employees of NSTAR. These defined contribution plans provided for employee and employer contributions up to statutory limits.

	The NUSCO 401(k) Plan matches employee contributions up to a maximum of three percent of eligible compensation. The NUSCO 401(k) Plan also contains a K-Vantage feature which provides an additional company contribution based on age and years of service. This feature covers the majority of NU non-represented employees hired after 2005 and certain NU bargaining unit employees hired after 2006 or as subject to collective bargaining agreements. In addition, NSTAR employees who participate in the NUSCO 401(k) Plan are eligible to participate in the K-Vantage program. Participants in the K-Vantage program are not eligible to actively participate in any NU defined benefit plan.

	The NSTAR Savings Plan matches employee contributions of 50 percent on up to the first 8 percent of eligible compensation.

	The total defined contribution plan matching contributions, including the K-Vantage program contributions, are as follows:
						NSTAR
	(Millions of Dollars)	NU ⁽¹⁾		CL&P		Electric		PSNH		WMECO
	2013	$	37	$	5.1	$	8.5	$	3.3	$	1
	2012		25.7		4.8		9		3.3		0.9
	2011		17.4		4.5		8.7		3.1		0.9

	NSTAR amounts were included in NU beginning April 10, 2012.

	Effective January 1, 2014, the NSTAR Savings Plan merged into the NUSCO 401(k) Plan. The merged Plan is a defined contribution plan that continues to provide for employer and employee contributions up to statutory limits. The merged Plan also retained the match guidelines and K-Vantage features for eligible employees as described above.

EMPLOYEE_STOCK_OWNERSHIP_PLAN

EMPLOYEE STOCK OWNERSHIP PLAN	12 Months Ended
EMPLOYEE STOCK OWNERSHIP PLAN	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Shareholders' Equity and Share-based Payments [Text Block]	'
	C. Employee Stock Ownership Plan
	NU maintains an ESOP for purposes of allocating shares to employees participating in the NUSCO 401(k) Plan. Allocations of NU common shares were made from NU treasury shares to satisfy the NUSCO 401(k) Plan obligation to provide a portion of the matching contribution in NU common shares.

	For treasury shares used to satisfy the 401(k) Plan matching contributions, compensation expense is recognized equal to the fair value of shares that have been allocated to participants. Any difference between the fair value and the average cost of the allocated treasury shares is charged or credited to Capital Surplus, Paid In. For the years ended December 31, 2013, 2012 and 2011, NU recognized $9.1 million, $8.9 million and $8.8 million, respectively, of compensation expense related to the ESOP.
	D. Share-Based Payments
	Share-based compensation awards are recorded using a fair-value-based method at the date of grant. NU, CL&P, NSTAR Electric, PSNH and WMECO record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as the allocation of costs associated with shares issued or sold to NU's service company employees and officers that support CL&P, NSTAR Electric, PSNH and WMECO.

	Upon consummation of the merger with NSTAR, the NSTAR 1997 Share Incentive Plan and the NSTAR 2007 Long-Term Incentive Plan were assumed by NU. Share-based awards granted under the NSTAR Plans and held by NSTAR employees and officers were generally converted into outstanding NU share-based compensation awards with an estimated fair value of $53.2 million. Refer to Note 2, "Merger of NU and NSTAR," for further information regarding the merger transaction. Specifically, as of the merger closing, and as adjusted by the exchange ratio, NU converted (1) outstanding NSTAR stock options into 2,664,894 NU stock options valued at $30.5 million, (2) NSTAR deferred shares and NSTAR performance shares into 421,775 NU RSU's valued at $15.5 million, and (3) NSTAR RSU retention awards into 195,619 NU RSU retention awards valued at $7.2 million.

	NU Incentive Plan: NU maintains long-term equity-based incentive plans under the NU Incentive Plan in which NU, CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are entitled to participate. The NU Incentive Plan was approved in 2007, and authorized NU to grant up to 4,500,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 2013 and 2012, NU had 2,462,668 and 2,502,512 common shares, respectively, available for issuance under the NU Incentive Plan. The aggregate number of common shares authorized for issuance under the NSTAR 2007 Long-Term Incentive Plan was 3,500,000. As of both December 31, 2013 and 2012, there were 977,922 NU common shares available for issuance under this Plan. No additional awards will be granted under the NSTAR 1997 Share Incentive Plan. NU also maintains an ESPP for eligible employees.

	NU accounts for its various share-based plans as follows:


	RSUs - NU records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of NU's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares.



	Performance Shares - NU records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. As of December 31, 2013, vesting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the achievement of the Company's share price as compared to an index of similar equity securities during the requisite service period. The fair value of performance shares is determined at the date of grant using a lattice model.



	Stock Options - Stock options issued under the NSTAR Incentive Plan that were outstanding immediately prior to the completion of the merger with NSTAR converted into fully vested options to acquire NU common shares, as adjusted by the exchange ratio. The fair value of these awards on the merger date was included in the purchase price as it represented consideration transferred in the merger. Accordingly, no compensation expense was recorded for these stock options. Additionally, no compensation expense was recorded for stock options issued under the NU Incentive Plan as these stock options were fully vested prior to January 1, 2006.



	ESPP Shares - For shares sold under the ESPP, no compensation expense was recorded as the ESPP qualifies as a non-compensatory plan.


	RSUs: NU granted RSUs under the annual Long-Term incentive programs that are subject to three-year graded vesting schedules for employees, and one-year graded vesting schedules, or immediate vesting for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes, subsequent to vesting. A summary of RSU transactions is as follows:
						Weighted Average
			RSUs			Grant-Date
			(Units)			Fair Value
	Outstanding as of January 1, 2011			1,014,479		$	24.31
	Granted			208,533		$	33.87
	Shares issued			-244,782		$	24.47
	Forfeited			-18,310		$	23.74
	Outstanding as of December 31, 2011			959,920		$	26.36
	Granted			614,930		$	33.04
	Converted NSTAR Awards upon Merger			617,394		$	36.79
	Converted from NU Performance Shares upon Merger			451,358		$	34.32
	Shares issued			-363,779		$	29.05
	Forfeited			-96,504		$	34.97
	Outstanding as of December 31, 2012			2,183,319		$	31.99
	Granted			373,939		$	39.56
	Shares issued			-891,129		$	32.15
	Forfeited			-29,689		$	33.75
	Outstanding as of December 31, 2013			1,636,440		$	33.61
	As of December 31, 2013 and 2012, the number and weighted average grant-date fair value of unvested RSUs was 1,162,216 and $36.58 per share, and 1,417,688 and $34.70 per share, respectively. The number and weighted average grant-date fair value of RSUs vested during 2013 was 583,101 and $34.34 per share, respectively. As of December 31, 2013, 474,224 RSUs were fully vested and an additional 1,104,106 are expected to vest.

	Performance Shares: NU granted performance shares under the annual Long-Term Incentive programs that vested based upon the extent to which the Company achieved targets at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows:
			Performance			Weighted Average
			Shares			Grant-Date
			(Units)			Fair Value
	Outstanding as of January 1, 2011			248,559		$	24.72
	Granted			244,870		$	33.76
	Shares issued			-		$	-
	Forfeited			-10,296		$	30.47
	Outstanding as of December 31, 2011			483,133		$	29.18
	Granted			225,935		$	35.09
	Converted to RSUs upon Merger			-451,358		$	34.32
	Shares issued			-106,773		$	24.52
	Forfeited			-		$	-
Outstanding as of December 31, 2012			150,937		$	25.04
Granted			191,961		$	40.96
Shares issued			-150,944		$	25.04
Forfeited			-1,526		$	40.93
Outstanding as of December 31, 2013			190,428		$	40.96
Upon closing of the merger with NSTAR, 451,358 performance shares under the NU 2011 and 2012 Long-Term Incentive Programs converted to RSUs according to the terms of these programs. The remaining performance shares were measured based upon a modified performance period through the date of the merger, in accordance with the terms of the NU 2010 Incentive Program, and were fully distributed in 2013. As of December 31, 2013, outstanding performance shares pertain to the NU 2013 Long-Term Incentive Program.

The total compensation expense and associated future income tax benefit recognized by NU, CL&P, NSTAR Electric, PSNH and WMECO for share-based compensation awards are as follows:
NU				For the Years Ended December 31,
(Millions of Dollars)				2013			2012 ⁽¹⁾			2011
Compensation Expense				$	27		$	25.8		$	12.3
Future Income Tax Benefit					10.7			10.2			4.9
		For the Years Ended December 31,
		2013											2012								2011
(Millions of Dollars)		CL&P			NSTAR Electric			PSNH			WMECO		CL&P		NSTAR Electric		PSNH		WMECO		CL&P		NSTAR Electric		PSNH		WMECO
Compensation
	Expense	$	6.8		$	7.5		$	2.3		$	1.3	$	4.8	$	7.4	$	1.8	$	1	$	7.1	$	7.7	$	2.5	$	1.4
Future Income Tax
	Benefit		2.7			3			0.9			0.5		1.9		2.9		0.7		0.4		2.8		3		1		0.6

NSTAR amounts were included in NU beginning April 10, 2012.


As of December 31, 2013, there was $19.5 million of total unrecognized compensation expense related to nonvested share-based awards for NU, $5.8 million for CL&P, $6.3 million for NSTAR Electric, $1.7 million for PSNH and $0.9 million for WMECO. This cost is expected to be recognized ratably over a weighted-average period of 1.64 years for NU, 1.85 years for CL&P, 1.47 years for NSTAR Electric, 1.79 years for PSNH and 1.80 years for WMECO.

For the year ended December 31, 2013, additional tax benefits totaling $5.5 million decreased cash flows from financing activities. For the years ended December 31, 2012 and 2011, additional tax benefits totaling $8.5 million and $1.3 million, respectively, increased cash flows from financing activities.

Stock Options: Stock options were granted under the NU and NSTAR Incentive Plans. Options currently outstanding expire ten years from the date of grant and are fully vested. The weighted average remaining contractual lives for the options outstanding as of December 31, 2013 is 4.3 years. A summary of stock option transactions is as follows:

					Weighted Average			Intrinsic Value
			Options		Exercise Price			(Millions)
Outstanding and Exercisable - January 1, 2011			112,599		$	18.8
Exercised			-65,225		$	18.81		$	1
Forfeited and Cancelled			-		$	-
Outstanding and Exercisable - December 31, 2011			47,374		$	18.78
Converted NSTAR Options upon Merger			2,664,894		$	23.99
Exercised			-1,166,511		$	22.53		$	18.7
Forfeited and Cancelled			-		$	-
Outstanding and Exercisable - December 31, 2012			1,545,757		$	24.92
Exercised			-324,382		$	20.97		$	6.7
Forfeited and Cancelled			-		$	-
Outstanding and Exercisable - December 31, 2013			1,221,375		$	25.97		$	20.1
Cash received for options exercised during the year ended December 31, 2013 totaled $6.8 million. The tax benefit realized from stock options exercised totaled $2.7 million for the year ended December 31, 2013.

Employee Share Purchase Plan: NU maintains an ESPP for eligible employees, which allows for NU common shares to be purchased by employees at the end of successive six-month offering periods at 95 percent of the closing market price on the last day of each six-month period. Employees are permitted to purchase shares having a value not exceeding 25 percent of their compensation as of the beginning of the offering period up to a limit of $25,000 per annum. The ESPP qualifies as a non-compensatory plan under accounting guidance for share-based payments, and no compensation expense is recorded for ESPP purchases.

During 2013, employees purchased 39,526 shares at discounted prices of $38.69 and $42.19. Employees purchased 39,422 shares in 2012 at discounted prices of $33.01 and $37.89. As of December 31, 2013 and 2012, 817,754 and 857,280 shares, respectively, remained available for future issuance under the ESPP.

An income tax rate of 40 percent is used to estimate the tax effect on total share-based payments determined under the fair value-based method for all awards. The Company generally settles stock option exercises and fully vested RSUs and performance shares with either the issuance of new common shares or the issuance of common shares purchased in the open market.

SHAREBASED_PAYMENTS

SHARE-BASED PAYMENTS	12 Months Ended
SHARE-BASED PAYMENTS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Shareholders' Equity and Share-based Payments [Text Block]	'
	C. Employee Stock Ownership Plan
	NU maintains an ESOP for purposes of allocating shares to employees participating in the NUSCO 401(k) Plan. Allocations of NU common shares were made from NU treasury shares to satisfy the NUSCO 401(k) Plan obligation to provide a portion of the matching contribution in NU common shares.

	For treasury shares used to satisfy the 401(k) Plan matching contributions, compensation expense is recognized equal to the fair value of shares that have been allocated to participants. Any difference between the fair value and the average cost of the allocated treasury shares is charged or credited to Capital Surplus, Paid In. For the years ended December 31, 2013, 2012 and 2011, NU recognized $9.1 million, $8.9 million and $8.8 million, respectively, of compensation expense related to the ESOP.
	D. Share-Based Payments
	Share-based compensation awards are recorded using a fair-value-based method at the date of grant. NU, CL&P, NSTAR Electric, PSNH and WMECO record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as the allocation of costs associated with shares issued or sold to NU's service company employees and officers that support CL&P, NSTAR Electric, PSNH and WMECO.

	Upon consummation of the merger with NSTAR, the NSTAR 1997 Share Incentive Plan and the NSTAR 2007 Long-Term Incentive Plan were assumed by NU. Share-based awards granted under the NSTAR Plans and held by NSTAR employees and officers were generally converted into outstanding NU share-based compensation awards with an estimated fair value of $53.2 million. Refer to Note 2, "Merger of NU and NSTAR," for further information regarding the merger transaction. Specifically, as of the merger closing, and as adjusted by the exchange ratio, NU converted (1) outstanding NSTAR stock options into 2,664,894 NU stock options valued at $30.5 million, (2) NSTAR deferred shares and NSTAR performance shares into 421,775 NU RSU's valued at $15.5 million, and (3) NSTAR RSU retention awards into 195,619 NU RSU retention awards valued at $7.2 million.

	NU Incentive Plan: NU maintains long-term equity-based incentive plans under the NU Incentive Plan in which NU, CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are entitled to participate. The NU Incentive Plan was approved in 2007, and authorized NU to grant up to 4,500,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 2013 and 2012, NU had 2,462,668 and 2,502,512 common shares, respectively, available for issuance under the NU Incentive Plan. The aggregate number of common shares authorized for issuance under the NSTAR 2007 Long-Term Incentive Plan was 3,500,000. As of both December 31, 2013 and 2012, there were 977,922 NU common shares available for issuance under this Plan. No additional awards will be granted under the NSTAR 1997 Share Incentive Plan. NU also maintains an ESPP for eligible employees.

	NU accounts for its various share-based plans as follows:


	RSUs - NU records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of NU's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares.



	Performance Shares - NU records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. As of December 31, 2013, vesting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the achievement of the Company's share price as compared to an index of similar equity securities during the requisite service period. The fair value of performance shares is determined at the date of grant using a lattice model.



	Stock Options - Stock options issued under the NSTAR Incentive Plan that were outstanding immediately prior to the completion of the merger with NSTAR converted into fully vested options to acquire NU common shares, as adjusted by the exchange ratio. The fair value of these awards on the merger date was included in the purchase price as it represented consideration transferred in the merger. Accordingly, no compensation expense was recorded for these stock options. Additionally, no compensation expense was recorded for stock options issued under the NU Incentive Plan as these stock options were fully vested prior to January 1, 2006.



	ESPP Shares - For shares sold under the ESPP, no compensation expense was recorded as the ESPP qualifies as a non-compensatory plan.


	RSUs: NU granted RSUs under the annual Long-Term incentive programs that are subject to three-year graded vesting schedules for employees, and one-year graded vesting schedules, or immediate vesting for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes, subsequent to vesting. A summary of RSU transactions is as follows:
						Weighted Average
			RSUs			Grant-Date
			(Units)			Fair Value
	Outstanding as of January 1, 2011			1,014,479		$	24.31
	Granted			208,533		$	33.87
	Shares issued			-244,782		$	24.47
	Forfeited			-18,310		$	23.74
	Outstanding as of December 31, 2011			959,920		$	26.36
	Granted			614,930		$	33.04
	Converted NSTAR Awards upon Merger			617,394		$	36.79
	Converted from NU Performance Shares upon Merger			451,358		$	34.32
	Shares issued			-363,779		$	29.05
	Forfeited			-96,504		$	34.97
	Outstanding as of December 31, 2012			2,183,319		$	31.99
	Granted			373,939		$	39.56
	Shares issued			-891,129		$	32.15
	Forfeited			-29,689		$	33.75
	Outstanding as of December 31, 2013			1,636,440		$	33.61
	As of December 31, 2013 and 2012, the number and weighted average grant-date fair value of unvested RSUs was 1,162,216 and $36.58 per share, and 1,417,688 and $34.70 per share, respectively. The number and weighted average grant-date fair value of RSUs vested during 2013 was 583,101 and $34.34 per share, respectively. As of December 31, 2013, 474,224 RSUs were fully vested and an additional 1,104,106 are expected to vest.

	Performance Shares: NU granted performance shares under the annual Long-Term Incentive programs that vested based upon the extent to which the Company achieved targets at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows:
			Performance			Weighted Average
			Shares			Grant-Date
			(Units)			Fair Value
	Outstanding as of January 1, 2011			248,559		$	24.72
	Granted			244,870		$	33.76
	Shares issued			-		$	-
	Forfeited			-10,296		$	30.47
	Outstanding as of December 31, 2011			483,133		$	29.18
	Granted			225,935		$	35.09
	Converted to RSUs upon Merger			-451,358		$	34.32
	Shares issued			-106,773		$	24.52
	Forfeited			-		$	-
Outstanding as of December 31, 2012			150,937		$	25.04
Granted			191,961		$	40.96
Shares issued			-150,944		$	25.04
Forfeited			-1,526		$	40.93
Outstanding as of December 31, 2013			190,428		$	40.96
Upon closing of the merger with NSTAR, 451,358 performance shares under the NU 2011 and 2012 Long-Term Incentive Programs converted to RSUs according to the terms of these programs. The remaining performance shares were measured based upon a modified performance period through the date of the merger, in accordance with the terms of the NU 2010 Incentive Program, and were fully distributed in 2013. As of December 31, 2013, outstanding performance shares pertain to the NU 2013 Long-Term Incentive Program.

The total compensation expense and associated future income tax benefit recognized by NU, CL&P, NSTAR Electric, PSNH and WMECO for share-based compensation awards are as follows:
NU				For the Years Ended December 31,
(Millions of Dollars)				2013			2012 ⁽¹⁾			2011
Compensation Expense				$	27		$	25.8		$	12.3
Future Income Tax Benefit					10.7			10.2			4.9
		For the Years Ended December 31,
		2013											2012								2011
(Millions of Dollars)		CL&P			NSTAR Electric			PSNH			WMECO		CL&P		NSTAR Electric		PSNH		WMECO		CL&P		NSTAR Electric		PSNH		WMECO
Compensation
	Expense	$	6.8		$	7.5		$	2.3		$	1.3	$	4.8	$	7.4	$	1.8	$	1	$	7.1	$	7.7	$	2.5	$	1.4
Future Income Tax
	Benefit		2.7			3			0.9			0.5		1.9		2.9		0.7		0.4		2.8		3		1		0.6

NSTAR amounts were included in NU beginning April 10, 2012.


As of December 31, 2013, there was $19.5 million of total unrecognized compensation expense related to nonvested share-based awards for NU, $5.8 million for CL&P, $6.3 million for NSTAR Electric, $1.7 million for PSNH and $0.9 million for WMECO. This cost is expected to be recognized ratably over a weighted-average period of 1.64 years for NU, 1.85 years for CL&P, 1.47 years for NSTAR Electric, 1.79 years for PSNH and 1.80 years for WMECO.

For the year ended December 31, 2013, additional tax benefits totaling $5.5 million decreased cash flows from financing activities. For the years ended December 31, 2012 and 2011, additional tax benefits totaling $8.5 million and $1.3 million, respectively, increased cash flows from financing activities.

Stock Options: Stock options were granted under the NU and NSTAR Incentive Plans. Options currently outstanding expire ten years from the date of grant and are fully vested. The weighted average remaining contractual lives for the options outstanding as of December 31, 2013 is 4.3 years. A summary of stock option transactions is as follows:

					Weighted Average			Intrinsic Value
			Options		Exercise Price			(Millions)
Outstanding and Exercisable - January 1, 2011			112,599		$	18.8
Exercised			-65,225		$	18.81		$	1
Forfeited and Cancelled			-		$	-
Outstanding and Exercisable - December 31, 2011			47,374		$	18.78
Converted NSTAR Options upon Merger			2,664,894		$	23.99
Exercised			-1,166,511		$	22.53		$	18.7
Forfeited and Cancelled			-		$	-
Outstanding and Exercisable - December 31, 2012			1,545,757		$	24.92
Exercised			-324,382		$	20.97		$	6.7
Forfeited and Cancelled			-		$	-
Outstanding and Exercisable - December 31, 2013			1,221,375		$	25.97		$	20.1
Cash received for options exercised during the year ended December 31, 2013 totaled $6.8 million. The tax benefit realized from stock options exercised totaled $2.7 million for the year ended December 31, 2013.

Employee Share Purchase Plan: NU maintains an ESPP for eligible employees, which allows for NU common shares to be purchased by employees at the end of successive six-month offering periods at 95 percent of the closing market price on the last day of each six-month period. Employees are permitted to purchase shares having a value not exceeding 25 percent of their compensation as of the beginning of the offering period up to a limit of $25,000 per annum. The ESPP qualifies as a non-compensatory plan under accounting guidance for share-based payments, and no compensation expense is recorded for ESPP purchases.

During 2013, employees purchased 39,526 shares at discounted prices of $38.69 and $42.19. Employees purchased 39,422 shares in 2012 at discounted prices of $33.01 and $37.89. As of December 31, 2013 and 2012, 817,754 and 857,280 shares, respectively, remained available for future issuance under the ESPP.

An income tax rate of 40 percent is used to estimate the tax effect on total share-based payments determined under the fair value-based method for all awards. The Company generally settles stock option exercises and fully vested RSUs and performance shares with either the issuance of new common shares or the issuance of common shares purchased in the open market.

OTHER_RETIREMENT_BENEFITS

OTHER RETIREMENT BENEFITS	12 Months Ended
OTHER RETIREMENT BENEFITS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Compensation Related Costs, General [Text Block]	'
	E. Other Retirement Benefits
	NU provides benefits for retirement and other benefits for certain current and past company officers of NU, including CL&P, PSNH and WMECO. These benefits are accounted for on an accrual basis and expensed over the service lives of the employees. The actuarially-determined liability for these benefits, which is included in Other Long-Term Liabilities on the balance sheets, as well as the related expense, are as follows:

	NU		For the Years Ended December 31,
	(Millions of Dollars)		2013			2012			2011
	Actuarially-Determined Liability		$	51.3		$	54.6		$	52.8
	Other Retirement Benefits Expense			4.4			4.7			4.7
		For the Years Ended December 31,
		2013									2012						2011
	(Millions of Dollars)	CL&P			PSNH			WMECO			CL&P		PSNH		WMECO		CL&P		PSNH		WMECO
	Actuarially-Determined Liability	$	0.4		$	2.3		$	0.1		$	0.4	$	2.5	$	0.2	$	1.2	$	2.5	$	0.2
	Other Retirement Benefits Expense		2.5			1			0.5			2.6		1		0.5		2.6		1		0.5

INCOME_TAXES

INCOME TAXES	12 Months Ended
INCOME TAXES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Income Tax Disclosure [Text Block]	'
	11. INCOME TAXES

	The tax effect of temporary differences is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and relevant accounting authoritative literature. The components of income tax expense are as follows:
	NU	For the Years Ended December 31,
	(Millions of Dollars)	2013			2012 ⁽¹⁾			2011
	Current Income Taxes:
	Federal	$	8.8		$	-30.9		$	3
	State		-9.4			17.6			-26
	Total Current		-0.6			-13.3			-23
	Deferred Income Taxes, Net:
	Federal		386.2			291.3			187.7
	State		45.4			0.8			9.1
	Total Deferred		431.6			292.1			196.8
	Investment Tax Credits, Net		-4.1			-3.9			-2.8
	Income Tax Expense	$	426.9		$	274.9		$	171
			For the Years Ended December 31,
			2013												2012												2011
						NSTAR												NSTAR												NSTAR
	(Millions of Dollars)		CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO
	Current Income
		Taxes:
		Federal	$	20.1		$	95.8		$	-8.2		$	-53.4		$	-47.8		$	93.5		$	-0.9		$	-24.7		$	13.9		$	64.9		$	-25.8		$	0.1
		State		-6.7			29.6			3.6			4.2			3.1			27.6			3.4			3.4			-34.4			30.2			0.1			0.3
	Total Current			13.4			125.4			-4.6			-49.2			-44.7			121.1			2.5			-21.3			-20.5			95.1			-25.7			0.4
	Deferred Income
		Taxes, Net:
		Federal		114.9			49.8			64.5			84.7			141.5			11.4			46.5			51.2			106.4			74.8			67.7			22.1
		State		15.1			-1			11.2			2.3			-0.5			-7.1			12			2.7			6.2			-2.8			7.9			1
	Total Deferred			130			48.8			75.7			87			141			4.3			58.5			53.9			112.6			72			75.6			23.1
	Investment Tax
		Credits, Net		-1.7			-1.3			0			-0.4			-1.9			-1.4			0			-0.5			-2.1			-1.4			-			-0.3
	Income Tax Expense		$	141.7		$	172.9		$	71.1		$	37.4		$	94.4		$	124		$	61		$	32.1		$	90		$	165.7		$	49.9		$	23.2

	(1) NSTAR amounts were included in NU beginning April 10, 2012.
	A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows:

	NU		For the Years Ended December 31,
	(Millions of Dollars, except percentages)		2013				2012 ⁽¹⁾				2011
	Income Before Income Tax Expense		$	1,220.60			$	808			$	571.5

	Statutory Federal Income Tax Expense at 35%			427.2				282.8				200
	Tax Effect of Differences:
		Depreciation		-7.4				-10.8				-14.2
		Investment Tax Credit Amortization		-4.1				-3.9				-2.8
		Other Federal Tax Credits		-3.7				-3.8				-3.5
		State Income Taxes, Net of Federal Impact		27.6				4.4				22.1
		ESOP		-8				-6.4				-2.2
		Tax Asset Valuation Allowance/Reserve Adjustments		-4.3				7.6				-33.1
		Other, Net		-0.4				5				4.7
	Income Tax Expense		$	426.9			$	274.9			$	171
	Effective Tax Rate			35.00%				34.00%				29.90%
			For the Years Ended December 31,
			2013												2012												2011
	(Millions of Dollars,					NSTAR												NSTAR												NSTAR
		except percentages)	CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO
	Income Before Income
		Tax Expense	$	421.1		$	441.4		$	182.5		$	97.8		$	304.2		$	314.2		$	157.9		$	86.6		$	340.2		$	418.2		$	150.2		$	66.2

	Statutory Federal Income
		Tax Expense at 35%		147.4			154.5			63.9			34.2			106.5			110			55.3			30.3			119.1			146.4			52.6			23.2
	Tax Effect of Differences:
		Depreciation		-7			0.1			0.6			0			-9			0			-0.3			0.2			-8.1			0			-4.4			0.1
		Investment Tax Credit
	Amortization		-1.7			-1.3			0			-0.4			-1.9			-1.4			0			-0.5			-2.1			-1.4			-			-0.3
	Other Federal Tax
	Credits		0			0			-3.7			0			0			0			-3.8			0			-0.1			0			-3.4			0
	State Income Taxes,
	Net of Federal Impact		5			18.6			9.6			4.2			0.1			13.4			10			4			4			17.9			5.2			0.9
	ESOP		0			0			0			0			0			0			0			0			-			0			-			-
	Tax Asset Valuation
	Allowance/Reserve
	Adjustments		0.4			0			0			0			1.6			0			0			0			-22.3			0			-			-
	Regulatory Decision Non-
	Plant Flow Through		0			0			0			0			0			0			0			-1.3			0			0			-			-
	Other, Net		-2.4			1			0.7			-0.6			-2.9			2			-0.2			-0.6			-0.5			2.8			-0.1			-0.7
Income Tax Expense		$	141.7		$	172.9		$	71.1		$	37.4		$	94.4		$	124		$	61		$	32.1		$	90		$	165.7		$	49.9		$	23.2
Effective Tax Rate			33.60%			39.20%			39.00%			38.20%			31.00%			39.50%			38.60%			37.10%			26.50%			39.60%			33.20%			35.00%

(1) NSTAR amounts were included in NU beginning April 10, 2012.
NU, CL&P, NSTAR Electric, PSNH and WMECO file a consolidated federal income tax return and unitary, combined and separate state income tax returns. These entities are also parties to a tax allocation agreement under which taxable subsidiaries do not pay any more taxes than they would have otherwise paid had they filed a separate company tax return, and subsidiaries generating tax losses, if any, are paid for their losses when utilized.

Deferred tax assets and liabilities are recognized for the future tax effects of temporary differences between the carrying amounts and the tax basis of assets and liabilities. The tax effects of temporary differences that give rise to the net accumulated deferred income tax obligations are as follows:
NU			As of December 31,
(Millions of Dollars)			2013			2012
Deferred Tax Assets:
	Employee Benefits		$	435.2		$	811.4
	Derivative Liabilities and Change in Fair Value of Energy Contracts			272.9			380.6
	Regulatory Deferrals			272.7			257.9
	Allowance for Uncollectible Accounts			65			64.2
	Tax Effect - Tax Regulatory Assets			16.2			17.2
	Federal Net Operating Loss Carryforwards			158			214.6
	Purchase Accounting Adjustment			132.8			146.4
	Other			230.6			242.4
Total Deferred Tax Assets				1,583.40			2,134.70
	Less: Valuation Allowance			24.3			4.2
Net Deferred Tax Assets			$	1,559.10		$	2,130.50
Deferred Tax Liabilities:
	Accelerated Depreciation and Other Plant-Related Differences		$	3,806.50		$	3,468.80
	Property Tax Accruals			95.1			89.6
	Regulatory Amounts:
		Other Regulatory Deferrals		1,146.70			1,561.10
		Tax Effect - Tax Regulatory Assets		248.2			217.2
		Goodwill Regulatory Asset - 1999 Merger		211.5			210.9
		Derivative Assets		30.1			36.2
		Securitized Contract Termination Costs		0.3			16.6
		Other		156.8			136.1
Total Deferred Tax Liabilities			$	5,695.20		$	5,736.50
			As of December 31,
			2013												2012
						NSTAR												NSTAR
(Millions of Dollars)			CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO
Deferred Tax Assets:
	Employee Benefits		$	56		$	38.3		$	15.5		$	-1.8		$	141.2		$	116.3		$	64.8		$	16.3
	Derivative Liabilities and Change in
		Fair Value of Energy Contracts		272.4			3.3			0			-2.9			375.9			5.8			-			-1.7
	Regulatory Deferrals			61.5			114.7			40.9			1			35.5			123.6			43.9			6.3
	Allowance for Uncollectible Accounts			31.2			15.4			3.1			3.3			30.4			16.2			2.9			3.2
	Tax Effect - Tax Regulatory Assets			4.7			5.4			2.1			1.6			5.2			6			1.7			1.7
	Federal Net Operating Loss Carryforwards			51			0			56.6			18.6			82			-			71.4			15.1
	Other			75.3			31.3			40.3			8.3			82.8			26			33.7			8
Total Deferred Tax Assets				552.1			208.4			158.5			28.1			753			293.9			218.4		$	48.9
	Less: Valuation Allowance			23.1			0			0			0			0			0			0			0
Net Deferred Tax Assets			$	529		$	208.4		$	158.5		$	28.1		$	753		$	293.9		$	218.4		$	48.9
Deferred Tax Liabilities:
	Accelerated Depreciation and Other
	Plant-Related Differences		$	1,238.10		$	1,179.40		$	526.6		$	361.1		$	1,194.70		$	1,079.30		$	476.5		$	261.3
	Property Tax Accruals			49.3			25.3			7.1			5.9			44.4			23.1			6.8			5.1
	Regulatory Amounts:
		Other Regulatory Deferrals		550.4			276.2			109.3			49.3			677.7			379.6			149.3			74.5
		Tax Effect - Tax Regulatory Assets		160.1			36			16.3			18.2			151.8			20.9			15.8			13.9
		Goodwill Regulatory Asset - 1999 Merger		-			181.6			-			-			-			181			-			-
		Derivative Assets		29			0.5			-			-			36.2			-			-			-
		Securitized Contract Termination Costs		-			0			0			0.3			-			5.5			7.9			3.3
		Other		20.6			26.4			28			3.3			10.1			30.2			14.1			2.3
Total Deferred Tax Liabilities			$	2,047.50		$	1,725.40		$	687.3		$	438.1		$	2,114.90		$	1,719.60		$	670.4		$	360.4
Carryforwards: The following tables provide the amounts and expiration dates of state tax credit and loss carryforwards and federal tax credit and net operating loss carryforwards:

	As of December 31, 2013
							NSTAR									Year
(Millions of Dollars)	NU			CL&P			Electric			PSNH			WMECO			Expiration Begins
Federal Net Operating Loss	$	451.3		$	145.8		$	0		$	161.8		$	53.3		2031
Federal Tax Credit		8			0			0			7.6			0		2031
State Tax Credit		104.7			86.8			0			0			0		2013
State Loss Carryforwards		12.1			0			0			0			0		2013

	As of December 31, 2012
							NSTAR									Year
(Millions of Dollars)	NU			CL&P			Electric			PSNH			WMECO			Expiration Begins
Federal Net Operating Loss	$	606.9		$	234.3		$	0		$	204		$	43.3		2031
Federal Tax Credit		3.8			0			0			3.8			0		2031
State Tax Credit		110.2			75.2			0			0			0		2013
State Loss Carryforwards		74.9			0			0			0			0		2013
For 2013, state credit and state loss carryforwards have been partially reserved by a valuation allowance of $23.7 million (net of federal income tax). For 2012, the state loss carryforwards had been partially reserved by a valuation allowance of $0.3 million (net of federal income tax).

Unrecognized Tax Benefits: A reconciliation of the activity in unrecognized tax benefits, all of which would impact the effective tax rate if recognized, is as follows:

(Millions of Dollars)		NU			CL&P
Balance as of January 1, 2011		$	101.2		$	80.8
	Gross Increases - Current Year		8			1.4
	Gross Decreases - Prior Year		-35.7			-35.7
Balance as of December 31, 2011			73.5			46.5
	Gross Increases - Current Year		10.3			2.5
	Gross Increases - Prior Year		0.1			-
	Gross Decreases - Prior Year		-0.8			-
Balance as of December 31, 2012			83.1			49
	Gross Increases - Current Year		8.2			2.1
	Gross Decreases - Prior Year		-1.1			-0.3
	Settlements		-49.8			-39.4
	Lapse of Statute of Limitations		-2.2			-
Balance as of December 31, 2013		$	38.2		$	11.4
Interest and Penalties: Interest on uncertain tax positions is recorded and generally classified as a component of Other Interest Expense on the statements of income. However, when resolution of uncertainties results in the Company receiving interest income, any related interest benefit is recorded in Other Income, Net on the statements of income. No penalties have been recorded. If penalties are recorded in the future, then the estimated penalties would be classified as a component of Other Income, Net on the statements of income. The amount of interest expense/(income) on uncertain tax positions recognized and the related accrued interest payable/(receivable) are as follows:
Other Interest		For the Years Ended December 31,									Accrued Interest		As of December 31,
Expense/(Income)		2013			2012			2011			Expense		2013			2012
(Millions of Dollars)											(Millions of Dollars)
NU ⁽¹⁾		$	-8.6		$	3.1		$	-2.8		NU		$	1.5		$	10.1
CL&P			-4			1.3			-3.7		CL&P			0			4
NSTAR Electric			0			0			2		NSTAR Electric			0			0
PSNH			0			0			-0.6		PSNH			0			0
(1) NSTAR amounts were included in NU beginning April 10, 2012.

Tax Positions: During 2013, NU received a Final Determination from the Connecticut Department of Revenue Services (DRS) that concluded its audit of NU's Connecticut income tax returns for the years 2005 through 2008. The DRS Determination resulted in total NU and CL&P after-tax benefits of $13.6 million and $6.9 million, respectively, that included a reduction in NU and CL&P pre-tax interest expense of $8.7 million and $4 million, or $5.2 million and $2.4 million after-tax, respectively. Further, the income tax expense impact resulted in a tax benefit to NU and CL&P of $8.4 million and $4.5 million after-tax, respectively.

During 2011, NU recorded an after-tax benefit of $29.1 million related to various state tax settlements and certain other adjustments. This benefit was recorded as a reduction to both interest expense and income tax expense (including NU and CL&P tax expense reductions of approximately $22.4 million).

Open Tax Years: The following table summarizes NU, CL&P, NSTAR Electric, PSNH and WMECO's tax years that remain subject to examination by major tax jurisdictions as of December 31, 2013:
Description		Tax Years
Federal		2013
Connecticut		2010-2013
Massachusetts		2010-2013
New Hampshire		2010-2013
NU estimates that during the next twelve months, differences of a non-timing nature could be resolved, resulting in a zero to $2.0 million decrease in unrecognized tax benefits by NU. These estimated changes are not expected to have a material impact on the earnings of NU. Other companies' impacts are not expected to be material.

2013 Federal Legislation: On January 2, 2013, the "American Taxpayer Relief Act of 2012" became law, which extended the accelerated deduction of depreciation to businesses through 2013. This extended stimulus provided NU with cash flow benefits of approximately $300 million (approximately $95 million at CL&P, $85 million at NSTAR Electric, $35 million at PSNH, and $50 million at WMECO).

On September 13, 2013, the Internal Revenue Service issued final Tangible Property regulations that are meant to simplify, clarify and make more administrable previously issued guidance. In the third quarter of 2013, CL&P recorded an after-tax valuation allowance of $10.5 million against its deferred tax assets as a result of these regulations. NU is in compliance with the new regulations, but continues to evaluate several new potential elections. Therefore, a change to the valuation allowance at CL&P could result once NU completes the review of the impact of the final regulations.

2013 Massachusetts: On July 24, 2013, Massachusetts enacted a law that changed the income tax rate applicable to utility companies effective January 1, 2014, from 6.5 percent to 8 percent. The tax law change required NU to remeasure its accumulated deferred income taxes and resulted in NU increasing its deferred tax liability with an offsetting regulatory asset of approximately $61 million at its utility companies ($46.3 million at NSTAR Electric and $9.8 million at WMECO).

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Commitments and Contingencies Disclosure [Text Block]	'
	12. COMMITMENTS AND CONTINGENCIES

	A. Environmental Matters
	General: NU, 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. NU, 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.

	Environmental reserves are accrued when assessments indicate it is probable that a liability has been incurred and an amount can be reasonably estimated. The approach used estimates the liability based on the most likely action plan from a variety of available remediation options, including no action required or several different remedies ranging from establishing institutional controls to full site remediation and monitoring.

	These estimates are subjective in nature as they take into consideration several different remediation options at each specific site. The reliability and precision of these estimates can be affected by several factors, including new information concerning either the level of contamination at the site, the extent of NU, CL&P, NSTAR Electric, PSNH and WMECO's responsibility or the extent of remediation required, recently enacted laws and regulations or a change in cost estimates due to certain economic factors.

	The amounts recorded as environmental liabilities included in Other Current Liabilities and Other Long-Term Liabilities on the balance sheets represent management's best estimate of the liability for environmental costs, and take into consideration site assessment, remediation and long-term monitoring costs. The environmental liability also takes into account recurring costs of managing hazardous substances and pollutants, mandated expenditures to remediate previously contaminated sites and any other infrequent and non-recurring clean-up costs. A reconciliation of the activity in the environmental reserves is as follows:
	(Millions of Dollars)	NU ⁽¹⁾			CL&P			NSTAR Electric			PSNH			WMECO
	Balance as of January 1, 2012	$	31.7		$	2.9		$	1.3		$	6.6		$	0.3
	Liabilities Assumed from Merger with NSTAR		11.8			-			-			-			-
	Additions		4.7			1.3			0.7			0.2			0.5
	Payments/Reductions		-8.8			-0.5			-0.3			-1.9			-0.2
	Balance as of December 31, 2012		39.4			3.7			1.7			4.9			0.6
	Additions		3.5			0.2			0.2			1			-
	Payments/Reductions		-7.5			-0.5			-0.7			-0.5			-0.2
	Balance as of December 31, 2013	$	35.4		$	3.4		$	1.2		$	5.4		$	0.4
	(1) NSTAR amounts were included in NU beginning April 10, 2012.

	These liabilities are estimated on an undiscounted basis and do not assume that any amounts are recoverable from insurance companies or other third parties. The environmental reserves include sites at different stages of discovery and remediation and do not include any unasserted claims.

	It is possible that new information or future developments could require a reassessment of the potential exposure to related environmental matters. As this information becomes available, management will continue to assess the potential exposure and adjust the reserves accordingly.

	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 December 31, 2013							As of December 31, 2012
					Reserve							Reserve
		Number of Sites			(in millions)				Number of Sites			(in millions)
	NU		68		$	35.4				77		$	39.4
	CL&P		18			3.4				19			3.7
	NSTAR Electric		12			1.2				16			1.7
	PSNH		15			5.4				16			4.9
	WMECO		5			0.4				6			0.6
	Included in the NU 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 $31.4 million and $34.5 million as of December 31, 2013 and 2012, respectively, and relates primarily to the natural gas business segment.

	As of December 31, 2013, for 6 environmental sites (2 for PSNH, and 1 for WMECO) that are included in the Company's reserve for environmental costs, the information known and nature of the remediation options at those sites allow for the Company to estimate the range of losses for environmental costs. As of December 31, 2013, $5.8 million ($0.7 million for PSNH) had been accrued as a liability for these sites, which represent management's best estimates of the liabilities for environmental costs. These amounts are the best estimates with estimated ranges of additional losses from zero to $30 million (zero to $4.2 million for PSNH, and zero to $8.6 million for WMECO).

	As of December 31, 2013, for 20 environmental sites (4 for CL&P, 1 for NSTAR Electric, 3 for PSNH, and 2 for WMECO) that are included in the Company's reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to undertake. As of December 31, 2013, $16.7 million ($1.6 million for CL&P, $0.1 million for PSNH, and $0.3 million for WMECO) had been accrued as a liability for these sites. As of December 31, 2013, for the remaining 42 environmental sites (14 for CL&P, 11 for NSTAR Electric, 10 for PSNH, and 2 for WMECO) that are included in the Company's reserve for environmental costs, the $12.9 million accrual ($1.8 million for CL&P, $1.2 million for NSTAR Electric, $4.6 million for PSNH, and $0.1 million for WMECO) represents management's best estimate of the liability and no additional loss is anticipated.

	CERCLA: The federal Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) and its amendments or state equivalents impose joint and several strict liabilities, regardless of fault, upon generators of hazardous substances resulting in removal and remediation costs and environmental damages. Liabilities under these laws can be material and in some instances may be imposed without regard to fault or for past acts that may have been lawful at the time they occurred. Of the 68 sites, 10 sites (2 for CL&P, 3 for NSTAR Electric, 4 for PSNH and 1 for WMECO) are superfund sites under CERCLA for which the Company has been notified that it is a potentially responsible party but for which the site assessment and remediation are not being managed by the Company. As of December 31, 2013, a liability of $1 million ($0.4 million for CL&P, and $0.3 million for PSNH) accrued on these sites represents management's best estimate of its potential remediation costs with respect to these superfund sites.

	Environmental Rate Recovery: PSNH, NSTAR Gas and Yankee Gas have rate recovery mechanisms for MGP related environmental costs. CL&P recovers a certain level of environmental costs currently in rates but does not have an environmental cost recovery tracking mechanism. Accordingly, changes in CL&P's environmental reserves impact CL&P's Net Income. WMECO does not have a separate regulatory mechanism to recover environmental costs from its customers, and changes in WMECO's environmental reserves impact WMECO's Net Income.
	B.			Long-Term Contractual Arrangements
	Estimated Future Annual Costs: The estimated future annual costs of significant long-term contractual arrangements as of
	December 31, 2013 are as follows:


	NU
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Supply and Stranded Cost				$	224.2		$	205.2		$	177.7		$	119.9		$	110.4		$	309.3		$	1,146.70
	Renewable Energy					194.5			203.8			214.1			211.9			177.3			1,885.70			2,887.30
	Peaker CfDs					49.1			46.9			44.3			36.2			28.6			24.7			229.8
	Natural Gas Procurement					134.4			117.6			76.5			37.7			24.2			103.9			494.3
	Coal, Wood and Other					75.3			15.2			5			5			5			16.8			122.3
	Transmission Support Commitments					27.9			26.9			20.5			18			22.6			45.2			161.1
	Total				$	705.4		$	615.6		$	538.1		$	428.7		$	368.1		$	2,385.60		$	5,041.50

	CL&P
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Supply and Stranded Cost				$	145.6		$	141.1		$	143.7		$	96.2		$	87.1		$	257.6		$	871.3
	Renewable Energy					48.9			49.9			50.3			50.8			51.4			560.2			811.5
	Peaker CfDs					49.1			46.9			44.3			36.2			28.6			24.7			229.8
Transmission Support Commitments					11			10.6			8.1			7.1			8.9			17.8			63.5
Yankee Billings					1.5			1.4			0.8			0.8			0.8			12.3			17.6
Total				$	256.1		$	249.9		$	247.2		$	191.1		$	176.8		$	872.6		$	1,993.70

NSTAR Electric
(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
Supply and Stranded Cost				$	36.2		$	36.1		$	15.8		$	5.6		$	5.5		$	36.8		$	136
Renewable Energy					87.1			86.3			85.8			81.9			45.4			207.4			593.9
Transmission Support Commitments					8.7			8.4			6.4			5.6			7			14.1			50.2
Yankee Billings					0.7			0.5			0.3			0.3			0.3			4.2			6.3
Total				$	132.7		$	131.3		$	108.3		$	93.4		$	58.2		$	262.5		$	786.4

PSNH
(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
Supply and Stranded Cost				$	42.4		$	28		$	18.2		$	18.1		$	17.8		$	14.9		$	139.4
Renewable Energy					56.8			57.7			67.9			69			70.1			995.2			1,316.70
Coal, Wood and Other					75.3			15.2			5			5			5			16.8			122.3
Transmission Support Commitments					5.9			5.7			4.3			3.8			4.8			9.6			34.1
Yankee Billings					0.3			0.3			0.3			0.3			0.3			4.9			6.4
Total				$	180.7		$	106.9		$	95.7		$	96.2		$	98		$	1,041.40		$	1,618.90

WMECO
(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
Renewable Energy				$	1.7		$	9.9		$	10.1		$	10.2		$	10.4		$	122.9		$	165.2
Transmission Support Commitments					2.3			2.2			1.7			1.5			1.9			3.7			13.3
Yankee Billings					0.4			0.4			0.2			0.2			0.2			3.1			4.5
Total				$	4.4		$	12.5		$	12		$	11.9		$	12.5		$	129.7		$	183
Supply and Stranded Cost: CL&P, NSTAR Electric and PSNH have various IPP contracts or purchase obligations for electricity, including payment obligations resulting from the buydown of electricity purchase contracts. Such contracts extend through 2024 for CL&P, 2030 for NSTAR Electric and 2023 for PSNH.

In addition, CL&P and UI have entered into four CfDs for a total of approximately 787 MW of capacity consisting of three generation projects and one demand response project. The capacity CfDs extend through 2026 and obligate the utilities 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 forward capacity market prices received by the generation facilities in the ISO-NE capacity markets. The contracts have terms of up to 15 years beginning in 2009 and are subject to a sharing agreement with UI, whereby UI will share 20 percent of the costs and benefits of these contracts. CL&P's portion of the costs and benefits of these contracts will be paid by or refunded to CL&P's customers.

The contractual obligations table does not include CL&P's SS or LRS, or NSTAR Electric's or WMECO's default service contracts, the amounts of which vary with customers' energy needs. The contractual obligations table also does not include PSNH's short-term power supply management.

Renewable Energy: Renewable energy contracts include non-cancellable commitments under contracts of CL&P, NSTAR Electric, PSNH, and WMECO for the purchase of energy and capacity from renewable energy facilities. Such contracts have terms extending for 20 years at CL&P, up to 40 years at NSTAR Electric, up to 30 years for PSNH and 15 years for WMECO.

On September 20, 2013, NSTAR Electric and WMECO, along with two other Massachusetts utilities, signed a long-term commitment, as required by the DPU, to purchase wind power from six wind farms in Maine and New Hampshire for a combined estimated generating capacity of approximately 565 MW. On November 21, 2013, the utility companies provided a supplemental filing to the DPU
to reflect the termination of three of the six wind farms. Over the 15-year life of the remaining contracts, the utilities will pay an average price of less than $0.08 per kWh. On September 19, 2013, CL&P, along with another Connecticut utility, signed long-term commitments, as required by the PURA, to purchase approximately 250 MW of wind power from a Maine wind farm and 20 MW of solar power from sites in Connecticut, at a combined average price of less than $0.08 per kWh. The table above does not include these commitments, as such commitments are contingent on the future construction of the respective energy facilities. The table above also does not include NSTAR Electric's commitment to purchase 129 MW of renewable energy from a wind facility to be constructed offshore and certain other CL&P and NSTAR Electric commitments for the purchase of renewable energy and related products that are contingent on the future construction of facilities.

Peaker CfDs: In 2008, CL&P entered into three CfDs with developers of peaking generation units approved by the PURA (Peaker CfDs). These units have a total of approximately 500 MW of peaking capacity. As directed by the PURA, CL&P and UI have entered into a sharing agreement, whereby CL&P is responsible for 80 percent and UI for 20 percent of the net costs or benefits of these CfDs. The Peaker CfDs pay the developer the difference between capacity, forward reserve and energy market revenues and a cost-of-service payment stream for 30 years. The ultimate cost or benefit to CL&P under these contracts will depend on the costs of plant operation and the prices that the projects receive for capacity and other products in the ISO-NE markets. CL&P's portion of the amounts paid or received under the Peaker CfDs will be recoverable from or refunded to CL&P's customers.

Natural Gas Procurement: NU's natural gas distribution businesses have long-term contracts for the purchase, transportation and storage of natural gas in the normal course of business as part of its portfolio of supplies. These contracts extend through 2029.

Coal, Wood and Other: PSNH has entered into various arrangements for the purchase of wood, coal and the transportation services for fuel supply for its electric generating assets. Also included in the table above is a contract for capacity on the Portland Natural Gas Transmission System (PNGTS) pipeline that extends through 2018. The costs on this contract are not recoverable from customers.

Transmission Support Commitments: Along with other New England utilities, CL&P, NSTAR Electric, PSNH and WMECO entered into agreements in 1985 to support transmission and terminal facilities that were built to import electricity from the Hydro-Québec system in Canada. CL&P, NSTAR Electric, PSNH and WMECO are obligated to pay, over a 30-year period ending in 2020, their proportionate shares of the annual operation and maintenance expenses and capital costs of those facilities.

The total costs incurred under these agreements in 2013, 2012, and 2011 were as follows:
NU		For the Years Ended December 31,
(Millions of Dollars)		2013			2012⁽¹⁾			2011
Supply and Stranded Cost		$	141		$	216.8		$	156
Renewable Energy			91.3			48.7			5.1
Peaker CfDs			51.9			59.3			40.2
Natural Gas Procurement			349.8			243.1			191.7
Coal, Wood and Other			112.6			105.2			113.2
Transmission Support Commitments			24.9			24.8			18.1
		For the Years Ended December 31,
		2013												2012											2011
					NSTAR												NSTAR										NSTAR
(Millions of Dollars)		CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO		CL&P		Electric		PSNH		WMECO
Supply and
	Stranded Cost	$	77.6		$	32.4		$	29		$	2		$	158.2		$	36.3		$	30.5		$	0.9	$	114.9	$	80.9	$	40.8	$	0.3
Renewable Energy			-			84.9			6.4			-			-			60.2			4.1			-		-		61.8		5.1		-
Peaker CfDs			51.9			-			-			-			59.3			-			-			-		40.2		-		-		-
Coal, Wood and Other			-			-			112.6			-			-			-			105.2			-		-		-		113.2		-
Transmission Support
	Commitments		9.8			7.7			5.3			2.1			9.6			7.6			5.2			2		10.3		8.1		5.6		2.2
C. Contractual Obligations - Yankee Companies
CL&P, NSTAR Electric, PSNH and WMECO have decommissioning and plant closure cost obligations to the Yankee Companies, which have each completed the physical decommissioning of their respective nuclear facilities and are now engaged in the long-term storage of their spent fuel. The Yankee Companies collect decommissioning and closure costs through wholesale, FERC-approved rates charged under power purchase agreements with several New England utilities, including CL&P, NSTAR Electric, PSNH and WMECO. These companies in turn recover these costs from their customers through state regulatory commission-approved retail rates.

CL&P, NSTAR Electric, PSNH and WMECO's percentage share of the obligations to support the Yankee Companies under FERC-approved rate tariffs is the same as their respective ownership percentages in the Yankee Companies. For further information on the ownership percentages, see Note 1J, "Summary of Significant Accounting Policies - Equity Method Investments," to the financial statements.

The Yankee Companies have collected or are currently collecting amounts that management believes are adequate to recover the remaining decommissioning and closure cost estimates for the respective plants. Management believes CL&P, NSTAR Electric and WMECO will recover their shares of these decommissioning and closure obligations from their customers. PSNH has already recovered its share of these costs from its customers.

Spent Nuclear Fuel Litigation:
DOE Phase I Damages – In 1998, the Yankee Companies filed separate complaints against the DOE in the Court of Federal Claims seeking monetary damages resulting from the DOE's failure to begin accepting spent nuclear fuel for disposal by January 31, 1998 pursuant to the terms of the 1983 spent fuel and high level waste disposal contracts between the Yankee Companies and the DOE (DOE Phase I Damages). Phase I covered damages for the period 1998 through 2002. Following multiple appeals and cross-appeals in December 2012, the judgment awarding CYAPC $39.6 million, YAEC $38.3 million and MYAPC $81.7 million became final.

In January 2013, the proceeds from the DOE Phase I Damages Claim were received by the Yankee Companies and transferred to each Yankee Company's respective decommissioning trust. As a result of NU's consolidation of CYAPC and YAEC, the financial statements reflected an increase of $77.9 million in marketable securities for CYAPC and YAEC's Phase I damage awards that were invested in the nuclear decommissioning trusts in 2013.

On May 1, 2013, CYAPC, YAEC and MYAPC filed applications with the FERC to reduce rates in their wholesale power contracts through the application of the DOE proceeds for the benefit of customers. In its June 27, 2013 order, the FERC granted the proposed rate reductions, and changes to the terms of the wholesale power contracts to become effective on July 1, 2013. In accordance with the FERC order, CL&P, NSTAR Electric, PSNH and WMECO began receiving the benefit of the DOE proceeds, and the benefits have been or will be passed on to customers.

DOE Phase II Damages - In December 2007, the Yankee Companies each filed subsequent lawsuits against the DOE seeking recovery of actual damages incurred in the years following 2001 and 2002 related to the alleged failure of the DOE to provide for a permanent facility to store spent nuclear fuel generated in years after 2001 for CYAPC and YAEC and after 2002 for MYAPC (DOE Phase II Damages). On November 18, 2011, the court ordered the record closed in the YAEC case, and closed the record in the CYAPC and MYAPC cases subject to a limited opportunity of the government to reopen the records for further limited proceedings.

On November 15, 2013, the court issued a final judgment awarding CYAPC $126.3 million, YAEC $73.3 million, and MYAPC $35.8 million. On January 14, 2014, the Yankee Companies received a letter from the U.S. Department of Justice stating that the DOE will not appeal the court's final judgment. As of December 31, 2013, CL&P, NSTAR Electric, PSNH, WMECO, CYAPC, and YAEC have not reflected the impact of these expected receivables on their financial statements.

The methodology for applying the DOE Phase II Damages recovered from the DOE for the benefit of customers of CL&P, NSTAR Electric, PSNH and WMECO will be addressed in FERC rate proceedings.

DOE Phase III Damages – On August 15, 2013, the Yankee Companies each filed subsequent lawsuits against the DOE seeking recovery of actual damages incurred in the years 2009 through 2012. Responsive pleading from the Department of Justice was filed on November 18, 2013, and discovery is expected to begin once a protective order is in place.

(1) NSTAR amounts were included in NU beginning April 10, 2012.

D. Guarantees and Indemnifications
NU 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.

NU provided guarantees and various indemnifications on behalf of external parties as a result of the sales of former subsidiaries of NU Enterprises, with maximum exposures either not specified or not material.

NU also issued a guaranty under which, beginning at the time the Northern Pass Transmission line goes into commercial operation, NU will guarantee the financial obligations of NPT under the TSA in an amount not to exceed $25 million. NU's obligations under the guaranty expire upon the full, final and indefeasible payment of the guaranteed obligations.

Management does not anticipate a material impact to Net Income as a result of these various guarantees and indemnifications.

The following table summarizes NU's guarantees of its subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, as of December 31, 2013:
				Maximum Exposure
Subsidiary		Description		(in millions)				Expiration Dates

Various		Surety Bonds		$	69.2			2014 - 2016⁽¹⁾

Various		NE Hydro Companies' Long-Term Debt		$	3.5			Unspecified

NUSCO and RRR		Lease Payments for Vehicles and Real Estate		$	17.7			2019 and 2024
(1) Surety bond expiration dates reflect termination dates, the majority of which will be renewed or extended.

Many of the underlying contracts that NU parent guarantees, as well as certain surety bonds, contain credit ratings triggers that would require NU parent to post collateral in the event that the unsecured debt credit ratings of NU are downgraded.
E. FERC Base ROE Complaint
On September 30, 2011, several New England state attorneys general, state regulatory commissions, consumer advocates and other parties filed a joint complaint with the FERC under Sections 206 and 306 of the Federal Power Act alleging that the base ROE used in calculating formula rates for transmission service under the ISO-NE Open Access Transmission Tariff by NETOs, including CL&P, NSTAR Electric, PSNH and WMECO, is unjust and unreasonable. The complainants asserted that the current 11.14 percent rate, which became effective in 2006, is excessive due to changes in the capital markets and are seeking an order to reduce the rate, which would be effective October 1, 2011. In response, the NETOs filed testimony and analysis based on standard FERC methodology and precedent demonstrating that the base ROE of 11.14 percent remained just and reasonable. The FERC set the case for trial before a FERC ALJ after settlement negotiations were unsuccessful in August 2012.

Hearings before the FERC ALJ were held in May 2013, followed by the filing of briefs by the complainants, the Massachusetts municipal electric utilities (late interveners to the case), the FERC trial staff and the NETOs. The NETOs recommended that the current base ROE of 11.14 percent should remain in effect for the refund period (October 1, 2011 through December 31, 2012) and the prospective period (beginning when FERC issues its final decision). The complainants, the Massachusetts municipal electric utilities, and the FERC trial staff each recommended a base ROE of 9 percent or below.

On August 6, 2013, the FERC ALJ issued an initial decision, finding that the base ROE in effect from October 2011 through December 2012 was not reasonable under the standard application of FERC methodology, but leaving policy considerations and additional adjustments to the FERC. Using the established FERC methodology, the FERC ALJ determined that separate base ROEs should be set for the refund period and the prospective period. The FERC ALJ found those base ROEs to be 10.6 percent and 9.7 percent, respectively. The FERC may adjust the prospective period base ROE in its final decision to reflect movement in 10-year Treasury bond rates from the date that the case was filed (April 2013) to the date of the final decision. The parties filed briefs on this decision with the FERC, and a decision from the FERC is expected in 2014. Though NU cannot predict the ultimate outcome of this proceeding, in 2013 the Company recorded a series of reserves at its electric subsidiaries to recognize the potential financial impact from the FERC ALJ's initial decision for the refund period. The aggregate after-tax charge to earnings totaled $14.3 million at NU, which represents reserves of $7.7 million at CL&P, $3.4 million at NSTAR Electric, $1.4 million at PSNH and $1.8 million at WMECO.

On December 27, 2012, several additional parties filed a separate complaint concerning the NETOs' base ROE with the FERC. This complaint seeks to reduce the NETOs' base ROE effective January 1, 2013, effectively extending the refund period for an additional 15 months, and to consolidate this complaint with the joint complaint filed on September 30, 2011. The NETOs have asked the FERC to reject this complaint. The FERC has not yet acted on this complaint, and management is unable to predict the ultimate outcome or estimate the impacts of this complaint on financial position, results of operations or cash flows.

As of December 31, 2013, the CL&P, NSTAR Electric, PSNH, and WMECO aggregate shareholder equity invested in their transmission facilities was approximately $2.3 billion. As a result, each 10 basis point change in the prospective period authorized base ROE would change annual consolidated earnings by an approximate $2.3 million.

F. DPU Safety and Reliability Programs - CPSL
Since 2006, NSTAR Electric has been recovering incremental costs related to the DPU-approved Safety and Reliability Programs. From 2006 through 2011, cumulative costs associated with the CPSL program resulted in an incremental revenue requirement to customers of approximately $83 million. These amounts included incremental operations and maintenance costs and the related revenue requirement for specific capital investments relative to the CPSL programs.

On May 28, 2010, the DPU issued an order on NSTAR Electric's 2006 CPSL cost recovery filing (the May 2010 Order). In October 2010, NSTAR Electric filed a reconciliation of the cumulative CPSL program activity for the periods 2006 through 2009 with the DPU in order to determine a proposed rate adjustment. The DPU allowed the proposed rates to go into effect January 1, 2011, subject to final reconciliation of CPSL program costs through a future DPU proceeding. In February 2013, NSTAR Electric updated the October 2010 filing with final activity through 2011. NSTAR Electric recorded its 2006 through 2011 revenues under the CPSL programs based on the May 2010 Order.

NSTAR Electric cannot predict the timing of a final DPU order related to its CPSL filings for the period 2006 through 2011. While management does not believe that any subsequent DPU order would result in revenues that are materially different than the amounts already recognized, it is reasonably possible that an order could have a material impact on NSTAR Electric's results of operations, financial position and cash flows.

The April 4, 2012 DPU-approved comprehensive merger settlement agreement with the Massachusetts Attorney General stipulates that NSTAR Electric must incur a revenue requirement of at least $15 million per year for 2012 through 2015 related to these programs. CPSL revenues will end once NSTAR Electric has recovered its 2015-related CPSL costs. Realization of these revenues is subject to maintaining certain performance metrics over the four-year period and DPU approval. As of December 31, 2013, NSTAR Electric was in compliance with the performance metrics and has recognized the entire $15 million revenue requirement during 2013 and 2012.

G. Basic Service Bad Debt Adder
In accordance with a generic DPU order, electric utilities in Massachusetts recover the energy-related portion of bad debt costs in their Basic Service rates. In 2007, NSTAR Electric filed its 2006 Basic Service reconciliation with the DPU proposing an adjustment related to the increase of its Basic Service bad debt charge-offs. The DPU issued an order approving the implementation of a revised Basic Service rate but instructed NSTAR Electric to reduce distribution rates by an amount equal to the increase in its Basic Service bad debt charge-offs. This adjustment to NSTAR Electric's distribution rates would eliminate 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. In 2012, the SJC vacated the DPU order and remanded the matter to the DPU for further review. The DPU has not taken any action on the remand.

NSTAR Electric deferred approximately $34 million of costs associated with energy-related bad debt as a regulatory asset through 2011 as NSTAR Electric had concluded that it was probable that these costs would ultimately be recovered from customers. Due to the delays and the duration of the proceedings, NSTAR Electric concluded that while an ultimate outcome on the matter in its favor remained "more likely than not," it could no longer be deemed "probable." As a result, NSTAR Electric recognized a reserve related to the regulatory asset in 2012. NSTAR Electric will continue to maintain the reserve until the proceeding has been concluded with the DPU.

H. Litigation and Legal Proceedings
NU, including CL&P, NSTAR Electric, PSNH and WMECO, are involved in legal, tax and regulatory proceedings regarding matters arising in the ordinary course of business, which involve management's assessment to determine the probability of whether a loss will occur and, if probable, its best estimate of probable loss. The Company records and discloses losses when these losses are probable and reasonably estimable, discloses matters when losses are probable but not estimable or reasonably possible, and expenses legal costs related to the defense of loss contingencies as incurred.

LEASES

LEASES	12 Months Ended
LEASES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Leases of Lessee Disclosure [Text Block]	'
	LEASES

	NU, including CL&P, NSTAR Electric, PSNH and WMECO, has entered into lease agreements, some of which are capital leases, for the use of data processing and office equipment, vehicles, service centers, and office space. In addition, CL&P, PSNH and WMECO incur costs associated with leases entered into by NUSCO and RRR, which are included below in their respective operating lease rental expenses and future minimum rental payments. These intercompany lease amounts are eliminated on an NU consolidated basis. The provisions of the NU, CL&P, NSTAR Electric, PSNH, and WMECO lease agreements generally contain renewal options. Certain lease agreements contain payments impacted by the commercial paper rate plus a credit spread or the consumer price index.

	Operating lease rental payments charged to expense are as follows:
									NSTAR
	(Millions of Dollars)		NU ⁽¹⁾			CL&P			Electric			PSNH			WMECO
	2013		$	16.3		$	8.1		$	6.7		$	1.7		$	2.9
	2012			14.8			8.2			6.2			2.5			3
	2011			8.4			8.3			19.8			2.1			2.8

	NSTAR amounts were included in NU beginning April 10, 2012.


	Future minimum rental payments to external third parties excluding executory costs, such as property taxes, state use taxes, insurance, and maintenance, under long-term noncancelable leases, as of December 31, 2013 are as follows:

	Capital Leases
	(Millions of Dollars)	NU			CL&P			PSNH
	2014	$	2.6		$	2.1		$	0.4
	2015		2.4			2			0.4
	2016		2.2			1.9			0.3
	2017		2.1			2			0.1
	2018		2.1			2			0.1
	Thereafter		5.4			5.4			0
	Future minimum lease payments		16.8			15.4			1.3
	Less amount representing interest		6.1			6.1			0
	Present value of future minimum lease payments	$	10.7		$	9.3		$	1.3
	Operating Leases
	(Millions of Dollars)	NU			CL&P			NSTAR Electric			PSNH			WMECO
	2014	$	20.1		$	4		$	10.9		$	1		$	1.1
	2015		18.1			3.6			10.1			0.9			0.7
	2016		15.4			2.9			8.9			0.8			0.5
	2017		12.4			1.7			7.7			0.6			0.3
	2018		8.5			1.2			5.1			0.5			0.2
	Thereafter		22.3			4.7			11.7			1.3			1
	Future minimum lease payments	$	96.8		$	18.1		$	54.4		$	5.1		$	3.8
	CL&P entered into certain contracts for the purchase of energy that qualify as leases. These contracts do not have minimum lease payments and therefore are not included in the tables above. However, such contracts have been included in the contractual obligations table in Note 12B, "Commitments and Contingencies - Long-Term Contractual Arrangements," to the financial statements.

FAIR_VALUE_OF_FINANCIAL_INSTRU

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
FAIR VALUE OF FINANCIAL INSTRUMENTS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Fair Value Disclosures [Text Block]	'
	14. 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, Long-Term Debt and Rate Reduction Bonds: 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 fixed-rate long-term debt securities and RRBs 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. Adjustable rate long-term debt securities are assumed to have a fair value equal to their carrying value. 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 December 31,
			2013				2012
	NU		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)		Amount		Value		Amount		Value
	Preferred Stock Not
		Subject to Mandatory Redemption	$	155.6	$	152.7	$	155.6	$	152.2
	Long-Term Debt			8,310.20		8,443.10		7,963.50		8,640.70
	Rate Reduction Bonds			-		-		82.1		83
			As of December 31, 2013
			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	$	110.5	$	43	$	42.2	$	-	$	-	$	-	$	-
	Long-Term Debt			2,741.20		2,952.80		1,801.10		1,888.00		1,049.00		1,073.90		629.4		640.1

			As of December 31, 2012
			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	$	110	$	43	$	42.2	$	-	$	-	$	-	$	-
	Long-Term Debt			2,862.80		3,295.40		1,602.60		1,818.80		997.9		1,088.00		605.3		660.4
	Rate Reduction Bonds			-		-		43.5		43.9		29.3		29.6		9.4		9.5
	Derivative Instruments: Derivative instruments are carried at fair value. For further information, see Note 5, "Derivative Instruments," to the financial statements.

	Other Financial Instruments: Investments in marketable securities are carried at fair value. For further information, see Note 1H, "Summary of Significant Accounting Policies - Fair Value Measurements," and Note 6, "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.

ACCUMULATED_OTHER_COMPREHENSIV

ACCUMULATED OTHER COMPREHENSIVE INCOME	12 Months Ended
ACCUMULATED OTHER COMPREHENSIVE INCOME	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Comprehensive Income Note [Text Block]	'
	15. ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)

	The changes in accumulated other comprehensive income/(loss) by component, net of tax effect, is as follows:
			For the Year Ended December 31, 2013
						Unrealized
			Qualified Cash			Gains/(Losses) on			Pension, SERP
			Flow Hedging			Available-for-Sale			and PBOP
	(Millions of Dollars)		Instruments			Securities			Benefit Plans			Total
	AOCI as of January 1, 2013		$	-16.4		$	1.3		$	-57.8		$	-72.9

	Other Comprehensive Income Before Reclassifications			-			-0.9			19.4			18.5
	Amounts Reclassified from AOCI			2			-			6.4			8.4
	Net Other Comprehensive Income			2			-0.9			25.8			26.9
	AOCI as of December 31, 2013		$	-14.4		$	0.4		$	-32		$	-46
	NU'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 tax effects of Pension, SERP and PBOP Benefit Plan actuarial gains and losses that arose during 2013, 2012 and 2011 were recognized in AOCI as a net deferred tax liability of $11.4 million in 2013 and net deferred tax assets of $6.2 million and $10.2 million in 2012 and 2011, respectively. In addition, the tax effect of the loss on qualified cash flow hedging instrument settlements that arose during 2011 was recognized in AOCI as a deferred tax asset of $10.2 million in 2011. The tax effects of unrealized gains and losses on available-for-sale securities that arose during 2013, 2012 and 2011 were not material.

	The following table sets forth the amount reclassified from AOCI by component and the impacted line item on the statements of income:
		For the Years Ended December 31,
		2013			2012			2011
		Amount Reclassified			Amount Reclassified			Amount Reclassified			Statements of Income
	(Millions of Dollars)	from AOCI			from AOCI			from AOCI			Line Item Impacted
	Qualified Cash Flow Hedging Instruments	$	-3.4		$	-3.3		$	-1.3		Interest Expense
	Tax Effect		1.4			1.3			0.6		Income Tax Expense
	Qualified Cash Flow Hedging Instruments, Net of Tax	$	-2		$	-2		$	-0.7

	Pension, SERP and PBOP Benefit Plan Costs:
	Amortization of Actuarial Losses	$	-10.5		$	-8.9		$	-5.7		Operations and Maintenance⁽¹⁾
	Amortization of Prior Service Cost		-0.2			-0.2			-0.3		Operations and Maintenance⁽¹⁾
	Amortization of Transition Obligation		-			-0.2			-0.2		Operations and Maintenance⁽¹⁾
	Total Pension, SERP and PBOP Benefit Plan Costs		-10.7			-9.3			-6.2		Operations and Maintenance⁽¹⁾
	Tax Effect		4.3			3.5			2.3		Income Tax Expense
	Pension, SERP and PBOP Benefit Plan Costs,
	Net of Tax	$	-6.4		$	-5.8		$	-3.9

	Total Amount Reclassified from AOCI, Net of Tax	$	-8.4		$	-7.8		$	-4.6

	(1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 10A, "Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pensions," for further information.

	As of December 31, 2013, it is estimated that a pre-tax amount of $3.4 million ($0.7 million for CL&P, $2 million for PSNH and $0.5 million for WMECO) will be reclassified from AOCI as a decrease to Net Income over the next 12 months as a result of the amortization of the interest rate swap agreements, which have been settled. In addition, it is estimated that a pre-tax amount of $6.5 million will be reclassified from AOCI as a decrease to Net Income over the next 12 months as a result of the amortization of Pension, SERP and PBOP costs.

DIVIDEND_RESTRICTIONS

DIVIDEND RESTRICTIONS	12 Months Ended
DIVIDEND RESTRICTIONS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Dividend Payment Restrictions [Table Text Block]	'
	16. DIVIDEND RESTRICTIONS

	NU parent's ability to pay dividends may be affected by certain state statutes, the ability of its subsidiaries to pay common dividends and the leverage restriction tied to its consolidated total debt to total capitalization ratio requirement in its revolving credit agreement.

	CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends for lawful and legitimate business purposes from retained earnings. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of NU, CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at all times. As of December 31, 2013, all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $2.1 billion for NU, $961.5 million for CL&P, $1.4 billion for NSTAR Electric, $438.5 million for PSNH and $181 million for WMECO as of December 31, 2013. As of December 31, 2013, NU, CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends. PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 2013, approximately $12.7 million of PSNH's Retained Earnings was subject to restriction under its FERC hydroelectric license conditions and PSNH was in compliance with this provision.

COMMON_SHARES

COMMON SHARES	12 Months Ended
COMMON SHARES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Stock by Class [Text Block]	'
	17. COMMON SHARES

	The following table sets forth the NU 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	Issued
		Per Share		As of December 31,	As of December 31,
		Par Value		2013 and 2012	2013		2012
	NU	$	5	380,000,000		333,113,492		332,509,383
	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 December 31, 2013 and 2012, there were 17,796,672 and 18,455,749 NU common shares held as treasury shares, respectively.

PREFFERED_STOCK_NOT_SUBJECT_TO

PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	12 Months Ended
PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Preferred Stock Text Block	'
	18. PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION

	The CL&P and NSTAR Electric preferred stock is not subject to mandatory redemption and is presented as a noncontrolling interest of a subsidiary in NU's financial statements.

	CL&P Preferred Stock: CL&P's charter authorizes it to issue up to 9 million shares of preferred stock ($50 par value per share). CL&P amended its charter on January 3, 2012 to remove references to various series of preferred stock, including the Class A preferred stock, which were no longer outstanding. The issuance of additional preferred shares would be subject to PURA approval. Preferred stockholders have liquidation rights equal to the par value of the preferred stock, which they would receive in preference to any distributions to any junior stock. Were there to be a shortfall, all preferred stockholders would share ratably in available liquidation assets.
	NSTAR Electric Preferred Stock: NSTAR Electric is authorized to issue 2,890,000 shares ($100 par value per share). NSTAR Electric has two outstanding series of cumulative preferred stock. Upon liquidation, holders of cumulative preferred stock are entitled to receive a liquidation preference before any distribution to holders of common stock. The liquidation preference for each outstanding series of cumulative preferred stock is equal to the par value, plus accrued and unpaid dividends. Were there to be a shortfall, holders of cumulative preferred stock would share ratably in available liquidation assets.

	Details of preferred stock not subject to mandatory redemption are as follows (in millions except in redemption price and shares):
					Redemption Price		Shares Outstanding as of	As of December 31,
	Series				Per Share		December 31, 2013 and 2012	2013		2012
	CL&P
	$	1.9		Series of 1947	$	52.5	163,912	$	8.2	$	8.2
	$	2		Series of 1947	$	54	336,088		16.8		16.8
	$	2.04		Series of 1949	$	52	100,000		5		5
	$	2.2		Series of 1949	$	52.5	200,000		10		10
		3.9	%	Series of 1949	$	50.5	160,000		8		8
	$	2.06		Series E of 1954	$	51	200,000		10		10
	$	2.09		Series F of 1955	$	51	100,000		5		5
		4.5	%	Series of 1956	$	50.75	104,000		5.2		5.2
		4.96	%	Series of 1958	$	50.5	100,000		5		5
		4.5	%	Series of 1963	$	50.5	160,000		8		8
		5.28	%	Series of 1967	$	51.43	200,000		10		10
	$	3.24		Series G of 1968	$	51.84	300,000		15		15
		6.56	%	Series of 1968	$	51.44	200,000		10		10
	Total CL&P						2,324,000	$	116.2	$	116.2

	NSTAR Electric
		4.25	%	Series	$	103.625	180,000	$	18	$	18
		4.78	%	Series	$	102.8	250,000		25		25
	Total NSTAR Electric						430,000	$	43	$	43
	Fair Value Adjustment due to Merger with NSTAR								-3.6		-3.6
	Total NU - Preferred Stock of Subsidiaries							$	155.6	$	155.6

COMMON_SHARESHOLDERS_EQUITY_AN

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU)	12 Months Ended
	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Stockholders' Equity Note Disclosure [Text Block]	'
	19	COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS

	A summary of the changes in Common Shareholders' Equity and Noncontrolling Interests of NU is as follows:

									Noncontrolling
			Common						Interest -
			Shareholders'		Noncontrolling		Total		Preferred Stock
	(Millions of Dollars)		Equity		Interest		Equity		of Subsidiaries
	Balance as of January 1, 2011		$	3,811.20	$	1.5	$	3,812.70	$	116.2
	Net Income			400.5		-		400.5		-
	Dividends on Common Shares			-195.6		-		-195.6		-
	Dividends on Preferred Stock			-5.6		-		-5.6		-5.6
	Issuance of Common Shares			5.9		-		5.9		-
	Contributions to NPT			-		1.2		1.2		-
	Other Transactions, Net			23.9		-		23.9		-
	Net Income Attributable to Noncontrolling Interests			-0.3		0.3		-		5.6
	Other Comprehensive Loss (Note 15)			-27.3		-		-27.3		-
	Balance as of December 31, 2011		$	4,012.70	$	3	$	4,015.70	$	116.2
	Net Income			533.1		-		533.1		-
	Purchase Price of NSTAR ⁽¹⁾			5,038.30		-		5,038.30		-
	Other Equity Impacts of Merger with NSTAR ⁽²⁾			3.4		-3.4		-		39.4
	Dividends on Common Shares			-375.5		-		-375.5		-
	Dividends on Preferred Stock			-7		-		-7		-7
	Issuance of Common Shares			13.3		-		13.3		-
	Contributions to NPT			-		0.3		0.3		-
	Other Transactions, Net			21.1		-		21.1		-
	Net Income Attributable to Noncontrolling Interests			-0.1		0.1		-		7
	Other Comprehensive Loss (Note 15)			-2.2		-		-2.2		-
	Balance as of December 31, 2012		$	9,237.10	$	-	$	9,237.10	$	155.6
	Net Income			793.7		-		793.7		-
	Dividends on Common Shares			-462.7		-		-462.7		-
	Dividends on Preferred Stock			-7.7		-		-7.7		-7.7
	Issuance of Common Shares			11.1		-		11.1		-
	Other Transactions, Net			13.2		-		13.2		-
	Net Income Attributable to Noncontrolling Interests			-		-		-		7.7
	Other Comprehensive Income (Note 15)			26.8		-		26.8		-
	Balance as of December 31, 2013		$	9,611.50	$	-	$	9,611.50	$	155.6
	(1) On April 10, 2012, NU issued approximately 136 million common shares to the NSTAR shareholders in connection with the merger. See Note 2, "Merger of NU and NSTAR," for further information.

	(2) The preferred stock of NSTAR Electric is not subject to mandatory redemption and has been presented as a noncontrolling interest in NSTAR Electric in NU's financial statements. In addition, upon completion of the merger, an NSTAR subsidiary that held 25 percent of NPT was merged into NUTV, resulting in NUTV owning 100 percent of NPT. Accordingly, the noncontrolling interest balance was eliminated and 100 percent ownership of NPT is reflected in Common Shareholders' Equity as of December 31, 2013 and 2012.

	For the years ended December 31, 2013, 2012 and 2011, there was no change in ownership of the common equity of CL&P and NSTAR Electric.

EARNINGS_PER_SHARE

EARNINGS PER SHARE	12 Months Ended
EARNINGS PER SHARE	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Earnings Per Share [Text Block]	'
	20. 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 if certain share-based compensation awards are converted into common shares. For the years ended December 31, 2013, 2012 and 2011, there were 1,575, 4,266, and 4,314, respectively, antidilutive share awards excluded from the computation.

	The following table sets forth the components of basic and diluted EPS:
			For the Years Ended December 31,
	(Millions of Dollars, except share information)		2013		2012		2011
	Net Income Attributable to Controlling Interest		$	786	$	525.9	$	394.7

	Weighted Average Common Shares Outstanding:
		Basic		315,311,387		277,209,819		177,410,167
		Dilutive Effect		899,773		783,812		394,401
		Diluted		316,211,160		277,993,631		177,804,568
	Basic EPS		$	2.49	$	1.9	$	2.22
	Diluted EPS		$	2.49	$	1.89	$	2.22
	On April 10, 2012, NU issued approximately 136 million common shares as a result of the merger with NSTAR, which are reflected in weighted average common shares outstanding as of December 31, 2013 and 2012.

	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	12 Months Ended
SEGMENT INFORMATION	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Segment Reporting Disclosure [Text Block]	'
	21. SEGMENT INFORMATION

	Presentation: NU 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 NU's total consolidated revenues for the years ended December 31, 2013, 2012 and 2011. 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 NU's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of NU parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of NU parent, 2) the revenues and expenses of NU's service company, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, and 4) the results of other non-regulated 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, for certain subsidiaries, the capitalized portions of pension expense.

	NU's reportable segments are determined based upon the level at which NU's chief operating decision maker assesses performance and makes decisions about the allocation of company resources. Each of NU's subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, has one reportable segment. NU's operating segments and reporting units are consistent with its reportable business segments.

	NSTAR amounts were included in NU beginning April 10, 2012.

	NU's segment information for the years ended December 31, 2013, 2012 and 2011 is as follows:
			For the Year Ended December 31, 2013
			Electric			Natural Gas
	(Millions of Dollars)		Distribution			Distribution			Transmission			Other			Eliminations			Total
	Operating Revenues		$	5,362.30		$	855.8		$	978.7		$	777.5		$	-673.1		$	7,301.20
	Depreciation and Amortization			-604.8			-66.7			-136.2			-62.2			10.2			-859.7
	Other Operating Expenses			-3,927.70			-659.4			-281.8			-715			671.8			-4,912.10
	Operating Income			829.8			129.7			560.7			0.3			8.9			1,529.40
	Interest Expense			-175			-33.1			-100.3			-35.5			5.2			-338.7
	Interest Income			4.1			-			0.7			5.4			-5.6			4.6
	Other Income, Net			12.9			0.8			10.9			858.9			-858.2			25.3
	Income Tax (Expense)/Benefit			-240			-36.5			-182.1			31.9			-0.2			-426.9
	Net Income			431.8			60.9			289.9			861			-849.9			793.7
	Net Income Attributable
		to Noncontrolling Interests		-4.8			-			-2.9			-			-			-7.7
	Net Income Attributable
		to Controlling Interest	$	427		$	60.9		$	287		$	861		$	-849.9		$	786
	Total Assets (as of)		$	17,260.00		$	2,759.70		$	6,745.80		$	11,842.40		$	-10,812.40		$	27,795.50
	Cash Flows Used for
		Investments in Plant	$	639		$	168.1		$	618.5		$	31.2		$	-		$	1,456.80
			For the Year Ended December 31, 2012
			Electric			Natural Gas
	(Millions of Dollars)		Distribution			Distribution			Transmission			Other			Eliminations			Total
	Operating Revenues		$	4,716.50		$	572.9		$	861.5		$	803.8		$	-680.9		$	6,273.80
	Depreciation and Amortization			-530.3			-49.1			-109.2			-56.4			4.2			-740.8
	Other Operating Expenses			-3,585.40			-445.2			-251.6			-817			684.4			-4,414.80
	Operating Income/(Loss)			600.8			78.6			500.7			-69.6			7.7			1,118.20
	Interest Expense			-165.6			-31.3			-96.7			-43.6			7.3			-329.9
	Interest Income			2.8			-			0.4			7.1			-7.1			3.2
	Other Income, Net			8.9			0.4			7.3			795			-795.1			16.5
	Income Tax (Expense)/Benefit			-150.2			-16.9			-159.2			55.5			-4.1			-274.9
	Net Income			296.7			30.8			252.5			744.4			-791.3			533.1
	Net Income Attributable
		to Noncontrolling Interests		-4.4			-			-2.8			-			-			-7.2
	Net Income Attributable
		to Controlling Interest	$	292.3		$	30.8		$	249.7		$	744.4		$	-791.3		$	525.9
	Total Assets (as of)		$	18,047.30		$	2,717.40		$	6,187.70		$	18,832.60		$	-17,482.20		$	28,302.80
	Cash Flows Used for
		Investments in Plant	$	611.7		$	148.7		$	663.6		$	48.3		$	-		$	1,472.30
			For the Year Ended December 31, 2011
			Electric			Natural Gas
	(Millions of Dollars)		Distribution			Distribution			Transmission			Other			Eliminations			Total
	Operating Revenues		$	3,343.10		$	430.8		$	635.4		$	541.3		$	-484.9		$	4,465.70
	Depreciation and Amortization			-337.2			-27.7			-84			-16.8			2.5			-463.2
	Other Operating Expenses			-2,637.40			-333.5			-188.2			-534.1			484.9			-3,208.30
	Operating Income/(Loss)			368.5			69.6			363.2			-9.6			2.5			794.2
	Interest Expense			-123.8			-21			-76.7			-33.7			4.8			-250.4
	Interest Income			3.7			-			0.5			5.3			-5.3			4.2
	Other Income, Net			11.6			1.3			10.7			455.2			-455.3			23.5
	Income Tax (Expense)/Benefit			-67.6			-18.2			-95.6			14.3			-3.9			-171
	Net Income			192.4			31.7			202.1			431.5			-457.2			400.5
Net Income Attributable
	to Noncontrolling Interests		-3.3			-			-2.5			-			-			-5.8
Net Income Attributable
	to Controlling Interest	$	189.1		$	31.7		$	199.6		$	431.5		$	-457.2		$	394.7
Cash Flows Used for
	Investments in Plant	$	540.7		$	98.2		$	388.9		$	48.9		$	-		$	1,076.70

VARIABLE_INTEREST_ENTITIES

VARIABLE INTEREST ENTITIES	12 Months Ended
VARIABLE INTEREST ENTITIES	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Variable Interest Entities Text Block	'
	22. VARIABLE INTEREST ENTITIES

	The Company's variable interests outside of the consolidated group are not material and consist of contracts that are required by regulation and provide for regulatory recovery of contract costs and benefits through customer rates. NU, CL&P and NSTAR Electric hold variable interests in variable interest entities (VIEs) through agreements with certain entities that own single renewable energy or peaking generation power plants and with other independent power producers. NU, CL&P and NSTAR Electric do not control the activities that are economically significant to these VIEs or provide financial or other support to these VIEs. Therefore, NU, CL&P and NSTAR Electric do not consolidate any power plant VIEs.

SUBSEQUENT_EVENTS

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Subsequent Events [Text Block]	'
	23. SUBSEQUENT EVENTS

	See Note 9, "Long-Term Debt," for information regarding the January 2014 Yankee Gas long-term debt issuance.

	See Note 3, "Regulatory Accounting," for information regarding the February 2014 PURA decision on CL&P's request for approval to recover the restoration costs of the 2012 and 2011 major storms.

	See Note 12C, "Commitments and Contingencies - Contractual Obligations - Yankee Companies," for information regarding a January 2014 letter received from the U.S. Department of Justice stating that the DOE will not appeal the court's final judgment on the Yankee Companies' lawsuits against the DOE.

QUARTERLY_FINANCIAL_DATA_Unaud

QUARTERLY FINANCIAL DATA (Unaudited)	12 Months Ended
QUARTERLY FINANCIAL DATA (Unaudited)	Dec. 31, 2013
Quarterly Financial Data [Abstract]	'
Quarterly Financial Information [Text Block]	'
	QUARTERLY FINANCIAL DATA (UNAUDITED)
	NU Consolidated Statements of Quarterly Financial Data	Quarter Ended
	(Millions of Dollars, except per share information)	March 31,		June 30,		September 30,		December 31,
	2013
	Operating Revenues	$	1,995.00	$	1,635.90	$	1,892.60	$	1,777.70
	Operating Income		418.9		350.6		399.3		360.6
	Net Income		230		173.1		211.4		179.2
	Net Income Attributable to Controlling Interest		228.1		171		209.5		177.4
	Basic and Diluted EPS (a)	$	0.72	$	0.54	$	0.66	$	0.56

	2012 ⁽¹⁾
	Operating Revenues	$	1,099.60	$	1,628.70	$	1,861.50	$	1,684.00
	Operating Income		214.4		159.5		412.9		331.4
	Net Income		100.8		46.2		209.5		176.6
	Net Income Attributable to Controlling Interest		99.3		44.3		207.6		174.7
	Basic and Diluted EPS (a)	$	0.56	$	0.15	$	0.66	$	0.55

	(a) The summation of quarterly EPS data may not equal annual data due to rounding.

	Statements of Quarterly Financial Data	Quarter Ended
	(Millions of Dollars)	March 31,		June 30,		September 30,		December 31,
	CL&P
	2013
	Operating Revenues	$	624.1	$	569.3	$	648.4	$	600.5
	Operating Income		149.7		136.8		133.9		119.2
	Net Income		85		67.9		66.3		60.2

	2012
	Operating Revenues	$	592	$	562.1	$	658.1	$	595.2
	Operating Income		111.9		40.4		139.7		135
	Net Income		54		6.9		74.9		73.9

	NSTAR Electric
	2013
	Operating Revenues	$	592.3	$	570.4	$	753.9	$	576.9
	Operating Income		94.5		112.5		192		109.2
	Net Income		48.1		58		107		55.4

	2012
	Operating Revenues	$	556.5	$	534.6	$	693.7	$	516.2
	Operating Income		22.5		93.9		194.1		70.9
	Net Income		3.9		45.5		106.8		34

	PSNH
	2013
	Operating Revenues	$	273.8	$	216.1	$	218.6	$	226.9
	Operating Income		58.1		54.3		56.6		56.2
	Net Income		29		27.2		28.4		26.8

	2012
	Operating Revenues	$	243	$	255.1	$	256.9	$	233
	Operating Income		45.4		47		61.3		51.4
	Net Income		21.3		21.2		27.2		27.2

	WMECO
	2013
	Operating Revenues	$	125	$	115	$	121.8	$	110.9
	Operating Income		35.6		32.4		28.9		22.4
	Net Income		18.6		16.4		15		10.4

	2012
	Operating Revenues	$	114	$	106.8	$	112.5	$	107.9
	Operating Income		28.7		25.1		28.1		28.9
Net Income		14.2		11.1		14.1		15.1
(1) NSTAR amounts were included in NU beginning April 10, 2012.

SIGNIFCANT_ACCOUNTING_POLICIES

SIGNIFCANT ACCOUNTING POLICIES (Policies)	12 Months Ended
SIGNIFCANT ACCOUNTING POLICIES (Policies)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Organization Consolidation And Presentation Of Financial Statements Disclosure Text Block	'
	The consolidated financial statements of NU, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of NU, NSTAR Electric and PSNH and the financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements."

	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.

	NU's consolidated financial information includes NSTAR and its subsidiaries' results of operations beginning April 10, 2012. The information disclosed for NSTAR Electric represents its results of operations for each of the years ended December 31, 2013, 2012 and 2011 presented on a comparable basis. NU did not apply "push-down accounting" to NSTAR Electric, whereby the adjustments of assets and liabilities to fair value and the resultant goodwill would be shown on the financial statements of the acquired subsidiary.

	NU consolidates CYAPC and YAEC as 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 NU financial statements. For CL&P, NSTAR Electric, PSNH and WMECO, the investments in CYAPC and YAEC continue to be accounted for under the equity method. See Note 1J, "Summary of Significant Accounting Policies – Equity Method Investments," for further information.

	NU's utility subsidiaries are subject to the application of accounting guidance for entities with rate-regulated operations that considers the effect of regulation resulting from differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. NU's utility subsidiaries' energy delivery business is subject to rate-regulation that is based on cost recovery and meets the criteria for application of rate-regulated accounting. See Note 3, "Regulatory Accounting," for further information.

	Certain reclassifications of prior year data were made in the accompanying balance sheets for NU, NSTAR Electric, PSNH and WMECO and the statements of cash flows for all companies presented. These reclassifications were made to conform to the current year presentation.

	In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by NU or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of NU. The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on the balance sheets of NU, CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Board of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric.

Receivables Policy Text Block	'
	NU, including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at net realizable value by maintaining a provision for uncollectible amounts. This provision is determined based upon a variety of factors, including applying an estimated uncollectible account percentage to each receivable aging category, based upon historical collection and write-off experience and management's assessment of collectibility from individual customers. Management assesses the collectibility of receivables, and if circumstances change, collectibility estimates are adjusted accordingly. Receivable balances are written off against the provision for uncollectible accounts when the accounts are terminated and these balances are deemed to be uncollectible.

Fair Value Of Financial Instruments Policy	'
	H. 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 investment valuations used to calculate the funded status of pension and PBOP plans and nonrecurring fair value measurements of nonfinancial assets such as goodwill and AROs.

	Fair Value Hierarchy: In measuring fair value, NU 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. NU evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and NU'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 NU's fair value measurements are described in Note 2, "Merger of NU and NSTAR," Note 5, "Derivative Instruments," Note 6, "Marketable Securities," Note 7, "Asset Retirement Obligations," and Note 14, "Fair Value of Financial Instruments," to the financial statements.

	Certain of NSTAR's stock-based compensation awards, including deferred shares, performance shares and all outstanding stock options, were replaced with NU awards using the exchange ratio upon consummation of the merger. In accordance with accounting guidance for business combinations, the portion of the fair value of these awards attributable to service provided prior to the merger was included in the purchase price as it represented consideration transferred in the merger. See Note 10D, "Employee Benefits – Share-Based Payments," for further information.

	Purchase Price Allocation: The allocation of the total purchase price to the estimated fair values of the assets acquired and liabilities assumed was determined based on the accounting guidance for fair value measurements, which defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The allocation of the total purchase price included adjustments to record the fair value of NSTAR's unregulated telecommunications business, regulatory assets not earning a return, lease agreements, long-term debt and the preferred stock of NSTAR Electric. The fair values of NSTAR's assets and liabilities were determined based on significant estimates and assumptions, including Level 3 inputs, that were judgmental in nature. These estimates and assumptions included the timing and amounts of projected future cash flows and discount rates reflecting risk inherent in future cash flows.

	The following methods and assumptions were used to estimate the fair value of each of the following financial instruments:

	Preferred Stock, Long-Term Debt and Rate Reduction Bonds: 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 fixed-rate long-term debt securities and RRBs 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. Adjustable rate long-term debt securities are assumed to have a fair value equal to their carrying value. The fair values provided in the tables below are classified as Level 2 within the fair value hierarchy.
Allowance For Funds Used During Construction Policy	'
	M. Allowance for Funds Used During Construction
	AFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the Regulated companies' utility plant. The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Other Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income. AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense.
	The Regulated companies' average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings as well as a company's capitalization (preferred stock, long-term debt and common equity). The average rate is applied to average eligible CWIP amounts to calculate AFUDC.

Other Taxes Policy	'Certain sales taxes are also collected by NU'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	'
	The rates charged to the customers of NU's Regulated companies are designed to collect each company's costs to provide service, including a return on investment. Therefore, the accounting policies of the Regulated companies reflect the application of accounting guidance for entities with rate-regulated operations and reflect the effects of the rate-making process.

	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	'
	I. Derivative Accounting
	Many of the Regulated companies' contracts for the purchase and sale of energy or energy-related products are derivatives. The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts, as costs are recovered from, or refunded to, customers in future rates.

	The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of the normal exception, and determination of the fair value of derivative contracts. All of these judgments can have a significant impact on the financial statements.

	The judgment applied in the election of the normal exception (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then the normal exception and accrual accounting is terminated and fair value accounting is applied prospectively.

	The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. Changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.

	For further information regarding derivative contracts, see Note 5, "Derivative Instruments," to the financial statements.
	5. DERIVATIVE INSTRUMENTS


	Fair Value Measurements of Derivative Instruments
	Valuation of Derivative Instruments: Derivative contracts classified as Level 2 in the fair value hierarchy relate to the financial contracts for natural gas futures and forward contracts to purchase energy. Prices are obtained from broker quotes and are based on actual market activity. The contracts are valued using the mid-point of the bid-ask spread. 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.

Marketable Securities Policy	'
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: NU, 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. NU, 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.

	These liabilities are estimated on an undiscounted basis and do not assume that any amounts are recoverable from insurance companies or other third parties. The environmental reserves include sites at different stages of discovery and remediation and do not include any unasserted claims.

	It is possible that new information or future developments could require a reassessment of the potential exposure to related environmental matters. As this information becomes available, management will continue to assess the potential exposure and adjust the reserves accordingly.

Earnings Per Share Policy Text Block	'
	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: NU 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 NU's total consolidated revenues for the years ended December 31, 2013, 2012 and 2011. 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 NU's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of NU parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of NU parent, 2) the revenues and expenses of NU's service company, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, and 4) the results of other non-regulated 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, for certain subsidiaries, the capitalized portions of pension expense.


Consolidation Variable Interest Entity Policy	'
	VARIABLE INTEREST ENTITIES

	The Company's variable interests outside of the consolidated group are not material and consist of contracts that are required by regulation and provide for regulatory recovery of contract costs and benefits through customer rates. NU, CL&P and NSTAR Electric hold variable interests in variable interest entities (VIEs) through agreements with certain entities that own single renewable energy or peaking generation power plants and with other independent power producers. NU, CL&P and NSTAR Electric do not control the activities that are economically significant to these VIEs or provide financial or other support to these VIEs. Therefore, NU, CL&P and NSTAR Electric do not consolidate any power plant VIEs.
Cash and Cash Equivalents, Policy [Policy Text Block]	'
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and cash equivalents include cash on hand and short-term cash investments that are highly liquid in nature and have original maturities of three months or less. At the end of each reporting period, any overdraft amounts are reclassified from Cash and Cash Equivalents to Accounts Payable on the balance sheets.
Asset Retirement Obligations, Policy [Policy Text Block]	'
Asset Retirement Obligations, Policy [Policy Text Block]	The Liability Assumed Upon Consolidation of CYAPC and YAEC represents the CYAPC and YAEC ARO fair value as of the merger date. The fair value of the ARO for CYAPC and YAEC includes uncertainties of the fuel off-load dates related to the DOE's timing of performance regarding its obligation to dispose of the spent nuclear fuel and high level waste. The incremental asset recorded as an offset to the ARO was fully depreciated since the plants have no remaining useful life. Any changes in the assumptions used to calculate the fair value of the ARO are recorded as an offset to the related regulatory asset. The assets held in the decommissioning trust are restricted for settling the asset retirement obligation and all other decommissioning obligations. For further information on the assets held in trust to support this obligation, see Note 6, “Marketable Securities,” to the financial statements
Goodwill and Intangible Assets, Policy [Policy Text Block]	'
	The goodwill from the merger with NSTAR of $3.2 billion was allocated to NU's reporting units based on their estimated fair values. NU's reporting units consist of Electric Distribution, Electric Transmission and Natural Gas Distribution. See the "Goodwill" section below for the allocation of goodwill to each reporting unit.

	Goodwill: In accordance with the accounting standards, goodwill is not subject to amortization. However, goodwill is subject to fair value-based rules for measuring impairment, and resulting write-downs, if any, are charged to Operating Expenses. These accounting standards require that goodwill be reviewed at least annually for impairment and whenever facts or circumstances indicate that there may be an impairment. NU uses October 1st as the annual goodwill impairment testing date.

	On April 10, 2012, upon consummation of the merger with NSTAR, NU recorded approximately $3.2 billion of goodwill. With the completion of the merger, NU reviewed its management structure and determined that the reporting units for the purpose of testing goodwill for impairment are Electric Distribution, Electric Transmission and Natural Gas Distribution. NU's reporting units are consistent with the operating segments underlying the reportable segments identified in Note 21, "Segment Information," to the financial statements. Accordingly, the goodwill resulting from the merger was allocated to the Electric Distribution, Electric Transmission and Natural Gas Distribution reporting units based on the estimated fair values of the reporting units as of the merger date.

	Prior to the merger with NSTAR, the only reporting unit that maintained goodwill was the Natural Gas Distribution reportable segment related to the acquisition of the parent of Yankee Gas in 2000. This goodwill was recorded at Yankee Gas. The goodwill balance at Yankee Gas as of December 31, 2013 and 2012 was $0.3 billion.

	NU completed its annual goodwill impairment test for each of its reporting units as of October 1, 2013 and determined that no impairment exists. There were no events subsequent to October 1, 2013 that indicated impairment of goodwill.


Pension And Other Postretirement Plans Policy	'
	A. Pension Benefits and Postretirement Benefits Other Than Pensions
	NUSCO sponsors a defined benefit retirement plan that covers most employees, including CL&P, PSNH, and WMECO employees, hired before 2006 (or as negotiated, for bargaining unit employees), referred to as the NUSCO Pension Plan. NSTAR Electric acts as plan sponsor for a defined benefit retirement plan that covers most employees of NSTAR Electric and certain affiliates, hired before October 1, 2012, or as negotiated by bargaining unit employees, referred to as the NSTAR Pension Plan. Both plans are subject to the provisions of ERISA, as amended by the PPA of 2006. NUSCO also maintains non-qualified defined benefit retirement plans (herein collectively referred to as the SERP Plans), which provide benefits in excess of Internal Revenue Code limitations to eligible current and retired participants.

	NUSCO also sponsors defined benefit postretirement plans that provide certain retiree health care benefits, primarily medical and dental, and life insurance benefits to retiring employees that meet certain age and service eligibility requirements (NUSCO PBOP Plans and NSTAR PBOP Plan). Under certain circumstances, eligible retirees are required to contribute to the costs of postretirement benefits. The benefits provided under the NUSCO and NSTAR PBOP Plans are not vested and the Company has the right to modify any benefit provision subject to applicable laws at that time.

	The funded status of the Pension, SERP and PBOP Plans is calculated based on the difference between the benefit obligation and the fair value of plan assets and is recorded on the balance sheets as an asset or a liability. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of an adjustment to Accumulated Other Comprehensive Income/(Loss). Regulatory accounting was also applied to the portions of the NUSCO costs that support the Regulated companies, as these costs are also recovered from customers. Adjustments to the Pension and PBOP funded status for the unregulated companies are recorded on an after-tax basis to Accumulated Other Comprehensive Income/(Loss). For further information, see Note 3, "Regulatory Accounting," and Note 15, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The SERP Plans do not have plan assets.

	For the NUSCO Pension and PBOP Plans, the expected return on plan assets is calculated by applying the assumed rate of return to a four-year rolling average of plan asset fair values, which reduces year-to-year volatility. This calculation recognizes investment gains or losses over a four-year period from the years in which they occur. Investment gains or losses for this purpose are the difference between the calculated expected return and the actual return. As investment gains and losses are reflected in the average plan asset fair values, they are subject to amortization with other unrecognized actuarial gains or losses. For the NSTAR Pension and PBOP Plans, the entire difference between the actual return and calculated expected return on plan assets is reflected as a component of unrecognized actuarial gain or loss. Unrecognized actuarial gains or losses are amortized as a component of Pension and PBOP expense over the estimated average future employee service period.

	Pension and SERP Plans: The funded status of each of the plans is recorded on the respective acting sponsor's balance sheet: NUSCO (NUSCO Pension, NUSCO SERP and NSTAR SERP) and NSTAR Electric (NSTAR Pension). The NUSCO plans are accounted for under the multiple-employer approach while the NSTAR plans are accounted for under the multi-employer approach. Accordingly, the balance sheet of NSTAR Electric reflects the full funded status of the NSTAR Pension Plan.

	Pension and SERP Expense: For the NUSCO Plans, NU allocates net periodic pension expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. Benefit payments to participants and contributions are also tracked for each subsidiary. The actual investment return in the trust each year is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the NSTAR Pension Plan, the net periodic pension expense recorded at NSTAR Electric represents the full cost of the plan and then a portion of the costs are allocated to affiliated companies based on participant demographic data.
	PBOP Expense: For the NUSCO Plans, NU allocates net periodic postretirement benefits expense to certain subsidiaries based on the actual participant demographic data for each subsidiary's participants. Benefit payments to participants and contributions are also tracked for each subsidiary. The actual investment return in the trust is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the NSTAR Plan, NU allocates the net periodic postretirement expenses to certain subsidiaries based on actual participant demographic data for each of its subsidiaries.
	Contributions: NU's policy is to annually fund the NUSCO and NSTAR Pension Plans in an amount at least equal to an amount that will satisfy federal requirements. NU contributed $202.7 million to the NUSCO Pension Plan in 2013, of which $108.3 million was contributed by PSNH. NSTAR Electric contributed $82 million to the NSTAR Pension Plan in 2013. Based on the current status of the NUSCO Pension Plan, NU expects to make a contribution of $68.6 million in 2014. NSTAR Electric expects to make a contribution of $3 million in 2014 to the NSTAR Pension Plan.
	For the PBOP Plans, it is NU's policy to annually fund the NUSCO PBOP Plans in an amount equal to the PBOP Plans' postretirement benefit cost, excluding curtailment and termination benefits, and the NSTAR PBOP Plan in an amount that approximates annual benefit payments. NU contributed $57.6 million to the PBOP Plans in 2013 and expects to make $39.7 million in contributions in 2014.

	Fair Value of Pension and PBOP Plan Assets: Pension and PBOP funds are held in external trusts. Trust assets, including accumulated earnings, must be used exclusively for Pension and PBOP payments. NU's investment strategy for its Pension and PBOP Plans is to maximize the long-term rates of return on these plans' assets within an acceptable level of risk. The investment strategy for each asset category includes a diversification of asset types, fund strategies and fund managers and establishes target asset allocations that are routinely reviewed and periodically rebalanced. In 2013 and 2012, PBOP assets were comprised of specific assets within the defined benefit pension plan trust (401(h) assets) as well as assets held in the PBOP Plans. The investment policy and strategy of the 401(h) assets is consistent with those of the defined benefit pension plans, which are detailed below. NU's expected long-term rates of return on Pension and PBOP Plan assets are based on these target asset allocation assumptions and related expected long-term rates of return. In developing its expected long-term rate of return assumptions for the Pension and PBOP Plans, NU evaluated input from consultants, as well as long-term inflation assumptions and historical returns. For the year ended December 31, 2013, management has assumed long-term rates of return of 8.25 percent for the Pension and PBOP Plan assets.
	The Company values assets based on observable inputs when available. Equity securities, exchange traded funds and futures contracts classified as Level 1 in the fair value hierarchy are priced based on the closing price on the primary exchange as of the balance sheet date. Commingled funds included in Level 2 equity securities are recorded at the net asset value provided by the asset manager, which is based on the market prices of the underlying equity securities. Swaps are valued using pricing models that incorporate interest rates and equity and fixed income index closing prices to determine a net present value of the cash flows. Fixed income securities, such as government issued securities, corporate bonds and high yield bond funds, are included in Level 2 and are valued using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The pricing models utilize observable inputs such as recent trades for the same or similar instruments, yield curves, discount margins and bond structures. Hedge funds and investments in opportunistic fixed income funds are recorded at net asset value based on the values of the underlying assets. The assets in the hedge funds and opportunistic fixed income funds are valued using observable inputs and are classified as Level 3 within the fair value hierarchy due to redemption restrictions. Private Equity investments and Real Estate and Other Assets are valued using the net asset value provided by the partnerships, which are based on discounted cash flows of the underlying investments, real estate appraisals or public market comparables of the underlying investments. These investments are classified as Level 3 due to redemption restrictions.

Property, Plant and Equipment, Depreciation Methods	'Utility property, plant and equipment is recorded at original cost. Original cost includes materials, labor, construction overhead and AFUDC for regulated property. The cost of repairs and maintenance, including planned major maintenance activities, is charged to Operating Expenses as incurred. Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution). The composite rates are subject to approval by the appropriate state regulatory agency. The composite rates include a cost of removal component, which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability. Depreciation rates are applied to property from the time it is placed in service. Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation. The actual incurred removal costs are applied against the related regulatory liability.
Income Tax, Policy [Policy Text Block]	'
	11. INCOME TAXES

	The tax effect of temporary differences is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and relevant accounting authoritative literature.
	Deferred tax assets and liabilities are recognized for the future tax effects of temporary differences between the carrying amounts and the tax basis of assets and liabilities.
	Interest and Penalties: Interest on uncertain tax positions is recorded and generally classified as a component of Other Interest Expense on the statements of income. However, when resolution of uncertainties results in the Company receiving interest income, any related interest benefit is recorded in Other Income, Net on the statements of income. No penalties have been recorded. If penalties are recorded in the future, then the estimated penalties would be classified as a component of Other Income, Net on the statements of income.
Member of Group Filing Consolidated Return, Policy [Policy Text Block]	'
	NU, CL&P, NSTAR Electric, PSNH and WMECO file a consolidated federal income tax return and unitary, combined and separate state income tax returns. These entities are also parties to a tax allocation agreement under which taxable subsidiaries do not pay any more taxes than they would have otherwise paid had they filed a separate company tax return, and subsidiaries generating tax losses, if any, are paid for their losses when utilized.

Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	'
	D. Share-Based Payments
	Share-based compensation awards are recorded using a fair-value-based method at the date of grant. NU, CL&P, NSTAR Electric, PSNH and WMECO record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as the allocation of costs associated with shares issued or sold to NU's service company employees and officers that support CL&P, NSTAR Electric, PSNH and WMECO.

	NU Incentive Plan: NU maintains long-term equity-based incentive plans under the NU Incentive Plan in which NU, CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are entitled to participate. The NU Incentive Plan was approved in 2007, and authorized NU to grant up to 4,500,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members.
	NU accounts for its various share-based plans as follows:


	RSUs - NU records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of NU's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares.



	Performance Shares - NU records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. As of December 31, 2013, vesting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the achievement of the Company's share price as compared to an index of similar equity securities during the requisite service period. The fair value of performance shares is determined at the date of grant using a lattice model.



	Stock Options - Stock options issued under the NSTAR Incentive Plan that were outstanding immediately prior to the completion of the merger with NSTAR converted into fully vested options to acquire NU common shares, as adjusted by the exchange ratio. The fair value of these awards on the merger date was included in the purchase price as it represented consideration transferred in the merger. Accordingly, no compensation expense was recorded for these stock options. Additionally, no compensation expense was recorded for stock options issued under the NU Incentive Plan as these stock options were fully vested prior to January 1, 2006.



	ESPP Shares - For shares sold under the ESPP, no compensation expense was recorded as the ESPP qualifies as a non-compensatory plan.


	RSUs: NU granted RSUs under the annual Long-Term incentive programs that are subject to three-year graded vesting schedules for employees, and one-year graded vesting schedules, or immediate vesting for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes, subsequent to vesting.
	As of December 31, 2013 and 2012, the number and weighted average grant-date fair value of unvested RSUs was 1,162,216 and $36.58 per share, and 1,417,688 and $34.70 per share, respectively. The number and weighted average grant-date fair value of RSUs vested during 2013 was 583,101 and $34.34 per share, respectively. As of December 31, 2013, 474,224 RSUs were fully vested and an additional 1,104,106 are expected to vest.

	Performance Shares: NU granted performance shares under the annual Long-Term Incentive programs that vested based upon the extent to which the Company achieved targets at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows:
	Upon closing of the merger with NSTAR, 451,358 performance shares under the NU 2011 and 2012 Long-Term Incentive Programs converted to RSUs according to the terms of these programs. The remaining performance shares were measured based upon a modified performance period through the date of the merger, in accordance with the terms of the NU 2010 Incentive Program, and were fully distributed in 2013. As of December 31, 2013, outstanding performance shares pertain to the NU 2013 Long-Term Incentive Program.

	Stock Options: Stock options were granted under the NU and NSTAR Incentive Plans. Options currently outstanding expire ten years from the date of grant and are fully vested. The weighted average remaining contractual lives for the options outstanding as of December 31, 2013 is 4.3 years. A summary of stock option transactions is as follows:
	Employee Share Purchase Plan: NU maintains an ESPP for eligible employees, which allows for NU common shares to be purchased by employees at the end of successive six-month offering periods at 95 percent of the closing market price on the last day of each six-month period. Employees are permitted to purchase shares having a value not exceeding 25 percent of their compensation as of the beginning of the offering period up to a limit of $25,000 per annum. The ESPP qualifies as a non-compensatory plan under accounting guidance for share-based payments, and no compensation expense is recorded for ESPP purchases.

	E. Other Retirement Benefits
	NU provides benefits for retirement and other benefits for certain current and past company officers of NU, including CL&P, PSNH and WMECO. These benefits are accounted for on an accrual basis and expensed over the service lives of the employees. The actuarially-determined liability for these benefits, which is included in Other Long-Term Liabilities on the balance sheets, as well as the related expense, are as follows:
Employee Stock Ownership Plan (ESOP), Policy [Policy Text Block]	'
	NU maintains an ESOP for purposes of allocating shares to employees participating in the NUSCO 401(k) Plan. Allocations of NU common shares were made from NU treasury shares to satisfy the NUSCO 401(k) Plan obligation to provide a portion of the matching contribution in NU common shares.

	For treasury shares used to satisfy the 401(k) Plan matching contributions, compensation expense is recognized equal to the fair value of shares that have been allocated to participants. Any difference between the fair value and the average cost of the allocated treasury shares is charged or credited to Capital Surplus, Paid In.

Provision_for_Uncollectible_Ac

Provision for Uncollectible Accounts (Tables)	12 Months Ended
	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Accounts Notes Loans And Financing Receivable Text Block	'
		As of December 31,
	(Millions of Dollars)	2013		2012
	NU	$	171.3	$	165.5
	CL&P		82		77.6
	NSTAR Electric		41.7		44.1
	PSNH		7.4		6.8
	WMECO		10		8.5

Equity_Method_Investments_Tabl

Equity Method Investments (Tables)	12 Months Ended
Equity Method Investments (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Equity Method Investments [Table Text Block]	'
	(Percent)	CYAPC		YAEC		MYAPC
	CL&P	34.5		24.5		12
	NSTAR Electric	14		14		4
	PSNH	5		7		5
	WMECO	9.5		7		3
		As of December 31,
	(Millions of Dollars)	2013		2012
	CL&P	$	1.2	$	1.4
	NSTAR Electric		0.5		0.6
	PSNH		0.3		0.3
	WMECO		0.3		0.4

Operating_Expenses_Tables

Operating Expenses (Tables)	12 Months Ended
Operating Expenses (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Fuel Costs [Table Text Block]	'
		For the Years Ended December 31,
	(Millions of Dollars)	2013		2012		2011
	NU- Natural Gas and Fuel⁽¹⁾	$	466.5	$	346.8	$	307.9
	PSNH - Fuel		104.8		103.4		115.9

	(1) NSTAR Gas natural gas costs were included in NU beginning April 10, 2012.

Allowance_for_Funds_Used_Durin

Allowance for Funds Used During Construction (Tables)	12 Months Ended
Allowance for Funds Used During Construction (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Allowance For Funds Used During Construction [Table Text Block]	'
	NU		For the Years Ended December 31,
	(Millions of Dollars, except percentages)		2013		2012 ⁽¹⁾		2011
	AFUDC:
		Borrowed Funds	$	4.1	$	5.3	$	11.8
		Equity Funds		7.1		6.8		22.5
	Total		$	11.2	$	12.1	$	34.3
	Average AFUDC Rate			2.70%		3.70%		7.30%

	(1) NSTAR amounts were included in NU beginning April 10, 2012.
			For the Years Ended December 31,
			2013								2012								2011
	(Millions of Dollars,				NSTAR								NSTAR								NSTAR
	except percentages)		CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	AFUDC:
		Borrowed Funds	$	2.2	$	0.5	$	0.5	$	0.5	$	2.5	$	0.3	$	1.6	$	0.5	$	3.3	$	0.2	$	7.1	$	0.5
		Equity Funds		2.9		-		0.2		1		1.9		-		1.9		1		6		-		13.2		1
	Total		$	5.1	$	0.5	$	0.7	$	1.5	$	4.4	$	0.3	$	3.5	$	1.5	$	9.3	$	0.2	$	20.3	$	1.5
	Average AFUDC Rate			3.70%		0.50%		1.10%		6.10%		3.60%		0.40%		5.90%		6.80%		8.30%		0.30%		7.10%		7.40%

Other_Taxes_Tables

Other Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
State Of Connecticut Gross Earnings Taxes [Table Text Block]	'
		For the Years Ended December 31,
	(Millions of Dollars)	2013		2012		2011
	NU	$	144.1	$	135	$	137.8
	CL&P		128.2		120.7		121.6

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information (Tables)	12 Months Ended
Supplemental Cash Flow Information (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	'
	P.			Supplemental Cash Flow Information

	NU				As of and For the Years Ended December 31,
	(Millions of Dollars)				2013			2012 ⁽¹⁾			2011
	Cash Paid/(Received) During the Year for:
		Interest, Net of Amounts Capitalized			$	343.3		$	356.5		$	256.3
		Income Taxes				50			-12.8			-76.6
	Non-Cash Investing Activities:
		Plant Additions Included in Accounts Payable (As of)				193.1			160.6			168.5

	(1) NSTAR amounts were included in NU beginning April 10, 2012.
			As of and For the Years Ended December 31,
			2013											2012								2011
						NSTAR										NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric			PSNH			WMECO		CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Cash Paid/(Received) During
		the Year for:
		Interest, Net of Amounts
		Capitalized	$	131.6		$	75.8		$	43.3		$	25.8	$	129.4	$	94.6	$	49.8	$	25.8	$	136.6	$	96.1	$	49.3	$	22.1
		Income Taxes		55			163.4			-30.1			-69		-42		88.1		14.7		-8.4		-27.5		-62.2		-29		-4.9
	Non-Cash Investing Activities:
		Plant Additions Included in
		Accounts Payable (As of)		51.4			57			34.9			19.5		42.8		50		16.8		30		32.7		34.3		51.1		61.3

MERGER_OF_NU_AND_NSTAR_Tables

MERGER OF NU AND NSTAR (Tables)	12 Months Ended
MERGER OF NU AND NSTAR (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Business Acquisitions by Acquisition Equity Interest Issued or Issuable [Table Text Block]	'
	NSTAR common shares outstanding as of April 9, 2012 (in thousands)*			103,696
	Exchange ratio			1.312
	NU common shares issued for NSTAR common shares outstanding (in thousands)			136,049
	Closing price of NU common shares on April 9, 2012		$	36.79
	Value of common shares issued (in millions)		$	5,005
	Fair value of NU replacement stock-based compensation awards related to
		pre-merger service (in millions)		33
	Total purchase price (in millions)		$	5,038
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	'
	(Millions of Dollars)
	Current Assets	$	739
	Property Plant and Equipment, Net		5,155
	Goodwill		3,232
	Other Long-Term Assets, excluding Goodwill		2,103
	Current Liabilities		-1,330
	Long-Term Liabilities		-2,723
	Long-Term Debt and Other Long-Term Obligations		-2,099
	Noncontrolling Interest		-39
	Total Purchase Price	$	5,038
Business Acquisition, Pro Forma Information	'
		For the Years Ended December 31,
	(Pro forma amounts in millions, except per share amounts)	2012			2011
	Operating Revenues	$	7,004		$	7,361
	Net Income Attributable to Controlling Interest		630			689
	Basic EPS		2			2.2
	Diluted EPS		1.99			2.19
Business Acquisition, Integration, Restructuring and Other Related Costs [Text Block]	'
			For the Years Ended December 31,
	(Millions of Dollars)		2012			2011
	Transaction and Other Costs		$	32		$	19
	Settlement Agreement Impacts			60			-
	Total After-Tax Non-Recurring Costs Excluded from
		Pro Forma Net Income Attributable to Controlling Interest	$	92		$	19
	(Millions of Dollars)	NU			CL&P			NSTAR Electric			WMECO
	Customer Rate Credits	$	46		$	25		$	15		$	3
	Storm Costs Deferral Reduction		40			40			-			-
	Establishment of Energy Efficiency Fund		15			-			-			-
	Total Pre-Tax Settlement Agreement Impacts	$	101		$	65		$	15		$	3
Schedule Of Goodwill Text Block	'
	(Billions of Dollars)			Electric			Electric			Natural Gas
				Distribution			Transmission			Distribution			Total
	Balance as of December 31, 2011			$	0		$	0		$	0.3		$	0.3
		Merger with NSTAR			2.5			0.6			0.1			3.2
	Balance as of December 31, 2012			$	2.5		$	0.6		$	0.4		$	3.5

	There were no changes to the goodwill balance or the allocation of goodwill for the year ended December 31, 2013.

REGULATORY_ACCOUNTING_Tables

REGULATORY ACCOUNTING (Tables)	12 Months Ended
REGULATORY ACCOUNTING (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Regulatory Assets Text Block	'
	NU	As of December 31,
	(Millions of Dollars)	2013			2012
	Benefit Costs	$	1,240.20		$	2,452.10
	Derivative Liabilities		638			885.6
	Goodwill		525.9			537.6
	Storm Restoration Costs		589.6			547.7
	Income Taxes, Net		626.2			516.2
	Securitized Assets		-			232.6
	Contractual Obligations - Yankee Companies		154.2			217.6
	Buy Out Agreements for Power Contracts		70.2			92.9
	Regulatory Tracker Mechanisms		323.4			190.1
	Other Regulatory Assets		126.8			165
	Total Regulatory Assets		4,294.50			5,837.40
	Less: Current Portion		535.8			705
	Total Long-Term Regulatory Assets	$	3,758.70		$	5,132.40
			As of December 31,
			2013									2012
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Benefit Costs		$	297.7		$	496.7	$	100.6	$	57.3	$	563.2	$	781.2	$	223.7	$	116
	Derivative Liabilities			630.4			7.7		-		-		866.2		14.9		-		3
	Goodwill			-			451.5		-		-		-		461.5		-		-
	Storm Restoration Costs			397.8			109.3		43.7		38.8		413.9		55.8		34.5		43.5
	Income Taxes, Net			415.5			84		40.3		43.7		367.5		47.1		36.2		31
	Securitized Assets			-			-		-		-		-		205.1		19.7		7.8
	Contractual Obligations -
		Yankee Companies		19.8			6.2		-		4.5		64		22.8		-		14.9
	Buy Out Agreements for Power Contracts			-			64.7		5.5		-		-		85.9		7		-
	Regulatory Tracker Mechanisms			8			169.5		83.3		32.6		12.2		71.4		49.3		31.9
	Other Regulatory Assets			44.8			49.7		38.1		12.2		57.3		46.3		43.6		16.1
	Total Regulatory Assets			1,814.00			1,439.30		311.5		189.1		2,344.30		1,792.00		414		264.2
	Less: Current Portion			150.9			204.1		92.2		43		185.9		347.1		62.9		42.4
	Total Long-Term Regulatory Assets		$	1,663.10		$	1,235.20	$	219.3	$	146.1	$	2,158.40	$	1,444.90	$	351.1	$	221.8
Schedule Of Regulatory Liabilities Text Block	'
	NU	As of December 31,
	(Millions of Dollars)	2013			2012
	Cost of Removal	$	435.1		$	440.8
	Regulatory Tracker Mechanisms		151.2			95.1
	AFUDC - Transmission		68.1			70
	Other Regulatory Liabilities		52.9			68.4
	Total Regulatory Liabilities		707.3			674.3
	Less: Current Portion		204.3			134.1
	Total Long-Term Regulatory Liabilities	$	503		$	540.2
			As of December 31,
			2013									2012
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Cost of Removal		$	29.1		$	250	$	49.7	$	-	$	44.2	$	240.3	$	51.2	$	-
	Regulatory Tracker Mechanisms			95.6			21.9		21.6		21.1		39.1		14.4		20.4		19
	AFUDC - Transmission			54.7			4.1		-		9.3		56.6		4.1		-		9.3
	Other Regulatory Liabilities			8.4			31.1		1		3.4		16.5		32.9		3.8		2.4
	Total Regulatory Liabilities			187.8			307.1		72.3		33.8		156.4		291.7		75.4		30.7
	Less: Current Portion			94			54		20.6		19.9		32.1		47.5		23		21
	Total Long-Term Regulatory Liabilities		$	93.8		$	253.1	$	51.7	$	13.9	$	124.3	$	244.2	$	52.4	$	9.7

PROPERTY_PLANT_AND_ACCUMULATED1

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables)	12 Months Ended
PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Public Utility Property, Plant, and Equipment [Text Block]	'
	NU			As of December 31,
	(Millions of Dollars)			2013			2012
	Distribution - Electric			$	11,950.20		$	11,438.20
	Distribution - Natural Gas				2,425.90			2,274.20
	Transmission				6,412.50			5,541.10
	Generation				1,152.30			1,146.60
	Electric and Natural Gas Utility				21,940.90			20,400.10
	Other⁽¹⁾				508.7			429.3
	Property, Plant and Equipment, Gross				22,449.60			20,829.40
	Less: Accumulated Depreciation
		Electric and Natural Gas Utility			-5,387.00			-5,065.10
		Other			-196.2			-171.5
	Total Accumulated Depreciation				-5,583.20			-5,236.60
	Property, Plant and Equipment, Net				16,866.40			15,592.80
	Construction Work in Progress				709.8			1,012.20
	Total Property, Plant and Equipment, Net			$	17,576.20		$	16,605.00
		As of December 31,
		2013												2012
					NSTAR												NSTAR
	(Millions of Dollars)	CL&P			Electric			PSNH			WMECO			CL&P			Electric		PSNH		WMECO
	Distribution	$	4,930.70		$	4,694.70		$	1,608.20		$	756.6		$	4,691.30		$	4,539.90	$	1,520.10	$	724.2
	Transmission		3,071.90			1,772.30			695.7			826.4			2,796.10			1,529.70		599.2		583.7
	Generation		-			-			1,131.20			21.1			-			-		1,125.50		21.1
	Property, Plant and
	Equipment, Gross		8,002.60			6,467.00			3,435.10			1,604.10			7,487.40			6,069.60		3,244.80		1,329.00
	Less: Accumulated Depreciation		-1,804.10			-1,631.30			-1,021.80			-271.5			-1,698.10			-1,540.10		-954		-252.1
	Property, Plant and Equipment, Net		6,198.50			4,835.70			2,413.30			1,332.60			5,789.30			4,529.50		2,290.80		1,076.90
	Construction Work in Progress		252.8			208.2			54.3			48.5			363.7			205.8		61.7		213.6
	Total Property, Plant and
	Equipment, Net	$	6,451.30		$	5,043.90		$	2,467.60		$	1,381.10		$	6,153.00		$	4,735.30	$	2,352.50	$	1,290.50
	(Percent)	2013			2012			2011
	NU		2.8			2.5			2.6
	CL&P		2.5			2.5			2.4
	NSTAR Electric		2.9			2.8			3
	PSNH		3			3			2.9
	WMECO		2.9			3.3			2.9
	The following table summarizes average useful lives of depreciable assets:

			Average Depreciable Life
	(Years)		NU			CL&P			NSTAR Electric			PSNH			WMECO
	Distribution			36.1			42			32.9			32.7			29.8
	Transmission			43			39.6			47.2			42.3			49.5
	Generation			32.2			-			-			32.4			25
	Other			14.6			-			-			-			-

DERIVATIVE_INSTRUMENTS_Tables

DERIVATIVE INSTRUMENTS (Tables)	12 Months Ended
DERIVATIVE INSTRUMENTS (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Derivative Instruments In Statement Of Financial Position Fair Value Text Block	'
			As of December 31, 2013
			Commodity Supply and						Net Amount Recorded as
	(Millions of Dollars)		Price Risk Management			Netting ⁽¹⁾			Derivative Asset/(Liability)
	Current Derivative Assets:
	Level 2:
		Other⁽¹⁾	$	1.9		$	-0.3		$	1.6
	Level 3:
		CL&P⁽¹⁾		17.1			-9.8			7.3
		NSTAR Electric		1.2			-			1.2
		WMECO		0.1			-			0.1
	Total Current Derivative Assets		$	20.3		$	-10.1		$	10.2

	Long-Term Derivative Assets:
	Level 2:
		Other	$	0.2		$	-		$	0.2
	Level 3:
		CL&P⁽¹⁾		113.6			-42.2			71.4
		WMECO		2.6			-			2.6
	Total Long-Term Derivative Assets		$	116.4		$	-42.2		$	74.2

	Current Derivative Liabilities:
	Level 3:
		CL&P	$	-92.2		$	-		$	-92.2
		NSTAR Electric		-1.5			-			-1.5
	Total Current Derivative Liabilities		$	-93.7		$	-		$	-93.7

	Long-Term Derivative Liabilities:
	Level 3:
		CL&P	$	-617.1		$	-		$	-617.1
		NSTAR Electric		-7			-			-7
	Total Long-Term Derivative Liabilities		$	-624.1		$	-		$	-624.1
			As of December 31, 2012
			Commodity Supply and						Net Amount Recorded as
	(Millions of Dollars)		Price Risk Management			Netting⁽¹⁾			Derivative Asset/(Liability)
	Current Derivative Assets:
	Level 2:
		Other	$	0.2		$	0		$	0.2
	Level 3:
		CL&P ⁽¹⁾		17.7			-12			5.7
		Other		5.5			-			5.5
	Total Current Derivative Assets		$	23.4		$	-12		$	11.4

	Long-Term Derivative Assets:
	Level 3:
		CL&P ⁽¹⁾	$	159.7		$	-69.1		$	90.6
	Total Long-Term Derivative Assets		$	159.7		$	-69.1		$	90.6

	Current Derivative Liabilities:
	Level 2:
		Other ^{(1) (2)}	$	-19.9		$	0.6		$	-19.3
	Level 3:
		CL&P		-96.9			-			-96.9
		NSTAR Electric		-1			-			-1
	Total Current Derivative Liabilities		$	-117.8		$	0.6		$	-117.2

	Long-Term Derivative Liabilities:
	Level 2:
		Other	$	-0.2		$	-		$	-0.2
	Level 3:
		CL&P		-865.6			-			-865.6
		NSTAR Electric		-13.9			-			-13.9
		WMECO		-3			-			-3
	Total Long-Term Derivative Liabilities		$	-882.7		$	-		$	-882.7
Schedule Of Derivative Instruments Gain Loss In Statement Of Financial Performance Text Block	'

	Location of Amounts				Amounts Recognized on Derivatives
	Recognized on Derivatives				For the Years Ended December 31,
	(Millions of Dollars)				2013			2012			2011
	NU
	Balance Sheet:
		Regulatory Assets and Liabilities			$	160.6		$	-29		$	-162
	Statement of Income:
		Purchased Power, Fuel and Transmission				1			-0.7			0.5
Schedule Of Cash Flow Hedges Included In Accumulated Other Comprehensive Income Loss [Table Text Block]	'
Schedule Of Credit Risk Contingent Features [Table Text Block]	'
Fairvalueinputsliabilitiesquantitativeinformationtabletextblock	'
		As of December 31, 2013									As of December 31, 2012
			Range						Period Covered			Range				Period Covered
	Energy Prices:
	NU	$	49	-		77	per MWh		2018-2029		$	43	-	90	per MWh	2018 - 2028
	CL&P	$	56	-		58	per MWh		2018-2029		$	50	-	55	per MWh	2018 - 2020
	WMECO	$	49	-		77	per MWh		2018-2029		$	43	-	90	per MWh	2018 - 2028

	Capacity Prices:
	NU	$	5.07	-		11.82	per kW-Month		2017-2029		$	1.4	-	10.53	per kW-Month	2016 - 2028
	CL&P	$	5.07	-		10.42	per kW-Month		2017-2026		$	1.4	-	9.83	per kW-Month	2016 - 2026
	NSTAR Electric	$	5.07	-		7.38	per kW-Month		2017-2019		$	1.4	-	3.39	per kW-Month	2016 - 2019
	WMECO	$	5.07	-		11.82	per kW-Month		2017-2029		$	1.4	-	10.53	per kW-Month	2016 - 2028

	Forward Reserve:
	NU, CL&P	$	3.3	-		3.3	per kW-Month		2014-2024		$	0.35	-	0.9	per kW-Month	2013 - 2024

	REC Prices:
	NU	$	36	-		87	per REC		2014-2029		$	25	-	85	per REC	2013 - 2028
	NSTAR Electric	$	36	-		70	per REC		2014-2018		$	25	-	71	per REC	2013 - 2018
	WMECO	$	36	-		87	per REC		2014-2029		$	25	-	85	per REC	2013 - 2028
FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock	'
	(Millions of Dollars)		NU ⁽¹⁾			CL&P			NSTAR Electric			WMECO
	Derivatives, Net:
	Fair Value as of January 1, 2012		$	-962.2		$	-931.6		$	-3.4		$	-7.3
	Liabilities Assumed due to Merger with NSTAR			-5.4			-			-			-
	Transfer to Level 2			32.2			-			-			-
	Net Realized/Unrealized Gains/(Losses) Included in:
		Net Income ⁽²⁾		10.9			-			-			-
		Regulatory Assets and Liabilities		-29.2			-21.6			-15.2			4.3
	Settlements			75.1			87			3.7			-
	Fair Value as of December 31, 2012		$	-878.6		$	-866.2		$	-14.9		$	-3
	Net Realized/Unrealized Gains/(Losses) Included in:
		Net Income ⁽²⁾		10.9			-			-			-
		Regulatory Assets and Liabilities		158.3			148.9			3.5			5.7
	Settlements			74.2			86.7			4.1			-
	Fair Value as of December 31, 2013		$	-635.2		$	-630.6		$	-7.3		$	2.7

MARKETABLE_SECURITIES_Tables

MARKETABLE SECURITIES (Tables)	12 Months Ended
MARKETABLE SECURITIES (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Available For Sale Securities Reconciliation [Table TextBlock]	'
			As of December 31, 2013
						Pre-Tax			Pre-Tax
			Amortized			Unrealized			Unrealized
	(Millions of Dollars)		Cost			Gains⁽¹⁾			Losses⁽¹⁾			Fair Value
	NU
		Debt Securities⁽²⁾	$	299.2		$	2.5		$	-2.1		$	299.6
		Equity Securities⁽²⁾		163.6			60.5			-			224.1

	WMECO
		Debt Securities		57.9			-			-			57.9

			As of December 31, 2012
						Pre-Tax			Pre-Tax
			Amortized			Unrealized			Unrealized
	(Millions of Dollars)		Cost			Gains⁽¹⁾			Losses⁽¹⁾			Fair Value
	NU
		Debt Securities⁽²⁾	$	266.6		$	13.3		$	-0.1		$	279.8
		Equity Securities⁽²⁾		145.5			20			-			165.5

	WMECO
		Debt Securities		57.7			0.1			-0.1			57.7
Investments Classified by Contractual Maturity Date [Table Text Block]	'

			NU						WMECO
			Amortized						Amortized
	(Millions of Dollars)		Cost			Fair Value			Cost			Fair Value
	Less than one year⁽¹⁾		$	72.4		$	72.3		$	26.5		$	26.6
	One to five years			62.1			62.7			25.6			25.5
	Six to ten years			59.4			59.3			1.7			1.7
	Greater than ten years			105.3			105.3			4.1			4.1
	Total Debt Securities		$	299.2		$	299.6		$	57.9		$	57.9
Fair Value Heirarchy [Table Text Block]	'
					NU						WMECO
					As of December 31,						As of December 31,
	(Millions of Dollars)				2013			2012			2013			2012
	Level 1:
		Mutual Funds and Equities			$	281.3		$	212.5		$	-		$	-
		Money Market Funds				32.9			40.2			10.9			5.2
	Total Level 1				$	314.2		$	252.7		$	10.9		$	5.2
	Level 2:
		U.S. Government Issued Debt Securities
			(Agency and Treasury)		$	61.4		$	69.9		$	6.8		$	18.7
		Corporate Debt Securities				53.6			33			15.1			7
		Asset-Backed Debt Securities				30.4			28.5			9			10.9
		Municipal Bonds				105.5			93.8			11.2			11.6
		Other Fixed Income Securities				15.8			14.4			4.9			4.3
	Total Level 2				$	266.7		$	239.6		$	47		$	52.5
	Total Marketable Securities				$	580.9		$	492.3		$	57.9		$	57.7

ASSET_RETIREMENT_OBLIGATIONS_T

ASSET RETIREMENT OBLIGATIONS (TABLE)	12 Months Ended
ASSET RETIREMENT OBLIGATIONS (TABLE)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Change in Asset Retirement Obligation [Table Text Block]	'
	NU			As of December 31,
	(Millions of Dollars)			2013		2012
	Balance as of Beginning of Year			$	412.2	$	56.2
	Liability Assumed Upon Consolidation of CYAPC and YAEC				-		284.2
	Liability Assumed Upon Merger With NSTAR				-		35.9
	Liabilities Incurred During the Year				0.1		1.5
	Liabilities Settled During the Year				-13.8		-7.2
	Accretion				23.8		20.2
	Revisions in Estimated Cash Flows				2.6		21.4
	Balance as of End of Year			$	424.9	$	412.2

		As of December 31,
		2013								2012
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Balance as of Beginning of Year	$	33.6	$	31.4	$	18.4	$	4.3	$	32.2	$	27.5	$	17	$	4
	Liabilities Incurred During the Year		-		-		-		-		-		-		0.3		-
	Liabilities Settled During the Year		-0.7		-0.1		-		-		-0.9		-1		-		-
	Accretion		2.2		1.5		1.2		0.3		2		1.5		1.1		0.3
	Revisions in Estimated Cash Flows		-0.1		-		-0.1		-0.1		0.3		3.4		-		-
	Balance as of End of Year	$	35	$	32.8	$	19.5	$	4.5	$	33.6	$	31.4	$	18.4	$	4.3

LONGTERM_DEBT_TABLES

LONG-TERM DEBT (TABLES)	12 Months Ended
LONG-TERM DEBT (TABLES)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Maturities of Long-term Debt [Table Text Block]	'
	(Millions of Dollars)	NU			CL&P			NSTAR Electric		PSNH		WMECO
	2014	$	576.7		$	150		$	301.7	$	50	$	-
	2015		216.7			162			4.7		-		50
	2016		200			-			200		-		-
	2017		745			250			400		70		-
	2018		810			300			-		110		-
	Thereafter		5,031.60			1,640.30			900		821.3		515
	Total	$	7,580.00		$	2,502.30		$	1,806.40	$	1,051.30	$	565
Schedule of Long-term Debt Instruments [Table Text Block]	'

		CL&P		As of December 31,
		(Millions of Dollars)		2013			2012
		First Mortgage Bonds:
			7.875% 1994 Series D due 2024	$	139.8		$	139.8
			4.800% 2004 Series A due 2014		150			150
			5.750% 2004 Series B due 2034		130			130
			5.000% 2005 Series A due 2015		100			100
			5.625% 2005 Series B due 2035		100			100
			6.350% 2006 Series A due 2036		250			250
			5.375% 2007 Series A due 2017		150			150
			5.750% 2007 Series B due 2037		150			150
			5.750% 2007 Series C due 2017		100			100
			6.375% 2007 Series D due 2037		100			100
			5.650% 2008 Series A due 2018		300			300
			5.500% 2009 Series A due 2019		250			250
			2.500% 2013 Series A due 2023⁽¹⁾		400			-
		Total First Mortgage Bonds			2,319.80			1,919.80
		Pollution Control Notes:
			4.375% Fixed Rate Tax Exempt due 2028		120.5			120.5
			1.25% Fixed Rate Tax Exempt due 2028⁽²⁾		-			125
			1.55% Fixed Rate Tax Exempt due 2031⁽²⁾		62			62
		Total Pollution Control Notes			182.5			307.5
		Total First Mortgage Bonds and Pollution Control Notes			2,502.30			2,227.30
		Fees and Interest due for Spent Nuclear Fuel Disposal Costs			244.4			244.3
		CL&P Commercial Paper and Revolver Borrowings⁽¹⁾			-			394.8
		Less Amounts due Within One Year			-150			-125
		Unamortized Premiums and Discounts, Net			-5.5			-3.6
		CL&P Long-Term Debt		$	2,591.20		$	2,737.80

		NSTAR Electric		As of December 31,
		(Millions of Dollars)		2013			2012
		Debentures:
			4.875% due 2014	$	300		$	300
			5.75% due 2036		200			200
			5.625% due 2017		400			400
			5.50% due 2040		300			300
			2.375% due 2022		400			400
			Variable Rate due 2016⁽³⁾		200			-
		Total Debentures			1,800.00			1,600.00
		Bonds:
			7.375% Tax Exempt Sewage Facility Revenue Bonds, due 2015		6.4			8
		Less Amounts due Within One Year			-301.7			-1.7
		Unamortized Premiums and Discounts, Net			-5.3			-5.4
		NSTAR Electric Long-Term Debt		$	1,499.40		$	1,600.90

		PSNH		As of December 31,
		(Millions of Dollars)		2013			2012
		First Mortgage Bonds:
			5.25% 2004 Series L due 2014	$	50		$	50
			5.60% 2005 Series M due 2035		50			50
			6.15% 2007 Series N due 2017		70			70
			6.00% 2008 Series O due 2018		110			110
			4.50% 2009 Series P due 2019		150			150
			4.05% 2011 Series Q due 2021		122			122
			3.20% 2011 Series R due 2021		160			160
			3.50% 2013 Series S due 2023⁽⁴⁾		250			-
		Total First Mortgage Bonds			962			712
		Pollution Control Revenue Bonds:
			4.75% - 5.45% Tax Exempt Series B and C due 2021⁽⁴⁾		-			198.2
			Adjustable Rate Series A due 2021		89.3			89.3
		Total Pollution Control Revenue Bonds			89.3			287.5
		Less Amounts due Within One Year			-50			-
	Unamortized Premiums and Discounts, Net			-2.3			-1.6
	PSNH Long-Term Debt		$	999		$	997.9

	WMECO		As of December 31,
	(Millions of Dollars)		2013			2012
	Other Notes:
		5.00% Senior Notes Series A, due 2013⁽⁵⁾	$	-		$	55
		5.90% Senior Notes Series B, due 2034		50			50
		5.24% Senior Notes Series C, due 2015		50			50
		6.70% Senior Notes Series D, due 2037		40			40
		5.10% Senior Notes Series E, due 2020		95			95
		3.50% Senior Notes Series F, due 2021		250			250
		3.88% Senior Notes Series G, due 2023⁽⁵⁾		80			-
	Total Other Notes			565			540
	Fees and Interest due for Spent Nuclear Fuel Disposal Costs			57.3			57.3
	Less Amounts due Within One Year⁽⁵⁾			-			-55
	Unamortized Premiums and Discounts, Net			7.1			8
	WMECO Long-Term Debt		$	629.4		$	550.3

	OTHER		As of December 31,
	(Millions of Dollars)		2013				2012
	Yankee Gas - First Mortgage Bonds:
		8.48% Series B due 2022	$	20		$	20
		4.80% Series G due 2014⁽⁶⁾		75			75
		5.26% Series H due 2019		50			50
		5.35% Series I due 2035		50			50
		6.90% Series J due 2018		100			100
		4.87% Series K due 2020		50			50
	Total First Mortgage Bonds			345			345
	Unamortized Premium			0.7			0.8
	Yankee Gas Long-Term Debt			345.7			345.8

	NSTAR Gas - First Mortgage Bonds:
		9.95% Series J due 2020		25			25
		7.11% Series K due 2033		35			35
		7.04% Series M due 2017		25			25
		4.46% Series N due 2020		125			125
	NSTAR Gas Long-Term Debt			210			210

	Other - Notes and Debentures:
		5.65% Senior Notes Series C due 2013 (NU Parent)⁽⁷⁾		-			250
		Variable Rate Senior Notes Series D due 2013 (NU Parent)⁽⁷⁾		-			300
		1.45% Senior Notes Series E due 2018 (NU Parent)⁽⁷⁾		300			-
		2.80% Senior Notes Series F due 2023 (NU Parent)⁽⁷⁾		450			-
		4.50% Debentures due 2019 (NU Parent)		350			350
		NU Commercial Paper Borrowings⁽⁶⁾		25			-
		Spent Nuclear Fuel Obligation (CYAPC)		179.4			179.3
	Total Other Long-Term Debt			1,304.40			1,079.30
	Fair Value Adjustment⁽⁸⁾			230.7			259.9
	Less Amounts due Within One Year			-			-550
	Less Fair Value Adjustment - Current Portion⁽⁸⁾			-31.7			-31.7
	Unamortized Premiums and Discounts, Net			-1.3			-
	Total NU Long-Term Debt		$	7,776.80		$	7,200.20

Recovered_Sheet1

Pension Benefits and Postretirement Benefits Other Than Pensions (Tables)	12 Months Ended
	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Net Benefit Costs [Table Text Block]	'
			Pension and SERP
			For the Year Ended December 31, 2013
									NSTAR
	(Millions of Dollars)		NU			CL&P			Electric⁽²⁾			PSNH			WMECO
	Service Cost		$	102.3		$	24.9		$	33.1		$	13.1		$	4.7
	Interest Cost			206.7			48.3			58			23.6			10
	Expected Return on Plan Assets			-278.1			-73.8			-84.4			-35.4			-17.4
	Actuarial Loss			210.5			55.9			58.1			21.6			11.8
	Prior Service Cost/(Credit)			4			1.8			-0.3			0.7			0.4
	Total Net Periodic Benefit Expense		$	245.4		$	57.1		$	64.5		$	23.6		$	9.5
	Related Intercompany Allocations			N/A		$	44.9		$	-8.4		$	10.5		$	8
	Capitalized Pension Expense		$	73.2		$	28		$	28.9		$	7.3		$	5.2

			Pension and SERP
			For the Year Ended December 31, 2012 ⁽¹⁾
									NSTAR
	(Millions of Dollars)		NU			CL&P			Electric⁽²⁾			PSNH			WMECO
	Service Cost		$	84.3		$	21.8		$	30.3		$	11.8		$	4.1
	Interest Cost			198.3			51.2			58.9			24.4			10.5
	Expected Return on Plan Assets			-220.9			-70.6			-65.6			-28.2			-16.4
	Actuarial Loss			172.4			49.6			63.1			16.2			10.7
	Prior Service Cost/(Credit)			7.9			3.6			-0.6			1.5			0.8
	Total Net Periodic Benefit Expense		$	242		$	55.6		$	86.1		$	25.7		$	9.7
	Curtailments and Settlements		$	2.2		$	-		$	-		$	-		$	-
	Related Intercompany Allocations			N/A		$	42.8		$	-12.3		$	10.1		$	8.1
	Capitalized Pension Expense		$	70.6		$	26.8		$	30.7		$	7.9		$	5.1

			Pension and SERP
			For the Year Ended December 31, 2011
									NSTAR
	(Millions of Dollars)		NU			CL&P			Electric⁽²⁾			PSNH			WMECO
	Service Cost		$	55.4		$	19.5		$	26		$	10.6		$	3.9
	Interest Cost			153.3			51.9			61			24.4			10.7
	Expected Return on Plan Assets			-170.8			-76.6			-71.4			-19.8			-17.7
	Actuarial Loss			84.2			33.4			48.6			10.7			7.1
	Prior Service Cost/(Credit)			9.7			4.2			-0.7			1.8			0.9
	Total Net Periodic Benefit Expense		$	131.8		$	32.4		$	63.5		$	27.7		$	4.9
	Related Intercompany Allocations			N/A		$	34.1		$	-10.2		$	7.6		$	6.2
	Capitalized Pension Expense		$	29.7		$	16.6		$	19.8		$	7.6		$	2.7

	-1	NSTAR Electric amounts were included in NU beginning April 10, 2012.
	-2	NSTAR Electric's allocated expense associated with the NSTAR SERP was $3.2 million, $3.6 million and $4.4 million for the years ended December 31, 2013, 2012 and 2011, respectively, and are not included in the NSTAR Electric amounts in the tables above.
				PBOP
			For the Years Ended December 31,
			2013												2012												2011
	(Millions of Dollars)		NU			CL&P			PSNH			WMECO			NU ⁽¹⁾			CL&P			PSNH			WMECO			NU		CL&P		PSNH		WMECO
	Service Cost		$	16.9		$	3.4		$	2.3		$	0.7		$	15.7		$	3		$	2		$	0.6		$	9.2	$	2.9	$	1.9	$	0.6
	Interest Cost			47.2			7.9			4			1.7			49			9.2			4.6			2			25.7		10		4.8		2.2
	Expected Return
		on Plan Assets		-55.4			-10.1			-5.2			-2.3			-39.2			-9.1			-4.6			-2.1			-21.6		-8.7		-4.3		-2
	Actuarial Loss			26			7.4			3.6			1.1			36			7.5			3.6			1.2			19		7.2		3.2		1.1
	Prior Service
		Cost/(Credit)		-2.1			-			-			-			-1.4			-			-			-			-0.3		-		-		-
	Net Transition
		Obligation Cost ⁽²⁾		-			-			-			-			12.2			6.1			2.5			1.3			11.6		6.2		2.5		1.3
	Total Net Periodic Benefit Expense		$	32.6		$	8.6		$	4.7		$	1.2		$	72.3		$	16.7		$	8.1		$	3		$	43.6	$	17.6	$	8.1	$	3.2
	Related Intercompany Allocations			N/A		$	7.1		$	1.6		$	1.3			N/A		$	7.9		$	2		$	1.5			N/A	$	8.2	$	2	$	1.5
	Capitalized PBOP Expense		$	8.8		$	3.9		$	1.3		$	0.6		$	26.6		$	8.2		$	2.3		$	1.6		$	12.7	$	8.7	$	2.2	$	1.5

	-1	NU results include NSTAR PBOP Plan activity beginning April 10, 2012.
	-2	The PBOP Plans' transition obligation costs were fully amortized in 2013.
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	'
	The accumulated benefit obligation for the Pension and SERP Plans is as follows:

			Pension and SERP
			As of December 31,
	(Millions of Dollars)		2013			2012
	NU		$	4,538.80		$	4,622.10
	CL&P			1,058.00			1,061.80
	NSTAR Electric ⁽¹⁾			1,280.60			1,353.10
	PSNH			520.1			515.9
	WMECO			220.6			221.3

	-1	NSTAR Electric amounts do not include the accumulated benefit obligation for the SERP Plan.

	The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status:
Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]	'
	The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income (OCI) as well as amounts in Regulatory Assets and OCI reclassified as net periodic benefit expense during the years presented:

			Amounts Reclassified To/From
			Regulatory Assets						OCI
	(Millions of Dollars)		For the Years Ended December 31,
	NU Pension and SERP Plans⁽¹⁾		2013			2012			2013			2012
	Actuarial (Gains)/Losses Arising During the Year		$	-635.2		$	245.7		$	-28.9		$	19.1
	Actuarial Losses Reclassified as Net Periodic Benefit Expense			-201.2			-164.6			-9.4			-7.8
	Prior Service Cost Reclassified as Net Periodic Benefit Expense			-3.8			-7.7			-0.2			-0.2

	(1) The NU amounts include the NSTAR Pension and SERP Plans beginning April 10, 2012.

	The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2013 and 2012, and the amounts that are expected to be recognized as components in 2014:

				Regulatory Assets as of						Expected			AOCI as of					Expected
	(Millions of Dollars)		December 31,							2014		December 31,						2014
	NU Pension and SERP Plans		2013			2012			Expense			2013			2012			Expense
	Actuarial Loss		$	1,137.40		$	1,973.80		$	126.2		$	43.2		$	81.5		$	5.6
	Prior Service Cost			17.4			21.2			4.2			1			1.2			0.2
	The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts in Regulatory Assets and OCI reclassified as net periodic benefit (expense)/income during the years presented:

			Amounts Reclassified To/From
		Regulatory Assets						OCI
	(Millions of Dollars)	For the Years Ended December 31,
	NU PBOP Plans ⁽¹⁾	2013			2012			2013			2012
	Actuarial Gains Arising During the Year	$	-262		$	-108.6		$	-1.9		$	-1.8
	Actuarial Losses Reclassified as Net Periodic Benefit Expense		-24.9			-34.9			-1.1			-1.1
	Prior Service Credit Reclassified as Net Periodic Benefit Income		2.1			1.4			-			-
	Transition Obligation Reclassified as Net Periodic Benefit Expense		-			-11.9			-			-0.2

	(1) The NU amounts include the NSTAR PBOP Plan beginning April 10, 2012.

	The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2013 and 2012, and the amounts that are expected to be recognized as components in 2014:

			Regulatory Assets as of					Expected				AOCI as of					Expected
	(Millions of Dollars)	December 31,						2014				December 31,					2014
	NU PBOP Plans	2013			2012			Expense			2013			2012			Expense
	Actuarial Loss	$	89.2		$	376.1		$	11.4		$	6.2		$	9.2		$	0.7
	Prior Service Credit		-4.6			-6.7			-2.8			-			-			-
Schedule of Assumptions Used [Table Text Block]	'
			Pension and SERP
			As of December 31,
			2013			2012
	NUSCO Pension and SERP Plans
	Discount Rate		5.03	%		4.24	%
	Compensation/Progression Rate		3.5	%		3.5	%

	NSTAR Pension and SERP Plans
	Discount Rate		4.85	%		4.13	%
	Compensation/Progression Rate		4	%		4	%
	The following actuarial assumptions were used to calculate Pension and SERP expense amounts:
			Pension and SERP
			For the Years Ended December 31,
	NUSCO Pension and SERP Plans		2013			2012			2011
	Discount Rate		4.24	%		5.03	%		5.57	%
	Expected Long-Term Rate of Return		8.25	%		8.25	%		8.25	%
	Compensation/Progression Rate		3.5	%		3.5	%		3.5	%

	NSTAR Pension and SERP Plans
	Discount Rate		4.13	%		4.52	%		5.3	%
	Expected Long-Term Rate of Return		8.25	%		7.3	%		8	%
	Compensation/Progression Rate		4	%		4	%		4	%

	The following actuarial assumptions were used in calculating the PBOP Plans' year end funded status:

				PBOP
				As of December 31,
				2013			2012
	NUSCO PBOP Plans
	Discount Rate			4.78	%		4.04	%
	Health Care Cost Trend Rate			7	%		7	%

	NSTAR PBOP Plan
	Discount Rate			5.1	%		4.35	%
	Health Care Cost Trend Rate			7	%		7.1	%
	The following actuarial assumptions were used to calculate PBOP expense amounts:

				PBOP
				For the Years Ended December 31,
				2013			2012			2011
	NUSCO PBOP Plans
	Discount Rate			4.04	%		4.84	%		5.28	%
	Expected Long-Term Rate of Return			8.25	%		8.25	%		8.25	%

	NSTAR PBOP Plan
	Discount Rate			4.35	%		4.58	%		N/A
	Expected Long-Term Rate of Return			8.25	%		7.3	%		N/A

	The health care cost trend rate assumption used to calculate the 2013 PBOP expense amounts was 7 percent for the NUSCO PBOP Plan, subsequently decreasing by 50 basis points per year to an ultimate rate of 5 percent in 2017, and 7.10 percent for the NSTAR PBOP Plan, subsequently decreasing to an ultimate rate of 4.5 percent in 2024. As of December 31, 2013, the health care cost trend rate assumption used to determine the NUSCO and NSTAR PBOP Plans' year end funded status is 7 percent, subsequently decreasing to an ultimate rate of 4.5 percent in 2024.

	Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. The effect of changing the assumed health care cost trend rate by one percentage point for the year ended December 31, 2013 would have the following effects:
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	'
	(Millions of Dollars)	One Percentage			One Percentage
	NU PBOP Plans	Point Increase			Point Decrease
	Effect on Postretirement Benefit Obligation	$	85.8		$	-70.4
	Effect on Total Service and Interest Cost Components		7.1			-5.5
Schedule of Expected Benefit Payments [Table Text Block]	'
	Estimated Future Benefit Payments: The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans:

	(Millions of Dollars)	Pension
	NU	and SERP			PBOP
	2014	$	263.3		$	61.6
	2015		273.3			63.3
	2016		282.9			64.5
	2017		287.4			65.6
	2018		299.4			66.6
	2019-2023		1,617.00			344.4

	NSTAR Pension Plan
	2014	$	88			N/A
	2015		90.6			N/A
	2016		88.4			N/A
	2017		88.5			N/A
	2018		90			N/A
	2019-2023		449.2			N/A
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets [Table Text Block]	'
			Pension and SERP
	NU		As of December 31,
	(Millions of Dollars)		2013			2012 ⁽¹⁾
	Change in Benefit Obligation
	Benefit Obligation as of Beginning of Year		$	-5,022.80		$	-3,098.90
	Liabilities Assumed from Merger with NSTAR			-			-1,409.70
	Service Cost			-102.3			-84.3
	Interest Cost			-206.7			-198.3
	Actuarial Gain/(Loss)			433.6			-429.7
	Benefits Paid - Pension			216.6			187.7
	Benefits Paid - SERP			5.1			4.2
	SERP Curtailment			-			6.2
	Benefit Obligation as of End of Year		$	-4,676.50		$	-5,022.80
	Change in Pension Plan Assets
	Fair Value of Plan Assets as of Beginning of Year		$	3,411.30		$	2,005.90
	Assets Assumed from Merger with NSTAR			-			984.7
	Employer Contributions			284.7			222.4
	Actual Return on Plan Assets			506.5			386
	Benefits Paid			-216.6			-187.7
	Fair Value of Plan Assets as of End of Year		$	3,985.90		$	3,411.30
	Funded Status as of December 31^st		$	-690.6		$	-1,611.50
			Pension and SERP
			As of December 31, 2013												As of December 31, 2012
						NSTAR												NSTAR
	(Millions of Dollars)		CL&P			Electric ⁽²⁾			PSNH			WMECO			CL&P			Electric ⁽²⁾			PSNH			WMECO
	Change in Benefit Obligation
	Benefit Obligation as of Beginning of Year		$	-1,178.00		$	-1,430.00		$	-576		$	-243.1		$	-1,043.80		$	-1,346.20		$	-497.9		$	-215.8
	Service Cost			-24.9			-33.1			-13.1			-4.7			-21.8			-30.3			-11.8			-4.1
	Interest Cost			-48.3			-58			-23.6			-10			-51.2			-58.9			-24.4			-10.5
	Actuarial Gain/(Loss)			110.7			96.6			62.4			22.4			-117.4			-63.6			-61.3			-24
	Benefits Paid - Pension			56.6			71.2			21.1			11.5			55.9			69			19.7			11.3
	Benefits Paid - SERP			0.5			-			0.2			-			0.3			-			-			-
	SERP Curtailment			-			-			-			-			-			-			-0.3			-
	Benefit Obligation as of End of Year		$	-1,083.40		$	-1,353.30		$	-529		$	-223.9		$	-1,178.00		$	-1,430.00		$	-576		$	-243.1
	Change in Pension Plan Assets
	Fair Value of Plan Assets as of Beginning of Year		$	937.6		$	1,069.10		$	386.6		$	218.5		$	869.6		$	988.5		$	279.7		$	202
	Employer Contributions			-			82			108.3			-			-			25			87.7			-
	Actual Return on Plan Assets			135.3			155.4			54.8			33.4			123.9			124.6			38.9			27.8
	Benefits Paid			-56.6			-71.2			-21.1			-11.5			-55.9			-69			-19.7			-11.3
	Fair Value of Plan Assets as of End of Year		$	1,016.30		$	1,235.30		$	528.6		$	240.4		$	937.6		$	1,069.10		$	386.6		$	218.5
	Funded Status as of December 31^st		$	-67.1		$	-118		$	-0.4		$	16.5		$	-240.4		$	-360.9		$	-189.4		$	-24.6

	(1) NSTAR amounts were included in NU beginning April 10, 2012.

	(2) NSTAR Electric amounts do not include benefit obligations of the NSTAR SERP Plan.

	As of December 31, 2013, prepaid pension assets of $3 million and $17 million for PSNH and WMECO, respectively, were included in Other Long-term Assets on their accompanying balance sheets. Pension and SERP benefits funded status includes the current portion of the SERP liability, which is included in Other Current Liabilities on the accompanying balance sheets.

	Although NU maintains marketable securities in a supplemental benefit trust, the plan itself does not contain any assets. See Note 6, "Marketable Securities," to the financial statements.
			PBOP
			As of December 31,
			2013												2012
	(Millions of Dollars)		NU			CL&P			PSNH			WMECO			NU ⁽¹⁾			CL&P			PSNH			WMECO
	Change in Benefit Obligation
	Benefit Obligation as of Beginning of Year		$	-1,233.30		$	-196.8		$	-100.2		$	-42.5		$	-520.9		$	-198.9		$	-99.2		$	-42.9
	Liabilities Assumed from Merger with NSTAR			-			-			-			-			-770.6			-			-			-
	Service Cost			-16.9			-3.4			-2.3			-0.7			-15.7			-3			-2			-0.6
	Interest Cost			-47.2			-7.9			-4			-1.7			-49			-9.2			-4.6			-2
	Actuarial Gain			200.9			13.3			7.2			3.3			70.9			1.2			0.3			0.1
	Federal Subsidy on Benefits Paid			-			-			-			-			-6.2			-1.7			-0.6			-0.3
	Benefits Paid			58.5			14.4			5.8			2.9			58.2			14.8			5.9			3.2
	Benefit Obligation as of End of Year		$	-1,038.00		$	-180.4		$	-93.5		$	-38.7		$	-1,233.30		$	-196.8		$	-100.2		$	-42.5
	Change in Plan Assets
Fair Value of Plan Assets as of Beginning of Year		$	709.1		$	132.2		$	69.5		$	31		$	285.4		$	112.2		$	58.7		$	27.1
Assets Assumed from Merger with NSTAR			-			-			-			-			330.4			-			-			-
Actual Return on Plan Assets			118.3			24.8			13.4			6			78.8			15			7.5			3.5
Employer Contributions			57.6			8.7			4.7			1.2			72.7			19.8			9.2			3.6
Benefits Paid			-58.5			-14.4			-5.8			-2.9			-58.2			-14.8			-5.9			-3.2
Fair Value of Plan Assets as of End of Year		$	826.5		$	151.3		$	81.8		$	35.3		$	709.1		$	132.2		$	69.5		$	31
Funded Status as of December 31^st		$	-211.5		$	-29.1		$	-11.7		$	-3.4		$	-524.2		$	-64.6		$	-30.7		$	-11.5

-1	NU results include NSTAR PBOP Plan activity beginning April 10, 2012.
Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]	'
			NU Pension Plans
			United												Real Estate
			States						Private			Fixed			and Other			Hedge
	(Millions of Dollars)		Equity			International			Equity			Income			Assets			Funds			Total
	Balance as of January 1, 2012		$	259.4		$	-		$	255.1		$	276.2		$	71.8		$	240		$	1,102.50
	Assets Assumed from Merger with NSTAR			-			41.4			-			-			111			126.6			279
	Actual Return/(Loss) on Plan Assets:
		Relating to Assets Still Held as of Year End		11.2			10.7			17			42.1			5.7			21.8			108.5
		Relating to Assets Distributed During the Year		-			-			15			0.7			7.6			-0.3			23
	Purchases, Sales and Settlements			-			-			-19.2			-3.9			39.3			30.8			47
	Balance as of December 31, 2012		$	270.6		$	52.1		$	267.9		$	315.1		$	235.4		$	418.9	0	$	1,560.00
	Transfer Between Categories			-			-			-			32.5			-			-32.5			-
	Actual Return/(Loss) on Plan Assets:
		Relating to Assets Still Held as of Year End		11.2			9.4			15.4			55.3			12.9			33.4			137.6
		Relating to Assets Distributed During the Year		12.2			-			13.7			-1			6.2			-			31.1
	Purchases, Sales and Settlements			-100			-			3.3			187.6			34			-2.9			122
	Balance as of December 31, 2013		$	194		$	61.5		$	300.3		$	589.5		$	288.5		$	416.9		$	1,850.70

			NU PBOP Plans
			United									Real Estate
			States			Private			Fixed			and Other				Hedge
	(Millions of Dollars)		Equity			Equity			Income			Assets				Funds			Total
	Balance as of January 1, 2012		$	10.7		$	5.1		$	26		$	2.5		$	16.1		$	60.4
	Assets Assumed from Merger with NSTAR			19.7			-			-			18.4			21.4			59.5
	Actual Return on Plan Assets:
		Relating to Assets Still Held as of Year End		5.9			1.6			4			3			2.1			16.6
	Purchases, Sales and Settlements			-			4.6			2.1			2.8			-			9.5
	Balance as of December 31, 2012		$	36.3		$	11.3		$	32.1		$	26.7		$	39.6		$	146
	Actual Return/(Loss) on Plan Assets:												-
		Relating to Assets Still Held as of Year End		20.8			1.5			4.1			3.9			5.4			35.7
		Relating to Assets Distributed During the Year		-			0.2			-			-0.1			-			0.1
	Purchases, Sales and Settlements			12			4.9			15.3			3.4			12			47.6
	Balance as of December 31, 2013		$	69.1		$	17.9		$	51.5		$	33.9		$	57		$	229.4

			NSTAR Pension Plan
			United												Real Estate
			States							Private		Fixed			and Other				Hedge
	(Millions of Dollars)		Equity			International				Equity		Income			Assets				Funds			Total
	Balance as of January 1, 2012		$	-		$	41.4		$	-		$	-		$	111		$	126.6		$	279
	Actual Return/(Loss) on Plan Assets:
		Relating to Assets Still Held as of Year End		-			10.7			-			-			9.9			5.6			26.2
		Relating to Assets Distributed During the Year		-			-			-			-			-			-0.3			-0.3
	Purchases, Sales and Settlements			-			-			-			-			6.3			-9.2			-2.9
	Balance as of December 31, 2012		$	-		$	52.1		$	-		$	-		$	127.2		$	122.7		$	302
	Transfer of Assets into NUSCO Pension Plan Trust			80.5			-36.6		$	79.7			93.8			-57.1			2			162.3
	Transfer Between Categories			-			-			-			9.7			-			-9.7			-
	Actual Return/(Loss) on Plan Assets:
		Relating to Assets Still Held as of Year End		3.5			2.8			4.6			16.4			3.5			9.9			40.7
		Relating to Assets Distributed During the Year		3.6			-			4.2			-0.3			1.8			-			9.3
	Purchases, Sales and Settlements			-29.8			-			0.9			55.8			10.2			-0.8			36.3
	Balance as of December 31, 2013		$	57.8		$	18.3		$	89.4		$	175.4		$	85.6		$	124.1		$	550.6
Schedule of Allocation of Plan Assets [Table Text Block]	'
			As of December 31,
			2013				2012
			NUSCO and NSTAR Pension				NUSCO Pension
			and Tax-Exempt PBOP Plans⁽¹⁾				and PBOP Plans				NSTAR Pension Plan				NSTAR PBOP Plan
			Target		Assumed		Target		Assumed		Target		Assumed		Target		Assumed
			Asset		Rate		Asset		Rate		Asset		Rate		Asset		Rate
			Allocation		of Return		Allocation		of Return		Allocation		of Return		Allocation		of Return
	Equity Securities:
		United States	24%		9%		24%		9%		25%		8.30%		25%		8.30%
		International	10%		9%		13%		9%		13%		8.60%		20%		8.60%
		Emerging Markets	6%		10%		3%		10%		5%		8.80%		5%		8.80%
		Private Equity	10%		13%		12%		13%		-		-		-		-
	Debt Securities:
		Fixed Income	15%		5%		20%		5%		21%		4.60%		30%		4.60%
		High Yield Fixed Income	9%		7.50%		3.50%		7.50%		9%		6.50%		-		-
		Emerging Markets Debt	6%		7.50%		3.50%		7.50%		4%		6.40%		-		-
	Real Estate and Other Assets		9%		7.50%		8%		7.50%		10%		7.90%		10%		7.90%
	Hedge Funds		11%		7%		13%		7%		13%		8.40%		10%		8.40%

				NU Pension Plans
				Fair Value Measurements as of December 31,
		(Millions of Dollars)		2013												2012
		Asset Category:		Level 1			Level 2			Level 3			Total			Level 1			Level 2			Level 3			Total
		Equity Securities:
			United States ⁽¹⁾	$	294.6		$	597.7		$	194		$	1,086.30		$	336.5		$	302.8		$	270.6		$	909.9
			International ⁽¹⁾		32.2			362.6			61.5			456.3			42			362.6			52.1			456.7
			Emerging Markets⁽¹⁾		-			211.8			-			211.8			-			135.3			-			135.3
			Private Equity		96.4			-			300.3			396.7			26.7			-			267.9			294.6
		Fixed Income⁽²⁾			11.6			605.1			589.5			1,206.20			54.9			629.2			315.1			999.2
		Real Estate and Other Assets			-			88.2			288.5			376.7			-			78.9			235.4			314.3
		Hedge Funds			-			-			416.9			416.9			-			-			418.9			418.9
		Total Master Trust Assets		$	434.8		$	1,865.40		$	1,850.70		$	4,150.90		$	460.1		$	1,508.80		$	1,560.00		$	3,528.90
			Less: 401(h) PBOP Assets⁽³⁾											-165												-117.6
		Total Pension Assets											$	3,985.90											$	3,411.30

				NSTAR Pension Plan
				Fair Value Measurements as of December 31,
		(Millions of Dollars)		2013												2012
		Asset Category:		Level 1			Level 2			Level 3			Total			Level 1			Level 2			Level 3			Total
		Equity Securities:
			United States ⁽¹⁾	$	87.7		$	177.9		$	57.8		$	323.4		$	96.7		$	246.4		$	-		$	343.1
			International⁽¹⁾		9.6			108			18.3			135.9			-			98.3			52.1			150.4
			Emerging Markets⁽¹⁾		-			63.1			-			63.1			-			55.9			-			55.9
			Private Equity		28.7			-			89.4			118.1
		Fixed Income⁽²⁾			3.4			180			175.4			358.8			54.9			292.5			-			347.4
		Real Estate and Other Assets			-			26.3			85.6			111.9			-			-			127.2			127.2
		Hedge Funds			-			-			124.1			124.1			-			-			122.7			122.7
		Total Master Trust Assets		$	129.4		$	555.3		$	550.6		$	1,235.30		$	151.6		$	693.1		$	302		$	1,146.70
			Less: 401(h) PBOP Assets⁽³⁾																							-77.6
		Total Pension Assets																							$	1,069.10

				NU PBOP Plans
				Fair Value Measurements as of December 31,
		(Millions of Dollars)		2013												2012
		Asset Category:		Level 1			Level 2			Level 3			Total			Level 1			Level 2			Level 3			Total
		Cash and Cash Equivalents		$	11.1		$	-		$	-		$	11.1		$	9.7		$	-		$	-		$	9.7
		Equity Securities:
			United States⁽¹⁾		67			120.6			69.1			256.7			116.3			57.7			36.3			210.3
			International⁽¹⁾		28.1			42.8			-			70.9			68			29.7			-			97.7
			Emerging Markets⁽¹⁾		15.2			13.4			-			28.6			7.7			14			-			21.7
			Private Equity		-			-			17.9			17.9			-			-			11.3			11.3
		Fixed Income ⁽²⁾			-			119.7			51.5			171.2			-			137.7			32.1			169.8
		Real Estate and Other Assets			-			14.2			33.9			48.1			-			4.7			26.7			31.4
	Hedge Funds			-			-			57			57			-			-			39.6			39.6
	Total		$	121.4		$	310.7		$	229.4		$	661.5		$	201.7		$	243.8		$	146		$	591.5
		Add: 401(h) PBOP Assets⁽³⁾											165												117.6
	Total PBOP Assets											$	826.5											$	709.1

DEFINED_CONTRIBUTION_PLANS_TAB

DEFINED CONTRIBUTION PLANS (TABLES)	12 Months Ended
DEFINED CONTRIBUTION PLANS (TABLES)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Defined Contribution Plans 401k [Table Text Block]	'
						NSTAR
	(Millions of Dollars)	NU ⁽¹⁾		CL&P		Electric		PSNH		WMECO
	2013	$	37	$	5.1	$	8.5	$	3.3	$	1
	2012		25.7		4.8		9		3.3		0.9
	2011		17.4		4.5		8.7		3.1		0.9

ShareBased_Payments_Tables

Share-Based Payments (Tables)	12 Months Ended
Share-Based Payments (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	'
						Weighted Average
			RSUs			Grant-Date
			(Units)			Fair Value
	Outstanding as of January 1, 2011			1,014,479		$	24.31
	Granted			208,533		$	33.87
	Shares issued			-244,782		$	24.47
	Forfeited			-18,310		$	23.74
	Outstanding as of December 31, 2011			959,920		$	26.36
	Granted			614,930		$	33.04
	Converted NSTAR Awards upon Merger			617,394		$	36.79
	Converted from NU Performance Shares upon Merger			451,358		$	34.32
	Shares issued			-363,779		$	29.05
	Forfeited			-96,504		$	34.97
	Outstanding as of December 31, 2012			2,183,319		$	31.99
	Granted			373,939		$	39.56
	Shares issued			-891,129		$	32.15
	Forfeited			-29,689		$	33.75
	Outstanding as of December 31, 2013			1,636,440		$	33.61
			Performance			Weighted Average
			Shares			Grant-Date
			(Units)			Fair Value
	Outstanding as of January 1, 2011			248,559		$	24.72
	Granted			244,870		$	33.76
	Shares issued			-		$	-
	Forfeited			-10,296		$	30.47
	Outstanding as of December 31, 2011			483,133		$	29.18
	Granted			225,935		$	35.09
	Converted to RSUs upon Merger			-451,358		$	34.32
	Shares issued			-106,773		$	24.52
	Forfeited			-		$	-
	Outstanding as of December 31, 2012			150,937		$	25.04
	Granted			191,961		$	40.96
	Shares issued			-150,944		$	25.04
	Forfeited			-1,526		$	40.93
	Outstanding as of December 31, 2013			190,428		$	40.96
	NU				For the Years Ended December 31,
	(Millions of Dollars)				2013			2012 ⁽¹⁾			2011
	Compensation Expense				$	27		$	25.8		$	12.3
	Future Income Tax Benefit					10.7			10.2			4.9
			For the Years Ended December 31,
			2013											2012								2011
	(Millions of Dollars)		CL&P			NSTAR Electric			PSNH			WMECO		CL&P		NSTAR Electric		PSNH		WMECO		CL&P		NSTAR Electric		PSNH		WMECO
	Compensation
		Expense	$	6.8		$	7.5		$	2.3		$	1.3	$	4.8	$	7.4	$	1.8	$	1	$	7.1	$	7.7	$	2.5	$	1.4
	Future Income Tax
		Benefit		2.7			3			0.9			0.5		1.9		2.9		0.7		0.4		2.8		3		1		0.6

						Weighted Average			Intrinsic Value
				Options		Exercise Price			(Millions)
	Outstanding and Exercisable - January 1, 2011			112,599		$	18.8
	Exercised			-65,225		$	18.81		$	1
	Forfeited and Cancelled			-		$	-
	Outstanding and Exercisable - December 31, 2011			47,374		$	18.78
	Converted NSTAR Options upon Merger			2,664,894		$	23.99
	Exercised			-1,166,511		$	22.53		$	18.7
	Forfeited and Cancelled			-		$	-
	Outstanding and Exercisable - December 31, 2012			1,545,757		$	24.92
	Exercised			-324,382		$	20.97		$	6.7
	Forfeited and Cancelled			-		$	-
	Outstanding and Exercisable - December 31, 2013			1,221,375		$	25.97		$	20.1

Other_Retirement_Benefits_Tabl

Other Retirement Benefits (Tables)	12 Months Ended
Other Retirement Benefits (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits by Title of Individual and Type of Deferred Compensation [Table Text Block]	'

	NU		For the Years Ended December 31,
	(Millions of Dollars)		2013			2012			2011
	Actuarially-Determined Liability		$	51.3		$	54.6		$	52.8
	Other Retirement Benefits Expense			4.4			4.7			4.7
		For the Years Ended December 31,
		2013									2012						2011
	(Millions of Dollars)	CL&P			PSNH			WMECO			CL&P		PSNH		WMECO		CL&P		PSNH		WMECO
	Actuarially-Determined Liability	$	0.4		$	2.3		$	0.1		$	0.4	$	2.5	$	0.2	$	1.2	$	2.5	$	0.2
	Other Retirement Benefits Expense		2.5			1			0.5			2.6		1		0.5		2.6		1		0.5

INCOME_TAXES_Tables

INCOME TAXES (Tables)	12 Months Ended
INCOME TAXES (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	'
	NU	For the Years Ended December 31,
	(Millions of Dollars)	2013			2012 ⁽¹⁾			2011
	Current Income Taxes:
	Federal	$	8.8		$	-30.9		$	3
	State		-9.4			17.6			-26
	Total Current		-0.6			-13.3			-23
	Deferred Income Taxes, Net:
	Federal		386.2			291.3			187.7
	State		45.4			0.8			9.1
	Total Deferred		431.6			292.1			196.8
	Investment Tax Credits, Net		-4.1			-3.9			-2.8
	Income Tax Expense	$	426.9		$	274.9		$	171
			For the Years Ended December 31,
			2013												2012												2011
						NSTAR												NSTAR											NSTAR
	(Millions of Dollars)		CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO			CL&P		Electric		PSNH		WMECO
	Current Income
		Taxes:
		Federal	$	20.1		$	95.8		$	-8.2		$	-53.4		$	-47.8		$	93.5		$	-0.9		$	-24.7		$	13.9	$	64.9	$	-25.8	$	0.1
		State		-6.7			29.6			3.6			4.2			3.1			27.6			3.4			3.4			-34.4		30.2		0.1		0.3
	Total Current			13.4			125.4			-4.6			-49.2			-44.7			121.1			2.5			-21.3			-20.5		95.1		-25.7		0.4
	Deferred Income
		Taxes, Net:
		Federal		114.9			49.8			64.5			84.7			141.5			11.4			46.5			51.2			106.4		74.8		67.7		22.1
		State		15.1			-1			11.2			2.3			-0.5			-7.1			12			2.7			6.2		-2.8		7.9		1
	Total Deferred			130			48.8			75.7			87			141			4.3			58.5			53.9			112.6		72		75.6		23.1
	Investment Tax
		Credits, Net		-1.7			-1.3			0			-0.4			-1.9			-1.4			0			-0.5			-2.1		-1.4		-		-0.3
	Income Tax Expense		$	141.7		$	172.9		$	71.1		$	37.4		$	94.4		$	124		$	61		$	32.1		$	90	$	165.7	$	49.9	$	23.2

	(1) NSTAR amounts were included in NU beginning April 10, 2012.
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	'
	A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows:

	NU		For the Years Ended December 31,
	(Millions of Dollars, except percentages)		2013				2012 ⁽¹⁾				2011
	Income Before Income Tax Expense		$	1,220.60			$	808			$	571.5

	Statutory Federal Income Tax Expense at 35%			427.2				282.8				200
	Tax Effect of Differences:
		Depreciation		-7.4				-10.8				-14.2
		Investment Tax Credit Amortization		-4.1				-3.9				-2.8
		Other Federal Tax Credits		-3.7				-3.8				-3.5
		State Income Taxes, Net of Federal Impact		27.6				4.4				22.1
		ESOP		-8				-6.4				-2.2
		Tax Asset Valuation Allowance/Reserve Adjustments		-4.3				7.6				-33.1
		Other, Net		-0.4				5				4.7
	Income Tax Expense		$	426.9			$	274.9			$	171
	Effective Tax Rate			35.00%				34.00%				29.90%
			For the Years Ended December 31,
			2013												2012												2011
	(Millions of Dollars,					NSTAR												NSTAR											NSTAR
		except percentages)	CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO			CL&P		Electric		PSNH		WMECO
	Income Before Income
		Tax Expense	$	421.1		$	441.4		$	182.5		$	97.8		$	304.2		$	314.2		$	157.9		$	86.6		$	340.2	$	418.2	$	150.2	$	66.2

	Statutory Federal Income
		Tax Expense at 35%		147.4			154.5			63.9			34.2			106.5			110			55.3			30.3			119.1		146.4		52.6		23.2
	Tax Effect of Differences:
		Depreciation		-7			0.1			0.6			0			-9			0			-0.3			0.2			-8.1		0		-4.4		0.1
		Investment Tax Credit
		Amortization		-1.7			-1.3			0			-0.4			-1.9			-1.4			0			-0.5			-2.1		-1.4		-		-0.3
		Other Federal Tax
		Credits		0			0			-3.7			0			0			0			-3.8			0			-0.1		0		-3.4		0
		State Income Taxes,
		Net of Federal Impact		5			18.6			9.6			4.2			0.1			13.4			10			4			4		17.9		5.2		0.9
		ESOP		0			0			0			0			0			0			0			0			-		0		-		-
		Tax Asset Valuation
		Allowance/Reserve
		Adjustments		0.4			0			0			0			1.6			0			0			0			-22.3		0		-		-
		Regulatory Decision Non-
		Plant Flow Through		0			0			0			0			0			0			0			-1.3			0		0		-		-
		Other, Net		-2.4			1			0.7			-0.6			-2.9			2			-0.2			-0.6			-0.5		2.8		-0.1		-0.7
	Income Tax Expense		$	141.7		$	172.9		$	71.1		$	37.4		$	94.4		$	124		$	61		$	32.1		$	90	$	165.7	$	49.9	$	23.2
	Effective Tax Rate			33.60%			39.20%			39.00%			38.20%			31.00%			39.50%			38.60%			37.10%			26.50%		39.60%		33.20%		35.00%

	(1) NSTAR amounts were included in NU beginning April 10, 2012.
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	'
	NU			As of December 31,
	(Millions of Dollars)			2013			2012
	Deferred Tax Assets:
		Employee Benefits		$	435.2		$	811.4
		Derivative Liabilities and Change in Fair Value of Energy Contracts			272.9			380.6
		Regulatory Deferrals			272.7			257.9
		Allowance for Uncollectible Accounts			65			64.2
		Tax Effect - Tax Regulatory Assets			16.2			17.2
		Federal Net Operating Loss Carryforwards			158			214.6
		Purchase Accounting Adjustment			132.8			146.4
		Other			230.6			242.4
	Total Deferred Tax Assets				1,583.40			2,134.70
		Less: Valuation Allowance			24.3			4.2
	Net Deferred Tax Assets			$	1,559.10		$	2,130.50
	Deferred Tax Liabilities:
		Accelerated Depreciation and Other Plant-Related Differences		$	3,806.50		$	3,468.80
		Property Tax Accruals			95.1			89.6
		Regulatory Amounts:
			Other Regulatory Deferrals		1,146.70			1,561.10
			Tax Effect - Tax Regulatory Assets		248.2			217.2
			Goodwill Regulatory Asset - 1999 Merger		211.5			210.9
			Derivative Assets		30.1			36.2
			Securitized Contract Termination Costs		0.3			16.6
			Other		156.8			136.1
	Total Deferred Tax Liabilities			$	5,695.20		$	5,736.50
				As of December 31,
				2013												2012
							NSTAR												NSTAR
	(Millions of Dollars)			CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO
	Deferred Tax Assets:
		Employee Benefits		$	56		$	38.3		$	15.5		$	-1.8		$	141.2		$	116.3		$	64.8		$	16.3
		Derivative Liabilities and Change in
			Fair Value of Energy Contracts		272.4			3.3			0			-2.9			375.9			5.8			-			-1.7
		Regulatory Deferrals			61.5			114.7			40.9			1			35.5			123.6			43.9			6.3
		Allowance for Uncollectible Accounts			31.2			15.4			3.1			3.3			30.4			16.2			2.9			3.2
		Tax Effect - Tax Regulatory Assets			4.7			5.4			2.1			1.6			5.2			6			1.7			1.7
		Federal Net Operating Loss Carryforwards			51			0			56.6			18.6			82			-			71.4			15.1
		Other			75.3			31.3			40.3			8.3			82.8			26			33.7			8
	Total Deferred Tax Assets				552.1			208.4			158.5			28.1			753			293.9			218.4		$	48.9
		Less: Valuation Allowance			23.1			0			0			0			0			0			0			0
	Net Deferred Tax Assets			$	529		$	208.4		$	158.5		$	28.1		$	753		$	293.9		$	218.4		$	48.9
	Deferred Tax Liabilities:
		Accelerated Depreciation and Other
		Plant-Related Differences		$	1,238.10		$	1,179.40		$	526.6		$	361.1		$	1,194.70		$	1,079.30		$	476.5		$	261.3
		Property Tax Accruals			49.3			25.3			7.1			5.9			44.4			23.1			6.8			5.1
		Regulatory Amounts:
			Other Regulatory Deferrals		550.4			276.2			109.3			49.3			677.7			379.6			149.3			74.5
			Tax Effect - Tax Regulatory Assets		160.1			36			16.3			18.2			151.8			20.9			15.8			13.9
			Goodwill Regulatory Asset - 1999 Merger		-			181.6			-			-			-			181			-			-
			Derivative Assets		29			0.5			-			-			36.2			-			-			-
			Securitized Contract Termination Costs		-			0			0			0.3			-			5.5			7.9			3.3
			Other		20.6			26.4			28			3.3			10.1			30.2			14.1			2.3
	Total Deferred Tax Liabilities			$	2,047.50		$	1,725.40		$	687.3		$	438.1		$	2,114.90		$	1,719.60		$	670.4		$	360.4
Summary of Operating Loss Carryforwards [Table Text Block]	'
	Carryforwards: The following tables provide the amounts and expiration dates of state tax credit and loss carryforwards and federal tax credit and net operating loss carryforwards:

		As of December 31, 2013
								NSTAR									Year
	(Millions of Dollars)	NU			CL&P			Electric			PSNH			WMECO			Expiration Begins
	Federal Net Operating Loss	$	451.3		$	145.8		$	0		$	161.8		$	53.3		2031
	Federal Tax Credit		8			0			0			7.6			0		2031
	State Tax Credit		104.7			86.8			0			0			0		2013
	State Loss Carryforwards		12.1			0			0			0			0		2013

		As of December 31, 2012
								NSTAR									Year
	(Millions of Dollars)	NU			CL&P			Electric			PSNH			WMECO			Expiration Begins
	Federal Net Operating Loss	$	606.9		$	234.3		$	0		$	204		$	43.3		2031
	Federal Tax Credit		3.8			0			0			3.8			0		2031
	State Tax Credit		110.2			75.2			0			0			0		2013
	State Loss Carryforwards		74.9			0			0			0			0		2013
Summary of Income Tax Contingencies [Table Text Block]	'

	(Millions of Dollars)		NU			CL&P
	Balance as of January 1, 2011		$	101.2		$	80.8
		Gross Increases - Current Year		8			1.4
		Gross Decreases - Prior Year		-35.7			-35.7
	Balance as of December 31, 2011			73.5			46.5
		Gross Increases - Current Year		10.3			2.5
		Gross Increases - Prior Year		0.1			-
		Gross Decreases - Prior Year		-0.8			-
	Balance as of December 31, 2012			83.1			49
		Gross Increases - Current Year		8.2			2.1
		Gross Decreases - Prior Year		-1.1			-0.3
		Settlements		-49.8			-39.4
		Lapse of Statute of Limitations		-2.2			-
	Balance as of December 31, 2013		$	38.2		$	11.4
	Other Interest		For the Years Ended December 31,									Accrued Interest		As of December 31,
	Expense/(Income)		2013			2012			2011			Expense		2013			2012
	(Millions of Dollars)											(Millions of Dollars)
	NU ⁽¹⁾		$	-8.6		$	3.1		$	-2.8		NU		$	1.5		$	10.1
	CL&P			-4			1.3			-3.7		CL&P			0			4
	NSTAR Electric			0			0			2		NSTAR Electric			0			0
	PSNH			0			0			-0.6		PSNH			0			0

Environmental_Matters_Tablels

Environmental Matters (Tablels)	12 Months Ended
Environmental Matters (Tablels)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Environmental Loss Contingencies By Site Text Block	'
	(Millions of Dollars)	NU ⁽¹⁾		CL&P		NSTAR Electric			PSNH			WMECO
	Balance as of January 1, 2012	$	31.7	$	2.9	$	1.3		$	6.6		$	0.3
	Liabilities Assumed from Merger with NSTAR		11.8		-		-			-			-
	Additions		4.7		1.3		0.7			0.2			0.5
	Payments/Reductions		-8.8		-0.5		-0.3			-1.9			-0.2
	Balance as of December 31, 2012		39.4		3.7		1.7			4.9			0.6
	Additions		3.5		0.2		0.2			1			-
	Payments/Reductions		-7.5		-0.5		-0.7			-0.5			-0.2
	Balance as of December 31, 2013	$	35.4	$	3.4	$	1.2		$	5.4		$	0.4
		As of December 31, 2013					As of December 31, 2012
				Reserve						Reserve
		Number of Sites		(in millions)			Number of Sites			(in millions)
	NU		68	$	35.4			77		$	39.4
	CL&P		18		3.4			19			3.7
	NSTAR Electric		12		1.2			16			1.7
	PSNH		15		5.4			16			4.9
	WMECO		5		0.4			6			0.6

LongTerm_Contractual_Arrangeme

Long-Term Contractual Arrangements (Tables)	12 Months Ended
Long-Term Contractual Arrangements (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Long-term Purchase Commitment [Table Text Block]	'
	B.			Long-Term Contractual Arrangements
	Estimated Future Annual Costs: The estimated future annual costs of significant long-term contractual arrangements as of
	December 31, 2013 are as follows:


	NU
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Supply and Stranded Cost				$	224.2		$	205.2		$	177.7		$	119.9		$	110.4		$	309.3		$	1,146.70
	Renewable Energy					194.5			203.8			214.1			211.9			177.3			1,885.70			2,887.30
	Peaker CfDs					49.1			46.9			44.3			36.2			28.6			24.7			229.8
	Natural Gas Procurement					134.4			117.6			76.5			37.7			24.2			103.9			494.3
	Coal, Wood and Other					75.3			15.2			5			5			5			16.8			122.3
	Transmission Support Commitments					27.9			26.9			20.5			18			22.6			45.2			161.1
	Total				$	705.4		$	615.6		$	538.1		$	428.7		$	368.1		$	2,385.60		$	5,041.50

	CL&P
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Supply and Stranded Cost				$	145.6		$	141.1		$	143.7		$	96.2		$	87.1		$	257.6		$	871.3
	Renewable Energy					48.9			49.9			50.3			50.8			51.4			560.2			811.5
	Peaker CfDs					49.1			46.9			44.3			36.2			28.6			24.7			229.8
	Transmission Support Commitments					11			10.6			8.1			7.1			8.9			17.8			63.5
	Yankee Billings					1.5			1.4			0.8			0.8			0.8			12.3			17.6
	Total				$	256.1		$	249.9		$	247.2		$	191.1		$	176.8		$	872.6		$	1,993.70

	NSTAR Electric
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Supply and Stranded Cost				$	36.2		$	36.1		$	15.8		$	5.6		$	5.5		$	36.8		$	136
	Renewable Energy					87.1			86.3			85.8			81.9			45.4			207.4			593.9
	Transmission Support Commitments					8.7			8.4			6.4			5.6			7			14.1			50.2
	Yankee Billings					0.7			0.5			0.3			0.3			0.3			4.2			6.3
	Total				$	132.7		$	131.3		$	108.3		$	93.4		$	58.2		$	262.5		$	786.4

	PSNH
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Supply and Stranded Cost				$	42.4		$	28		$	18.2		$	18.1		$	17.8		$	14.9		$	139.4
	Renewable Energy					56.8			57.7			67.9			69			70.1			995.2			1,316.70
	Coal, Wood and Other					75.3			15.2			5			5			5			16.8			122.3
	Transmission Support Commitments					5.9			5.7			4.3			3.8			4.8			9.6			34.1
	Yankee Billings					0.3			0.3			0.3			0.3			0.3			4.9			6.4
	Total				$	180.7		$	106.9		$	95.7		$	96.2		$	98		$	1,041.40		$	1,618.90

	WMECO
	(Millions of Dollars)				2014			2015			2016			2017			2018			Thereafter			Total
	Renewable Energy				$	1.7		$	9.9		$	10.1		$	10.2		$	10.4		$	122.9		$	165.2
	Transmission Support Commitments					2.3			2.2			1.7			1.5			1.9			3.7			13.3
	Yankee Billings					0.4			0.4			0.2			0.2			0.2			3.1			4.5
	Total				$	4.4		$	12.5		$	12		$	11.9		$	12.5		$	129.7		$	183
	NU		For the Years Ended December 31,
	(Millions of Dollars)		2013			2012⁽¹⁾			2011
	Supply and Stranded Cost		$	141		$	216.8		$	156
	Renewable Energy			91.3			48.7			5.1
	Peaker CfDs			51.9			59.3			40.2
	Natural Gas Procurement			349.8			243.1			191.7
	Coal, Wood and Other			112.6			105.2			113.2
	Transmission Support Commitments			24.9			24.8			18.1
			For the Years Ended December 31,
			2013												2012											2011
						NSTAR												NSTAR										NSTAR
	(Millions of Dollars)		CL&P			Electric			PSNH			WMECO			CL&P			Electric			PSNH			WMECO		CL&P		Electric		PSNH		WMECO
	Supply and
		Stranded Cost	$	77.6		$	32.4		$	29		$	2		$	158.2		$	36.3		$	30.5		$	0.9	$	114.9	$	80.9	$	40.8	$	0.3
	Renewable Energy			-			84.9			6.4			-			-			60.2			4.1			-		-		61.8		5.1		-
	Peaker CfDs			51.9			-			-			-			59.3			-			-			-		40.2		-		-		-
Coal, Wood and Other			-			-			112.6			-			-			-			105.2			-		-		-		113.2		-
Transmission Support
	Commitments		9.8			7.7			5.3			2.1			9.6			7.6			5.2			2		10.3		8.1		5.6		2.2

Guarantees_and_Indemnification

Guarantees and Indemnifications (Tables)	12 Months Ended
Guarantees and Indemnifications (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Guarantee Obligations Text Block	'
			Maximum Exposure
	Subsidiary	Description	(in millions)		Expiration Dates

	Various	Surety Bonds	$	69.2	2014 - 2016⁽¹⁾

	Various	NE Hydro Companies' Long-Term Debt	$	3.5	Unspecified

	NUSCO and RRR	Lease Payments for Vehicles and Real Estate	$	17.7	2019 and 2024

LEASES_Tables

LEASES (Tables)	12 Months Ended
LEASES (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Rent Expense [Table Text Block]	'
									NSTAR
	(Millions of Dollars)		NU ⁽¹⁾			CL&P			Electric			PSNH			WMECO
	2013		$	16.3		$	8.1		$	6.7		$	1.7		$	2.9
	2012			14.8			8.2			6.2			2.5			3
	2011			8.4			8.3			19.8			2.1			2.8
Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block]	'
	Capital Leases
	(Millions of Dollars)	NU			CL&P			PSNH
	2014	$	2.6		$	2.1		$	0.4
	2015		2.4			2			0.4
	2016		2.2			1.9			0.3
	2017		2.1			2			0.1
	2018		2.1			2			0.1
	Thereafter		5.4			5.4			0
	Future minimum lease payments		16.8			15.4			1.3
	Less amount representing interest		6.1			6.1			0
	Present value of future minimum lease payments	$	10.7		$	9.3		$	1.3
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	'
	Operating Leases
	(Millions of Dollars)	NU			CL&P			NSTAR Electric			PSNH			WMECO
	2014	$	20.1		$	4		$	10.9		$	1		$	1.1
	2015		18.1			3.6			10.1			0.9			0.7
	2016		15.4			2.9			8.9			0.8			0.5
	2017		12.4			1.7			7.7			0.6			0.3
	2018		8.5			1.2			5.1			0.5			0.2
	Thereafter		22.3			4.7			11.7			1.3			1
	Future minimum lease payments	$	96.8		$	18.1		$	54.4		$	5.1		$	3.8

FAIR_VALUE_OF_FINANCIAL_INSTRU1

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Fair Value By Balance Sheet Grouping Text Block	'
			As of December 31,
			2013				2012
	NU		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)		Amount		Value		Amount		Value
	Preferred Stock Not
		Subject to Mandatory Redemption	$	155.6	$	152.7	$	155.6	$	152.2
	Long-Term Debt			8,310.20		8,443.10		7,963.50		8,640.70
	Rate Reduction Bonds			-		-		82.1		83
			As of December 31, 2013
			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	$	110.5	$	43	$	42.2	$	-	$	-	$	-	$	-
	Long-Term Debt			2,741.20		2,952.80		1,801.10		1,888.00		1,049.00		1,073.90		629.4		640.1

			As of December 31, 2012
			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	$	110	$	43	$	42.2	$	-	$	-	$	-	$	-
	Long-Term Debt			2,862.80		3,295.40		1,602.60		1,818.80		997.9		1,088.00		605.3		660.4
	Rate Reduction Bonds			-		-		43.5		43.9		29.3		29.6		9.4		9.5

ACCUMULATED_OTHER_COMPREHENSIV1

ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	12 Months Ended
ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Accumulated Other Comprehensive Income Loss Table Text Block	'
			For the Year Ended December 31, 2013
						Unrealized
			Qualified Cash			Gains/(Losses) on			Pension, SERP
			Flow Hedging			Available-for-Sale			and PBOP
	(Millions of Dollars)		Instruments			Securities			Benefit Plans			Total
	AOCI as of January 1, 2013		$	-16.4		$	1.3		$	-57.8		$	-72.9

	Other Comprehensive Income Before Reclassifications			-			-0.9			19.4			18.5
	Amounts Reclassified from AOCI			2			-			6.4			8.4
	Net Other Comprehensive Income			2			-0.9			25.8			26.9
	AOCI as of December 31, 2013		$	-14.4		$	0.4		$	-32		$	-46
Schedule Of Comprehensive Income Loss [Table Text Block]	'
		For the Years Ended December 31,
		2013			2012			2011
		Amount Reclassified			Amount Reclassified			Amount Reclassified			Statements of Income
	(Millions of Dollars)	from AOCI			from AOCI			from AOCI			Line Item Impacted
	Qualified Cash Flow Hedging Instruments	$	-3.4		$	-3.3		$	-1.3		Interest Expense
	Tax Effect		1.4			1.3			0.6		Income Tax Expense
	Qualified Cash Flow Hedging Instruments, Net of Tax	$	-2		$	-2		$	-0.7

	Pension, SERP and PBOP Benefit Plan Costs:
	Amortization of Actuarial Losses	$	-10.5		$	-8.9		$	-5.7		Operations and Maintenance⁽¹⁾
	Amortization of Prior Service Cost		-0.2			-0.2			-0.3		Operations and Maintenance⁽¹⁾
	Amortization of Transition Obligation		-			-0.2			-0.2		Operations and Maintenance⁽¹⁾
	Total Pension, SERP and PBOP Benefit Plan Costs		-10.7			-9.3			-6.2		Operations and Maintenance⁽¹⁾
	Tax Effect		4.3			3.5			2.3		Income Tax Expense
	Pension, SERP and PBOP Benefit Plan Costs,
	Net of Tax	$	-6.4		$	-5.8		$	-3.9

	Total Amount Reclassified from AOCI, Net of Tax	$	-8.4		$	-7.8		$	-4.6

COMMON_SHARES_Tables

COMMON SHARES (Tables)	12 Months Ended
COMMON SHARES (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Stock by Class [Text Block]	'
	17. COMMON SHARES

	The following table sets forth the NU 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	Issued
		Per Share		As of December 31,	As of December 31,
		Par Value		2013 and 2012	2013		2012
	NU	$	5	380,000,000		333,113,492		332,509,383
	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 December 31, 2013 and 2012, there were 17,796,672 and 18,455,749 NU common shares held as treasury shares, respectively.

PREFFERED_STOCK_TABLES

PREFFERED STOCK (TABLES)	12 Months Ended
PREFFERED STOCK (TABLES)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Preferred Stock [Text Block]	'
					Redemption Price		Shares Outstanding as of	As of December 31,
	Series				Per Share		December 31, 2013 and 2012	2013		2012
	CL&P
	$	1.9		Series of 1947	$	52.5	163,912	$	8.2	$	8.2
	$	2		Series of 1947	$	54	336,088		16.8		16.8
	$	2.04		Series of 1949	$	52	100,000		5		5
	$	2.2		Series of 1949	$	52.5	200,000		10		10
		3.9	%	Series of 1949	$	50.5	160,000		8		8
	$	2.06		Series E of 1954	$	51	200,000		10		10
	$	2.09		Series F of 1955	$	51	100,000		5		5
		4.5	%	Series of 1956	$	50.75	104,000		5.2		5.2
		4.96	%	Series of 1958	$	50.5	100,000		5		5
		4.5	%	Series of 1963	$	50.5	160,000		8		8
		5.28	%	Series of 1967	$	51.43	200,000		10		10
	$	3.24		Series G of 1968	$	51.84	300,000		15		15
		6.56	%	Series of 1968	$	51.44	200,000		10		10
	Total CL&P						2,324,000	$	116.2	$	116.2

	NSTAR Electric
		4.25	%	Series	$	103.625	180,000	$	18	$	18
		4.78	%	Series	$	102.8	250,000		25		25
	Total NSTAR Electric						430,000	$	43	$	43
	Fair Value Adjustment due to Merger with NSTAR								-3.6		-3.6
	Total NU - Preferred Stock of Subsidiaries							$	155.6	$	155.6

COMMON_SHARESHOLDERS_EQUITY_AN1

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) (Tables)	12 Months Ended
	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Minority Interest Disclosure Text Block	'
	19	COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS

	A summary of the changes in Common Shareholders' Equity and Noncontrolling Interests of NU is as follows:

									Noncontrolling
			Common						Interest -
			Shareholders'		Noncontrolling		Total		Preferred Stock
	(Millions of Dollars)		Equity		Interest		Equity		of Subsidiaries
	Balance as of January 1, 2011		$	3,811.20	$	1.5	$	3,812.70	$	116.2
	Net Income			400.5		-		400.5		-
	Dividends on Common Shares			-195.6		-		-195.6		-
	Dividends on Preferred Stock			-5.6		-		-5.6		-5.6
	Issuance of Common Shares			5.9		-		5.9		-
	Contributions to NPT			-		1.2		1.2		-
	Other Transactions, Net			23.9		-		23.9		-
	Net Income Attributable to Noncontrolling Interests			-0.3		0.3		-		5.6
	Other Comprehensive Loss (Note 15)			-27.3		-		-27.3		-
	Balance as of December 31, 2011		$	4,012.70	$	3	$	4,015.70	$	116.2
	Net Income			533.1		-		533.1		-
	Purchase Price of NSTAR ⁽¹⁾			5,038.30		-		5,038.30		-
	Other Equity Impacts of Merger with NSTAR ⁽²⁾			3.4		-3.4		-		39.4
	Dividends on Common Shares			-375.5		-		-375.5		-
	Dividends on Preferred Stock			-7		-		-7		-7
	Issuance of Common Shares			13.3		-		13.3		-
	Contributions to NPT			-		0.3		0.3		-
	Other Transactions, Net			21.1		-		21.1		-
	Net Income Attributable to Noncontrolling Interests			-0.1		0.1		-		7
	Other Comprehensive Loss (Note 15)			-2.2		-		-2.2		-
	Balance as of December 31, 2012		$	9,237.10	$	-	$	9,237.10	$	155.6
	Net Income			793.7		-		793.7		-
	Dividends on Common Shares			-462.7		-		-462.7		-
	Dividends on Preferred Stock			-7.7		-		-7.7		-7.7
	Issuance of Common Shares			11.1		-		11.1		-
	Other Transactions, Net			13.2		-		13.2		-
	Net Income Attributable to Noncontrolling Interests			-		-		-		7.7
	Other Comprehensive Income (Note 15)			26.8		-		26.8		-
	Balance as of December 31, 2013		$	9,611.50	$	-	$	9,611.50	$	155.6

EARNINGS_PER_SHARE_Tables

EARNINGS PER SHARE (Tables)	12 Months Ended
EARNINGS PER SHARE (Tables)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Earnings Per Share Basic And Diluted [Table Text Block]	'
			For the Years Ended December 31,
	(Millions of Dollars, except share information)		2013		2012		2011
	Net Income Attributable to Controlling Interest		$	786	$	525.9	$	394.7

	Weighted Average Common Shares Outstanding:
		Basic		315,311,387		277,209,819		177,410,167
		Dilutive Effect		899,773		783,812		394,401
		Diluted		316,211,160		277,993,631		177,804,568
	Basic EPS		$	2.49	$	1.9	$	2.22
	Diluted EPS		$	2.49	$	1.89	$	2.22

SEGMENT_INFORMATION_Tables

SEGMENT INFORMATION (Tables)	12 Months Ended
SEGMENT INFORMATION (Tables)	Dec. 31, 2013
Segment Reporting Information [Line Items]	'
Schedule Of Segment Reporting Information By Segment Text Block	'
			For the Year Ended December 31, 2013
			Electric		Natural Gas
	(Millions of Dollars)		Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues		$	5,362.30	$	855.8	$	978.7	$	777.5	$	-673.1	$	7,301.20
	Depreciation and Amortization			-604.8		-66.7		-136.2		-62.2		10.2		-859.7
	Other Operating Expenses			-3,927.70		-659.4		-281.8		-715		671.8		-4,912.10
	Operating Income			829.8		129.7		560.7		0.3		8.9		1,529.40
	Interest Expense			-175		-33.1		-100.3		-35.5		5.2		-338.7
	Interest Income			4.1		-		0.7		5.4		-5.6		4.6
	Other Income, Net			12.9		0.8		10.9		858.9		-858.2		25.3
	Income Tax (Expense)/Benefit			-240		-36.5		-182.1		31.9		-0.2		-426.9
	Net Income			431.8		60.9		289.9		861		-849.9		793.7
	Net Income Attributable
		to Noncontrolling Interests		-4.8		-		-2.9		-		-		-7.7
	Net Income Attributable
		to Controlling Interest	$	427	$	60.9	$	287	$	861	$	-849.9	$	786
	Total Assets (as of)		$	17,260.00	$	2,759.70	$	6,745.80	$	11,842.40	$	-10,812.40	$	27,795.50
	Cash Flows Used for
		Investments in Plant	$	639	$	168.1	$	618.5	$	31.2	$	-	$	1,456.80
			For the Year Ended December 31, 2012
			Electric		Natural Gas
	(Millions of Dollars)		Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues		$	4,716.50	$	572.9	$	861.5	$	803.8	$	-680.9	$	6,273.80
	Depreciation and Amortization			-530.3		-49.1		-109.2		-56.4		4.2		-740.8
	Other Operating Expenses			-3,585.40		-445.2		-251.6		-817		684.4		-4,414.80
	Operating Income/(Loss)			600.8		78.6		500.7		-69.6		7.7		1,118.20
	Interest Expense			-165.6		-31.3		-96.7		-43.6		7.3		-329.9
	Interest Income			2.8		-		0.4		7.1		-7.1		3.2
	Other Income, Net			8.9		0.4		7.3		795		-795.1		16.5
	Income Tax (Expense)/Benefit			-150.2		-16.9		-159.2		55.5		-4.1		-274.9
	Net Income			296.7		30.8		252.5		744.4		-791.3		533.1
	Net Income Attributable
		to Noncontrolling Interests		-4.4		-		-2.8		-		-		-7.2
	Net Income Attributable
		to Controlling Interest	$	292.3	$	30.8	$	249.7	$	744.4	$	-791.3	$	525.9
	Total Assets (as of)		$	18,047.30	$	2,717.40	$	6,187.70	$	18,832.60	$	-17,482.20	$	28,302.80
	Cash Flows Used for
		Investments in Plant	$	611.7	$	148.7	$	663.6	$	48.3	$	-	$	1,472.30
			For the Year Ended December 31, 2011
			Electric		Natural Gas
	(Millions of Dollars)		Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues		$	3,343.10	$	430.8	$	635.4	$	541.3	$	-484.9	$	4,465.70
	Depreciation and Amortization			-337.2		-27.7		-84		-16.8		2.5		-463.2
	Other Operating Expenses			-2,637.40		-333.5		-188.2		-534.1		484.9		-3,208.30
	Operating Income/(Loss)			368.5		69.6		363.2		-9.6		2.5		794.2
	Interest Expense			-123.8		-21		-76.7		-33.7		4.8		-250.4
	Interest Income			3.7		-		0.5		5.3		-5.3		4.2
	Other Income, Net			11.6		1.3		10.7		455.2		-455.3		23.5
	Income Tax (Expense)/Benefit			-67.6		-18.2		-95.6		14.3		-3.9		-171
	Net Income			192.4		31.7		202.1		431.5		-457.2		400.5
	Net Income Attributable
		to Noncontrolling Interests		-3.3		-		-2.5		-		-		-5.8
	Net Income Attributable
		to Controlling Interest	$	189.1	$	31.7	$	199.6	$	431.5	$	-457.2	$	394.7
	Cash Flows Used for
		Investments in Plant	$	540.7	$	98.2	$	388.9	$	48.9	$	-	$	1,076.70

QUARTERLY_FINANCIAL_DATA_Unaud1

QUARTERLY FINANCIAL DATA (Unaudited) (Tables)	12 Months Ended
QUARTERLY FINANCIAL DATA (Unaudited) (Tables)	Dec. 31, 2013
Quarterly Financial Data [Abstract]	'
Schedule of Quarterly Financial Information [Table Text Block]	'
	NU Consolidated Statements of Quarterly Financial Data	Quarter Ended
	(Millions of Dollars, except per share information)	March 31,		June 30,		September 30,		December 31,
	2013
	Operating Revenues	$	1,995.00	$	1,635.90	$	1,892.60	$	1,777.70
	Operating Income		418.9		350.6		399.3		360.6
	Net Income		230		173.1		211.4		179.2
	Net Income Attributable to Controlling Interest		228.1		171		209.5		177.4
	Basic and Diluted EPS (a)	$	0.72	$	0.54	$	0.66	$	0.56

	2012 ⁽¹⁾
	Operating Revenues	$	1,099.60	$	1,628.70	$	1,861.50	$	1,684.00
	Operating Income		214.4		159.5		412.9		331.4
	Net Income		100.8		46.2		209.5		176.6
	Net Income Attributable to Controlling Interest		99.3		44.3		207.6		174.7
	Basic and Diluted EPS (a)	$	0.56	$	0.15	$	0.66	$	0.55

	(a) The summation of quarterly EPS data may not equal annual data due to rounding.

	Statements of Quarterly Financial Data	Quarter Ended
	(Millions of Dollars)	March 31,		June 30,		September 30,		December 31,
	CL&P
	2013
	Operating Revenues	$	624.1	$	569.3	$	648.4	$	600.5
	Operating Income		149.7		136.8		133.9		119.2
	Net Income		85		67.9		66.3		60.2

	2012
	Operating Revenues	$	592	$	562.1	$	658.1	$	595.2
	Operating Income		111.9		40.4		139.7		135
	Net Income		54		6.9		74.9		73.9

	NSTAR Electric
	2013
	Operating Revenues	$	592.3	$	570.4	$	753.9	$	576.9
	Operating Income		94.5		112.5		192		109.2
	Net Income		48.1		58		107		55.4

	2012
	Operating Revenues	$	556.5	$	534.6	$	693.7	$	516.2
	Operating Income		22.5		93.9		194.1		70.9
	Net Income		3.9		45.5		106.8		34

	PSNH
	2013
	Operating Revenues	$	273.8	$	216.1	$	218.6	$	226.9
	Operating Income		58.1		54.3		56.6		56.2
	Net Income		29		27.2		28.4		26.8

	2012
	Operating Revenues	$	243	$	255.1	$	256.9	$	233
	Operating Income		45.4		47		61.3		51.4
	Net Income		21.3		21.2		27.2		27.2

	WMECO
	2013
	Operating Revenues	$	125	$	115	$	121.8	$	110.9
	Operating Income		35.6		32.4		28.9		22.4
	Net Income		18.6		16.4		15		10.4

	2012
	Operating Revenues	$	114	$	106.8	$	112.5	$	107.9
	Operating Income		28.7		25.1		28.1		28.9
	Net Income		14.2		11.1		14.1		15.1

Provision_for_Uncollectible_Ac1

Provision for Uncollectible Accounts (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	$171.30	$165.50
The Connecticut Light And Power Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	82	77.6
Uncollectible Hardship Accounts Receivable Reserve	67.3	65.2
NSTAR Electric Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	41.7	44.1
Public Service Company Of New Hampshire [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	7.4	6.8
Western Massachusetts Electric Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	10	8.5
Uncollectible Hardship Accounts Receivable Reserve	5.5	4.7
Yankee Gas Services Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Uncollectible Hardship Accounts Receivable Reserve	$8.40	$6.40

Fuel_Materials_and_Supplies_an

Fuel, Materials and Supplies and Allowance Inventory (Details) (Public Service Company Of New Hampshire [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
	Dec. 31, 2013	Emission Allowances [Member]	Emission Allowances [Member]	Emission Allowances [Member]
Other Inventory, Capitalized Costs	'	$0.40	'	$0.20
Other Inventory, Noncurrent	'	19.4	'	19.4
Amortization of Power Contracts Emission Credits	0.3	0.4	5.1	'
EmissionAllowanceAuctionProceeds	$6.80	'	'	'

Restricted_Cash_and_Other_Depo

Restricted Cash and Other Deposits (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Special Deposits [Line Items]	'	'
Rate Reduction Bond Deposits	'	$69.40
Restricted Cash And Cash Equivalents	1.7	3.3
Cash Collateral Deposited	17.9	14.6
The Connecticut Light And Power Company [Member]	'	'
Special Deposits [Line Items]	'	'
Restricted Cash And Cash Equivalents	1.4	1.3
NSTAR Electric Company [Member]	'	'
Special Deposits [Line Items]	'	'
Rate Reduction Bond Deposits	'	42.2
Cash Collateral Deposited	9	'
Public Service Company Of New Hampshire [Member]	'	'
Special Deposits [Line Items]	'	'
Rate Reduction Bond Deposits	'	22
Restricted Cash And Cash Equivalents	'	1.7
Western Massachusetts Electric Company [Member]	'	'
Special Deposits [Line Items]	'	'
Rate Reduction Bond Deposits	'	$5.10

Equity_Method_Investments_Deta

Equity Method Investments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
The Connecticut Light And Power Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	$1,200	$1,400
NSTAR Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	500	600
Western Massachusetts Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	300	400
Public Service Company Of New Hampshire [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	300	300
CYAPC [Member] \| The Connecticut Light And Power Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	34.50%	'
CYAPC [Member] \| NSTAR Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	14.00%	'
CYAPC [Member] \| Western Massachusetts Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	9.50%	'
CYAPC [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	5.00%	'
YAEC [Member] \| The Connecticut Light And Power Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	24.50%	'
YAEC [Member] \| NSTAR Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	14.00%	'
YAEC [Member] \| Western Massachusetts Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	7.00%	'
YAEC [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	7.00%	'
MYAPC [Member] \| The Connecticut Light And Power Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	12.00%	'
MYAPC [Member] \| NSTAR Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	4.00%	'
MYAPC [Member] \| Western Massachusetts Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	3.00%	'
MYAPC [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investment, Ownership Percentage	5.00%	'
Regional Transmission Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	5,100	6,000
Equity Method Investment, Ownership Percentage	37.20%	37.20%
Regional Transmission Company [Member] \| NSTAR Electric Company [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	2,000	2,300
Equity Method Investment, Ownership Percentage	14.50%	'
Energy Investment Fund [Member]	'	'
Schedule of Equity Method Investments [Line Items]	'	'
Equity Method Investments	$9,800	'

Operating_Expenses_Details

Operating Expenses (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fuel [Line Items]	'	'	'
Fuel Power Costs	$466.50	$346.80	$307.90
Public Service Company Of New Hampshire [Member]	'	'	'
Fuel [Line Items]	'	'	'
Fuel Power Costs	$104.80	$103.40	$115.90

Allowance_for_Funds_Used_Durin1

Allowance for Funds Used During Construction (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance For Funds Used During Construction [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Capitalized Interest	$4.10	$5.30	$11.80
Public Utilities Allowance For Funds Used During Construction Additions	7.1	6.8	22.5
Public Utilities Allowance For Funds Used During Construction Capitalized Total	11.2	12.1	34.3
Public Utilities Allowance For Funds Used During Construction Rate	2.70%	3.70%	7.30%
The Connecticut Light And Power Company [Member]	'	'	'
Allowance For Funds Used During Construction [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Capitalized Interest	2.2	2.5	3.3
Public Utilities Allowance For Funds Used During Construction Additions	2.9	1.9	6
Public Utilities Allowance For Funds Used During Construction Capitalized Total	5.1	4.4	9.3
Public Utilities Allowance For Funds Used During Construction Rate	3.70%	3.60%	8.30%
NSTAR Electric Company [Member]	'	'	'
Allowance For Funds Used During Construction [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Capitalized Interest	0.5	0.3	0.2
Public Utilities Allowance For Funds Used During Construction Capitalized Total	0.5	0.3	0.2
Public Utilities Allowance For Funds Used During Construction Rate	0.50%	0.40%	0.30%
Public Service Company Of New Hampshire [Member]	'	'	'
Allowance For Funds Used During Construction [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Capitalized Interest	0.5	1.6	7.1
Public Utilities Allowance For Funds Used During Construction Additions	0.2	1.9	13.2
Public Utilities Allowance For Funds Used During Construction Capitalized Total	0.7	3.5	20.3
Public Utilities Allowance For Funds Used During Construction Rate	1.10%	5.90%	7.10%
Western Massachusetts Electric Company [Member]	'	'	'
Allowance For Funds Used During Construction [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Capitalized Interest	0.5	0.5	0.5
Public Utilities Allowance For Funds Used During Construction Additions	1	1	1
Public Utilities Allowance For Funds Used During Construction Capitalized Total	$1.50	$1.50	$1.50
Public Utilities Allowance For Funds Used During Construction Rate	6.10%	6.80%	7.40%

Other_Income_Net_Details

Other Income, Net (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Component Of Other Income Nonoperating [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Additions	$7.10	$6.80	$22.50
The Connecticut Light And Power Company [Member]	'	'	'
Component Of Other Income Nonoperating [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Additions	2.9	1.9	6
Public Service Company Of New Hampshire [Member]	'	'	'
Component Of Other Income Nonoperating [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Additions	0.2	1.9	13.2
Western Massachusetts Electric Company [Member]	'	'	'
Component Of Other Income Nonoperating [Line Items]	'	'	'
Public Utilities Allowance For Funds Used During Construction Additions	$1	$1	$1

Other_Taxes_Details

Other Taxes (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Excise And Sales Taxes	$144.10	$135	$137.80
The Connecticut Light And Power Company [Member]	'	'	'
Excise And Sales Taxes	$128.20	$120.70	$121.60

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Details) (USD $)	12 Months Ended
Supplemental Cash Flow Information (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Capital Expenditures Incurred But Not Yet Paid	$193,100,000	$160,600,000	$168,500,000
Interest Paid, Net of Amounts Capitalized	343,300,000	356,500,000	256,300,000
Income Taxes Paid	50,000,000	-12,800,000	-76,600,000
The Connecticut Light And Power Company [Member]	'	'	'
Capital Expenditures Incurred But Not Yet Paid	51,400,000	42,800,000	32,700,000
Interest Paid, Net of Amounts Capitalized	131,600,000	129,400,000	136,600,000
Income Taxes Paid	55,000,000	-42,000,000	-27,500,000
NSTAR Electric Company [Member]	'	'	'
Capital Expenditures Incurred But Not Yet Paid	57,000,000	50,000,000	34,300,000
Interest Paid, Net of Amounts Capitalized	75,800,000	94,600,000	96,100,000
Income Taxes Paid	163,400,000	88,100,000	-62,200,000
Public Service Company Of New Hampshire [Member]	'	'	'
Capital Expenditures Incurred But Not Yet Paid	34,900,000	16,800,000	51,100,000
Interest Paid, Net of Amounts Capitalized	43,300,000	49,800,000	49,300,000
Income Taxes Paid	-30,100,000	14,700,000	-29,000,000
Western Massachusetts Electric Company [Member]	'	'	'
Capital Expenditures Incurred But Not Yet Paid	19,500,000	30,000,000	61,300,000
Interest Paid, Net of Amounts Capitalized	25,800,000	25,800,000	22,100,000
Income Taxes Paid	($69,000,000)	($8,400,000)	($4,900,000)

Severance_Benefits_Details

Severance Benefits (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Description Of Postemployment Benefits	'During 2013, NU recorded severance benefit expenses of $9.7 million in connection with the partial outsourcing of information technology functions made as part of ongoing post-merger integration. As of December 31, 2013, the severance accrual totaled $14.7 million and was included in Other Current Liabilities on the balance sheet.
Postemployment Benefits Period Expense	$9.70
Postemployment Benefits Liability Current	$14.70

Related_Parties_Details

Related Parties (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
The Connecticut Light And Power Company [Member]	'	'
Related Party Transaction [Line Items]	'	'
Long Term Receivable From Nusco	$25	$25
NSTAR Electric Company [Member]	'	'
Related Party Transaction [Line Items]	'	'
Long Term Payable for Pension Payments Received From Affliates	64.2	70.2
Public Service Company Of New Hampshire [Member]	'	'
Related Party Transaction [Line Items]	'	'
Long Term Receivable From Nusco	3.8	3.8
Western Massachusetts Electric Company [Member]	'	'
Related Party Transaction [Line Items]	'	'
Long Term Receivable From Nusco	$5.50	$5.50

MERGER_OF_NU_AND_NSTAR_Details

MERGER OF NU AND NSTAR (Details) (USD $)	0 Months Ended	12 Months Ended
Share data in Thousands, except Per Share data, unless otherwise specified	Apr. 09, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Business Combination Consideration Transferred [Abstract]	'	'	'	'
Number of NSTAR Shares Outstanding	103,696	'	'	'
Exchange Ratio	1.312	'	'	'
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	136,049	'	'	'
Business Acquisition Share Price	$36.79	'	'	'
Business Acquisition Cost Of Acquired Entity Equity Interests Issued And Issuable	$5,005,000,000	'	'	'
Business Combination Consideration Transferred Other	33,000,000	'	'	'
Total Purchase Price, Business Combination Consideration Transferred	5,038,000,000	'	'	'
Business Acquisition, Number of Shares Awarded Vested Immediately Prior to Merger	109	'	'	'
Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest [Abstract]	'	'	'	'
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Assets	'	739,000,000	'	'
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment	'	5,155,000,000	'	'
Goodwill Acquired During Period	'	3,232,000,000	'	'
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Assets	'	2,103,000,000	'	'
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities	'	-1,330,000,000	'	'
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Other	'	-2,723,000,000	'	'
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Long Term Debt	'	-2,099,000,000	'	'
Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest	'	5,038,000,000	'	'
BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue 0	'	39,000,000	'	'
Business Acquisition, Pro Forma Information [Abstract]	'	'	'	'
Business Acquisition, Pro Forma Revenue	'	7,004,000,000	7,361,000,000	'
Business Acquisition, Pro Forma Net Income	'	630,000,000	689,000,000	'
Business Acquisition, Pro Forma Earnings Per Share, Basic	'	$2	$2.20	'
Business Acquisition, Pro Forma Earnings Per Share, Diluted	'	$1.99	$2.19	'
Customer Rate Credits for Business Combination	'	46,000,000	'	'
Storm Cost Deferral Reduction	'	40,000,000	'	'
Establishment of Energy Efficiency Fund	'	15,000,000	'	'
Total Pre-Tax Settlement Agreement Impacts	'	101,000,000	'	'
Business Combination After Tax Transaction Costs	'	32,000,000	19,000,000	'
After Tax Settlement Costs Incurred	'	60,000,000	0	'
After-Tax Costs Transaction and Other Non Recurring Costs Excluded from Pro Forma Net Income	'	92,000,000	19,000,000	'
Business Combination, Description	'	'	'	'
Business Acquisition, Percentage of Voting Interests Acquired	100.00%	'	'	'
Business Acquisition, Description of Settlement Agreements	'	'Regulatory Approvals: On February 15, 2012, NU and NSTAR reached comprehensive merger settlement agreements with the Massachusetts Attorney General and the DOER. The Attorney General settlement agreement covered a variety of rate-making and rate design issues, including a base distribution rate freeze through 2015 for NSTAR Electric, NSTAR Gas and WMECO and $15 million, $3 million and $3 million in the form of rate credits to their respective customers. The settlement agreement reached with the DOER covered the same rate-making and rate design issues as the Attorney General's settlement agreement, as well as a variety of matters impacting the advancement of Massachusetts clean energy policy established by the Green Communities Act and Global Warming Solutions Act. On April 4, 2012, the DPU approved the settlement agreements and the merger of NU and NSTAR. On March 13, 2012, NU and NSTAR reached a comprehensive merger settlement agreement with both the Connecticut Attorney General and the Connecticut Office of Consumer Counsel. The settlement agreement covered a variety of matters, including a $25 million rate credit to CL&P customers, a CL&P base distribution rate freeze until December 1, 2014, and the establishment of a $15 million fund for energy efficiency and other initiatives to be disbursed at the direction of the DEEP. In the agreement, CL&P agreed to forego rate recovery of $40 million of the deferred storm restoration costs associated with restoration activities following Tropical Storm Irene and the October 2011 snowstorm. On April 2, 2012, the PURA approved the settlement agreement and the merger of NU and NSTAR.	'	'
Goodwill Roll Forward [Abstract]	'	'	'	'
Goodwill, Beginning Balance	'	300,000,000	'	3,519,401,000
Goodwill Acquired During Period	'	3,232,000,000	'	'
Goodwill, Ending Balance	'	3,519,401,000	300,000,000	3,519,401,000
Electric Distribution Member	'	'	'	'
Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest [Abstract]	'	'	'	'
Goodwill Acquired During Period	'	2,500,000,000	'	'
Goodwill Roll Forward [Abstract]	'	'	'	'
Goodwill, Beginning Balance	'	'	'	2,500,000,000
Goodwill Acquired During Period	'	2,500,000,000	'	'
Goodwill, Ending Balance	'	2,500,000,000	'	2,500,000,000
Transmission [Member]	'	'	'	'
Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest [Abstract]	'	'	'	'
Goodwill Acquired During Period	'	600,000,000	'	'
Goodwill Roll Forward [Abstract]	'	'	'	'
Goodwill, Beginning Balance	'	'	'	600,000,000
Goodwill Acquired During Period	'	600,000,000	'	'
Goodwill, Ending Balance	'	600,000,000	'	600,000,000
Natural Gas Distribution [Member]	'	'	'	'
Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest [Abstract]	'	'	'	'
Goodwill Acquired During Period	'	100,000,000	'	'
Goodwill Roll Forward [Abstract]	'	'	'	'
Goodwill, Beginning Balance	'	300,000,000	'	400,000,000
Goodwill Acquired During Period	'	100,000,000	'	'
Goodwill, Ending Balance	'	400,000,000	'	400,000,000
The Connecticut Light And Power Company [Member]	'	'	'	'
Business Acquisition, Pro Forma Information [Abstract]	'	'	'	'
Customer Rate Credits for Business Combination	'	25,000,000	'	'
Storm Cost Deferral Reduction	'	40,000,000	'	'
Total Pre-Tax Settlement Agreement Impacts	'	65,000,000	'	'
NSTAR Electric Company [Member]	'	'	'	'
Business Acquisition, Pro Forma Information [Abstract]	'	'	'	'
Customer Rate Credits for Business Combination	'	15,000,000	'	'
Total Pre-Tax Settlement Agreement Impacts	'	15,000,000	'	'
Western Massachusetts Electric Company [Member]	'	'	'	'
Business Acquisition, Pro Forma Information [Abstract]	'	'	'	'
Customer Rate Credits for Business Combination	'	3,000,000	'	'
Total Pre-Tax Settlement Agreement Impacts	'	$3,000,000	'	'

REGULATORY_ACCOUNTING_Details

REGULATORY ACCOUNTING (Details) (USD $)	12 Months Ended
REGULATORY ACCOUNTING (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Regulatory Asset [Line Items]	'	'
Regulatory Assets Current	$535,791,000	$705,025,000
Regulatory Assets Long Term	3,758,694,000	5,132,411,000
Regulatory Assets, Total	4,294,500,000	5,837,400,000
Regulatory Assets And Liabilities Other Disclosures Abstract	'	'
Description of Regulatory Costs Not yet Approved	'Regulatory Costs in Other Long-Term Assets: The Regulated companies had $65.1 million ($7.3 million for CL&P, $33.4 million for NSTAR Electric, and $10.1 million for WMECO) and $69.9 million ($3.9 million for CL&P, $25.4 million for NSTAR Electric, $35.7 million for PSNH, and $1.4 million for WMECO) of additional regulatory costs as of December 31, 2013 and 2012, 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 PSNH balance as of December 31, 2012 primarily related to storm restoration costs incurred for Tropical Storm Irene, the October 2011 snowstorm and Storm Sandy that met the NHPUC criteria for cost deferral and recovery. Refer to the "Storm Restoration Costs" section in this Note for further discussion. The NSTAR Electric balance as of December 31, 2013 and 2012 primarily related to costs deferred in connection with the basic service bad debt adder. See Note 12G, "Commitments and Contingencies – Basic Service Bad Debt Adder," for further information.	'
Description of Regulatory Assets and Liabilities	'Regulatory Assets - The following provides further information about regulatory assets: Benefit Costs: NU's Pension, SERP and PBOP Plans are accounted for in accordance with accounting guidance on defined benefit pension and other postretirement plans. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of a charge to Accumulated Other Comprehensive Income/(Loss) to reflect the liability that is recognized for the funded status of the pension and other postretirement plans and is remeasured annually. Regulatory accounting was also applied to the portions of NU's service company costs that support the Regulated companies, as these amounts are also recoverable. CL&P, NSTAR Electric, PSNH and WMECO do not collect carrying charges on these benefit costs regulatory assets. CL&P, NSTAR Electric, PSNH and WMECO recover benefit costs related to their distribution and transmission operations from customers in rates as allowed by their applicable regulatory commissions. NSTAR Electric and WMECO each recover their qualified pension and postretirement expenses related to distribution operations through rate reconciling mechanisms that fully track the change in net pension and postretirement expenses each year. NSTAR Electric earns a carrying charge on the excess cumulative benefit plan trust fund contributions it has made over what it has cumulatively recognized as net periodic benefit expense, net of deferred income taxes. As of December 31, 2013 and 2012, these balances were $379.9 million and $366.8 million of the total benefit costs regulatory asset, respectively. Derivative Liabilities: Regulatory assets recorded as an offset to derivative liabilities relate to the fair value of contracts used to purchase energy and energy-related products that will be recovered from customers in future rates. See Note 5, "Derivative Instruments," to the financial statements for further information. These assets are excluded from rate base and are being recovered as the actual settlements occur over the duration of the contracts. Goodwill: The goodwill regulatory asset originated from the transaction that created NSTAR in 1999. This regulatory asset is currently being amortized and recovered from customers in rates without a carrying charge over a 40-year period (as of December 31, 2013, there were 26 years of amortization remaining). Storm Restoration Costs: The storm restoration cost deferrals relate to costs incurred at CL&P, NSTAR Electric, PSNH and WMECO that each company expects to recover from customers. A storm must meet certain criteria to be declared a major storm with the criteria specific to each state jurisdiction and utility company as follows: Connecticut - qualifying storm restoration costs must exceed $5 million for a storm to be declared a major storm; Massachusetts - qualifying storm restoration costs must exceed $1 million for NSTAR Electric and $300,000 for WMECO and an emergency response plan must be initiated for a storm to be declared a major storm; and New Hampshire - For a storm to be declared a major storm: (1) at least 10 percent of customers must be without power with at least 200 concurrent locations requiring repairs (trouble spots), or (2) at least 300 concurrent trouble spots must be reported. Once a storm is declared major, all qualifying expenses prudently incurred during storm restoration efforts are deferred and recovered from customers. In addition to storm restoration costs, PSNH is allowed recovery of prudently incurred storm pre-staging costs in accordance with NHPUC regulation. In 2013, 2012 and 2011, CL&P, NSTAR Electric, PSNH and WMECO experienced significant storms, including Tropical Storm Irene, the October 2011 snowstorm, Storm Sandy, and the February 2013 blizzard. As a result of these storm events, each Company suffered extensive damage to its distribution and transmission systems resulting in customer outages, which required the incurrence of costs to repair damage and restore customer service. The storm restoration cost regulatory asset balance at CL&P, NSTAR Electric, PSNH and WMECO reflects costs incurred for major storm events. Management believes the storm restoration costs were prudent and meet the criteria for specific cost recovery in Connecticut, Massachusetts and New Hampshire and as a result, are probable of recovery. Storm Filings: Each electric utility is seeking recovery of its deferred storm restoration costs through its applicable regulatory recovery process. On February 3, 2014, the PURA issued a draft decision on CL&P’s request to recover storm restoration costs associated with five major storms, all of which occurred in 2011 and 2012. In its draft decision, the PURA approved recovery of $365 million of deferred storm restoration costs and ordered CL&P to capitalize approximately $18 million of the deferred storm restoration costs as utility plant, which will be included in depreciation expense in future rate proceedings. PURA will allow recovery of the $365 million with carrying charges in CL&P’s distribution rates over a six-year period beginning December 1, 2014. The remaining costs were either disallowed or are probable of recovery in future rates and did not have a material impact on CL&P’s financial position, results of operations or cash flows. On December 30, 2013, the DPU approved NSTAR Electric’s request to recover storm restoration costs, plus carrying costs, related to Tropical Storm Irene and the October 2011 snowstorm. The DPU approved recovery of $34.2 million of the $38 million requested costs. NSTAR Electric will recover these costs, plus carrying costs, in its distribution rates over a five-year period beginning on January 1, 2014. On June 27, 2013, the NHPUC approved an increase to PSNH’s distribution rates effective July 1, 2013, which included a $5 million increase to the current level of funding for the major storm cost reserve. The major storm cost reserve is used to offset the storm restoration cost regulatory asset. On August 30, 2013, WMECO submitted its 2013 Annual SRRCA filing to begin recovering the restoration costs associated with the October 2011 snowstorm and Storm Sandy. On December 20, 2013, the DPU approved the 2013 Annual SRRCA filing for effect on January 1, 2014, subject to further review and reconciliation. Income Taxes, Net: The tax effect of temporary book-tax differences (differences between the periods in which transactions affect income in the financial statements and the periods in which they affect the determination of taxable income, including those differences relating to uncertain tax positions) is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and accounting guidance for income taxes. Differences in income taxes between the accounting guidance and the rate-making treatment of the applicable regulatory commissions are recorded as regulatory assets. As these assets are offset by deferred income tax liabilities, no carrying charge is collected. For further information regarding income taxes, see Note 11, "Income Taxes," to the financial statements. Securitized Assets: NSTAR Electric's securitized regulatory asset balance primarily included costs related to purchase power contract divestitures and certain costs related to NSTAR Electric’s former generation business that were recovered with a return through the transition charge and amounted to $186.1 million as of December 31, 2012. These costs were fully recovered from customers in 2013. The securitized regulatory asset balance as of December 31, 2012 also included proceeds received from the issuance of RRBs at NSTAR Electric, PSNH and WMECO that were used to buy out or buy down purchase power contracts. The collateralized amounts reflected as securitized regulatory assets for NSTAR Electric, PSNH and WMECO as of December 31, 2012 were $14.1 million, $19.7 million and $7.8 million, respectively. As of December 31, 2013, NSTAR Electric's, PSNH's and WMECO's RRBs were fully redeemed and the related regulatory assets were fully recovered from customers. Contractual Obligations - Yankee Companies: CL&P, NSTAR Electric, PSNH and WMECO are responsible for their proportionate share of the remaining costs of the CYAPC, YAEC and MYAPC nuclear facilities, including decommissioning. A portion of these amounts was recorded as a regulatory asset. Amounts for CL&P are earning a return and are being recovered through the CTA. Amounts for NSTAR Electric and WMECO are being recovered without a return through the transition charge. Amounts for PSNH were fully recovered in 2006. As a result of NU's consolidation of CYAPC and YAEC, NU's regulatory asset balance also includes the regulatory assets of CYAPC and YAEC, which totalled $129.8 million and $214 million as of December 31, 2013 and 2012, respectively. At the NU consolidated level, intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation. Buy Out Agreements for Power Contracts: NSTAR Electric's balance represents the contract termination liability related to certain purchase power contract buy out agreements that were executed in 2004. The contracts’ termination payments occur through September 2016 and are collected from customers through NSTAR Electric’s transition charge over the same period. Therefore, NSTAR Electric does not earn a return on this regulatory asset. PSNH's balance represents payments associated with the termination of various power purchase contracts that were recorded as regulatory assets and are amortized over the remaining life of the contracts. Regulatory Tracker Mechanisms: The Regulated companies’ approved rates are designed to recover their incurred costs to provide service to customers. The Regulated companies are permitted to recover certain of their costs on a fully-reconciling basis through regulatory commission-approved tracking mechanisms. The difference between the costs incurred (or the rate recovery allowed) and the actual revenues is recorded as regulatory assets (for undercollections) or regulatory liabilities (for overcollections) to be included in future customer rates each year. Carrying charges are recorded on all material regulatory tracker mechanisms. CL&P, NSTAR Electric, PSNH and WMECO each recover the costs associated with the procurement of energy, transmission related costs from FERC-approved transmission tariffs, energy efficiency programs, low income assistance programs, and restructuring and stranded costs as a result of deregulation, on a fully reconciling basis. Energy procurement costs at PSNH include the costs related to its generating stations. WMECO’s distribution revenue is decoupled from its customer sales volume. WMECO reconciles its annual base distribution rate recovery to a pre-established level of baseline distribution delivery service revenue. Any difference between the allowed level of distribution revenue and the actual amount incurred in a calendar year is adjusted through rates in the following year. Other Regulatory Assets: Other Regulatory Assets primarily include asset retirement obligations, environmental remediation costs, losses associated with the reacquisition or redemption of long-term debt and various other items, partially offset by purchase price adjustments recorded as Regulatory Assets in connection with the merger with NSTAR. The ARO costs associated with the depreciation of the Regulated companies' ARO assets and accretion of the ARO liabilities are recorded as regulatory assets. For CL&P, NSTAR Electric and WMECO, ARO assets, regulatory assets and liabilities offset and are excluded from rate base. PSNH's ARO assets, regulatory assets and liabilities are included in rate base; these costs are being recovered over the life of the underlying property, plant and equipment. Cost of Removal: NU's Regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. The estimated cost to remove utility assets from service is recognized as a component of depreciation expense and the cumulative amounts collected from customers but not yet expended is recognized as a regulatory liability. Expended costs that exceed amounts collected from customers are recognized as regulatory assets, as they are probable of recovery in future rates. AFUDC - Transmission: AFUDC was recorded by CL&P and WMECO for their NEEWS projects through May 31, 2011, all of which was reserved as a regulatory liability to reflect rate base recovery for 100 percent of the CWIP as a result of FERC-approved transmission incentives. Effective June 1, 2011, FERC approved changes to the ISO-NE Tariff in order to include 100 percent of the NEEWS CWIP in regional rate base. As a result, CL&P and WMECO no longer record AFUDC on NEEWS CWIP. NSTAR Electric recorded AFUDC on reliability-related projects over $5 million through December 31, 2013, 50 percent of which was recorded as a regulatory liability to reflect rate base recovery for 50 percent of the CWIP as a result of FERC-approved transmission incentives. Other Regulatory Liabilities: Other Regulatory Liabilities primarily includes amounts that are subject to various rate reconciling mechanisms that, as of each period end date, would result in refunds to customers.	'
Description Of Accumulated Equity Return	'Equity Return on Regulatory Assets: For rate-making purposes, the Regulated companies recover the carrying cost related to their regulatory assets. For certain regulatory assets, the carrying cost recovered includes an equity return component. This equity return, which is not recorded on the balance sheets, totaled $1.9 million and $2.5 million for CL&P and $33.1 million and $21.8 million for PSNH as of December 31, 2013 and 2012, respectively. These carrying costs will be recovered from customers in future rates.	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liability Current	204,278,000	134,115,000
Regulatory Liabilities Long-Term	502,984,000	540,162,000
Regulatory Liabilities, Total	707,300,000	674,300,000
Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	435,100,000	440,800,000
Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	151,200,000	95,100,000
AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	68,100,000	70,000,000
Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	52,900,000	68,400,000
The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets Current	150,943,000	185,858,000
Regulatory Assets Long Term	1,663,147,000	2,158,363,000
Regulatory Assets, Total	1,814,000,000	2,344,300,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liability Current	93,961,000	32,119,000
Regulatory Liabilities Long-Term	93,757,000	124,319,000
Regulatory Liabilities, Total	187,800,000	156,400,000
The Connecticut Light And Power Company [Member] \| Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	29,100,000	44,200,000
The Connecticut Light And Power Company [Member] \| Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	95,600,000	39,100,000
The Connecticut Light And Power Company [Member] \| AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	54,700,000	56,600,000
The Connecticut Light And Power Company [Member] \| Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	8,400,000	16,500,000
NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets Current	204,144,000	347,081,000
Regulatory Assets Long Term	1,235,156,000	1,444,870,000
Regulatory Assets, Total	1,439,300,000	1,792,000,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liability Current	53,958,000	47,539,000
Regulatory Liabilities Long-Term	253,108,000	244,224,000
Regulatory Liabilities, Total	307,100,000	291,700,000
NSTAR Electric Company [Member] \| Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	250,000,000	240,300,000
NSTAR Electric Company [Member] \| Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	21,900,000	14,400,000
NSTAR Electric Company [Member] \| AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	4,100,000	4,100,000
NSTAR Electric Company [Member] \| Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	31,100,000	32,900,000
Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets Current	92,194,000	62,882,000
Regulatory Assets Long Term	219,346,000	351,059,000
Regulatory Assets, Total	311,500,000	414,000,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liability Current	20,643,000	23,002,000
Regulatory Liabilities Long-Term	51,723,000	52,418,000
Regulatory Liabilities, Total	72,300,000	75,400,000
Public Service Company Of New Hampshire [Member] \| Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	49,700,000	51,200,000
Public Service Company Of New Hampshire [Member] \| Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	21,600,000	20,400,000
Public Service Company Of New Hampshire [Member] \| AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	0	0
Public Service Company Of New Hampshire [Member] \| Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	1,000,000	3,800,000
Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets Current	43,024,000	42,370,000
Regulatory Assets Long Term	146,088,000	221,752,000
Regulatory Assets, Total	189,100,000	264,200,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liability Current	19,858,000	21,037,000
Regulatory Liabilities Long-Term	13,873,000	9,686,000
Regulatory Liabilities, Total	33,800,000	30,700,000
Western Massachusetts Electric Company [Member] \| Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	0	0
Western Massachusetts Electric Company [Member] \| Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	21,100,000	19,000,000
Western Massachusetts Electric Company [Member] \| AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	9,300,000	9,300,000
Western Massachusetts Electric Company [Member] \| Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	3,400,000	2,400,000
Benefit Costs [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	1,240,200,000	2,452,100,000
Benefit Costs [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	297,700,000	563,200,000
Benefit Costs [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	496,700,000	781,200,000
Benefit Costs [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	100,600,000	223,700,000
Benefit Costs [Member] \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	57,300,000	116,000,000
Regulatory Assets Offsetting Derivative Liabilities [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	638,000,000	885,600,000
Regulatory Assets Offsetting Derivative Liabilities [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	630,400,000	866,200,000
Regulatory Assets Offsetting Derivative Liabilities [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	7,700,000	14,900,000
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	3,000,000
Goodwill Regulatory Asset [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	525,900,000	537,600,000
Goodwill Regulatory Asset [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	451,500,000	461,500,000
Storm Restoration Costs [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	589,600,000	547,700,000
Storm Restoration Costs [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	397,800,000	413,900,000
Storm Restoration Costs [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	109,300,000	55,800,000
Storm Restoration Costs [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	43,700,000	34,500,000
Storm Restoration Costs [Member] \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	38,800,000	43,500,000
Deferred Income Tax Charges Member	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	626,200,000	516,200,000
Deferred Income Tax Charges Member \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	415,500,000	367,500,000
Deferred Income Tax Charges Member \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	84,000,000	47,100,000
Deferred Income Tax Charges Member \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	40,300,000	36,200,000
Deferred Income Tax Charges Member \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	43,700,000	31,000,000
Securitized Assets [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	232,600,000
Securitized Assets [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	0
Securitized Assets [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	205,100,000
Securitized Assets [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	19,700,000
Securitized Assets [Member] \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	7,800,000
Unrecovered Contractual Obligations [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	154,200,000	217,600,000
Unrecovered Contractual Obligations [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	19,800,000	64,000,000
Unrecovered Contractual Obligations [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	6,200,000	22,800,000
Unrecovered Contractual Obligations [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	0
Unrecovered Contractual Obligations [Member] \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	4,500,000	14,900,000
Power Contracts Buy Out Agreements [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	70,200,000	92,900,000
Power Contracts Buy Out Agreements [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	64,700,000	85,900,000
Power Contracts Buy Out Agreements [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	5,500,000	7,000,000
Regulatory Tracker Deferrals Regulatory Assets [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	323,400,000	190,100,000
Regulatory Tracker Deferrals Regulatory Assets [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	8,000,000	12,200,000
Regulatory Tracker Deferrals Regulatory Assets [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	169,500,000	71,400,000
Regulatory Tracker Deferrals Regulatory Assets [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	83,300,000	49,300,000
Regulatory Tracker Deferrals Regulatory Assets [Member] \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	32,600,000	31,900,000
Other Regulatory Assets [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	126,800,000	165,000,000
Other Regulatory Assets [Member] \| The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	44,800,000	57,300,000
Other Regulatory Assets [Member] \| NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	49,700,000	46,300,000
Other Regulatory Assets [Member] \| Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	38,100,000	43,600,000
Other Regulatory Assets [Member] \| Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	$12,200,000	$16,100,000

PROPERTY_PLANT_AND_ACCUMULATED2

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Public Utility Property Plant And Equipment [Line Items]	'	'	'
Public Utilities Property Plant And Equipment Distribution	$11,950,200,000	$11,438,200,000	'
Public Utilities Property Plant And Equipment Distribution Natural Gas	2,425,900,000	2,274,200,000	'
Public Utilities Property Plant And Equipment Transmission	6,412,500,000	5,541,100,000	'
Public Utilities Property Plant And Equipment Generation Or Processing	1,152,300,000	1,146,600,000	'
Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total	21,940,900,000	20,400,100,000	'
Public Utilities Property Plant And Equipment Other Property Plant And Equipment	508,700,000	429,300,000	'
Public Utilities Property Plant And Equipment Plant In Service	22,449,600,000	20,829,400,000	'
Electric And Natural Gas Utility Accumulated Depreciation	-5,387,000,000	-5,065,100,000	'
Other Accumulated Depreciation	-196,200,000	-171,500,000	'
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-5,583,200,000	-5,236,600,000	'
Property Plant And Equipment Net Excluding Construction Work In Progress	16,866,400,000	15,592,800,000	'
Public Utilities Property Plant And Equipment Construction Work In Progress	709,800,000	1,012,200,000	'
Property, Plant and Equipment, Net	17,576,186,000	16,605,010,000	'
Public Utilities Property Plant and Equipment Depreciation Rates	2.80%	2.50%	2.60%
Useful Lives [Abstract]	'	'	'
Distribution Assets Average Useful Life	36.1	'	'
Transmission Assets Average Useful Life	43	'	'
Generation Assets Average Useful Life	32.2	'	'
Other Assets Average Useful Life	14.6	'	'
The Connecticut Light And Power Company [Member]	'	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'	'
Public Utilities Property Plant And Equipment Distribution	4,930,700,000	4,691,300,000	'
Public Utilities Property Plant And Equipment Transmission	3,071,900,000	2,796,100,000	'
Public Utilities Property Plant And Equipment Generation Or Processing	0	0	'
Public Utilities Property Plant And Equipment Plant In Service	8,002,600,000	7,487,400,000	'
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,804,100,000	-1,698,100,000	'
Property Plant And Equipment Net Excluding Construction Work In Progress	6,198,500,000	5,789,300,000	'
Public Utilities Property Plant And Equipment Construction Work In Progress	252,800,000	363,700,000	'
Property, Plant and Equipment, Net	6,451,259,000	6,152,959,000	'
Public Utilities Property Plant and Equipment Depreciation Rates	2.50%	2.50%	2.40%
Useful Lives [Abstract]	'	'	'
Distribution Assets Average Useful Life	42	'	'
Transmission Assets Average Useful Life	39.6	'	'
Generation Assets Average Useful Life	0	'	'
Other Assets Average Useful Life	0	'	'
NSTAR Electric Company [Member]	'	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'	'
Public Utilities Property Plant And Equipment Distribution	4,694,700,000	4,539,900,000	'
Public Utilities Property Plant And Equipment Transmission	1,772,300,000	1,529,700,000	'
Public Utilities Property Plant And Equipment Generation Or Processing	0	0	'
Public Utilities Property Plant And Equipment Plant In Service	6,467,000,000	6,069,600,000	'
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,631,300,000	-1,540,100,000	'
Property Plant And Equipment Net Excluding Construction Work In Progress	4,835,700,000	4,529,500,000	'
Public Utilities Property Plant And Equipment Construction Work In Progress	208,200,000	205,800,000	'
Property, Plant and Equipment, Net	5,043,887,000	4,735,297,000	'
Public Utilities Property Plant and Equipment Depreciation Rates	2.90%	2.80%	3.00%
Useful Lives [Abstract]	'	'	'
Distribution Assets Average Useful Life	32.9	'	'
Transmission Assets Average Useful Life	47.2	'	'
Generation Assets Average Useful Life	0	'	'
Other Assets Average Useful Life	0	'	'
Public Service Company Of New Hampshire [Member]	'	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'	'
Public Utilities Property Plant And Equipment Distribution	1,608,200,000	1,520,100,000	'
Public Utilities Property Plant And Equipment Transmission	695,700,000	599,200,000	'
Public Utilities Property Plant And Equipment Generation Or Processing	1,131,200,000	1,125,500,000	'
Public Utilities Property Plant And Equipment Plant In Service	3,435,100,000	3,244,800,000	'
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,021,800,000	-954,000,000	'
Property Plant And Equipment Net Excluding Construction Work In Progress	2,413,300,000	2,290,800,000	'
Public Utilities Property Plant And Equipment Construction Work In Progress	54,300,000	61,700,000	'
Property, Plant and Equipment, Net	2,467,556,000	2,352,515,000	'
Public Utilities Property Plant and Equipment Depreciation Rates	3.00%	3.00%	2.90%
Useful Lives [Abstract]	'	'	'
Distribution Assets Average Useful Life	32.7	'	'
Transmission Assets Average Useful Life	42.3	'	'
Generation Assets Average Useful Life	32.4	'	'
Other Assets Average Useful Life	0	'	'
Western Massachusetts Electric Company [Member]	'	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'	'
Public Utilities Property Plant And Equipment Distribution	756,600,000	724,200,000	'
Public Utilities Property Plant And Equipment Transmission	826,400,000	583,700,000	'
Public Utilities Property Plant And Equipment Generation Or Processing	21,100,000	21,100,000	'
Public Utilities Property Plant And Equipment Plant In Service	1,604,100,000	1,329,000,000	'
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-271,500,000	-252,100,000	'
Property Plant And Equipment Net Excluding Construction Work In Progress	1,332,600,000	1,076,900,000	'
Public Utilities Property Plant And Equipment Construction Work In Progress	48,500,000	213,600,000	'
Property, Plant and Equipment, Net	$1,381,060,000	$1,290,498,000	'
Public Utilities Property Plant and Equipment Depreciation Rates	2.90%	3.30%	2.90%
Useful Lives [Abstract]	'	'	'
Distribution Assets Average Useful Life	29.8	'	'
Transmission Assets Average Useful Life	49.5	'	'
Generation Assets Average Useful Life	25	'	'
Other Assets Average Useful Life	0	'	'

DERIVATIVE_INSTURMENTS_Details

DERIVATIVE INSTURMENTS (Details) (USD $)	12 Months Ended
DERIVATIVE INSTURMENTS (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative Instrument Detail Abstract	'	'	'
Derivative Liabilities, Noncurrent	($624,050,000)	($882,654,000)	'
Derivative Assets Noncurrent	74,155,000	90,612,000	'
Current Derivative Assets Consolidated	10,200,000	11,400,000	'
Derivative Assets Subject to Credit Risk with investment grade counterparty	80,000,000	'	'
DerivativeCollateralRightToReclaimCash	'	4,100,000	'
Consolidated Current Derivative Liabilities	93,700,000	117,200,000	'
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract	'	'	'
Description of Derivative Activity Volume	'As of December 31, 2013 and 2012, NU had NYMEX future contracts in order to reduce variability associated with the purchase price of approximately 9.1 million and 11.5 million MMBtu of natural gas, respectively. As of December 31, 2012, NU had approximately 24 thousand MWh of supply volumes remaining in its unregulated wholesale portfolio when expected sales were compared with supply contracts. These contracts expired on December 31, 2013.	'	'
Derivative Credit Risk Related Contingent Features Abstract	'	'	'
Derivative Net Liability Position Aggregate Fair Value	0	-15,300,000	'
Collateral Already Posted Aggregate Fair Value	'	0	'
Additional Collateral Aggregate Fair Value	0	17,400,000	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsExitPricePremium	'Exit price premiums of 10 percent through 32 percent are also applied on these contracts and reflect the most recent market activity available for similar type contracts.	'	'
The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Liabilities - Current	-92,233,000	-96,931,000	'
Derivative Liabilities, Noncurrent	-617,072,000	-865,571,000	'
Derivative Assets Noncurrent	71,384,000	90,612,000	'
Derivative Assets Subject to Credit Risk with investment grade counterparty	79,000,000	'	'
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.	'	'
Western Massachusetts Electric Company [Member]	'	'	'
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract	'	'	'
Description of Derivative Activity Volume	'WMECO has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2029 with a facility that has not yet achieved commercial operation.	'	'
Fair Value Inputs Level 2 [Member] \| Subsidiaries [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	1,600,000	200,000	'
Derivative Liabilities - Current	'	-19,300,000	'
Derivative Liabilities, Noncurrent	'	-200,000	'
Derivative Assets Noncurrent	200,000	'	'
Fair Value Inputs Level 3 [Member] \| MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	5.07	1.4	'
FairValueInputsEnergyPrices	49	43	'
FairValueInputsRenewableEnergyCreditPrices	36	25	'
FairValueInputsForwardReserve	3.3	0.35	'
Fair Value Inputs Level 3 [Member] \| MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	11.82	10.53	'
FairValueInputsEnergyPrices	77	90	'
FairValueInputsRenewableEnergyCreditPrices	87	85	'
FairValueInputsForwardReserve	3.3	0.9	'
Fair Value Inputs Level 3 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	7,300,000	5,700,000	'
Derivative Liabilities - Current	-92,200,000	-96,900,000	'
Derivative Liabilities, Noncurrent	-617,100,000	-865,600,000	'
Derivative Assets Noncurrent	71,400,000	90,600,000	'
Fair Value Inputs Level 3 [Member] \| The Connecticut Light And Power Company [Member] \| MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	5.07	1.4	'
FairValueInputsEnergyPrices	56	50	'
FairValueInputsForwardReserve	3.3	0.35	'
Fair Value Inputs Level 3 [Member] \| The Connecticut Light And Power Company [Member] \| MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	10.42	9.83	'
FairValueInputsEnergyPrices	58	55	'
FairValueInputsForwardReserve	3.3	0.9	'
Fair Value Inputs Level 3 [Member] \| NSTAR Electric Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	1,200,000	'	'
Derivative Liabilities - Current	-1,500,000	-1,000,000	'
Derivative Liabilities, Noncurrent	-7,000,000	-13,900,000	'
Fair Value Inputs Level 3 [Member] \| NSTAR Electric Company [Member] \| MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	5.07	1.4	'
FairValueInputsRenewableEnergyCreditPrices	36	25	'
Fair Value Inputs Level 3 [Member] \| NSTAR Electric Company [Member] \| MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	7.38	3.39	'
FairValueInputsRenewableEnergyCreditPrices	70	71	'
Fair Value Inputs Level 3 [Member] \| Western Massachusetts Electric Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	100,000	'	'
Derivative Liabilities, Noncurrent	'	-3,000,000	'
Derivative Assets Noncurrent	2,600,000	'	'
Fair Value Inputs Level 3 [Member] \| Western Massachusetts Electric Company [Member] \| MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	5.07	1.4	'
FairValueInputsEnergyPrices	49	43	'
FairValueInputsRenewableEnergyCreditPrices	36	25	'
Fair Value Inputs Level 3 [Member] \| Western Massachusetts Electric Company [Member] \| MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	11.82	10.53	'
FairValueInputsEnergyPrices	77	90	'
FairValueInputsRenewableEnergyCreditPrices	87	85	'
Fair Value Inputs Level 3 [Member] \| Subsidiaries [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	'	5,500,000	'
Netting And Collateral [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	-10,100,000	-12,000,000	'
Derivative Liabilities - Current	0	600,000	'
Derivative Liabilities, Noncurrent	0	0	'
Derivative Assets Noncurrent	-42,200,000	-69,100,000	'
Netting And Collateral [Member] \| Subsidiaries [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Liabilities - Current	'	600,000	'
Netting And Collateral [Member] \| Fair Value Inputs Level 2 [Member] \| Subsidiaries [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	-300,000	'	'
Netting And Collateral [Member] \| Fair Value Inputs Level 3 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	'	-12,000,000	'
Derivative Liabilities, Noncurrent	0	'	'
Derivative Assets Noncurrent	-42,200,000	-69,100,000	'
Commodity [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	20,300,000	23,400,000	'
Derivative Liabilities - Current	-93,700,000	-117,800,000	'
Derivative Liabilities, Noncurrent	-624,100,000	-882,700,000	'
Derivative Assets Noncurrent	116,400,000	159,700,000	'
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract	'	'	'
Derivative Gain Loss On Derivative Net	1,000,000	-700,000	500,000
Derivative Instruments Gain Loss Recognized In Regulatory Asset Liability	160,600,000	-29,000,000	-162,000,000
Commodity [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract	'	'	'
Description of Derivative Activity Volume	'Commodity Supply and Price Risk Management: As required by regulation, CL&P has capacity-related contracts with generation facilities. These contracts and similar UI contracts have an expected capacity of 787 MW. 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 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 forward 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.	'	'
Commodity [Member] \| Fair Value Inputs Level 2 [Member] \| Subsidiaries [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	'	200,000	'
Derivative Liabilities - Current	'	-19,900,000	'
Derivative Liabilities, Noncurrent	'	-200,000	'
Derivative Assets Noncurrent	200,000	'	'
Commodity [Member] \| Fair Value Inputs Level 3 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	17,100,000	17,700,000	'
Derivative Liabilities - Current	-92,200,000	-96,900,000	'
Derivative Liabilities, Noncurrent	-617,100,000	-865,600,000	'
Derivative Assets Noncurrent	113,600,000	159,700,000	'
Commodity [Member] \| Fair Value Inputs Level 3 [Member] \| NSTAR Electric Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	1,200,000	'	'
Derivative Liabilities - Current	-1,500,000	-1,000,000	'
Derivative Liabilities, Noncurrent	-7,000,000	-13,900,000	'
Commodity [Member] \| Fair Value Inputs Level 3 [Member] \| Western Massachusetts Electric Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	100,000	'	'
Derivative Liabilities, Noncurrent	'	-3,000,000	'
Derivative Assets Noncurrent	2,600,000	'	'
Commodity [Member] \| Fair Value Inputs Level 3 [Member] \| Subsidiaries [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	'	$5,500,000	'

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	($878.60)	($962.20)
DerivativeLiabilityRecordedAtMergerDateLevel3	'	-5.4
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3	'	32.2
Net Realized/Unrealized Gains Losses included in Net Income	10.9	10.9
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	158.3	-29.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	74.2	75.1
Ending Balance	-635.2	-878.6
The Connecticut Light And Power Company [Member]	'	'
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	-866.2	-931.6
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	148.9	-21.6
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	86.7	87
Ending Balance	-630.6	-866.2
NSTAR Electric Company [Member]	'	'
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	-14.9	-3.4
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	3.5	-15.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	4.1	3.7
Ending Balance	-7.3	-14.9
Western Massachusetts Electric Company [Member]	'	'
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	-3	-7.3
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	5.7	4.3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0	'
Ending Balance	$2.70	($3)

MARKETABLE_SECURITIES_Details

MARKETABLE SECURITIES (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities [Line Items]	'	'
Fair Value Of Securities Under Fair Value Option	$57.20	$47
Fair Value, Option, Changes in Fair Value, Gain (Loss)	10.2	5.9
Investments, Debt and Equity Securities [Abstract]	'	'
Marketable Securities, Restricted	424	340.4
Available For Sale Securities Debt Maturities Fair Value Abstract	'	'
Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value	59.3	'
Available For Sale Securities Debt Maturities After Ten Years Fair Value	105.3	'
Available For Sale Securities Debt Maturities After One Year Through Five Years Fair Value	62.7	'
Available For Sale Securities Debt Maturities Within One Year Fair Value	72.3	'
Available For Sale Securities Debt Maturities Fair Value	299.6	'
Available For Sale Securities Debt Maturities Amortized Cost Abstract	'	'
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	62.1	'
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	72.4	'
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost	105.3	'
Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost	59.4	'
Available For Sale Securities Debt Maturities Amortized Cost	299.2	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	580.9	492.3
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	1.7	'
Available For Sale Securities Debt Maturities After Ten Years Fair Value	4.1	'
Available For Sale Securities Debt Maturities After One Year Through Five Years Fair Value	25.5	'
Available For Sale Securities Debt Maturities Within One Year Fair Value	26.6	'
Available For Sale Securities Debt Maturities Fair Value	57.9	'
Available For Sale Securities Debt Maturities Amortized Cost Abstract	'	'
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	25.6	'
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	26.5	'
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost	4.1	'
Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost	1.7	'
Available For Sale Securities Debt Maturities Amortized Cost	57.9	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	57.9	57.7
Fair Value Inputs Level 1 Member	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	314.2	252.7
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	10.9	5.2
Fair Value Inputs Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	266.7	239.6
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	52.5
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	61.4	69.9
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	6.8	18.7
Corporate Bond Securities Member \| Fair Value Inputs Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	53.6	33
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	15.1	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	30.4	28.5
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	9	10.9
Municipal Bonds Member \| Fair Value Inputs Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	105.5	93.8
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	11.2	11.6
Other Debt Securities Member \| Fair Value Inputs Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	15.8	14.4
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	4.9	4.3
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	40.2
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	10.9	5.2
Mutual Funds [Member] \| Fair Value Inputs Level 1 Member	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract	'	'
Investments Fair Value Disclosure	281.3	212.5
Debt Securities	'	'
Investments, Debt and Equity Securities [Abstract]	'	'
Available For Sale Securities Fair Value Disclosure	299.6	279.8
Available-for-sale Securities, Gross Unrealized Gains	2.5	13.3
AvailableForSaleSecuritiesGrossUnrealizedLoss	2.1	0.1
Available For Sale Securities Amortized Cost	299.2	266.6
Debt Securities \| Western Massachusetts Electric Company [Member]	'	'
Investments, Debt and Equity Securities [Abstract]	'	'
Available For Sale Securities Fair Value Disclosure	57.9	-57.7
Available-for-sale Securities, Gross Unrealized Gains	0	0.1
AvailableForSaleSecuritiesGrossUnrealizedLoss	0	0.1
Available For Sale Securities Amortized Cost	57.9	57.7
Equity Securities	'	'
Investments, Debt and Equity Securities [Abstract]	'	'
Available For Sale Securities Fair Value Disclosure	224.1	165.5
Available-for-sale Securities, Gross Unrealized Gains	60.5	20
AvailableForSaleSecuritiesGrossUnrealizedLoss	0	0
Available For Sale Securities Amortized Cost	$163.60	$145.50

ASSET_RETIREMENT_OBLIGATIONS_D

ASSET RETIREMENT OBLIGATIONS (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
Asset Retirement Obligation, Beginning Balance	$412.20	$56.20
Liability Assumed Upon Consolidation of CYAPC and YAEC	'	284.2
Liability Assumed Upon Merger With Nstar	'	35.9
Asset Retirement Obligation, Liabilities Incurred	0.1	1.5
Asset Retirement Obligation, Liabilities Settled	-13.8	-7.2
Asset Retirement Obligation, Accretion Expense	23.8	20.2
Asset Retirement Obligation, Revision of Estimate	2.6	21.4
Asset Retirement Obligation, Ending Balance	424.9	412.2
The Connecticut Light And Power Company [Member]	'	'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
Asset Retirement Obligation, Beginning Balance	33.6	32.2
Asset Retirement Obligation, Liabilities Settled	-0.7	-0.9
Asset Retirement Obligation, Accretion Expense	2.2	2
Asset Retirement Obligation, Revision of Estimate	-0.1	0.3
Asset Retirement Obligation, Ending Balance	35	33.6
NSTAR Electric Company [Member]	'	'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
Asset Retirement Obligation, Beginning Balance	31.4	27.5
Asset Retirement Obligation, Liabilities Settled	-0.1	-1
Asset Retirement Obligation, Accretion Expense	1.5	1.5
Asset Retirement Obligation, Revision of Estimate	'	3.4
Asset Retirement Obligation, Ending Balance	32.8	31.4
Public Service Company Of New Hampshire [Member]	'	'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
Asset Retirement Obligation, Beginning Balance	18.4	17
Asset Retirement Obligation, Liabilities Incurred	'	0.3
Asset Retirement Obligation, Accretion Expense	1.2	1.1
Asset Retirement Obligation, Revision of Estimate	-0.1	'
Asset Retirement Obligation, Ending Balance	19.5	18.4
Western Massachusetts Electric Company [Member]	'	'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'	'
Asset Retirement Obligation, Beginning Balance	4.3	4
Asset Retirement Obligation, Accretion Expense	0.3	0.3
Asset Retirement Obligation, Revision of Estimate	-0.1	'
Asset Retirement Obligation, Ending Balance	$4.50	$4.30

SHORT_TERM_DEBT_Details

SHORT TERM DEBT (Details) (USD $)	12 Months Ended
SHORT TERM DEBT (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Line of Credit Facility [Line Items]	'	'
Short Term Debt Regulatory Limits	'The amount of short-term borrowings that may be incurred by CL&P, NSTAR Electric and WMECO is subject to periodic approval by the FERC. On July 31, 2013, the FERC granted authorization to allow CL&P and WMECO to incur total short-term borrowings up to a maximum of $600 million and $300 million, respectively, effective January 1, 2014 through December 31, 2015. On May 16, 2012, the FERC granted authorization to allow NSTAR Electric to issue total short-term debt securities in an aggregate principal amount not to exceed $655 million outstanding at any one time, effective October 23, 2012 through October 23, 2014. As a result of the NHPUC having jurisdiction over PSNH's short-term debt, PSNH is not currently required to obtain FERC approval for its short-term borrowings. CL&P's certificate of incorporation contains preferred stock provisions restricting the amount of unsecured debt that CL&P may incur, including limiting unsecured indebtedness with a maturity of less than 10 years to 10 percent of total capitalization. In November 2003, CL&P obtained from its preferred stockholders a waiver of such 10 percent limit for a ten-year period expiring in March 2014, provided that all unsecured indebtedness does not exceed 20 percent of total capitalization. As of December 31, 2013, CL&P had $776.9 million of unsecured debt capacity available under this authorization.	'
Description of commercial paper program	'NU parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year revolving credit facility. The revolving credit facility is to be used primarily to backstop the commercial paper program at NU, which commenced July 25, 2012. The commercial paper program allows NU parent to issue commercial paper as a form of short-term debt. On September 6, 2013, the $1.15 billion revolving credit facility dated July 25, 2012 was amended to increase the aggregate principal amount available thereunder by $300 million to $1.45 billion, to extend the expiration date from July 25, 2017 to September 6, 2018, and to increase CL&P's borrowing sublimit from $300 million to $600 million. PSNH and WMECO each have borrowing sublimits of $300 million. On September 6, 2013, NU parent’s $1.15 billion commercial paper program was increased by $300 million to $1.45 billion. NSTAR Electric has a five-year $450 million revolving credit facility. This facility serves to backstop NSTAR Electric’s existing $450 million commercial paper program. On September 6, 2013, NSTAR Electric amended its revolving credit facility dated July 25, 2012 to extend the expiration date from July 25, 2017 to September 6, 2018.	'
Description of Working Capital	'Each of NU, CL&P, NSTAR Electric, PSNH and WMECO use its available capital resources to fund its respective construction expenditures, meet debt requirements, pay operating costs, including storm-related costs, pay dividends and fund other corporate obligations, such as pension contributions. The current growth in NU’s transmission construction expenditures utilizes a significant amount of cash for projects that have a long-term return on investment and recovery period. In addition, NU’s Regulated companies recover its electric and natural gas distribution construction expenditures as the related project costs are depreciated over the life of the assets. This impacts the timing of the revenue stream designed to fully recover the total investment plus a return on the equity portion of the cost and related financing costs. These factors have resulted in current liabilities exceeding current assets by approximately $1.2 billion, $398 million and $339 million at NU, CL&P and NSTAR Electric, respectively, as of December 31, 2013. As of December 31, 2013, $501.7 million of NU's obligations classified as current liabilities relates to long-term debt that will be paid in the next 12 months, consisting of $150 million for CL&P, $301.7 million for NSTAR Electric and $50 million for PSNH. In addition, $31.7 million relates to the amortization of the purchase accounting fair value adjustment that will be amortized in the next twelve months. NU, with its strong credit ratings, has several options available in the financial markets to repay or refinance these maturities with the issuance of new long-term debt. NU, CL&P, NSTAR Electric, PSNH and WMECO will reduce their short-term borrowings with cash received from operating cash flows or with the issuance of new long-term debt, determined considering capital requirements and maintenance of NU's credit rating and profile. Management expects the future operating cash flows of NU, CL&P, NSTAR Electric, PSNH and WMECO, along with the access to financial markets, will be sufficient to meet any future operating requirements and capital investment forecasted opportunities.	'
Description of ST debt reclassified to LT	'On January 2, 2014, Yankee Gas issued $100 million of Series L First Mortgage Bonds. A portion of the proceeds was used to pay short-term borrowings outstanding under the NU commercial paper program. As a result and in accordance with applicable accounting guidance, $25 million of the NU commercial paper program borrowings have been classified as Long-Term Debt as of December 31, 2013.	'As of December 31, 2012, CL&P had $89 million in borrowings outstanding under this credit agreement with a weighted average interest rate of 3.325 percent.
Notes Payable to Banks	$1,093,000,000	$1,120,196,000
The Connecticut Light And Power Company [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Line of Credit Facility, Amount Outstanding	'	89,000,000
Short-term Debt, Weighted Average Interest Rate	'	3.33%
Notes Payable To Affiliated Companies	287,300,000	99,296,000
NSTAR Electric Company [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Line of Credit Facility, Current Borrowing Capacity	346,500,000	'
Line of Credit Facility, Remaining Borrowing Capacity	346,500,000	174,000,000
CommercialPaper	103,500,000	276,000,000
WeightedAverageDiscountRatePercent	0.13%	0.31%
Notes Payable to Banks	103,500,000	276,000,000
Public Service Company Of New Hampshire [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Notes Payable To Affiliated Companies	86,500,000	63,300,000
Western Massachusetts Electric Company [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Notes Payable To Affiliated Companies	0	31,900,000
Nu Parent [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Line of Credit Facility, Remaining Borrowing Capacity	435,500,000	'
CommercialPaper	1,010,000,000	1,150,000,000
WeightedAverageDiscountRatePercent	0.24%	0.46%
Notes Payable to Banks	$1,014,500,000	$1,150,000,000

LONGTERM_DEBT_Details

LONG-TERM DEBT (Details) (USD $)	12 Months Ended
LONG-TERM DEBT (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]	'	'
Long-Term Debt - Current Portion	$533,346,000	$763,338,000
Long-Term Debt	7,776,833,000	7,200,156,000
Maturities of Long-term Debt [Abstract]	'	'
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	576,700,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Two	216,700,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Three	200,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Four	745,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Five	810,000,000	'
Long-term Debt, Maturities, Repayments of Principal after Year Five	5,031,600,000	'
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	7,580,000,000	'
Long-term Debt, Description	'On January 15, 2013, CL&P issued $400 million of 2.50 percent Series A First and Refunding Mortgage Bonds with a maturity date of January 15, 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings outstanding under the CL&P credit agreement of $89 million and the NU commercial paper program of $305.8 million. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on the balance sheet as of December 31, 2012. In April 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. The PCRBs, which mature on May 1, 2031, carry a coupon rate of 1.55 percent during the current three-year fixed rate period and are subject to mandatory tender for purchase on April 1, 2015. On September 3, 2013, CL&P redeemed at par $125 million of 1.25 percent Series B 2011 PCRBs, which were subject to mandatory tender for purchase, using short-term debt. On May 17, 2013, NSTAR Electric issued $200 million of three-year floating rate debentures due in May 2016. The proceeds, net of issuance costs, were used to repay commercial paper borrowings and for general corporate purposes. The debentures have a coupon rate reset quarterly based on 3-month LIBOR plus a credit spread of 0.24 percent. The interest rate as of December 31, 2013 was 0.478 percent. On May 1, 2013, PSNH redeemed at par approximately $109 million of the 2001 Series C PCRBs that were due to mature in 2021 using short-term debt. On November 14, 2013, PSNH issued $250 million of 3.50 percent Series S First Mortgage Bonds due in 2023. On December 23, 2013, PSNH redeemed approximately $89 million of the Series B PCRBs that were due to mature in 2021. The proceeds of the Series S issuance were used to repay the short term debt used to redeem the $109 million 2001 Series C PCRBs and to redeem the $89 million Series B PCRBs and pay the associated call premium. The remaining proceeds of the offering were used to refinance short-term debt. On September 1, 2013, WMECO repaid at maturity the $55 million Series A Senior Notes using short-term debt. On November 15, 2013, WMECO issued $80 million of 3.88 percent Series G Senior Notes due in 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings and for other working capital purposes. On January 2, 2014, Yankee Gas issued $100 million of 4.82 percent Series L First Mortgage Bonds due to mature in 2044. The proceeds, net of issuance costs, were used to repay the Series G $75 million First Mortgage Bonds that matured on January 1, 2014 and to pay $25 million in short-term borrowings. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on NU’s balance sheet as of December 31, 2013. On May 13, 2013, NU parent issued $750 million of Senior Notes, consisting of $300 million of 1.45 percent Series E Senior Notes due to mature in 2018 and $450 million of 2.80 percent Series F Senior Notes due to mature in 2023. The proceeds, net of issuance costs, were used to repay the NU parent $250 million Series C Senior Notes at a coupon rate of 5.65 percent that matured on June 1, 2013 and the NU parent $300 million floating rate Series D Senior Notes that matured on September 20, 2013. The remaining net proceeds were used to repay commercial paper program borrowings and for working capital purposes. The DOE is responsible for the selection and development of repositories for, and the disposal of, spent nuclear fuel and high-level radioactive waste. For nuclear fuel used to generate electricity prior to April 7, 1983 (Prior Period Spent Nuclear Fuel) for CL&P and WMECO, an accrual has been recorded for the full liability, and payment must be made by CL&P and WMECO to the DOE prior to the first delivery of spent fuel to the DOE. After the sale of Millstone, CL&P and WMECO remained responsible for their share of the disposal costs associated with the Prior Period Spent Nuclear Fuel. Until such payment to the DOE is made, the outstanding liability will continue to accrue interest at the 3-month Treasury bill yield rate. In addition, as a result of consolidating CYAPC, NU has consolidated $179.4 million in additional spent nuclear fuel obligations, including interest, as of December 31, 2013. Fees due to the DOE for the disposal of CL&P's and WMECO's Prior Period Spent Nuclear Fuel and CYAPC's spent nuclear fuel obligation include accumulated interest costs of $350.3 million and $350 million ($177.9 million and $177.8 million for CL&P and $41.7 million and $41.7 million for WMECO) as of December 31, 2013 and 2012, respectively.	'
The Connecticut Light And Power Company [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt - Current Portion	150,000,000	125,000,000
Long-Term Debt	2,591,208,000	2,737,790,000
Maturities of Long-term Debt [Abstract]	'	'
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	150,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Two	162,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Three	0	'
Long-term Debt, Maturities, Repayments of Principal in Year Four	250,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Five	300,000,000	'
Long-term Debt, Maturities, Repayments of Principal after Year Five	1,640,300,000	'
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	2,502,300,000	'
Long-term Debt, Description	'On January 15, 2013, CL&P issued $400 million of 2.50 percent Series A First and Refunding Mortgage Bonds with a maturity date of January 15, 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings outstanding under the CL&P credit agreement of $89 million and the NU commercial paper program of $305.8 million. As a result and in accordance with applicable accounting guidance, these amounts were classified as Long-Term Debt on the balance sheet as of December 31, 2012. In April 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. The PCRBs, which mature on May 1, 2031, carry a coupon rate of 1.55 percent during the current three-year fixed rate period and are subject to mandatory tender for purchase on April 1, 2015. On September 3, 2013, CL&P redeemed at par $125 million of 1.25 percent Series B 2011 PCRBs, which were subject to mandatory tender for purchase, using short-term debt. CL&P’s obligation to repay each series of PCRBs is secured by first mortgage bonds. Each such series of first mortgage bonds contains similar terms and provisions as the applicable series of PCRBs. If CL&P fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. CL&P’s $62 million tax-exempt PCRBs, which is subject to mandatory tender for purchase on April 1, 2015, cannot be redeemed prior to its tender date. CL&P’s $120.5 million tax-exempt PCRBs will be subject to redemption at par on or after September 1, 2021. All other long-term debt securities are subject to make-whole provisions.	'
The Connecticut Light And Power Company [Member] \| Series D 1994 Due 2024 7.875 % [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	139,800,000	139,800,000
The Connecticut Light And Power Company [Member] \| Series A 2004 Due 2014 4.800% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	150,000,000	150,000,000
The Connecticut Light And Power Company [Member] \| Series B 2004 Due 2034 5.750% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	130,000,000	130,000,000
The Connecticut Light And Power Company [Member] \| Series A 2005 Due 2015 5.000% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	100,000,000	100,000,000
The Connecticut Light And Power Company [Member] \| Series B 2005 Due 2035 5.625% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	100,000,000	100,000,000
The Connecticut Light And Power Company [Member] \| Series A 2006 Due 2036 6.350% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	250,000,000	250,000,000
The Connecticut Light And Power Company [Member] \| Series A 2007 Due 2017 5.375% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	150,000,000	150,000,000
The Connecticut Light And Power Company [Member] \| Series B 2007 Due 2037 5.750% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	150,000,000	150,000,000
The Connecticut Light And Power Company [Member] \| Series D 2007 Due 2037 6.375% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	100,000,000	100,000,000
The Connecticut Light And Power Company [Member] \| Series A 2008 Due 2018 5.650% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	300,000,000	300,000,000
The Connecticut Light And Power Company [Member] \| Series A 2009 Due 2019 5.500% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	250,000,000	250,000,000
The Connecticut Light And Power Company [Member] \| One-Year Fixed Rate Tax Exempt Due 2031 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	62,000,000	62,000,000
The Connecticut Light And Power Company [Member] \| Fees And Interest Due For Spent Nuclear Fuel Disposal Costs [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	244,400,000	244,300,000
The Connecticut Light And Power Company [Member] \| Total First Mortgage Bonds [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	2,319,800,000	1,919,800,000
The Connecticut Light And Power Company [Member] \| Total Pollution Control Bonds [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	182,500,000	307,500,000
The Connecticut Light And Power Company [Member] \| Total First Mortgage Bonds and Pollution Control Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	2,502,300,000	2,227,300,000
The Connecticut Light And Power Company [Member] \| Unamortized Premiums and Discounts, Net [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	-5,500,000	-3,600,000
The Connecticut Light And Power Company [Member] \| Serires C 2007 5.750% Due 2017 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	100,000,000	100,000,000
The Connecticut Light And Power Company [Member] \| Fixed Rate 4.375% due 2028 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	120,500,000	120,500,000
The Connecticut Light And Power Company [Member] \| Fixed Rate 1.25% due 2028 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	0	125,000,000
The Connecticut Light And Power Company [Member] \| Commerical Paper and Revolver Borrowings [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	0	394,800,000
The Connecticut Light And Power Company [Member] \| Series A Due 2023 2.5 percent [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	400,000,000	'
NSTAR Electric Company [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt - Current Portion	301,650,000	1,650,000
Long-Term Debt	1,499,417,000	1,600,911,000
Maturities of Long-term Debt [Abstract]	'	'
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	301,700,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Two	4,700,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Three	200,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Four	400,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Five	0	'
Long-term Debt, Maturities, Repayments of Principal after Year Five	900,000,000	'
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	1,806,400,000	'
Long-term Debt, Description	'On May 17, 2013, NSTAR Electric issued $200 million of three-year floating rate debentures due in May 2016. The proceeds, net of issuance costs, were used to repay commercial paper borrowings and for general corporate purposes. The debentures have a coupon rate reset quarterly based on 3-month LIBOR plus a credit spread of 0.24 percent. The interest rate as of December 31, 2013 was 0.478 percent. On May 1, 2013, PSNH redeemed at par approximately $109 million of the 2001 Series C PCRBs that were due to mature in 2021 using short-term debt. On November 14, 2013, PSNH issued $250 million of 3.50 percent Series S First Mortgage Bonds due in 2023. On December 23, 2013, PSNH redeemed approximately $89 million of the Series B PCRBs that were due to mature in 2021. The proceeds of the Series S issuance were used to repay the short term debt used to redeem the $109 million 2001 Series C PCRBs and to redeem the $89 million Series B PCRBs and pay the associated call premium. The remaining proceeds of the offering were used to refinance short-term debt.	'
NSTAR Electric Company [Member] \| Unamortized Premiums and Discounts, Net [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	-5,300,000	-5,400,000
NSTAR Electric Company [Member] \| Total Other [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	1,800,000,000	1,600,000,000
NSTAR Electric Company [Member] \| Due 2014 4.875% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	300,000,000	300,000,000
NSTAR Electric Company [Member] \| Due 2022 2.375% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	400,000,000	400,000,000
NSTAR Electric Company [Member] \| Due 2017 5.625% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	400,000,000	400,000,000
NSTAR Electric Company [Member] \| Due 2036 5.75% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	200,000,000	200,000,000
NSTAR Electric Company [Member] \| Due 2040 5.5% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	300,000,000	300,000,000
NSTAR Electric Company [Member] \| TaxExempt Sewage Facility Revenue Bonds Due 2015 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	6,400,000	8,000,000
NSTAR Electric Company [Member] \| Variable Due 2016 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	200,000,000	'
Public Service Company Of New Hampshire [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt - Current Portion	50,000,000	'
Long-Term Debt	999,006,000	997,932,000
Maturities of Long-term Debt [Abstract]	'	'
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	50,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Two	0	'
Long-term Debt, Maturities, Repayments of Principal in Year Three	0	'
Long-term Debt, Maturities, Repayments of Principal in Year Four	70,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Five	110,000,000	'
Long-term Debt, Maturities, Repayments of Principal after Year Five	821,300,000	'
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	1,051,300,000	'
Long-term Debt, Description	'On May 1, 2013, PSNH redeemed at par approximately $109 million of the 2001 Series C PCRBs that were due to mature in 2021 using short-term debt. On November 14, 2013, PSNH issued $250 million of 3.50 percent Series S First Mortgage Bonds due in 2023. On December 23, 2013, PSNH redeemed approximately $89 million of the Series B PCRBs that were due to mature in 2021. The proceeds of the Series S issuance were used to repay the short term debt used to redeem the $109 million 2001 Series C PCRBs and to redeem the $89 million Series B PCRBs and pay the associated call premium. The remaining proceeds of the offering were used to refinance short-term debt. PSNH's obligation to repay the PCRBs is secured by first mortgage bonds and bond insurance. The first mortgage bonds contain similar terms and provisions as the PCRBs. If PSNH fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. The PSNH Series A tax-exempt PCRBs are currently callable at 100 percent of par. The PCRBs bear interest at a rate that is periodically set pursuant to auctions. PSNH is not obligated to purchase these PCRBs, which mature in 2021, from the remarketing agent. The interest rate as of December 31, 2013 was 0.088 percent.	'
Public Service Company Of New Hampshire [Member] \| Series L 2004 Due 2014 5.25% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
Public Service Company Of New Hampshire [Member] \| Series M 2005 Due 2035 5.60% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
Public Service Company Of New Hampshire [Member] \| Series N 2007 Due 2017 6.15% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	70,000,000	70,000,000
Public Service Company Of New Hampshire [Member] \| Series O 2008 Due 2018 6.00% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	110,000,000	110,000,000
Public Service Company Of New Hampshire [Member] \| Series P 2009 Due 2019 4.50% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	150,000,000	150,000,000
Public Service Company Of New Hampshire [Member] \| Adjustablerateseriesadue 2021 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	89,300,000	89,300,000
Public Service Company Of New Hampshire [Member] \| Total First Mortgage Bonds [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	962,000,000	712,000,000
Public Service Company Of New Hampshire [Member] \| Total Pollution Control Bonds [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	89,300,000	287,500,000
Public Service Company Of New Hampshire [Member] \| Unamortized Premiums and Discounts, Net [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	-2,300,000	-1,600,000
Public Service Company Of New Hampshire [Member] \| Series Q 4.05% 2011 Due 2021 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	122,000,000	122,000,000
Public Service Company Of New Hampshire [Member] \| Series R 2011 3.30% due 2021 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	160,000,000	160,000,000
Public Service Company Of New Hampshire [Member] \| Tax Exempt Series B and C Due 2021 4.75% to 5.45% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	0	198,200,000
Public Service Company Of New Hampshire [Member] \| Series2013due2023member [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	250,000,000	'
Western Massachusetts Electric Company [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt - Current Portion	0	55,000,000
Long-Term Debt	629,389,000	550,270,000
Maturities of Long-term Debt [Abstract]	'	'
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0	'
Long-term Debt, Maturities, Repayments of Principal in Year Two	50,000,000	'
Long-term Debt, Maturities, Repayments of Principal in Year Three	0	'
Long-term Debt, Maturities, Repayments of Principal in Year Four	0	'
Long-term Debt, Maturities, Repayments of Principal in Year Five	0	'
Long-term Debt, Maturities, Repayments of Principal after Year Five	515,000,000	'
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	565,000,000	'
Long-term Debt, Description	'On September 1, 2013, WMECO repaid at maturity the $55 million Series A Senior Notes using short-term debt. On November 15, 2013, WMECO issued $80 million of 3.88 percent Series G Senior Notes due in 2023. The proceeds, net of issuance costs, were used to pay short-term borrowings and for other working capital purposes.	'
Western Massachusetts Electric Company [Member] \| Senior Note Series A 5.00% Due 2013 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	0	55,000,000
Western Massachusetts Electric Company [Member] \| Senior Notes Series B 5.90% Due 2034 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
Western Massachusetts Electric Company [Member] \| Senior Notes Series C 5.24% Due 2015 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
Western Massachusetts Electric Company [Member] \| Senior Notes Series D 6.70% Due 2037 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	40,000,000	40,000,000
Western Massachusetts Electric Company [Member] \| Senior Notes Series E 5.10% Due 2020 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	95,000,000	95,000,000
Western Massachusetts Electric Company [Member] \| Fees And Interest Due For Spent Nuclear Fuel Disposal Costs [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	57,300,000	57,300,000
Western Massachusetts Electric Company [Member] \| Unamortized Premiums and Discounts, Net [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	7,100,000	8,000,000
Western Massachusetts Electric Company [Member] \| Senior Notes Series F 3.50% due 2021 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	250,000,000	250,000,000
Western Massachusetts Electric Company [Member] \| Total Pollution Control Notes and Other Notes [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	565,000,000	540,000,000
Western Massachusetts Electric Company [Member] \| Series g 2013 due 2023 member [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	80,000,000	'
Yankee Gas Services Company [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	345,700,000	345,800,000
Yankee Gas Services Company [Member] \| Total First Mortgage Bonds [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	345,000,000	345,000,000
Yankee Gas Services Company [Member] \| Unamortized Premiums and Discounts, Net [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	700,000	800,000
Yankee Gas Services Company [Member] \| Series B due 2022 8.48% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	20,000,000	20,000,000
Yankee Gas Services Company [Member] \| Series G due 2014 4.80% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	75,000,000	75,000,000
Yankee Gas Services Company [Member] \| Series H due 2019 5.26% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
Yankee Gas Services Company [Member] \| Series I due 2035 5.35% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
Yankee Gas Services Company [Member] \| Series J due 2018 6.90% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	100,000,000	100,000,000
Yankee Gas Services Company [Member] \| Series K due 2020 4.87% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	50,000,000	50,000,000
NSTAR Gas Company [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	210,000,000	210,000,000
NSTAR Gas Company [Member] \| Series J Due 202 9.95% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	25,000,000	25,000,000
NSTAR Gas Company [Member] \| Series K Due 2033 7.11% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	35,000,000	35,000,000
NSTAR Gas Company [Member] \| Series M Due 2017 7.04% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	25,000,000	25,000,000
NSTAR Gas Company [Member] \| Series N Due 2020 4.46% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	125,000,000	125,000,000
Subsidiaries [Member] \| Unamortized Premiums and Discounts, Net [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	-1,300,000	'
Subsidiaries [Member] \| Fair Value Adjustment [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	230,700,000	259,900,000
Subsidiaries [Member] \| Total Other [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	1,304,400,000	1,079,300,000
Subsidiaries [Member] \| Series C due 2013 5.65% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	'	250,000,000
Subsidiaries [Member] \| Commerical Paper and Revolver Borrowings [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	25,000,000	'
Subsidiaries [Member] \| Debentures Due 2019 4.50% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	350,000,000	350,000,000
Subsidiaries [Member] \| Spent Nuclear Fuel Obilgation CY [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	179,400,000	179,300,000
Subsidiaries [Member] \| FairValueAdjustmentMemberCurrentPortion [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	31,700,000	31,700,000
Subsidiaries [Member] \| Variable Rates Series D Due 2013 [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	'	300,000,000
Subsidiaries [Member] \| Series F Due 2023 2.8% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	450,000,000	'
Subsidiaries [Member] \| Series E Due 2018 1.45% [Member]	'	'
Debt Instrument [Line Items]	'	'
Long-Term Debt	$300,000,000	'

PENSION_BENEFITS_AND_POSTRETIR1

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	$896,844,000	$2,130,497,000	'
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]	'	'	'
Amortization of actuarial gain or loss	10,500,000	8,900,000	5,700,000
OCI Amortization of Prior Service Cost	200,000	200,000	300,000
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]	'	'	'
Description of allocation of assets to subsidiaries	'Effective January 1, 2013, the NSTAR Pension Plan assets were transferred into the NUSCO Pension Plan master trust. The, NUSCO Pension Plan is entitled to approximately 66 percent of each asset category in the master trust, the NSTAR Pension Plan is entitled to approximately 30 percent of each asset category in the master trust and the 401(h) plans are entitled to approximately four percent of each asset category in the master trust. CL&P, PSNH and WMECO participate in the NUSCO Pension and PBOP Plans. Each company participating in the plans is allocated a portion of the total plan assets. As of December 31, 2013 and 2012, the NUSCO Pension Plan had total assets of $2,750.4 million and $2,342.6 million, respectively. CL&P’s, PSNH’s and WMECO’s portion of these total Pension Plan assets was 37 percent, 19 percent and 9 percent, respectively, as of December 31, 2013, and 40 percent, 17 percent and 9 percent, respectively, as of December 31, 2012. The NUSCO PBOP Plans had total assets of $391 million and $334.9 million as of December 31, 2013 and 2012, respectively. CL&P’s, PSNH’s and WMECO’s portion of these total PBOP Plan assets was 39 percent, 21 percent and 9 percent, respectively, as of December 31, 2013 and 2012.	'	'
Pension Plans Defined Benefit Member	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
us-gaap_DefinedBenefitPlanBusinessCombinationsAndAcquisitionsBenefitObligation	0	-1,409,700,000	'
Benefit Obligation Beginning Balance	-5,022,800,000	-3,098,900,000	'
Defined Benefit Plan Service Cost	-102,300,000	-84,300,000	-55,400,000
Defined Benefit Plan Interest Cost	-206,700,000	-198,300,000	-153,300,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	433,600,000	-429,700,000	'
Defined Benefit Plan, Benefits Paid	216,600,000	187,700,000	'
Defined Benefit Plan, Payments SERP	5,100,000	4,200,000	'
Benefit Obligation Ending Balance	-4,676,500,000	-5,022,800,000	-3,098,900,000
DefinedBenefitPlanSettlementsBenefitObligation	0	6,200,000	'
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	102,300,000	84,300,000	55,400,000
Defined Benefit Plan Interest Cost	206,700,000	198,300,000	153,300,000
Defined Benefit Plan, Expected Return on Plan Assets	-278,100,000	-220,900,000	-170,800,000
Defined Benefit Plan, Amortization of Gains (Losses)	210,500,000	172,400,000	84,200,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	4,000,000	7,900,000	9,700,000
Defined Benefit Plan Net Periodic Benefit Cost	245,400,000	242,000,000	131,800,000
Amount Capitalized Defined Benefit Expense	73,200,000	70,600,000	29,700,000
us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsAndCurtailments	0	2,200,000	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Defined Benefit Plan, Business Combinations and Acquisitions, Plan Assets	'	984,700,000	'
Fair Value of Plan Assets Beginning Balance	3,411,300,000	2,005,900,000	'
Defined Benefit Plan, Actual Return on Plan Assets	506,500,000	386,000,000	'
Defined Benefit Plan, Contributions by Employer	284,700,000	222,400,000	'
Defined Benefit Plan, Benefits Paid	-216,600,000	-187,700,000	'
Fair Value of Plan Assets Ending Balance	3,985,900,000	3,411,300,000	2,005,900,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-690,600,000	-1,611,500,000	'
Defined Benefit Plan, Accumulated Benefit Obligation	4,538,800,000	4,622,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	3,411,300,000	2,005,900,000	'
Fair Value of Plan Assets Ending Balance	3,985,900,000	3,411,300,000	2,005,900,000
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]	'	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	-28,900,000	19,100,000	'
Amortization of actuarial gain or loss	-9,400,000	-7,800,000	'
OCI Amortization of Prior Service Cost	-200,000	-200,000	'
RegulatoryAssetDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-635,200,000	245,700,000	'
RegulatoryAssetReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostBeforeTax	-201,200,000	-164,600,000	'
RegulatoryAssetAmortizationOfDefinedBenefitPlanNetPriorServiceCostCreditRecognizedInNetPeriodicBenefitCostBeforeTax	-3,800,000	-7,700,000	'
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]	'	'	'
ension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	43,200,000	81,500,000	'
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	1,000,000	1,200,000	'
DefinedBenefitPlanRegulatoryAssetIncomeNetGainsLossesBeforeTax	1,137,400,000	1,973,800,000	'
DefinedBenefitPlanRegulatoryAssetNetPriorServiceCostCreditBeforeTax	17,400,000	21,200,000	'
Defined Benefit Amounts to be Reclassified from AOCI in next fiscal year	'	'	'
Defined Benefit Plan Future Amortization Of Gain Loss.	5,600,000	'	'
Defined Benefit Plan Future Amortization of Prior Service cost	200,000	'	'
RegulatoryAssetDefinedBenefitPlanAmortizationOfNetGainsLosses	126,200,000	'	'
RegulatoryAssetDefinedBenefitPlanAmortizationOfNetPriorServiceCostCredit	4,200,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	8.25%	'	'
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]	'	'	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	263,300,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	273,300,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	282,900,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	287,400,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	299,400,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	1,617,000,000	'	'
DescriptionOfDefinedContributionPensionAndOtherPostretirementPlans	'NU’s policy is to annually fund the NUSCO and NSTAR Pension Plans in an amount at least equal to an amount that will satisfy federal requirements. NU contributed $202.7 million to the NUSCO Pension Plan in 2013, of which $108.3 million was contributed by PSNH. NSTAR Electric contributed $82 million to the NSTAR Pension Plan in 2013. Based on the current status of the NUSCO Pension Plan, NU expects to make a contribution of $68.6 million in 2014. NSTAR Electric expects to make a contribution of $3 million in 2014 to the NSTAR Pension Plan.	'	'
Pension Plans Defined Benefit Member \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	434,800,000	460,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	434,800,000	460,100,000	'
Pension Plans Defined Benefit Member \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	1,865,400,000	1,508,800,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	1,865,400,000	1,508,800,000	'
Pension Plans Defined Benefit Member \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	1,560,000,000	1,102,500,000	'
Fair Value of Plan Assets Ending Balance	1,850,700,000	1,560,000,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	1,560,000,000	1,102,500,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	137,600,000	108,500,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	31,100,000	23,000,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	122,000,000	47,000,000	'
Fair Value of Plan Assets Ending Balance	1,850,700,000	1,560,000,000	'
Level3PlanAssetsAssumedinMerger	'	279,000,000	'
Pension Plans Defined Benefit Member \| United States Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	909,900,000	'	'
Fair Value of Plan Assets Ending Balance	1,086,300,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	909,900,000	'	'
Fair Value of Plan Assets Ending Balance	1,086,300,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	9.00%	'	'
Target Allocation	24.00%	'	'
Pension Plans Defined Benefit Member \| United States Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	294,600,000	336,500,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	294,600,000	336,500,000	'
Pension Plans Defined Benefit Member \| United States Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	597,700,000	302,800,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	597,700,000	302,800,000	'
Pension Plans Defined Benefit Member \| United States Equity Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	270,600,000	259,400,000	'
Fair Value of Plan Assets Ending Balance	194,000,000	270,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	270,600,000	259,400,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	11,200,000	11,200,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	12,200,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	-100,000,000	'	'
Fair Value of Plan Assets Ending Balance	194,000,000	270,600,000	'
Pension Plans Defined Benefit Member \| International Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	456,700,000	'	'
Fair Value of Plan Assets Ending Balance	456,300,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	456,700,000	'	'
Fair Value of Plan Assets Ending Balance	456,300,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	9.00%	'	'
Target Allocation	10.00%	'	'
Pension Plans Defined Benefit Member \| International Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	32,200,000	42,000,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	32,200,000	42,000,000	'
Pension Plans Defined Benefit Member \| International Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	362,600,000	362,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	362,600,000	362,600,000	'
Pension Plans Defined Benefit Member \| International Equity Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	52,100,000	'	'
Fair Value of Plan Assets Ending Balance	61,500,000	52,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	52,100,000	'	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	9,400,000	10,700,000	'
Fair Value of Plan Assets Ending Balance	61,500,000	52,100,000	'
Level3PlanAssetsAssumedinMerger	'	41,400,000	'
Pension Plans Defined Benefit Member \| Emergining Markets Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	135,300,000	'	'
Fair Value of Plan Assets Ending Balance	211,800,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	135,300,000	'	'
Fair Value of Plan Assets Ending Balance	211,800,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	10.00%	'	'
Target Allocation	6.00%	'	'
Pension Plans Defined Benefit Member \| Emergining Markets Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	211,800,000	135,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	211,800,000	135,300,000	'
Pension Plans Defined Benefit Member \| Private Equity Funds [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	294,600,000	'	'
Fair Value of Plan Assets Ending Balance	396,700,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	294,600,000	'	'
Fair Value of Plan Assets Ending Balance	396,700,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	13.00%	'	'
Target Allocation	10.00%	'	'
Pension Plans Defined Benefit Member \| Private Equity Funds [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	96,400,000	26,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	96,400,000	26,700,000	'
Pension Plans Defined Benefit Member \| Private Equity Funds [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	267,900,000	255,100,000	'
Fair Value of Plan Assets Ending Balance	300,300,000	267,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	267,900,000	255,100,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	15,400,000	17,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	13,700,000	15,000,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	3,300,000	-19,200,000	'
Fair Value of Plan Assets Ending Balance	300,300,000	267,900,000	'
Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	999,200,000	'	'
Fair Value of Plan Assets Ending Balance	1,206,200,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	999,200,000	'	'
Fair Value of Plan Assets Ending Balance	1,206,200,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	5.00%	'	'
Target Allocation	15.00%	'	'
Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	11,600,000	54,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	11,600,000	54,900,000	'
Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	605,100,000	629,200,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	605,100,000	629,200,000	'
Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	315,100,000	276,200,000	'
Fair Value of Plan Assets Ending Balance	589,500,000	315,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	315,100,000	276,200,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	55,300,000	42,100,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	-1,000,000	700,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	187,600,000	-3,900,000	'
Fair Value of Plan Assets Ending Balance	589,500,000	315,100,000	'
TransferBetweenCategories	32,500,000	'	'
Pension Plans Defined Benefit Member \| High Yield Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	8.00%	'	'
Target Allocation	9.00%	'	'
Pension Plans Defined Benefit Member \| Emerging Markets Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	8.00%	'	'
Target Allocation	6.00%	'	'
Pension Plans Defined Benefit Member \| Hedge Funds [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	418,900,000	'	'
Fair Value of Plan Assets Ending Balance	416,900,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	418,900,000	'	'
Fair Value of Plan Assets Ending Balance	416,900,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	7.00%	'	'
Target Allocation	11.00%	'	'
Pension Plans Defined Benefit Member \| Hedge Funds [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	418,900,000	240,000,000	'
Fair Value of Plan Assets Ending Balance	416,900,000	418,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	418,900,000	240,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	33,400,000	21,800,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	-300,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	-2,900,000	30,800,000	'
Fair Value of Plan Assets Ending Balance	416,900,000	418,900,000	'
Level3PlanAssetsAssumedinMerger	'	126,600,000	'
TransferBetweenCategories	-32,500,000	'	'
Pension Plans Defined Benefit Member \| Real Estate [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	314,300,000	'	'
Fair Value of Plan Assets Ending Balance	376,700,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	314,300,000	'	'
Fair Value of Plan Assets Ending Balance	376,700,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	7.50%	'	'
Target Allocation	9.00%	'	'
Pension Plans Defined Benefit Member \| Real Estate [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	0	0	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	0	0	'
Pension Plans Defined Benefit Member \| Real Estate [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	88,200,000	78,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	88,200,000	78,900,000	'
Pension Plans Defined Benefit Member \| Real Estate [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	235,400,000	71,800,000	'
Fair Value of Plan Assets Ending Balance	288,500,000	235,400,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	235,400,000	71,800,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	12,900,000	5,700,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	6,200,000	7,600,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	34,000,000	39,300,000	'
Fair Value of Plan Assets Ending Balance	288,500,000	235,400,000	'
Level3PlanAssetsAssumedinMerger	'	111,000,000	'
Pension Plans Defined Benefit Member \| Assetsrelatedto401h [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	165,000,000	117,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	165,000,000	117,600,000	'
PBOP Plan	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
us-gaap_DefinedBenefitPlanBusinessCombinationsAndAcquisitionsBenefitObligation	'	-770,600,000	'
Benefit Obligation Beginning Balance	-1,233,300,000	-520,900,000	'
Defined Benefit Plan Service Cost	-16,900,000	-15,700,000	-9,200,000
Defined Benefit Plan Interest Cost	-47,200,000	-49,000,000	-25,700,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	200,900,000	70,900,000	'
Defined Benefit Plan, Benefits Paid	58,500,000	58,200,000	'
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	0	-6,200,000	'
Benefit Obligation Ending Balance	-1,038,000,000	-1,233,300,000	-520,900,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	16,900,000	15,700,000	9,200,000
Defined Benefit Plan Interest Cost	47,200,000	49,000,000	25,700,000
Defined Benefit Plan, Expected Return on Plan Assets	-55,400,000	-39,200,000	-21,600,000
Defined Benefit Plan, Amortization of Gains (Losses)	26,000,000	36,000,000	19,000,000
Defined Benefit Plan Amortization Of Transition Obligations Assets	0	12,200,000	11,600,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	-2,100,000	-1,400,000	-300,000
Defined Benefit Plan Net Periodic Benefit Cost	32,600,000	72,300,000	43,600,000
Amount Capitalized Defined Benefit Expense	8,800,000	26,600,000	12,700,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Defined Benefit Plan, Business Combinations and Acquisitions, Plan Assets	'	330,400,000	'
Fair Value of Plan Assets Beginning Balance	709,100,000	285,400,000	'
Defined Benefit Plan, Actual Return on Plan Assets	118,300,000	78,800,000	'
Defined Benefit Plan, Contributions by Employer	57,600,000	72,700,000	'
Defined Benefit Plan, Benefits Paid	-58,500,000	-58,200,000	'
Fair Value of Plan Assets Ending Balance	826,500,000	709,100,000	285,400,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-211,500,000	-524,200,000	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'	'	'
Defined Benefit Plan, Description of Direction and Pattern of Change for Assumed Health Care Cost Trend Rate	'The health care cost trend rate assumption used to calculate the 2013 PBOP expense amounts was 7 percent for the NUSCO PBOP Plan, subsequently decreasing by 50 basis points per year to an ultimate rate of 5 percent in 2017, and 7.10 percent for the NSTAR PBOP Plan, subsequently decreasing to an ultimate rate of 4.5 percent in 2024. As of December 31, 2013, the health care cost trend rate assumption used to determine the NUSCO and NSTAR PBOP Plans’ year end funded status is 7 percent, subsequently decreasing to an ultimate rate of 4.5 percent in 2024.	'	'
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]	'	'	'
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	85,800,000	'	'
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	-70,400,000	'	'
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	7,100,000	'	'
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components	-5,500,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	709,100,000	285,400,000	'
Fair Value of Plan Assets Ending Balance	826,500,000	709,100,000	285,400,000
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]	'	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	-1,900,000	-1,800,000	'
Amortization of actuarial gain or loss	-1,100,000	-1,100,000	'
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Transition Asset (Obligation), Recognized in Net Periodic Benefit Cost, before Tax	0	-200,000	'
RegulatoryAssetDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-262,000,000	-108,600,000	'
RegulatoryAssetReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostBeforeTax	-24,900,000	-34,900,000	'
RegulatoryAssetAmortizationOfDefinedBenefitPlanNetPriorServiceCostCreditRecognizedInNetPeriodicBenefitCostBeforeTax	2,100,000	1,400,000	'
RegulatoryAssetReclassificationOfDefinedBenefitPlanNetTransitionAssetObligationRecognizedInNetPeriodicBenefitCostBeforeTax	0	-11,900,000	'
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]	'	'	'
ension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	6,200,000	9,200,000	'
DefinedBenefitPlanRegulatoryAssetIncomeNetGainsLossesBeforeTax	89,200,000	376,100,000	'
DefinedBenefitPlanRegulatoryAssetNetPriorServiceCostCreditBeforeTax	-4,600,000	-6,700,000	'
Defined Benefit Amounts to be Reclassified from AOCI in next fiscal year	'	'	'
Defined Benefit Plan Future Amortization Of Gain Loss.	700,000	'	'
RegulatoryAssetDefinedBenefitPlanAmortizationOfNetGainsLosses	11,400,000	'	'
RegulatoryAssetDefinedBenefitPlanAmortizationOfNetPriorServiceCostCredit	-2,800,000	'	'
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]	'	'	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	61,600,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	63,300,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	64,500,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	65,600,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	66,600,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	344,400,000	'	'
DescriptionOfDefinedContributionPensionAndOtherPostretirementPlans	'For the PBOP Plans, it is NU’s policy to annually fund the NUSCO PBOP Plans in an amount equal to the PBOP Plans' postretirement benefit cost, excluding curtailment and termination benefits, and the NSTAR PBOP Plan in an amount that approximates annual benefit payments. NU contributed $57.6 million to the PBOP Plans in 2013 and expects to make $39.7 million in contributions in 2014.	'	'
PBOP Plan \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	121,400,000	201,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	121,400,000	201,700,000	'
PBOP Plan \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	310,700,000	243,800,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	310,700,000	243,800,000	'
PBOP Plan \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	146,000,000	60,400,000	'
Fair Value of Plan Assets Ending Balance	229,400,000	146,000,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	146,000,000	60,400,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	35,700,000	16,600,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	100,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	47,600,000	9,500,000	'
Fair Value of Plan Assets Ending Balance	229,400,000	146,000,000	'
Level3PlanAssetsAssumedinMerger	'	59,500,000	'
PBOP Plan \| United States Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	256,700,000	210,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	256,700,000	210,300,000	'
PBOP Plan \| United States Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	67,000,000	116,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	67,000,000	116,300,000	'
PBOP Plan \| United States Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	120,600,000	57,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	120,600,000	57,700,000	'
PBOP Plan \| United States Equity Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	36,300,000	10,700,000	'
Fair Value of Plan Assets Ending Balance	69,100,000	36,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	36,300,000	10,700,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	20,800,000	5,900,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	12,000,000	0	'
Fair Value of Plan Assets Ending Balance	69,100,000	36,300,000	'
Level3PlanAssetsAssumedinMerger	'	19,700,000	'
PBOP Plan \| International Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	70,900,000	97,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	70,900,000	97,700,000	'
PBOP Plan \| International Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	28,100,000	68,000,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	28,100,000	68,000,000	'
PBOP Plan \| International Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	42,800,000	29,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	42,800,000	29,700,000	'
PBOP Plan \| Emergining Markets Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	28,600,000	21,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	28,600,000	21,700,000	'
PBOP Plan \| Emergining Markets Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	15,200,000	7,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	15,200,000	7,700,000	'
PBOP Plan \| Emergining Markets Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	13,400,000	14,000,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	13,400,000	14,000,000	'
PBOP Plan \| Private Equity Funds [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	17,900,000	11,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	17,900,000	11,300,000	'
PBOP Plan \| Private Equity Funds [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	11,300,000	5,100,000	'
Fair Value of Plan Assets Ending Balance	17,900,000	11,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	11,300,000	5,100,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	1,500,000	1,600,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	200,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	4,900,000	4,600,000	'
Fair Value of Plan Assets Ending Balance	17,900,000	11,300,000	'
PBOP Plan \| Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	171,200,000	169,800,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	171,200,000	169,800,000	'
PBOP Plan \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	119,700,000	137,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	119,700,000	137,700,000	'
PBOP Plan \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	32,100,000	26,000,000	'
Fair Value of Plan Assets Ending Balance	51,500,000	32,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	32,100,000	26,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	4,100,000	4,000,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	15,300,000	2,100,000	'
Fair Value of Plan Assets Ending Balance	51,500,000	32,100,000	'
PBOP Plan \| Hedge Funds [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	57,000,000	39,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	57,000,000	39,600,000	'
PBOP Plan \| Hedge Funds [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	39,600,000	16,100,000	'
Fair Value of Plan Assets Ending Balance	57,000,000	39,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	39,600,000	16,100,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	5,400,000	2,100,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	12,000,000	'	'
Fair Value of Plan Assets Ending Balance	57,000,000	39,600,000	'
Level3PlanAssetsAssumedinMerger	'	21,400,000	'
PBOP Plan \| Real Estate [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	48,100,000	31,400,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	48,100,000	31,400,000	'
PBOP Plan \| Real Estate [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	14,200,000	4,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	14,200,000	4,700,000	'
PBOP Plan \| Real Estate [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	26,700,000	2,500,000	'
Fair Value of Plan Assets Ending Balance	33,900,000	26,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	26,700,000	2,500,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	3,900,000	3,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	-100,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	3,400,000	2,800,000	'
Fair Value of Plan Assets Ending Balance	33,900,000	26,700,000	'
Level3PlanAssetsAssumedinMerger	'	18,400,000	'
PBOP Plan \| Cash And Cash Equivalents Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	11,100,000	9,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	11,100,000	9,700,000	'
PBOP Plan \| Cash And Cash Equivalents Member \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	11,100,000	9,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	11,100,000	9,700,000	'
PBOP Plan \| Assetsrelatedto401h [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	165,000,000	117,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	165,000,000	117,600,000	'
NUSCO Pension Plan [Member]	'	'	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	5.03%	4.24%	'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.50%	3.50%	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.24%	5.03%	5.57%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.50%	3.50%	3.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.25%	8.25%	8.25%
Nstar pbop Plans [Member]	'	'	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	5.10%	4.35%	'
Health Care Trend Assumption Used In Funded Status	7.00%	7.10%	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.35%	4.58%	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.25%	7.30%	'
Nstar pbop Plans [Member] \| United States Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.30%	'
Target Allocation	'	25.00%	'
Nstar pbop Plans [Member] \| International Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.60%	'
Target Allocation	'	20.00%	'
Nstar pbop Plans [Member] \| Emergining Markets Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.80%	'
Target Allocation	'	5.00%	'
Nstar pbop Plans [Member] \| Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	4.60%	'
Target Allocation	'	30.00%	'
Nstar pbop Plans [Member] \| Hedge Funds [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.40%	'
Target Allocation	'	10.00%	'
Nstar pbop Plans [Member] \| Real Estate [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	7.90%	'
Target Allocation	'	10.00%	'
NUSCO PBOP Plan [Member]	'	'	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.78%	4.04%	'
Health Care Trend Assumption Used In Funded Status	7.00%	7.00%	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.04%	4.84%	5.28%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.25%	8.25%	8.25%
NUSCOPensionandPBOP [Member] \| United States Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	9.00%	'
Target Allocation	'	24.00%	'
NUSCOPensionandPBOP [Member] \| International Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	9.00%	'
Target Allocation	'	13.00%	'
NUSCOPensionandPBOP [Member] \| Emergining Markets Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	10.00%	'
Target Allocation	'	3.00%	'
NUSCOPensionandPBOP [Member] \| Private Equity Funds [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	13.00%	'
Target Allocation	'	12.00%	'
NUSCOPensionandPBOP [Member] \| Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	5.00%	'
Target Allocation	'	20.00%	'
NUSCOPensionandPBOP [Member] \| High Yield Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	7.50%	'
Target Allocation	'	3.50%	'
NUSCOPensionandPBOP [Member] \| Emerging Markets Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	7.50%	'
Target Allocation	'	3.50%	'
NUSCOPensionandPBOP [Member] \| Hedge Funds [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	7.00%	'
Target Allocation	'	13.00%	'
NUSCOPensionandPBOP [Member] \| Real Estate [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	7.50%	'
Target Allocation	'	8.00%	'
The Connecticut Light And Power Company [Member]	'	'	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	95,895,000	304,696,000	'
The Connecticut Light And Power Company [Member] \| Pension Plans Defined Benefit Member	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-1,178,000,000	-1,043,800,000	'
Defined Benefit Plan Service Cost	-24,900,000	-21,800,000	-19,500,000
Defined Benefit Plan Interest Cost	-48,300,000	-51,200,000	-51,900,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	110,700,000	-117,400,000	'
Defined Benefit Plan, Benefits Paid	56,600,000	55,900,000	'
Defined Benefit Plan, Payments SERP	500,000	300,000	'
Benefit Obligation Ending Balance	-1,083,400,000	-1,178,000,000	-1,043,800,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	24,900,000	21,800,000	19,500,000
Defined Benefit Plan Interest Cost	48,300,000	51,200,000	51,900,000
Defined Benefit Plan, Expected Return on Plan Assets	-73,800,000	-70,600,000	-76,600,000
Defined Benefit Plan, Amortization of Gains (Losses)	55,900,000	49,600,000	33,400,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	1,800,000	3,600,000	4,200,000
Defined Benefit Plan Net Periodic Benefit Cost	57,100,000	55,600,000	32,400,000
Related Intercompany Allocationsof Defined Benefit Expense	44,900,000	42,800,000	34,100,000
Amount Capitalized Defined Benefit Expense	28,000,000	26,800,000	16,600,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	937,600,000	869,600,000	'
Defined Benefit Plan, Actual Return on Plan Assets	135,300,000	123,900,000	'
Defined Benefit Plan, Contributions by Employer	'	0	'
Defined Benefit Plan, Benefits Paid	-56,600,000	-55,900,000	'
Fair Value of Plan Assets Ending Balance	1,016,300,000	937,600,000	869,600,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-67,100,000	-240,400,000	'
Defined Benefit Plan, Accumulated Benefit Obligation	1,058,000,000	1,061,800,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	937,600,000	869,600,000	'
Fair Value of Plan Assets Ending Balance	1,016,300,000	937,600,000	869,600,000
The Connecticut Light And Power Company [Member] \| PBOP Plan	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-196,800,000	-198,900,000	'
Defined Benefit Plan Service Cost	-3,400,000	-3,000,000	-2,900,000
Defined Benefit Plan Interest Cost	-7,900,000	-9,200,000	-10,000,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	13,300,000	1,200,000	'
Defined Benefit Plan, Benefits Paid	14,400,000	14,800,000	'
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	0	-1,700,000	'
Benefit Obligation Ending Balance	-180,400,000	-196,800,000	-198,900,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	3,400,000	3,000,000	2,900,000
Defined Benefit Plan Interest Cost	7,900,000	9,200,000	10,000,000
Defined Benefit Plan, Expected Return on Plan Assets	-10,100,000	-9,100,000	-8,700,000
Defined Benefit Plan, Amortization of Gains (Losses)	7,400,000	7,500,000	7,200,000
Defined Benefit Plan Amortization Of Transition Obligations Assets	0	6,100,000	6,200,000
Defined Benefit Plan Net Periodic Benefit Cost	8,600,000	16,700,000	17,600,000
Related Intercompany Allocationsof Defined Benefit Expense	7,100,000	7,900,000	8,200,000
Amount Capitalized Defined Benefit Expense	3,900,000	8,200,000	8,700,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	132,200,000	112,200,000	'
Defined Benefit Plan, Actual Return on Plan Assets	24,800,000	15,000,000	'
Defined Benefit Plan, Contributions by Employer	8,700,000	19,800,000	'
Defined Benefit Plan, Benefits Paid	-14,400,000	-14,800,000	'
Fair Value of Plan Assets Ending Balance	151,300,000	132,200,000	112,200,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-29,100,000	-64,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	132,200,000	112,200,000	'
Fair Value of Plan Assets Ending Balance	151,300,000	132,200,000	112,200,000
NSTAR Electric Company [Member]	'	'	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	118,010,000	360,932,000	'
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]	'	'	'
RegulatoryAssetAmortizationOfDefinedBenefitPlanNetPriorServiceCostCreditRecognizedInNetPeriodicBenefitCostBeforeTax	'	-600,000	'
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]	'	'	'
Pension Contribution	82,000,000	25,000,000	125,000,000
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-1,430,000,000	-1,346,200,000	'
Defined Benefit Plan Service Cost	-33,100,000	-30,300,000	-26,000,000
Defined Benefit Plan Interest Cost	-58,000,000	-58,900,000	-61,000,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	96,600,000	-63,600,000	'
Defined Benefit Plan, Benefits Paid	71,200,000	69,000,000	'
Defined Benefit Plan, Payments SERP	'	0	'
Benefit Obligation Ending Balance	-1,353,300,000	-1,430,000,000	-1,346,200,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	33,100,000	30,300,000	26,000,000
Defined Benefit Plan Interest Cost	58,000,000	58,900,000	61,000,000
Defined Benefit Plan, Expected Return on Plan Assets	-84,400,000	-65,600,000	-71,400,000
Defined Benefit Plan, Amortization of Gains (Losses)	58,100,000	63,100,000	48,600,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	-300,000	-600,000	-700,000
Defined Benefit Plan Net Periodic Benefit Cost	64,500,000	86,100,000	63,500,000
Related Intercompany Allocationsof Defined Benefit Expense	-8,400,000	-12,300,000	-10,200,000
Amount Capitalized Defined Benefit Expense	28,900,000	30,700,000	19,800,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	1,069,100,000	988,500,000	'
Defined Benefit Plan, Actual Return on Plan Assets	155,400,000	124,600,000	'
Defined Benefit Plan, Contributions by Employer	82,000,000	25,000,000	'
Defined Benefit Plan, Benefits Paid	-71,200,000	-69,000,000	'
Fair Value of Plan Assets Ending Balance	1,235,300,000	1,069,100,000	988,500,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-118,000,000	-360,900,000	'
Defined Benefit Plan, Accumulated Benefit Obligation	1,280,600,000	1,353,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	1,069,100,000	988,500,000	'
Fair Value of Plan Assets Ending Balance	1,235,300,000	1,069,100,000	988,500,000
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]	'	'	'
RegulatoryAssetDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	168,000,000	4,600,000	'
RegulatoryAssetReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostBeforeTax	-58,100,000	-62,800,000	'
RegulatoryAssetAmortizationOfDefinedBenefitPlanNetPriorServiceCostCreditRecognizedInNetPeriodicBenefitCostBeforeTax	'	-300,000	'
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]	'	'	'
DefinedBenefitPlanRegulatoryAssetIncomeNetGainsLossesBeforeTax	497,900,000	724,000,000	'
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]	'	'	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	88,000,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	90,600,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	88,400,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	88,500,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	90,000,000	'	'
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	449,200,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	129,400,000	151,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	129,400,000	151,600,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	555,300,000	693,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	555,300,000	693,100,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	302,000,000	279,000,000	'
Fair Value of Plan Assets Ending Balance	550,600,000	302,000,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	302,000,000	279,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	40,700,000	26,200,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	9,300,000	-300,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	36,300,000	-2,900,000	'
Fair Value of Plan Assets Ending Balance	550,600,000	302,000,000	'
TransferResultingFromPlanAssetConsolidations	162,300,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| United States Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	343,100,000	'	'
Fair Value of Plan Assets Ending Balance	323,400,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	343,100,000	'	'
Fair Value of Plan Assets Ending Balance	323,400,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	9.00%	'	'
Target Allocation	24.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| United States Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	87,700,000	96,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	87,700,000	96,700,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| United States Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	177,900,000	246,400,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	177,900,000	246,400,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| United States Equity Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	57,800,000	'	'
Level 3 Rollforwards	'	'	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	3,500,000	'	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	3,600,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	-29,800,000	'	'
Fair Value of Plan Assets Ending Balance	57,800,000	'	'
TransferResultingFromPlanAssetConsolidations	80,500,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| International Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	150,400,000	'	'
Fair Value of Plan Assets Ending Balance	135,900,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	150,400,000	'	'
Fair Value of Plan Assets Ending Balance	135,900,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	9.00%	'	'
Target Allocation	10.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| International Equity Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	'	0	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	'	0	'
Level3PlanAssetsAssumedinMerger	9,600,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| International Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	108,000,000	98,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	108,000,000	98,300,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| International Equity Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	52,100,000	41,400,000	'
Fair Value of Plan Assets Ending Balance	18,300,000	52,100,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	52,100,000	41,400,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	2,800,000	10,700,000	'
Fair Value of Plan Assets Ending Balance	18,300,000	52,100,000	'
TransferResultingFromPlanAssetConsolidations	-36,600,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Emergining Markets Equity Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	55,900,000	'	'
Fair Value of Plan Assets Ending Balance	63,100,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	55,900,000	'	'
Fair Value of Plan Assets Ending Balance	63,100,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	10.00%	'	'
Target Allocation	6.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Emergining Markets Equity Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	63,100,000	55,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	63,100,000	55,900,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Private Equity Funds [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	118,100,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	118,100,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	13.00%	'	'
Target Allocation	10.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Private Equity Funds [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	28,700,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	28,700,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Private Equity Funds [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	89,400,000	'	'
Level 3 Rollforwards	'	'	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	4,600,000	'	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	4,200,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	900,000	'	'
Fair Value of Plan Assets Ending Balance	89,400,000	'	'
TransferResultingFromPlanAssetConsolidations	79,700,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	347,400,000	'	'
Fair Value of Plan Assets Ending Balance	358,800,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	347,400,000	'	'
Fair Value of Plan Assets Ending Balance	358,800,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	5.00%	'	'
Target Allocation	15.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 1 Member	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	3,400,000	54,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	3,400,000	54,900,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	180,000,000	292,500,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	180,000,000	292,500,000	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Fixed Income Debt Securities [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	175,400,000	'	'
Level 3 Rollforwards	'	'	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	16,400,000	'	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	-300,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	55,800,000	'	'
Fair Value of Plan Assets Ending Balance	175,400,000	'	'
TransferResultingFromPlanAssetConsolidations	93,800,000	'	'
TransferBetweenCategories	9,700,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Hedge Funds [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	122,700,000	'	'
Fair Value of Plan Assets Ending Balance	124,100,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	122,700,000	'	'
Fair Value of Plan Assets Ending Balance	124,100,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	7.00%	'	'
Target Allocation	11.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Hedge Funds [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	122,700,000	126,600,000	'
Fair Value of Plan Assets Ending Balance	124,100,000	122,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	122,700,000	126,600,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	9,900,000	5,600,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	'	-300,000	'
Defined Benefit Plan, Purchases, Sales, and Settlements	-800,000	-9,200,000	'
Fair Value of Plan Assets Ending Balance	124,100,000	122,700,000	'
TransferResultingFromPlanAssetConsolidations	2,000,000	'	'
TransferBetweenCategories	-9,700,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Real Estate [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	127,200,000	'	'
Fair Value of Plan Assets Ending Balance	111,900,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	127,200,000	'	'
Fair Value of Plan Assets Ending Balance	111,900,000	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	7.50%	'	'
Target Allocation	9.00%	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Real Estate [Member] \| Fair Value Inputs Level 2 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	26,300,000	'	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	26,300,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Real Estate [Member] \| Fair Value Inputs Level 3 [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	127,200,000	111,000,000	'
Fair Value of Plan Assets Ending Balance	85,600,000	127,200,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	127,200,000	111,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets Still Held	3,500,000	9,900,000	'
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	1,800,000	'	'
Defined Benefit Plan, Purchases, Sales, and Settlements	10,200,000	6,300,000	'
Fair Value of Plan Assets Ending Balance	85,600,000	127,200,000	'
TransferResultingFromPlanAssetConsolidations	-57,100,000	'	'
NSTAR Electric Company [Member] \| Pension Plans Defined Benefit Member \| Assetsrelatedto401h [Member]	'	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Ending Balance	'	77,600,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Ending Balance	'	77,600,000	'
NSTAR Electric Company [Member] \| Supplemental Employee Retirement Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Net Periodic Benefit Cost	3,200,000	3,600,000	4,100,000
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member]	'	'	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.85%	4.13%	'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	4.00%	4.00%	'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.13%	4.52%	5.30%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	4.00%	4.00%	4.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.25%	7.30%	8.00%
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| United States Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.30%	'
Target Allocation	'	25.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| International Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.60%	'
Target Allocation	'	13.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| Emergining Markets Equity Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.80%	'
Target Allocation	'	5.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	4.60%	'
Target Allocation	'	21.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| High Yield Fixed Income Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	6.50%	'
Target Allocation	'	9.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| Emerging Markets Debt Securities [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	6.40%	'
Target Allocation	'	4.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| Hedge Funds [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	8.40%	'
Target Allocation	'	13.00%	'
NSTAR Electric Company [Member] \| NSTAR Pension Plan [Member] \| Real Estate [Member]	'	'	'
Defined Benefit Plan, Assets, Target Allocations [Abstract]	'	'	'
Assumed Rate of Return on Defined Benefit Plan Assets	'	7.90%	'
Target Allocation	'	10.00%	'
Public Service Company Of New Hampshire [Member]	'	'	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	15,272,000	33,981,000	'
Public Service Company Of New Hampshire [Member] \| Pension Plans Defined Benefit Member	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-576,000,000	-497,900,000	'
Defined Benefit Plan Service Cost	-13,100,000	-11,800,000	-10,600,000
Defined Benefit Plan Interest Cost	-23,600,000	-24,400,000	-24,400,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	62,400,000	-61,300,000	'
Defined Benefit Plan, Benefits Paid	21,100,000	19,700,000	'
Defined Benefit Plan, Payments SERP	200,000	0	'
Benefit Obligation Ending Balance	-529,000,000	-576,000,000	-497,900,000
DefinedBenefitPlanSettlementsBenefitObligation	0	-300,000	'
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	13,100,000	11,800,000	10,600,000
Defined Benefit Plan Interest Cost	23,600,000	24,400,000	24,400,000
Defined Benefit Plan, Expected Return on Plan Assets	-35,400,000	-28,200,000	-19,800,000
Defined Benefit Plan, Amortization of Gains (Losses)	21,600,000	16,200,000	10,700,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	700,000	1,500,000	1,800,000
Defined Benefit Plan Net Periodic Benefit Cost	23,600,000	25,700,000	27,700,000
Related Intercompany Allocationsof Defined Benefit Expense	10,500,000	10,100,000	7,600,000
Amount Capitalized Defined Benefit Expense	7,300,000	7,900,000	7,600,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	386,600,000	279,700,000	'
Defined Benefit Plan, Actual Return on Plan Assets	54,800,000	38,900,000	'
Defined Benefit Plan, Contributions by Employer	108,300,000	87,700,000	'
Defined Benefit Plan, Benefits Paid	-21,100,000	-19,700,000	'
Fair Value of Plan Assets Ending Balance	528,600,000	386,600,000	279,700,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-400,000	-189,400,000	'
Defined Benefit Plan, Accumulated Benefit Obligation	520,100,000	515,900,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	386,600,000	279,700,000	'
Fair Value of Plan Assets Ending Balance	528,600,000	386,600,000	279,700,000
Public Service Company Of New Hampshire [Member] \| PBOP Plan	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-100,200,000	-99,200,000	'
Defined Benefit Plan Service Cost	-2,300,000	-2,000,000	-1,900,000
Defined Benefit Plan Interest Cost	-4,000,000	-4,600,000	-4,800,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	7,200,000	300,000	'
Defined Benefit Plan, Benefits Paid	5,800,000	5,900,000	'
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	0	-600,000	'
Benefit Obligation Ending Balance	-93,500,000	-100,200,000	-99,200,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	2,300,000	2,000,000	1,900,000
Defined Benefit Plan Interest Cost	4,000,000	4,600,000	4,800,000
Defined Benefit Plan, Expected Return on Plan Assets	-5,200,000	-4,600,000	-4,300,000
Defined Benefit Plan, Amortization of Gains (Losses)	3,600,000	3,600,000	3,200,000
Defined Benefit Plan Amortization Of Transition Obligations Assets	0	2,500,000	2,500,000
Defined Benefit Plan Net Periodic Benefit Cost	4,700,000	8,100,000	8,100,000
Related Intercompany Allocationsof Defined Benefit Expense	1,600,000	2,000,000	2,000,000
Amount Capitalized Defined Benefit Expense	1,300,000	2,300,000	2,200,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	69,500,000	58,700,000	'
Defined Benefit Plan, Actual Return on Plan Assets	13,400,000	7,500,000	'
Defined Benefit Plan, Contributions by Employer	4,700,000	9,200,000	'
Defined Benefit Plan, Benefits Paid	-5,800,000	-5,900,000	'
Fair Value of Plan Assets Ending Balance	81,800,000	69,500,000	58,700,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-11,700,000	-30,700,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	69,500,000	58,700,000	'
Fair Value of Plan Assets Ending Balance	81,800,000	69,500,000	58,700,000
Public Service Company Of New Hampshire [Member] \| NUSCO Pension Plan [Member]	'	'	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	3,000,000	'	'
Western Massachusetts Electric Company [Member]	'	'	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	3,911,000	11,884,000	'
Western Massachusetts Electric Company [Member] \| Pension Plans Defined Benefit Member	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-243,100,000	-215,800,000	'
Defined Benefit Plan Service Cost	-4,700,000	-4,100,000	-3,900,000
Defined Benefit Plan Interest Cost	-10,000,000	-10,500,000	-10,700,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	22,400,000	-24,000,000	'
Defined Benefit Plan, Benefits Paid	11,500,000	11,300,000	'
Defined Benefit Plan, Payments SERP	0	'	'
Benefit Obligation Ending Balance	-223,900,000	-243,100,000	-215,800,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	4,700,000	4,100,000	3,900,000
Defined Benefit Plan Interest Cost	10,000,000	10,500,000	10,700,000
Defined Benefit Plan, Expected Return on Plan Assets	-17,400,000	-16,400,000	-17,700,000
Defined Benefit Plan, Amortization of Gains (Losses)	11,800,000	10,700,000	7,100,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	400,000	800,000	900,000
Defined Benefit Plan Net Periodic Benefit Cost	9,500,000	9,700,000	4,900,000
Related Intercompany Allocationsof Defined Benefit Expense	8,000,000	8,100,000	6,200,000
Amount Capitalized Defined Benefit Expense	5,200,000	5,100,000	2,700,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	218,500,000	202,000,000	'
Defined Benefit Plan, Actual Return on Plan Assets	33,400,000	27,800,000	'
Defined Benefit Plan, Benefits Paid	-11,500,000	-11,300,000	'
Fair Value of Plan Assets Ending Balance	240,400,000	218,500,000	202,000,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	16,500,000	-24,600,000	'
Defined Benefit Plan, Accumulated Benefit Obligation	220,600,000	221,300,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	218,500,000	202,000,000	'
Fair Value of Plan Assets Ending Balance	240,400,000	218,500,000	202,000,000
Western Massachusetts Electric Company [Member] \| PBOP Plan	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit Obligation Beginning Balance	-42,500,000	-42,900,000	'
Defined Benefit Plan Service Cost	-700,000	-600,000	-600,000
Defined Benefit Plan Interest Cost	-1,700,000	-2,000,000	-2,200,000
Defined Benefit Plan, Actuarial Net (Gains) Losses	3,300,000	100,000	'
Defined Benefit Plan, Benefits Paid	2,900,000	3,200,000	'
Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received	0	-300,000	'
Benefit Obligation Ending Balance	-38,700,000	-42,500,000	-42,900,000
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'
Defined Benefit Plan Service Cost	700,000	600,000	600,000
Defined Benefit Plan Interest Cost	1,700,000	2,000,000	2,200,000
Defined Benefit Plan, Expected Return on Plan Assets	-2,300,000	-2,100,000	-2,000,000
Defined Benefit Plan, Amortization of Gains (Losses)	1,100,000	1,200,000	1,100,000
Defined Benefit Plan Amortization Of Transition Obligations Assets	0	1,300,000	1,300,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	'	0	'
Defined Benefit Plan Net Periodic Benefit Cost	1,200,000	3,000,000	3,200,000
Related Intercompany Allocationsof Defined Benefit Expense	1,300,000	1,500,000	1,500,000
Amount Capitalized Defined Benefit Expense	600,000	1,600,000	1,500,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair Value of Plan Assets Beginning Balance	31,000,000	27,100,000	'
Defined Benefit Plan, Actual Return on Plan Assets	6,000,000	3,500,000	'
Defined Benefit Plan, Contributions by Employer	1,200,000	3,600,000	'
Defined Benefit Plan, Benefits Paid	-2,900,000	-3,200,000	'
Fair Value of Plan Assets Ending Balance	35,300,000	31,000,000	27,100,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Defined Benefit Plan, Funded Status of Plan	-3,400,000	-11,500,000	'
Level 3 Rollforwards	'	'	'
Fair Value of Plan Assets Beginning Balance	31,000,000	27,100,000	'
Fair Value of Plan Assets Ending Balance	35,300,000	31,000,000	27,100,000
Western Massachusetts Electric Company [Member] \| NUSCO Pension Plan [Member]	'	'	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Accrued Pension, PBOP and SERP	$17,000,000	'	'

Defined_Contribution_Plans_Det

Defined Contribution Plans (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Contribution Plan, Cost Recognized	$37	$25.70	$17.40
The Connecticut Light And Power Company [Member]	'	'	'
Defined Contribution Plan, Cost Recognized	5.1	4.8	4.5
NSTAR Electric Company [Member]	'	'	'
Defined Contribution Plan, Cost Recognized	8.5	9	8.7
Western Massachusetts Electric Company [Member]	'	'	'
Defined Contribution Plan, Cost Recognized	1	0.9	0.9
Public Service Company Of New Hampshire [Member]	'	'	'
Defined Contribution Plan, Cost Recognized	$3.30	$3.30	$3.10

Employee_Stock_Ownership_Plan_

Employee Stock Ownership Plan (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Notes To Consolidated Financial Statements [Abstract]	'	'	'
Employee Stock Ownership Plan (ESOP), Compensation Expense	$9.10	$8.90	$8.80

ShareBased_Payments_Details

Share-Based Payments (Details) (USD $)	0 Months Ended	12 Months Ended
Share-Based Payments (Details) (USD $)	Apr. 09, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]	'	'	'	'	'
Excess Tax Benefit from Share-based Compensation, Financing Activities	'	$5,500,000	$8,500,000	$1,300,000	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	'	4,500,000	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	'	2,462,668	2,502,512	'	'
AllocatedShareBasedCompensationExpense	'	27,000,000	25,800,000	12,300,000	'
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	'	10,700,000	10,200,000	4,900,000	'
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	'	19,500,000	'	'	'
Description Of Compensation Cost Not Yet Recognized Period For Recognition	'	'This cost is expected to be recognized ratably over a weighted-average period of 1.64 years for NU, 1.85 years for CL&P, 1.47 years for NSTAR Electric, 1.79 years for PSNH and 1.80 years for WMECO.	'	'	'
Employee Service Share Based Compensation Awards Other Than Options Disclosures [Abstract]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	'	1,162,216	1,417,688	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	'	$36.58	$34.70	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	'	583,101	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	'	$34.34	'	'	'
Share Based Compensation Arrangement By Share Based Payment Award Vested Outstanding Number	'	474,224	'	'	'
Share Based Compensation Arrangement By Share Based Payment Award Expected To Vest	'	1,104,106	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, NSTAR Deferred And Performance Awards Converted Upon Merger	421,775	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award Equity Instruments Other Than Options NSTAR Deferred And Performance Awards Converted Upon Merger, Value	15.5	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, NSTAR RSU Retention Awards Converted To NU RSU's Upon Merger	195,619	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, NSTAR RSU Retention Awards Converted To NU RSU's Upon Merger, Value	7.2	'	'	'	'
Employee Service Share Based Compensation Stock Option Disclosures [Abstract]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	'	1,221,375	1,545,757	47,374	112,599
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	'	-324,382	-1,166,511	-65,225	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	'	$25.97	$24.92	$18.78	$18.80
ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	'	$20.97	$22.53	$18.81	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	'	6,700,000	18,700,000	1,000,000	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	'	20,100,000	'	'	'
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options	'	6,800,000	'	'	'
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	'	2,700,000	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Options, Converted NSTAR Options Upon Merger	2,664,894	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Options, Converted NSTAR Options Upon Merger, Weighted Average Exercise Price	$23.99	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Options, Converted NSTAR Options Upon Merger, Total Value	30.5	'	'	'	'
Employee Service Share Based Compensation E S P P Disclosures [Abstract]	'	'	'	'	'
Stock Issued During Period, Shares, Employee Stock Purchase Plans	'	39,526	39,422	'	'
Employee Stock Purchase Plan Shares Remaining For Future Issuance	'	817,754	857,280	'	'
ESPP Discounted Purchase Price First Six Months	'	38.69	33.01	'	'
ESPP Discounted Purchase Price Second Six Months	'	42.19	37.89	'	'
Deferred Compensation Liability, Classified, Noncurrent [Abstract]	'	'	'	'	'
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	'	51,300,000	54,600,000	52,800,000	'
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	'	4,400,000	4,700,000	4,700,000	'
The Connecticut Light And Power Company [Member]	'	'	'	'	'
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]	'	'	'	'	'
AllocatedShareBasedCompensationExpense	'	6,800,000	4,800,000	7,100,000	'
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	'	2,700,000	1,900,000	2,800,000	'
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	'	5,800,000	'	'	'
Deferred Compensation Liability, Classified, Noncurrent [Abstract]	'	'	'	'	'
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	'	400,000	400,000	1,200,000	'
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	'	2,500,000	2,600,000	2,600,000	'
NSTAR Electric Company [Member]	'	'	'	'	'
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]	'	'	'	'	'
AllocatedShareBasedCompensationExpense	'	7,500,000	7,400,000	7,700,000	'
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	'	3,000,000	2,900,000	3,000,000	'
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	'	6,300,000	'	'	'
Public Service Company Of New Hampshire [Member]	'	'	'	'	'
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]	'	'	'	'	'
AllocatedShareBasedCompensationExpense	'	2,300,000	1,800,000	2,500,000	'
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	'	900,000	700,000	1,000,000	'
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	'	1,700,000	'	'	'
Deferred Compensation Liability, Classified, Noncurrent [Abstract]	'	'	'	'	'
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	'	2,300,000	2,500,000	2,500,000	'
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	'	1,000,000	1,000,000	1,000,000	'
Western Massachusetts Electric Company [Member]	'	'	'	'	'
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]	'	'	'	'	'
AllocatedShareBasedCompensationExpense	'	1,300,000	1,000,000	1,400,000	'
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	'	500,000	400,000	600,000	'
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	'	900,000	'	'	'
Deferred Compensation Liability, Classified, Noncurrent [Abstract]	'	'	'	'	'
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	'	100,000	200,000	200,000	'
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	'	$500,000	$500,000	$500,000	'
NSTAR [Member]	'	'	'	'	'
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	'	3,500,000	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	'	977,922	977,922	'	'
Restricted Stock Units (RSUs) [Member]	'	'	'	'	'
Employee Service Share Based Compensation Awards Other Than Options Disclosures [Abstract]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	'	373,939	614,930	208,533	'
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	'	-891,129	-363,779	-244,782	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	'	-29,689	-96,504	-18,310	'
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Ending Balance	'	1,636,440	2,183,319	959,920	1,014,479
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	'	$39.56	$33.04	$33.87	'
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Issued In Period Weighted Average Grant Date Fair Value	'	$32.15	$29.05	$24.47	'
ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	'	$33.75	$34.97	$23.74	'
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Weighted Average Grant Date Fair Value Ending Balance	'	$33.61	$31.99	$26.36	$24.31
Share-based Compensation Arrangement By Share-based Payment Award Equity Instruments Other Than Options NSTAR Awards Converted To NU RSU's Upon Merger	617,394	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, NSTAR Awards Converted To NU RSU's Upon Merger, Weighted Average Grant Date Fair Value	$36.79	'	'	'	'
Employee Service Share Based Compensation Performance Share Disclosures [Abstract]	'	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Performance Shares Converted To RSU's Upon Merger	451,358	'	'	'	'
Share-based Compensation Arrangement By Share-based Payment Award, Performance Shares Converted To RSU's Upon Merger, Weighted Average Grant-Date Fair Value	$34.32	'	'	'	'
Performance Shares [Member]	'	'	'	'	'
Employee Service Share Based Compensation Awards Other Than Options Disclosures [Abstract]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	'	191,961	225,935	244,870	'
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	'	-150,944	-106,773	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	'	-1,526	'	-10,296	'
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Ending Balance	'	190,428	150,937	483,133	248,559
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	'	$40.96	$35.09	$33.76	'
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Issued In Period Weighted Average Grant Date Fair Value	'	$25.04	$24.52	'	'
ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	'	$40.93	'	$30.47	'
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Weighted Average Grant Date Fair Value Ending Balance	'	$40.96	$25.04	$29.18	$24.72

INCOME_TAXES_Details

INCOME TAXES (Details) (USD $)	12 Months Ended
INCOME TAXES (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Current Federal Tax Expense (Benefit)	$8,800,000	($30,900,000)	$3,000,000
Current State and Local Tax Expense (Benefit)	-9,400,000	17,600,000	-26,000,000
Total Current Income Tax Expense (Benefit)	-600,000	-13,300,000	-23,000,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Deferred Federal Income Tax Expense (Benefit)	386,200,000	291,300,000	187,700,000
Deferred State and Local Income Tax Expense (Benefit)	45,400,000	800,000	9,100,000
Total Deferred Income Taxes	431,413,000	292,000,000	196,761,000
Investment Tax Credit	-4,100,000	-3,900,000	-2,800,000
Income Tax Expense	426,941,000	274,926,000	170,953,000
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]	'	'	'
Income Before Income Tax Expense	1,220,630,000	808,003,000	571,466,000
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	427,200,000	282,800,000	200,000,000
Tax Effect Of Differences [Abstract]	'	'	'
Income Tax Reconciliation, Nondeductible Expense, Depreciation	-7,400,000	-10,800,000	-14,200,000
Investment Tax Credit	-4,100,000	-3,900,000	-2,800,000
Income Tax Reconciliation, Tax Credits, Other	-3,700,000	-3,800,000	-3,500,000
Income Tax Reconciliation, State and Local Income Taxes	27,600,000	4,400,000	22,100,000
Income Tax Reconciliation Medicare Subsidy	-8,000,000	-6,400,000	-2,200,000
Tax Asset Valuation Allowance / Reserve Adjustments	-4,300,000	7,600,000	-33,100,000
Income Tax Reconciliation, Other Adjustments	-400,000	5,000,000	4,700,000
Income Tax Expense	426,941,000	274,926,000	170,953,000
Effective Income Tax Rate, Continuing Operations	35.00%	34.00%	29.90%
Deferred Tax Assets, Net [Abstract]	'	'	'
Deferred Tax Assets Employee Benefits	435,200,000	811,400,000	'
Deferred Tax Assets, Derivative Instruments	272,900,000	380,600,000	'
Deferred Tax Assets, Regulatory Assets and Liabilities	272,700,000	257,900,000	'
Deferred Tax Assets, Allowance for Doubtful Accounts	65,000,000	64,200,000	'
Deferred Tax Assets Tax Effect Tax Regulatory Assets	16,200,000	17,200,000	'
Deferred Tax Assets, Operating Loss Carryforwards	158,000,000	214,600,000	'
Purchase Accounting Deferred Tax Asset	132,800,000	146,400,000	'
Deferred Tax Assets, Other	230,600,000	242,400,000	'
Deferred Tax Assets, Gross	1,583,400,000	2,134,700,000	'
Deferred Tax Assets, Valuation Allowance	24,300,000	4,200,000	'
Deferred Tax Assets, Net	1,559,100,000	2,130,500,000	'
Deferred Tax Liabilities [Abstract]	'	'	'
Deferred Tax Liabilities, Property, Plant and Equipment	3,806,500,000	3,468,800,000	'
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	95,100,000	89,600,000	'
Deferred Tax Liabilities, Regulatory Amounts [Abstract]	'	'	'
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	1,146,700,000	1,561,100,000	'
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	248,200,000	217,200,000	'
Deferred Tax Liabilities Goodwill Regulatory Asset	211,500,000	210,900,000	'
Deferred Tax Liabilities Regulatory Assets Derivative Assets	30,100,000	36,200,000	'
Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs	300,000	16,600,000	'
Deferred Tax Liabilities, Other	156,800,000	136,100,000	'
Deferred Tax Liabilities, Total	5,695,200,000	5,736,500,000	'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'	'
Unrecognized Tax Benefits, Beginning Balance	83,100,000	73,500,000	101,200,000
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	8,200,000	10,300,000	8,000,000
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions	'	100,000	'
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions	-1,100,000	-800,000	-35,700,000
Unrecognized Tax Benefits, Decreases Resulting from Settlements with Taxing Authorities	-49,800,000	'	'
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations	-2,200,000	'	'
Unrecognized Tax Benefits, Ending Balance	38,200,000	83,100,000	73,500,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense and Accrued Interest [Abstract]	'	'	'
Unrecognized Tax Benefits, Interest on Income Taxes Expense	-8,600,000	3,100,000	-2,800,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	1,500,000	10,100,000	'
Income Tax Uncertainties [Abstract]	'	'	'
Income Tax Examination Description	'Tax Positions: During 2013, NU received a Final Determination from the Connecticut Department of Revenue Services (DRS) that concluded its audit of NU's Connecticut income tax returns for the years 2005 through 2008. The DRS Determination resulted in total NU and CL&P after-tax benefits of $13.6 million and $6.9 million, respectively, that included a reduction in NU and CL&P pre-tax interest expense of $8.7 million and $4 million, or $5.2 million and $2.4 million after-tax, respectively. Further, the income tax expense impact resulted in a tax benefit to NU and CL&P of $8.4 million and $4.5 million after-tax, respectively. During 2011, NU recorded an after-tax benefit of $29.1 million related to various state tax settlements and certain other adjustments. This benefit was recorded as a reduction to both interest expense and income tax expense (including NU and CL&P tax expense reductions of approximately $22.4 million).	'	'
Tax Adjustments, Settlements - Total Impact	-13,600,000	'	-29,100,000
Tax Adjustments, Settlements - Tax Expense Impact	-8,400,000	'	-22,400,000
Federal [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	451,300,000	606,900,000	'
Tax Credit Carryforward, Amount	8,000,000	3,800,000	'
State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	12,100,000	74,900,000	'
Tax Credit Carryforward, Amount	104,700,000	110,200,000	'
Operating Loss Carryforwards, Valuation Allowance	'	300,000	'
The Connecticut Light And Power Company [Member]	'	'	'
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Current Federal Tax Expense (Benefit)	20,100,000	-47,800,000	13,900,000
Current State and Local Tax Expense (Benefit)	-6,700,000	3,100,000	-34,400,000
Total Current Income Tax Expense (Benefit)	13,400,000	-44,700,000	-20,500,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Deferred Federal Income Tax Expense (Benefit)	114,900,000	141,500,000	106,400,000
Deferred State and Local Income Tax Expense (Benefit)	15,100,000	-500,000	6,200,000
Total Deferred Income Taxes	130,038,000	140,993,000	112,620,000
Investment Tax Credit	-1,700,000	-1,900,000	-2,100,000
Income Tax Expense	141,663,000	94,437,000	90,033,000
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]	'	'	'
Income Before Income Tax Expense	421,075,000	304,162,000	340,197,000
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	147,400,000	106,500,000	119,100,000
Tax Effect Of Differences [Abstract]	'	'	'
Income Tax Reconciliation, Nondeductible Expense, Depreciation	-7,000,000	-9,000,000	-8,100,000
Investment Tax Credit	-1,700,000	-1,900,000	-2,100,000
Income Tax Reconciliation, Tax Credits, Other	0	0	-100,000
Income Tax Reconciliation, State and Local Income Taxes	5,000,000	100,000	4,000,000
Income Tax Reconciliation Medicare Subsidy	0	0	0
Tax Asset Valuation Allowance / Reserve Adjustments	400,000	1,600,000	-22,300,000
Income Tax Reconciliation, Other Adjustments	-2,400,000	-2,900,000	-500,000
Income Tax Expense	141,663,000	94,437,000	90,033,000
Effective Income Tax Rate, Continuing Operations	33.60%	31.00%	26.50%
Deferred Tax Assets, Net [Abstract]	'	'	'
Deferred Tax Assets Employee Benefits	56,000,000	141,200,000	'
Deferred Tax Assets, Derivative Instruments	272,400,000	375,900,000	'
Deferred Tax Assets, Regulatory Assets and Liabilities	61,500,000	35,500,000	'
Deferred Tax Assets, Allowance for Doubtful Accounts	31,200,000	30,400,000	'
Deferred Tax Assets Tax Effect Tax Regulatory Assets	4,700,000	5,200,000	'
Deferred Tax Assets, Operating Loss Carryforwards	51,000,000	82,000,000	'
Deferred Tax Assets, Other	75,300,000	82,800,000	'
Deferred Tax Assets, Gross	552,100,000	753,000,000	'
Deferred Tax Assets, Valuation Allowance	23,100,000	'	'
Deferred Tax Assets, Net	529,000,000	'	'
Deferred Tax Liabilities [Abstract]	'	'	'
Deferred Tax Liabilities, Property, Plant and Equipment	1,238,100,000	1,194,700,000	'
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	49,300,000	44,400,000	'
Deferred Tax Liabilities, Regulatory Amounts [Abstract]	'	'	'
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	550,400,000	677,700,000	'
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	160,100,000	151,800,000	'
Deferred Tax Liabilities Regulatory Assets Derivative Assets	29,000,000	36,200,000	'
Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs	0	0	'
Deferred Tax Liabilities, Other	20,600,000	10,100,000	'
Deferred Tax Liabilities, Total	2,047,500,000	2,114,900,000	'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'	'
Unrecognized Tax Benefits, Beginning Balance	49,000,000	46,500,000	80,800,000
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	2,100,000	2,500,000	1,400,000
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions	'	0	'
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions	-300,000	0	-35,700,000
Unrecognized Tax Benefits, Decreases Resulting from Settlements with Taxing Authorities	-39,400,000	'	'
Unrecognized Tax Benefits, Ending Balance	11,400,000	49,000,000	46,500,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense and Accrued Interest [Abstract]	'	'	'
Unrecognized Tax Benefits, Interest on Income Taxes Expense	-4,000,000	1,300,000	-3,700,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	4,000,000	'
Income Tax Uncertainties [Abstract]	'	'	'
Income Tax Examination Description	'Tax Positions: During 2013, NU received a Final Determination from the Connecticut Department of Revenue Services (DRS) that concluded its audit of NU's Connecticut income tax returns for the years 2005 through 2008. The DRS Determination resulted in total NU and CL&P after-tax benefits of $13.6 million and $6.9 million, respectively, that included a reduction in NU and CL&P pre-tax interest expense of $8.7 million and $4 million, or $5.2 million and $2.4 million after-tax, respectively. Further, the income tax expense impact resulted in a tax benefit to NU and CL&P of $8.4 million and $4.5 million after-tax, respectively. During 2011, NU recorded an after-tax benefit of $29.1 million related to various state tax settlements and certain other adjustments. This benefit was recorded as a reduction to both interest expense and income tax expense (including NU and CL&P tax expense reductions of approximately $22.4 million).	'	'
Tax Adjustments, Settlements - Total Impact	-6,900,000	'	'
Tax Adjustments, Settlements - Tax Expense Impact	-4,500,000	'	-22,400,000
The Connecticut Light And Power Company [Member] \| Federal [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	145,800,000	234,300,000	'
Tax Credit Carryforward, Amount	0	0	'
The Connecticut Light And Power Company [Member] \| State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	0	0	'
Tax Credit Carryforward, Amount	86,800,000	75,200,000	'
NSTAR Electric Company [Member]	'	'	'
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Current Federal Tax Expense (Benefit)	95,800,000	93,500,000	64,900,000
Current State and Local Tax Expense (Benefit)	29,600,000	27,600,000	30,200,000
Total Current Income Tax Expense (Benefit)	125,400,000	121,100,000	95,100,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Deferred Federal Income Tax Expense (Benefit)	49,800,000	11,400,000	74,800,000
Deferred State and Local Income Tax Expense (Benefit)	-1,000,000	-7,100,000	-2,800,000
Total Deferred Income Taxes	48,808,000	4,264,000	72,006,000
Investment Tax Credit	-1,300,000	-1,400,000	-1,400,000
Income Tax Expense	172,866,000	123,966,000	165,686,000
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]	'	'	'
Income Before Income Tax Expense	441,412,000	314,208,000	418,180,000
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	154,500,000	110,000,000	146,400,000
Tax Effect Of Differences [Abstract]	'	'	'
Income Tax Reconciliation, Nondeductible Expense, Depreciation	100,000	0	0
Investment Tax Credit	-1,300,000	-1,400,000	-1,400,000
Income Tax Reconciliation, Tax Credits, Other	0	0	0
Income Tax Reconciliation, State and Local Income Taxes	18,600,000	13,400,000	17,900,000
Income Tax Reconciliation Medicare Subsidy	0	0	0
Tax Asset Valuation Allowance / Reserve Adjustments	0	0	0
Income Tax Reconciliation, Other Adjustments	1,000,000	2,000,000	2,800,000
Income Tax Expense	172,866,000	123,966,000	165,686,000
Effective Income Tax Rate, Continuing Operations	39.20%	39.50%	39.60%
Deferred Tax Assets, Net [Abstract]	'	'	'
Deferred Tax Assets Employee Benefits	38,300,000	116,300,000	'
Deferred Tax Assets, Derivative Instruments	3,300,000	5,800,000	'
Deferred Tax Assets, Regulatory Assets and Liabilities	114,700,000	123,600,000	'
Deferred Tax Assets, Allowance for Doubtful Accounts	15,400,000	16,200,000	'
Deferred Tax Assets Tax Effect Tax Regulatory Assets	5,400,000	6,000,000	'
Deferred Tax Assets, Operating Loss Carryforwards	0	0	'
Deferred Tax Assets, Other	31,300,000	26,000,000	'
Deferred Tax Assets, Gross	208,400,000	293,900,000	'
Deferred Tax Liabilities [Abstract]	'	'	'
Deferred Tax Liabilities, Property, Plant and Equipment	1,179,400,000	1,079,300,000	'
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	25,300,000	23,100,000	'
Deferred Tax Liabilities, Regulatory Amounts [Abstract]	'	'	'
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	276,200,000	379,600,000	'
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	36,000,000	20,900,000	'
Deferred Tax Liabilities Goodwill Regulatory Asset	181,600,000	181,000,000	'
Deferred Tax Liabilities Regulatory Assets Derivative Assets	500,000	0	'
Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs	0	5,500,000	'
Deferred Tax Liabilities, Other	26,400,000	30,200,000	'
Deferred Tax Liabilities, Total	1,725,400,000	1,719,600,000	'
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense and Accrued Interest [Abstract]	'	'	'
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	0	2,000,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	0	'
NSTAR Electric Company [Member] \| Federal [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	0	0	'
Tax Credit Carryforward, Amount	0	0	'
NSTAR Electric Company [Member] \| State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	0	0	'
Tax Credit Carryforward, Amount	0	0	'
Public Service Company Of New Hampshire [Member]	'	'	'
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Current Federal Tax Expense (Benefit)	-8,200,000	-900,000	-25,800,000
Current State and Local Tax Expense (Benefit)	3,600,000	3,400,000	100,000
Total Current Income Tax Expense (Benefit)	-4,600,000	2,500,000	-25,700,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Deferred Federal Income Tax Expense (Benefit)	64,500,000	46,500,000	67,700,000
Deferred State and Local Income Tax Expense (Benefit)	11,200,000	12,000,000	7,900,000
Total Deferred Income Taxes	75,693,000	58,552,000	75,628,000
Investment Tax Credit	0	0	0
Income Tax Expense	71,101,000	60,993,000	49,945,000
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]	'	'	'
Income Before Income Tax Expense	182,498,000	157,875,000	150,212,000
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	63,900,000	55,300,000	52,600,000
Tax Effect Of Differences [Abstract]	'	'	'
Income Tax Reconciliation, Nondeductible Expense, Depreciation	600,000	-300,000	-4,400,000
Investment Tax Credit	0	0	0
Income Tax Reconciliation, Tax Credits, Other	-3,700,000	-3,800,000	-3,400,000
Income Tax Reconciliation, State and Local Income Taxes	9,600,000	10,000,000	5,200,000
Income Tax Reconciliation Medicare Subsidy	0	0	0
Tax Asset Valuation Allowance / Reserve Adjustments	0	0	0
Income Tax Reconciliation, Other Adjustments	700,000	-200,000	-100,000
Income Tax Expense	71,101,000	60,993,000	49,945,000
Effective Income Tax Rate, Continuing Operations	39.00%	38.60%	33.20%
Deferred Tax Assets, Net [Abstract]	'	'	'
Deferred Tax Assets Employee Benefits	15,500,000	64,800,000	'
Deferred Tax Assets, Derivative Instruments	0	0	'
Deferred Tax Assets, Regulatory Assets and Liabilities	40,900,000	43,900,000	'
Deferred Tax Assets, Allowance for Doubtful Accounts	3,100,000	2,900,000	'
Deferred Tax Assets Tax Effect Tax Regulatory Assets	2,100,000	1,700,000	'
Deferred Tax Assets, Operating Loss Carryforwards	56,600,000	71,400,000	'
Deferred Tax Assets, Other	40,300,000	33,700,000	'
Deferred Tax Assets, Gross	158,500,000	218,400,000	'
Deferred Tax Liabilities [Abstract]	'	'	'
Deferred Tax Liabilities, Property, Plant and Equipment	526,600,000	476,500,000	'
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	7,100,000	6,800,000	'
Deferred Tax Liabilities, Regulatory Amounts [Abstract]	'	'	'
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	109,300,000	149,300,000	'
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	16,300,000	15,800,000	'
Deferred Tax Liabilities Regulatory Assets Derivative Assets	0	0	'
Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs	0	7,900,000	'
Deferred Tax Liabilities, Other	28,000,000	14,100,000	'
Deferred Tax Liabilities, Total	687,300,000	670,400,000	'
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense and Accrued Interest [Abstract]	'	'	'
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	0	-600,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0	0	'
Public Service Company Of New Hampshire [Member] \| Federal [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	161,800,000	204,000,000	'
Tax Credit Carryforward, Amount	7,600,000	3,800,000	'
Public Service Company Of New Hampshire [Member] \| State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	0	0	'
Tax Credit Carryforward, Amount	0	0	'
Western Massachusetts Electric Company [Member]	'	'	'
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Current Federal Tax Expense (Benefit)	-53,400,000	-24,700,000	100,000
Current State and Local Tax Expense (Benefit)	4,200,000	3,400,000	300,000
Total Current Income Tax Expense (Benefit)	-49,200,000	-21,300,000	400,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]	'	'	'
Deferred Federal Income Tax Expense (Benefit)	84,700,000	51,200,000	22,100,000
Deferred State and Local Income Tax Expense (Benefit)	2,300,000	2,700,000	1,000,000
Total Deferred Income Taxes	87,028,000	53,942,000	23,056,000
Investment Tax Credit	-400,000	-500,000	-300,000
Income Tax Expense	37,368,000	32,140,000	23,186,000
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]	'	'	'
Income Before Income Tax Expense	97,806,000	86,643,000	66,240,000
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	34,200,000	30,300,000	23,200,000
Tax Effect Of Differences [Abstract]	'	'	'
Income Tax Reconciliation, Nondeductible Expense, Depreciation	0	200,000	100,000
Investment Tax Credit	-400,000	-500,000	-300,000
Income Tax Reconciliation, Tax Credits, Other	0	0	0
Income Tax Reconciliation, State and Local Income Taxes	4,200,000	4,000,000	900,000
Income Tax Reconciliation Medicare Subsidy	0	0	0
Tax Asset Valuation Allowance / Reserve Adjustments	0	0	0
Income Tax Reconciliation Regulatory Decision Non-Plant Flow Through	0	-1,300,000	0
Income Tax Reconciliation, Other Adjustments	-600,000	-600,000	-700,000
Income Tax Expense	37,368,000	32,140,000	23,186,000
Effective Income Tax Rate, Continuing Operations	38.20%	37.10%	35.00%
Deferred Tax Assets, Net [Abstract]	'	'	'
Deferred Tax Assets Employee Benefits	-1,800,000	16,300,000	'
Deferred Tax Assets, Derivative Instruments	-2,900,000	-1,700,000	'
Deferred Tax Assets, Regulatory Assets and Liabilities	1,000,000	6,300,000	'
Deferred Tax Assets, Allowance for Doubtful Accounts	3,300,000	3,200,000	'
Deferred Tax Assets Tax Effect Tax Regulatory Assets	1,600,000	1,700,000	'
Deferred Tax Assets, Operating Loss Carryforwards	18,600,000	15,100,000	'
Deferred Tax Assets, Other	8,300,000	8,000,000	'
Deferred Tax Assets, Gross	28,100,000	48,900,000	'
Deferred Tax Liabilities [Abstract]	'	'	'
Deferred Tax Liabilities, Property, Plant and Equipment	361,100,000	261,300,000	'
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	5,900,000	5,100,000	'
Deferred Tax Liabilities, Regulatory Amounts [Abstract]	'	'	'
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	49,300,000	74,500,000	'
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	18,200,000	13,900,000	'
Deferred Tax Liabilities Regulatory Assets Derivative Assets	0	0	'
Deferred Tax Liabilities Regulatory Assets Securitized Contract Termination Costs	300,000	3,300,000	'
Deferred Tax Liabilities, Other	3,300,000	2,300,000	'
Deferred Tax Liabilities, Total	438,100,000	360,400,000	'
Western Massachusetts Electric Company [Member] \| Federal [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	53,300,000	43,300,000	'
Tax Credit Carryforward, Amount	0	0	'
Western Massachusetts Electric Company [Member] \| State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	0	0	'
Tax Credit Carryforward, Amount	0	0	'
Northeast Utilities \| State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]	'	'	'
Operating Loss Carryforwards	$23,700,000	'	'

Environmental_Matters_Details

Environmental Matters (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Site Contingency [Line Items]	'	'
Environmental Site Quantity	68	77
Range Of Potential Loss On Enivornmental Sites	'As of December 31, 2013, for 6 environmental sites (2 for PSNH, and 1 for WMECO) that are included in the Company's reserve for environmental costs, the information known and nature of the remediation options at those sites allow for the Company to estimate the range of losses for environmental costs. As of December 31, 2013, $5.8 million ($0.7 million for PSNH) had been accrued as a liability for these sites, which represent management's best estimates of the liabilities for environmental costs. These amounts are the best estimates with estimated ranges of additional losses from zero to $30 million (zero to $4.2 million for PSNH, and zero to $8.6 million for WMECO). As of December 31, 2013, for 20 environmental sites (4 for CL&P, 1 for NSTAR Electric, 3 for PSNH, and 2 for WMECO) that are included in the Company’s reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to undertake. As of December 31, 2013, $16.7 million ($1.6 million for CL&P, $0.1 million for PSNH, and $0.3 million for WMECO) had been accrued as a liability for these sites. As of December 31, 2013, for the remaining 42 environmental sites (14 for CL&P, 11 for NSTAR Electric, 10 for PSNH, and 2 for WMECO) that are included in the Company’s reserve for environmental costs, the $12.9 million accrual ($1.8 million for CL&P, $1.2 million for NSTAR Electric, $4.6 million for PSNH, and $0.1 million for WMECO) represents management’s best estimate of the liability and no additional loss is anticipated.	'
Superfund Site Information	'CERCLA: The federal Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) and its amendments or state equivalents impose joint and several strict liabilities, regardless of fault, upon generators of hazardous substances resulting in removal and remediation costs and environmental damages. Liabilities under these laws can be material and in some instances may be imposed without regard to fault or for past acts that may have been lawful at the time they occurred. Of the 68 sites, 10 sites (2 for CL&P, 3 for NSTAR Electric, 4 for PSNH and 1 for WMECO) are superfund sites under CERCLA for which the Company has been notified that it is a potentially responsible party but for which the site assessment and remediation are not being managed by the Company. As of December 31, 2013, a liability of $1 million ($0.4 million for CL&P, and $0.3 million for PSNH) accrued on these sites represents management's best estimate of its potential remediation costs with respect to these superfund sites.	'
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	$39.40	$31.70
Environmental Liability assumed in merger	'	11.8
Accrual For Environmental Loss Contingencies Provision For New Losses	3.5	4.7
Accrual for Environmental Loss Contingencies, Payments	-7.5	-8.8
Ending Balance	35.4	39.4
MGP Site accrual [Member]	'	'
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Accrual For Environmental Loss Contingencies Component Amount	31.4	34.5
The Connecticut Light And Power Company [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	18	19
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	3.7	2.9
Accrual For Environmental Loss Contingencies Provision For New Losses	0.2	1.3
Accrual for Environmental Loss Contingencies, Payments	-0.5	-0.5
Ending Balance	3.4	3.7
NSTAR Electric Company [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	12	16
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	1.7	1.3
Accrual For Environmental Loss Contingencies Provision For New Losses	0.2	0.7
Accrual for Environmental Loss Contingencies, Payments	-0.7	-0.3
Ending Balance	1.2	1.7
Public Service Company Of New Hampshire [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	15	16
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	4.9	6.6
Accrual For Environmental Loss Contingencies Provision For New Losses	1	0.2
Accrual for Environmental Loss Contingencies, Payments	-0.5	-1.9
Ending Balance	5.4	4.9
Western Massachusetts Electric Company [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	5	6
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	0.6	0.3
Accrual For Environmental Loss Contingencies Provision For New Losses	0	0.5
Accrual for Environmental Loss Contingencies, Payments	-0.2	-0.2
Ending Balance	$0.40	$0.60

LongTerm_Contractual_Arrangeme1

Long-Term Contractual Arrangements (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	$705.40	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	615.6	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	538.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	428.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	368.1	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	2,385.60	'	'
Unrecorded Unconditional Purchase Obligation, Total	5,041.50	'	'
Supply And Stranded Costs Obligations Incurred	141	216.8	156
Natural Gas Procurement Costs Incurred	349.8	243.1	191.7
Fuel Costs Incurred	112.6	105.2	113.2
Transmission Support Commitment Costs Incurred	24.9	24.8	18.1
Peaker CfD Expense Incurred	51.9	59.3	40.2
Renewable Energy Costs Incurred	91.3	48.7	5.1
Supply And Stranded Cost Obligations [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	224.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	205.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	177.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	119.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	110.4	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	309.3	'	'
Unrecorded Unconditional Purchase Obligation, Total	1,146.70	'	'
Renewable Energy Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	194.5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	203.8	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	214.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	211.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	177.3	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,885.70	'	'
Unrecorded Unconditional Purchase Obligation, Total	2,887.30	'	'
Peaker Contracts For Differences [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	49.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	46.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	44.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	36.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	28.6	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	24.7	'	'
Unrecorded Unconditional Purchase Obligation, Total	229.8	'	'
Natural Gas Procurement Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	134.4	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	117.6	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	76.5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	37.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	24.2	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	103.9	'	'
Unrecorded Unconditional Purchase Obligation, Total	494.3	'	'
Wood, Coal And Transporation Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	75.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	15.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	5	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	16.8	'	'
Unrecorded Unconditional Purchase Obligation, Total	122.3	'	'
Transmission Support Commitments [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	27.9	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	26.9	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	20.5	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	18	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	22.6	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	45.2	'	'
Recorded Unconditional Purchase Obligation, Total	161.1	'	'
The Connecticut Light And Power Company [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	256.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	249.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	247.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	191.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	176.8	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	872.6	'	'
Unrecorded Unconditional Purchase Obligation, Total	1,993.70	'	'
Supply And Stranded Costs Obligations Incurred	77.6	158.2	114.9
Transmission Support Commitment Costs Incurred	9.8	9.6	10.3
Peaker CfD Expense Incurred	51.9	59.3	40.2
The Connecticut Light And Power Company [Member] \| Supply And Stranded Cost Obligations [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	145.6	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	141.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	143.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	96.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	87.1	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	257.6	'	'
Unrecorded Unconditional Purchase Obligation, Total	871.3	'	'
The Connecticut Light And Power Company [Member] \| Renewable Energy Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	48.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	49.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	50.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	50.8	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	51.4	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	560.2	'	'
Unrecorded Unconditional Purchase Obligation, Total	811.5	'	'
The Connecticut Light And Power Company [Member] \| Peaker Contracts For Differences [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	49.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	46.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	44.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	36.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	28.6	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	24.7	'	'
Unrecorded Unconditional Purchase Obligation, Total	229.8	'	'
The Connecticut Light And Power Company [Member] \| Transmission Support Commitments [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	11	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	10.6	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	8.1	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	7.1	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	8.9	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	17.8	'	'
Recorded Unconditional Purchase Obligation, Total	63.5	'	'
The Connecticut Light And Power Company [Member] \| Yankee Companies Billings [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	1.5	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	1.4	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	0.8	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.8	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.8	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	12.3	'	'
Recorded Unconditional Purchase Obligation, Total	17.6	'	'
NSTAR Electric Company [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	132.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	131.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	108.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	93.4	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	58.2	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	262.5	'	'
Unrecorded Unconditional Purchase Obligation, Total	786.4	'	'
Supply And Stranded Costs Obligations Incurred	32.4	36.3	80.9
Transmission Support Commitment Costs Incurred	7.7	7.6	8.1
Renewable Energy Costs Incurred	84.9	60.2	61.8
NSTAR Electric Company [Member] \| Supply And Stranded Cost Obligations [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	36.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	36.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	15.8	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.6	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	5.5	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	36.8	'	'
Unrecorded Unconditional Purchase Obligation, Total	136	'	'
NSTAR Electric Company [Member] \| Renewable Energy Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	87.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	86.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	85.8	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	81.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	45.4	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	207.4	'	'
Unrecorded Unconditional Purchase Obligation, Total	593.9	'	'
NSTAR Electric Company [Member] \| Transmission Support Commitments [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	8.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	8.4	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	6.4	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.6	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	7	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	14.1	'	'
Unrecorded Unconditional Purchase Obligation, Total	50.2	'	'
NSTAR Electric Company [Member] \| Yankee Companies Billings [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	0.7	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	0.5	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	4.2	'	'
Recorded Unconditional Purchase Obligation, Total	6.3	'	'
Public Service Company Of New Hampshire [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	180.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	106.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	95.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	96.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	98	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	1,041.40	'	'
Unrecorded Unconditional Purchase Obligation, Total	1,618.90	'	'
Supply And Stranded Costs Obligations Incurred	29	30.5	40.8
Fuel Costs Incurred	112.6	105.2	113.2
Transmission Support Commitment Costs Incurred	5.3	5.2	5.6
Renewable Energy Costs Incurred	6.4	4.1	5.1
Public Service Company Of New Hampshire [Member] \| Supply And Stranded Cost Obligations [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	42.4	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	28	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	18.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	18.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	17.8	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	14.9	'	'
Unrecorded Unconditional Purchase Obligation, Total	139.4	'	'
Public Service Company Of New Hampshire [Member] \| Renewable Energy Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	56.8	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	57.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	67.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	69	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	70.1	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	995.2	'	'
Unrecorded Unconditional Purchase Obligation, Total	1,316.70	'	'
Public Service Company Of New Hampshire [Member] \| Wood, Coal And Transporation Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	75.3	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	15.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	5	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	16.8	'	'
Unrecorded Unconditional Purchase Obligation, Total	122.3	'	'
Public Service Company Of New Hampshire [Member] \| Transmission Support Commitments [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	5.9	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	5.7	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	4.3	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	3.8	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	4.8	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	9.6	'	'
Recorded Unconditional Purchase Obligation, Total	34.1	'	'
Public Service Company Of New Hampshire [Member] \| Yankee Companies Billings [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.3	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	4.9	'	'
Recorded Unconditional Purchase Obligation, Total	6.4	'	'
Western Massachusetts Electric Company [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	4.4	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	12.5	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	12	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	11.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	12.5	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	129.7	'	'
Unrecorded Unconditional Purchase Obligation, Total	183	'	'
Supply And Stranded Costs Obligations Incurred	2	0.9	0.3
Transmission Support Commitment Costs Incurred	2.1	2	2.2
Western Massachusetts Electric Company [Member] \| Renewable Energy Contracts [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due within One Year	1.7	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	9.9	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	10.1	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	10.2	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	10.4	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	122.9	'	'
Unrecorded Unconditional Purchase Obligation, Total	165.2	'	'
Western Massachusetts Electric Company [Member] \| Transmission Support Commitments [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	2.3	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	2.2	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	1.7	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	1.5	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	1.9	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	3.7	'	'
Recorded Unconditional Purchase Obligation, Total	13.3	'	'
Western Massachusetts Electric Company [Member] \| Yankee Companies Billings [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Recorded Unconditional Purchase Obligation Due within One Year	0.4	'	'
Recorded Unconditional Purchase Obligation Due in Second Year	0.4	'	'
Recorded Unconditional Purchase Obligation Due in Third Year	0.2	'	'
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.2	'	'
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.2	'	'
Recorded Unconditional Purchase Obligation Due after Fifth Year	3.1	'	'
Recorded Unconditional Purchase Obligation, Total	$4.50	'	'

Deferred_Contractual_Obligatio

Deferred Contractual Obligations (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Loss Contingency, Information about Litigation Matters [Abstract]	'	'
Court of Federal Claims Ruling To CYAPC	$126.30	$39.60
Court Of Federal Claims Ruling To YAEC	73.3	38.3
Court Of Federal Claims Ruling To MYAPC	35.8	81.7
Increase In Marketable Securities Current Period	$77.90	'

Guarantees_and_Indemnification1

Guarantees and Indemnifications (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified	Dec. 31, 2013
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 2013 And 2015 [Member]	'
Guarantee Obligations [Line Items]	'
Guarantee Obligations Maximum Exposure	69.2
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	17.7
Guarantee Of Debt Of Ne Hydros [Member]	'
Guarantee Obligations [Line Items]	'
Guarantee Obligations Maximum Exposure	$3.50

Other_Contingencies_Details

Other Contingencies (Details)	12 Months Ended
Other Contingencies (Details)	Dec. 31, 2013
Loss Contingencies Line Items	'
Loss Contingency, Description	'E. FERC Base ROE Complaint On September 30, 2011, several New England state attorneys general, state regulatory commissions, consumer advocates and other parties filed a joint complaint with the FERC under Sections 206 and 306 of the Federal Power Act alleging that the base ROE used in calculating formula rates for transmission service under the ISO-NE Open Access Transmission Tariff by NETOs, including CL&P, NSTAR Electric, PSNH and WMECO, is unjust and unreasonable. The complainants asserted that the current 11.14 percent rate, which became effective in 2006, is excessive due to changes in the capital markets and are seeking an order to reduce the rate, which would be effective October 1, 2011. In response, the NETOs filed testimony and analysis based on standard FERC methodology and precedent demonstrating that the base ROE of 11.14 percent remained just and reasonable. The FERC set the case for trial before a FERC ALJ after settlement negotiations were unsuccessful in August 2012. Hearings before the FERC ALJ were held in May 2013, followed by the filing of briefs by the complainants, the Massachusetts municipal electric utilities (late interveners to the case), the FERC trial staff and the NETOs. The NETOs recommended that the current base ROE of 11.14 percent should remain in effect for the refund period (October 1, 2011 through December 31, 2012) and the prospective period (beginning when FERC issues its final decision). The complainants, the Massachusetts municipal electric utilities, and the FERC trial staff each recommended a base ROE of 9 percent or below. On August 6, 2013, the FERC ALJ issued an initial decision, finding that the base ROE in effect from October 2011 through December 2012 was not reasonable under the standard application of FERC methodology, but leaving policy considerations and additional adjustments to the FERC. Using the established FERC methodology, the FERC ALJ determined that separate base ROEs should be set for the refund period and the prospective period. The FERC ALJ found those base ROEs to be 10.6 percent and 9.7 percent, respectively. The FERC may adjust the prospective period base ROE in its final decision to reflect movement in 10-year Treasury bond rates from the date that the case was filed (April 2013) to the date of the final decision. The parties filed briefs on this decision with the FERC, and a decision from the FERC is expected in 2014. Though NU cannot predict the ultimate outcome of this proceeding, in 2013 the Company recorded a series of reserves at its electric subsidiaries to recognize the potential financial impact from the FERC ALJ's initial decision for the refund period. The aggregate after-tax charge to earnings totaled $14.3 million at NU, which represents reserves of $7.7 million at CL&P, $3.4 million at NSTAR Electric, $1.4 million at PSNH and $1.8 million at WMECO. On December 27, 2012, several additional parties filed a separate complaint concerning the NETOs' base ROE with the FERC. This complaint seeks to reduce the NETOs’ base ROE effective January 1, 2013, effectively extending the refund period for an additional 15 months, and to consolidate this complaint with the joint complaint filed on September 30, 2011. The NETOs have asked the FERC to reject this complaint. The FERC has not yet acted on this complaint, and management is unable to predict the ultimate outcome or estimate the impacts of this complaint on financial position, results of operations or cash flows. As of December 31, 2013, the CL&P, NSTAR Electric, PSNH, and WMECO aggregate shareholder equity invested in their transmission facilities was approximately $2.3 billion. As a result, each 10 basis point change in the prospective period authorized base ROE would change annual consolidated earnings by an approximate $2.3 million. F. DPU Safety and Reliability Programs - CPSL Since 2006, NSTAR Electric has been recovering incremental costs related to the DPU-approved Safety and Reliability Programs. From 2006 through 2011, cumulative costs associated with the CPSL program resulted in an incremental revenue requirement to customers of approximately $83 million. These amounts included incremental operations and maintenance costs and the related revenue requirement for specific capital investments relative to the CPSL programs. On May 28, 2010, the DPU issued an order on NSTAR Electric’s 2006 CPSL cost recovery filing (the May 2010 Order). In October 2010, NSTAR Electric filed a reconciliation of the cumulative CPSL program activity for the periods 2006 through 2009 with the DPU in order to determine a proposed rate adjustment. The DPU allowed the proposed rates to go into effect January 1, 2011, subject to final reconciliation of CPSL program costs through a future DPU proceeding. In February 2013, NSTAR Electric updated the October 2010 filing with final activity through 2011. NSTAR Electric recorded its 2006 through 2011 revenues under the CPSL programs based on the May 2010 Order. NSTAR Electric cannot predict the timing of a final DPU order related to its CPSL filings for the period 2006 through 2011. While management does not believe that any subsequent DPU order would result in revenues that are materially different than the amounts already recognized, it is reasonably possible that an order could have a material impact on NSTAR Electric’s results of operations, financial position and cash flows. The April 4, 2012 DPU-approved comprehensive merger settlement agreement with the Massachusetts Attorney General stipulates that NSTAR Electric must incur a revenue requirement of at least $15 million per year for 2012 through 2015 related to these programs. CPSL revenues will end once NSTAR Electric has recovered its 2015-related CPSL costs. Realization of these revenues is subject to maintaining certain performance metrics over the four-year period and DPU approval. As of December 31, 2013, NSTAR Electric was in compliance with the performance metrics and has recognized the entire $15 million revenue requirement during 2013 and 2012. G. Basic Service Bad Debt Adder In accordance with a generic DPU order, electric utilities in Massachusetts recover the energy-related portion of bad debt costs in their Basic Service rates. In 2007, NSTAR Electric filed its 2006 Basic Service reconciliation with the DPU proposing an adjustment related to the increase of its Basic Service bad debt charge-offs. The DPU issued an order approving the implementation of a revised Basic Service rate but instructed NSTAR Electric to reduce distribution rates by an amount equal to the increase in its Basic Service bad debt charge-offs. This adjustment to NSTAR Electric’s distribution rates would eliminate 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. In 2012, the SJC vacated the DPU order and remanded the matter to the DPU for further review. The DPU has not taken any action on the remand. NSTAR Electric deferred approximately $34 million of costs associated with energy-related bad debt as a regulatory asset through 2011 as NSTAR Electric had concluded that it was probable that these costs would ultimately be recovered from customers. Due to the delays and the duration of the proceedings, NSTAR Electric concluded that while an ultimate outcome on the matter in its favor remained "more likely than not," it could no longer be deemed "probable." As a result, NSTAR Electric recognized a reserve related to the regulatory asset in 2012. NSTAR Electric will continue to maintain the reserve until the proceeding has been concluded with the DPU.

LEASES_Details

LEASES (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Leased Assets [Line Items]	'	'	'
Capital Leases, Future Minimum Payments Due, Current	$2.60	'	'
Capital Leases, Future Minimum Payments Due in Two Years	2.4	'	'
Capital Leases, Future Minimum Payments Due in Three Years	2.2	'	'
Capital Leases, Future Minimum Payments Due in Four Years	2.1	'	'
Capital Leases, Future Minimum Payments Due in Five Years	2.1	'	'
Capital Leases, Future Minimum Payments Due Thereafter	5.4	'	'
Capital Leases, Future Minimum Payments Due	16.8	'	'
Capital Leases, Future Minimum Payments, Interest Included in Payments	6.1	'	'
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	10.7	'	'
Operating Leases, Rent Expense	16.3	14.8	8.4
Operating Leases, Future Minimum Payments Due, Current	20.1	'	'
Operating Leases, Future Minimum Payments, Due in Two Years	18.1	'	'
Operating Leases, Future Minimum Payments, Due in Three Years	15.4	'	'
Operating Leases, Future Minimum Payments, Due in Four Years	12.4	'	'
Operating Leases, Future Minimum Payments, Due in Five Years	8.5	'	'
Operating Leases, Future Minimum Payments, Due Thereafter	22.3	'	'
Operating Leases, Future Minimum Payments Due	96.8	'	'
The Connecticut Light And Power Company [Member]	'	'	'
Operating Leased Assets [Line Items]	'	'	'
Capital Leases, Future Minimum Payments Due, Current	2.1	'	'
Capital Leases, Future Minimum Payments Due in Two Years	2	'	'
Capital Leases, Future Minimum Payments Due in Three Years	1.9	'	'
Capital Leases, Future Minimum Payments Due in Four Years	2	'	'
Capital Leases, Future Minimum Payments Due in Five Years	2	'	'
Capital Leases, Future Minimum Payments Due Thereafter	5.4	'	'
Capital Leases, Future Minimum Payments Due	15.4	'	'
Capital Leases, Future Minimum Payments, Interest Included in Payments	6.1	'	'
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	9.3	'	'
Operating Leases, Rent Expense	8.1	8.2	8.3
Operating Leases, Future Minimum Payments Due, Current	4	'	'
Operating Leases, Future Minimum Payments, Due in Two Years	3.6	'	'
Operating Leases, Future Minimum Payments, Due in Three Years	2.9	'	'
Operating Leases, Future Minimum Payments, Due in Four Years	1.7	'	'
Operating Leases, Future Minimum Payments, Due in Five Years	1.2	'	'
Operating Leases, Future Minimum Payments, Due Thereafter	4.7	'	'
Operating Leases, Future Minimum Payments Due	18.1	'	'
NSTAR Electric Company [Member]	'	'	'
Operating Leased Assets [Line Items]	'	'	'
Operating Leases, Rent Expense	6.7	6.2	19.8
Operating Leases, Future Minimum Payments Due, Current	10.9	'	'
Operating Leases, Future Minimum Payments, Due in Two Years	10.1	'	'
Operating Leases, Future Minimum Payments, Due in Three Years	8.9	'	'
Operating Leases, Future Minimum Payments, Due in Four Years	7.7	'	'
Operating Leases, Future Minimum Payments, Due in Five Years	5.1	'	'
Operating Leases, Future Minimum Payments, Due Thereafter	11.7	'	'
Operating Leases, Future Minimum Payments Due	54.4	'	'
Public Service Company Of New Hampshire [Member]	'	'	'
Operating Leased Assets [Line Items]	'	'	'
Capital Leases, Future Minimum Payments Due, Current	0.4	'	'
Capital Leases, Future Minimum Payments Due in Two Years	0.4	'	'
Capital Leases, Future Minimum Payments Due in Three Years	0.3	'	'
Capital Leases, Future Minimum Payments Due in Four Years	0.1	'	'
Capital Leases, Future Minimum Payments Due in Five Years	0.1	'	'
Capital Leases, Future Minimum Payments Due Thereafter	0	'	'
Capital Leases, Future Minimum Payments Due	1.3	'	'
Capital Leases, Future Minimum Payments, Interest Included in Payments	0	'	'
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	1.3	'	'
Operating Leases, Rent Expense	1.7	2.5	2.1
Operating Leases, Future Minimum Payments Due, Current	1	'	'
Operating Leases, Future Minimum Payments, Due in Two Years	0.9	'	'
Operating Leases, Future Minimum Payments, Due in Three Years	0.8	'	'
Operating Leases, Future Minimum Payments, Due in Four Years	0.6	'	'
Operating Leases, Future Minimum Payments, Due in Five Years	0.5	'	'
Operating Leases, Future Minimum Payments, Due Thereafter	1.3	'	'
Operating Leases, Future Minimum Payments Due	5.1	'	'
Western Massachusetts Electric Company [Member]	'	'	'
Operating Leased Assets [Line Items]	'	'	'
Operating Leases, Rent Expense	2.9	3	2.8
Operating Leases, Future Minimum Payments Due, Current	1.1	'	'
Operating Leases, Future Minimum Payments, Due in Two Years	0.7	'	'
Operating Leases, Future Minimum Payments, Due in Three Years	0.5	'	'
Operating Leases, Future Minimum Payments, Due in Four Years	0.3	'	'
Operating Leases, Future Minimum Payments, Due in Five Years	0.2	'	'
Operating Leases, Future Minimum Payments, Due Thereafter	1	'	'
Operating Leases, Future Minimum Payments Due	$3.80	'	'

FAIR_VALUE_OF_FINANCIAL_INSTRU2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	$155,568,000	$155,568,000
Rate Reduction Bonds	0	82,139,000
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
Rate Reduction Bonds	0	82,100,000
Other Long Term Debt	8,310,200,000	7,963,500,000
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	152,700,000	152,200,000
Rate Reduction Bonds	0	83,000,000
Other Long Term Debt	8,443,100,000	8,640,700,000
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	2,741,200,000	2,862,800,000
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	110,500,000	110,000,000
Other Long Term Debt	2,952,800,000	3,295,400,000
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
Rate Reduction Bonds	0	43,493,000
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
Rate Reduction Bonds	'	43,500,000
Other Long Term Debt	1,801,100,000	1,602,600,000
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	42,200,000	42,200,000
Rate Reduction Bonds	'	43,900,000
Other Long Term Debt	1,888,000,000	1,818,800,000
Public Service Company Of New Hampshire [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Rate Reduction Bonds	0	29,294,000
Public Service Company Of New Hampshire [Member] \| Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Rate Reduction Bonds	'	29,300,000
Other Long Term Debt	1,049,000,000	997,900,000
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]	'	'
Rate Reduction Bonds	'	29,600,000
Other Long Term Debt	1,073,900,000	1,088,000,000
Western Massachusetts Electric Company [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Rate Reduction Bonds	0	9,352,000
Western Massachusetts Electric Company [Member] \| Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Rate Reduction Bonds	'	9,400,000
Other Long Term Debt	629,400,000	605,300,000
Western Massachusetts Electric Company [Member] \| Estimate Of Fair Value Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Rate Reduction Bonds	'	9,500,000
Other Long Term Debt	$640,100,000	$660,400,000

ACCUMULATED_OTHER_COMPREHENSIV2

ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	12 Months Ended
ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent [Abstract]	'	'	'
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months	$3,400,000	'	'
Pension Serp And Pbop Gain Loss To Be Reclassified Within Twelve Months	6,500,000	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'	'
Beginning Balance -AOCI From CF Hedges Effect Net Of Tax	-16,400,000	'	'
OCI Amortization of Cash Flow Hedge, Net of Tax	2,000,000	2,000,000	700,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	-2,049,000	-1,971,000	14,177,000
Ending Balance - AOCI From CFHedges Effect Net Of Tax	-14,400,000	-16,400,000	'
AOCI Unrealized GainLoss component [Abstract]	'	'	'
AOCI Unrealized Gains/Losses on Other Securities	1,300,000	'	'
OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax	-900,000	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-940,000	217,000	506,000
AOCI Unrealized Gains/Losses on Other Securities-Ending Balance	400,000	1,300,000	'
AOCI Defined Benefit Component [Abstract]	'	'	'
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	-57,800,000	'	'
Reclassification of DB Plans	6,400,000	5,800,000	3,900,000
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	25,714,000	-4,356,000	-13,645,000
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	-32,000,000	-57,800,000	'
Losses arising before reclassification	19,400,000	'	'
AOCI Rollforward [Abstract]	'	'	'
AOCI Beginning Balance	-72,854,000	'	'
AmountReclassifiedFromAOCI	8,400,000	7,800,000	4,600,000
OtherComprehensiveIncomeBeforeReclassifications	18,500,000	'	'
Other Comprehensive Income (Loss), Net of Tax, Total	26,823,000	-2,168,000	-27,316,000
AOCI ending Balance	-46,031,000	-72,854,000	'
Reclassication of Items out of AOCI [Abstract]	'	'	'
OCI Reclass CF Hedging Tax	1,400,000	1,300,000	600,000
OCI Amortization of Cash Flow Hedges, Before Tax	-3,400,000	-3,300,000	-1,300,000
OCI Amortization of Cash Flow Hedge, Net of Tax	-2,000,000	-2,000,000	-700,000
OCI Amortization of Prior Service Cost	-200,000	-200,000	-300,000
Amortization of actuarial gain or loss	-10,500,000	-8,900,000	-5,700,000
Amortization of Transition Obligation	'	-200,000	-200,000
OCI Defined Benefit Plan Adjustment Before Tax	-10,700,000	-9,300,000	-6,200,000
OCI Defined Benefit Plan Tax	4,300,000	3,500,000	2,300,000
Reclassification of DB Plans	-6,400,000	-5,800,000	-3,900,000
AmountReclassifiedFromAOCI	-8,400,000	-7,800,000	-4,600,000
OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeReclassificationAdjustmentsNetOfTaxAbstract	'	'	'
OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax	-11,400,000	6,200,000	10,200,000
OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax	'	'	10,200,000
The Connecticut Light And Power Company [Member]	'	'	'
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent [Abstract]	'	'	'
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months	700,000	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	-444,000	-444,000	-445,000
AOCI Unrealized GainLoss component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-31,000	7,000	17,000
AOCI Rollforward [Abstract]	'	'	'
AOCI Beginning Balance	-1,800,000	'	'
Other Comprehensive Income (Loss), Net of Tax, Total	413,000	451,000	462,000
AOCI ending Balance	-1,387,000	-1,800,000	'
Public Service Company Of New Hampshire [Member]	'	'	'
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent [Abstract]	'	'	'
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months	2,000,000	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	-1,162,000	-1,162,000	10,260,000
AOCI Unrealized GainLoss component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-54,000	13,000	29,000
AOCI Defined Benefit Component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	-3,000	2,000	0
AOCI Rollforward [Abstract]	'	'	'
AOCI Beginning Balance	-9,655,000	'	'
Other Comprehensive Income (Loss), Net of Tax, Total	1,105,000	1,177,000	-10,231,000
AOCI ending Balance	-8,550,000	-9,655,000	'
Western Massachusetts Electric Company [Member]	'	'	'
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent [Abstract]	'	'	'
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months	500,000	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	-338,000	-338,000	4,108,000
AOCI Unrealized GainLoss component [Abstract]	'	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	-9,000	2,000	5,000
AOCI Rollforward [Abstract]	'	'	'
AOCI Beginning Balance	-3,846,000	'	'
Other Comprehensive Income (Loss), Net of Tax, Total	329,000	340,000	-4,103,000
AOCI ending Balance	($3,517,000)	($3,846,000)	'

DIVIDEND_RESTRICTIONS_Details

DIVIDEND RESTRICTIONS (Details)	12 Months Ended
DIVIDEND RESTRICTIONS (Details)	Dec. 31, 2013
Line of Credit Facility, Dividend Restrictions	'CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends for lawful and legitimate business purposes from retained earnings. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of NU, CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at all times. As of December 31, 2013, all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $2.1 billion for NU, $961.5 million for CL&P, $1.4 billion for NSTAR Electric, $438.5 million for PSNH and $181 million for WMECO as of December 31, 2013.
Public Service Company Of New Hampshire [Member]	'
Statutory Dividend Payment Restrictions Disclosure	'As of December 31, 2013, NU, CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends. PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 2013, approximately $12.7 million of PSNH's Retained Earnings was subject to restriction under its FERC hydroelectric license conditions and PSNH was in compliance with this provision.

COMMON_SHARES_Details

COMMON SHARES (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
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	333,113,492	332,509,383
Treasury Stock Shares	17,796,672	18,455,749
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

PREFFERED_STOCK_NOT_SUBJECT_TO1

PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (DETAILS) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Value, Outstanding	$155,600,000	$155,600,000	'
Cash Dividends on Preferred Stock	7,682,000	7,029,000	5,559,000
The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	2,324,000	'	'
Preferred Stock, Value, Outstanding	116,200,000	116,200,000	'
Cash Dividends on Preferred Stock	5,559,000	5,559,000	5,559,000
Preferred Stock Authorized Description	'The CL&P and NSTAR Electric preferred stock is not subject to mandatory redemption and is presented as a noncontrolling interest of a subsidiary in NU’s financial statements. CL&P Preferred Stock: CL&P's charter authorizes it to issue up to 9 million shares of preferred stock ($50 par value per share).	'	'
NSTAR Electric Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	430,000	'	'
Preferred Stock, Value, Outstanding	43,000,000	43,000,000	'
Cash Dividends on Preferred Stock	2,123,000	1,960,000	1,960,000
Preferred Stock Authorized Description	'NSTAR Electric is authorized to issue 2,890,000 shares ($100 par value per share).	'	'
Series 1947 $1.90 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	163,912	'	'
Preferred Stock, Redemption Price Per Share	$52.50	'	'
Preferred Stock, Value, Outstanding	8,200,000	8,200,000	'
Series 1947 $2.00 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	336,088	'	'
Preferred Stock, Redemption Price Per Share	$54	'	'
Preferred Stock, Value, Outstanding	16,800,000	16,800,000	'
Series 1949 $2.04 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	100,000	'	'
Preferred Stock, Redemption Price Per Share	$52	'	'
Preferred Stock, Value, Outstanding	5,000,000	5,000,000	'
Series 1949 $2.20 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	200,000	'	'
Preferred Stock, Redemption Price Per Share	$52.50	'	'
Preferred Stock, Value, Outstanding	10,000,000	10,000,000	'
Series 1949 3.90% [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	160,000	'	'
Preferred Stock, Redemption Price Per Share	$50.50	'	'
Preferred Stock, Value, Outstanding	8,000,000	8,000,000	'
Series E 1954 $2.06 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	200,000	'	'
Preferred Stock, Redemption Price Per Share	$51	'	'
Preferred Stock, Value, Outstanding	10,000,000	10,000,000	'
Series F 1955 $2.09 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	100,000	'	'
Preferred Stock, Redemption Price Per Share	$51	'	'
Preferred Stock, Value, Outstanding	5,000,000	5,000,000	'
Series 1956 4.5% [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	104,000	'	'
Preferred Stock, Redemption Price Per Share	$50.75	'	'
Preferred Stock, Value, Outstanding	5,200,000	5,200,000	'
Series 1958 4.96% [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	100,000	'	'
Preferred Stock, Redemption Price Per Share	$50.50	'	'
Preferred Stock, Value, Outstanding	5,000,000	5,000,000	'
Series 1963 4.5% [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	160,000	'	'
Preferred Stock, Redemption Price Per Share	$50.50	'	'
Preferred Stock, Value, Outstanding	8,000,000	8,000,000	'
Series 1967 5.28% [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	200,000	'	'
Preferred Stock, Redemption Price Per Share	$51.43	'	'
Preferred Stock, Value, Outstanding	10,000,000	10,000,000	'
Series G of 1968 $3.24 [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	300,000	'	'
Preferred Stock, Redemption Price Per Share	$51.84	'	'
Preferred Stock, Value, Outstanding	15,000,000	15,000,000	'
Series 1968 6.56% [Member] \| The Connecticut Light And Power Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	200,000	'	'
Preferred Stock, Redemption Price Per Share	$51.44	'	'
Preferred Stock, Value, Outstanding	10,000,000	10,000,000	'
Preferred Stock 4.25% [Member] \| NSTAR Electric Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	180,000	'	'
Preferred Stock, Redemption Price Per Share	$103.63	'	'
Preferred Stock, Value, Outstanding	18,000,000	18,000,000	'
Preferred Stock 4.78% [Member] \| NSTAR Electric Company [Member]	'	'	'
Class Of Stock [Line Items]	'	'	'
Preferred Stock, Shares Outstanding	250,000	'	'
Preferred Stock, Redemption Price Per Share	$102.80	'	'
Preferred Stock, Value, Outstanding	$25,000,000	$25,000,000	'

COMMON_SHAREHOLDER_EQUIT_AND_N

COMMON SHAREHOLDER EQUIT AND NCI (Details) (USD $)	3 Months Ended								12 Months Ended
COMMON SHAREHOLDER EQUIT AND NCI (Details) (USD $)	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Shareholders' Equity, Beginning Balance	'	'	'	$9,237,050,000	'	'	'	'	$9,237,050,000	'	'
Net Income	179,200,000	211,400,000	173,100,000	230,000,000	176,600,000	209,500,000	46,200,000	100,800,000	793,689,000	533,077,000	400,513,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	7,682,000	7,132,000	5,820,000
Other Comprehensive Income (Loss), Net of Tax	'	'	'	'	'	'	'	'	26,823,000	-2,168,000	-27,316,000
Shareholders' Equity, Ending Balance	9,611,528,000	'	'	'	9,237,050,000	'	'	'	9,611,528,000	9,237,050,000	'
Other Impacts of Merger with NSTAR	'	'	'	'	'	'	'	'	'	'	39,400,000
Common Shareholders Equity [Member]	'	'	'	'	'	'	'	'	'	'	'
Shareholders' Equity, Beginning Balance	'	'	'	9,237,100,000	'	'	'	4,012,700,000	9,237,100,000	4,012,700,000	3,811,200,000
Net Income	'	'	'	'	'	'	'	'	793,689,000	533,077,000	400,513,000
Dividends on Common Shares	'	'	'	'	'	'	'	'	-462,741,000	-375,527,000	-195,595,000
Dividends, Preferred Stock	'	'	'	'	'	'	'	'	-7,682,000	-7,029,000	-5,559,000
Issuance of Common Shares	'	'	'	'	'	'	'	'	11,078,000	13,327,000	5,851,000
Other Transcations, Net	'	'	'	'	'	'	'	'	13,200,000	21,100,000	23,900,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	'	-103,000	-261,000
Other Comprehensive Income (Loss), Net of Tax	'	'	'	'	'	'	'	'	26,823,000	-2,168,000	-27,316,000
Shareholders' Equity, Ending Balance	9,611,500,000	'	'	'	9,237,100,000	'	'	'	9,611,500,000	9,237,100,000	4,012,700,000
Purchase Price of NSTAR	'	'	'	'	'	'	'	'	'	5,038,300,000	'
Other Impacts of Merger with NSTAR	'	'	'	'	'	'	'	'	'	3,400,000	'
Noncontrolling Interest Member	'	'	'	'	'	'	'	'	'	'	'
Shareholders' Equity, Beginning Balance	'	'	'	0	'	'	'	3,000,000	0	3,000,000	'
Contributions To Northern Pass Trans	'	'	'	'	'	'	'	'	'	300,000	1,200,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	100,000	300,000
Shareholders' Equity, Ending Balance	0	'	'	'	0	'	'	'	0	0	3,000,000
Other Impacts of Merger with NSTAR	'	'	'	'	'	'	'	'	'	-3,400,000	'
Total Equity [Member]	'	'	'	'	'	'	'	'	'	'	'
Shareholders' Equity, Beginning Balance	'	'	'	9,237,100,000	'	'	'	4,015,700,000	9,237,100,000	4,015,700,000	3,812,700,000
Net Income	'	'	'	'	'	'	'	'	793,700,000	533,100,000	400,500,000
Dividends on Common Shares	'	'	'	'	'	'	'	'	-462,700,000	-375,500,000	-195,600,000
Dividends, Preferred Stock	'	'	'	'	'	'	'	'	-7,700,000	-7,000,000	-5,600,000
Issuance of Common Shares	'	'	'	'	'	'	'	'	11,100,000	13,300,000	5,900,000
Contributions To Northern Pass Trans	'	'	'	'	'	'	'	'	'	300,000	1,200,000
Other Transcations, Net	'	'	'	'	'	'	'	'	13,200,000	21,100,000	23,900,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	'	'
Other Comprehensive Income (Loss), Net of Tax	'	'	'	'	'	'	'	'	26,800,000	-2,200,000	-27,300,000
Shareholders' Equity, Ending Balance	9,611,500,000	'	'	'	9,237,100,000	'	'	'	9,611,500,000	9,237,100,000	4,015,700,000
Purchase Price of NSTAR	'	'	'	'	'	'	'	'	'	5,038,300,000	'
Preferred Stock Member	'	'	'	'	'	'	'	'	'	'	'
Shareholders' Equity, Beginning Balance	'	'	'	155,600,000	'	'	'	116,200,000	155,600,000	116,200,000	116,200,000
Dividends, Preferred Stock	'	'	'	'	'	'	'	'	-7,700,000	-7,000,000	-5,600,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	7,700,000	7,000,000	5,600,000
Shareholders' Equity, Ending Balance	$155,600,000	'	'	'	$155,600,000	'	'	'	$155,600,000	$155,600,000	$116,200,000

EARNINGS_PER_SHARE_Details

EARNINGS PER SHARE (Details) (USD $)

0 Months Ended

3 Months Ended

12 Months Ended

In Thousands, except Share data, unless otherwise specified

Apr. 09, 2012

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Notes To Consolidated Financial Statements [Abstract]

Net Income Attributable to Controlling Interests

$177,400

$209,500

$171,000

$228,100

$174,700

$207,600

$44,300

$99,300

$786,007

$525,945

$394,693

Basic

315,311,387

277,209,819

177,410,167

Weighted Average Number Diluted Shares Outstanding Adjustment

899,773

783,812

394,401

Diluted

316,211,160

277,993,631

177,804,568

Earnings Per Share Basic And Diluted

$0.56

$0.66

$0.54

$0.72

$0.55

$0.66

$0.15

$0.56

Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount

1,575

4,266

4,314

Basic Earnings Per Common Share

$2.49

$1.90

$2.22

Diluted Earnings Per Common Share

$2.49

$1.89

$2.22

Common Stock Issuance Merger With Nstar [Abstract]

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares

136,049,000

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details) (USD $)	3 Months Ended								12 Months Ended
SEGMENT INFORMATION (Details) (USD $)	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	$1,777,700,000	$1,892,600,000	$1,635,900,000	$1,995,000,000	$1,684,000,000	$1,861,500,000	$1,628,700,000	$1,099,600,000	$7,301,204,000	$6,273,787,000	$4,465,657,000
Operating Income	360,600,000	399,300,000	350,600,000	418,900,000	331,400,000	412,900,000	159,500,000	214,400,000	1,529,435,000	1,118,206,000	794,176,000
Total Interest Expense	'	'	'	'	'	'	'	'	-338,699,000	-329,945,000	-250,425,000
Income Tax Expense	'	'	'	'	'	'	'	'	-426,941,000	-274,926,000	-170,953,000
Net Income	179,200,000	211,400,000	173,100,000	230,000,000	176,600,000	209,500,000	46,200,000	100,800,000	793,689,000	533,077,000	400,513,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	-7,682,000	-7,132,000	-5,820,000
Net Income Attributable to Controlling Interests	177,400,000	209,500,000	171,000,000	228,100,000	174,700,000	207,600,000	44,300,000	99,300,000	786,007,000	525,945,000	394,693,000
Total Assets	27,795,537,000	'	'	'	28,302,824,000	'	'	'	27,795,537,000	28,302,824,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	1,456,787,000	1,472,272,000	1,076,730,000
Electric Distribution Member	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	5,362,300,000	4,716,500,000	3,343,100,000
Depreciation And Amortization	'	'	'	'	'	'	'	'	-604,800,000	-530,300,000	-337,200,000
Operating Expenses, Other	'	'	'	'	'	'	'	'	-3,927,700,000	-3,585,400,000	-2,637,400,000
Operating Income	'	'	'	'	'	'	'	'	829,800,000	600,800,000	368,500,000
Total Interest Expense	'	'	'	'	'	'	'	'	-175,000,000	-165,600,000	-123,800,000
Interest Income	'	'	'	'	'	'	'	'	4,100,000	2,800,000	3,700,000
Other Income/(Loss)	'	'	'	'	'	'	'	'	12,900,000	8,900,000	11,600,000
Income Tax Expense	'	'	'	'	'	'	'	'	-240,000,000	-150,200,000	-67,600,000
Net Income	'	'	'	'	'	'	'	'	431,800,000	296,700,000	192,400,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	-4,800,000	-4,400,000	-3,300,000
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	427,000,000	292,300,000	189,100,000
Total Assets	17,260,000,000	'	'	'	18,047,300,000	'	'	'	17,260,000,000	18,047,300,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	639,000,000	611,700,000	540,700,000
Natural Gas Distribution [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	855,800,000	572,900,000	430,800,000
Depreciation And Amortization	'	'	'	'	'	'	'	'	-66,700,000	-49,100,000	-27,700,000
Operating Expenses, Other	'	'	'	'	'	'	'	'	-659,400,000	-445,200,000	-333,500,000
Operating Income	'	'	'	'	'	'	'	'	129,700,000	78,600,000	69,600,000
Total Interest Expense	'	'	'	'	'	'	'	'	-33,100,000	-31,300,000	-21,000,000
Interest Income	'	'	'	'	'	'	'	'	0	0	0
Other Income/(Loss)	'	'	'	'	'	'	'	'	800,000	400,000	1,300,000
Income Tax Expense	'	'	'	'	'	'	'	'	-36,500,000	-16,900,000	-18,200,000
Net Income	'	'	'	'	'	'	'	'	60,900,000	30,800,000	31,700,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	0	0
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	60,900,000	30,800,000	31,700,000
Total Assets	2,759,700,000	'	'	'	2,717,400,000	'	'	'	2,759,700,000	2,717,400,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	168,100,000	148,700,000	98,200,000
Transmission [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	978,700,000	861,500,000	635,400,000
Depreciation And Amortization	'	'	'	'	'	'	'	'	-136,200,000	-109,200,000	-84,000,000
Operating Expenses, Other	'	'	'	'	'	'	'	'	-281,800,000	-251,600,000	-188,200,000
Operating Income	'	'	'	'	'	'	'	'	560,700,000	500,700,000	363,200,000
Total Interest Expense	'	'	'	'	'	'	'	'	-100,300,000	-96,700,000	-76,700,000
Interest Income	'	'	'	'	'	'	'	'	700,000	400,000	500,000
Other Income/(Loss)	'	'	'	'	'	'	'	'	10,900,000	7,300,000	10,700,000
Income Tax Expense	'	'	'	'	'	'	'	'	-182,100,000	-159,200,000	-95,600,000
Net Income	'	'	'	'	'	'	'	'	289,900,000	252,500,000	202,100,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	-2,900,000	-2,800,000	-2,500,000
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	287,000,000	249,700,000	199,600,000
Total Assets	6,745,800,000	'	'	'	6,187,700,000	'	'	'	6,745,800,000	6,187,700,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	618,500,000	663,600,000	388,900,000
Other Segment [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	777,500,000	803,800,000	541,300,000
Depreciation And Amortization	'	'	'	'	'	'	'	'	-62,200,000	-56,400,000	-16,800,000
Operating Expenses, Other	'	'	'	'	'	'	'	'	-715,000,000	-817,000,000	-534,100,000
Operating Income	'	'	'	'	'	'	'	'	300,000	-69,600,000	-9,600,000
Total Interest Expense	'	'	'	'	'	'	'	'	-35,500,000	-43,600,000	-33,700,000
Interest Income	'	'	'	'	'	'	'	'	5,400,000	7,100,000	5,300,000
Other Income/(Loss)	'	'	'	'	'	'	'	'	858,900,000	795,000,000	455,200,000
Income Tax Expense	'	'	'	'	'	'	'	'	31,900,000	55,500,000	14,300,000
Net Income	'	'	'	'	'	'	'	'	861,000,000	744,400,000	431,500,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	0	0
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	861,000,000	744,400,000	431,500,000
Total Assets	11,842,400,000	'	'	'	18,832,600,000	'	'	'	11,842,400,000	18,832,600,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	31,200,000	48,300,000	48,900,000
Eliminations Segment [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	-673,100,000	-680,900,000	-484,900,000
Depreciation And Amortization	'	'	'	'	'	'	'	'	10,200,000	4,200,000	2,500,000
Operating Expenses, Other	'	'	'	'	'	'	'	'	671,800,000	684,400,000	484,900,000
Operating Income	'	'	'	'	'	'	'	'	8,900,000	7,700,000	2,500,000
Total Interest Expense	'	'	'	'	'	'	'	'	5,200,000	7,300,000	4,800,000
Interest Income	'	'	'	'	'	'	'	'	-5,600,000	-7,100,000	-5,300,000
Other Income/(Loss)	'	'	'	'	'	'	'	'	-858,200,000	-795,100,000	-455,300,000
Income Tax Expense	'	'	'	'	'	'	'	'	-200,000	-4,100,000	-3,900,000
Net Income	'	'	'	'	'	'	'	'	-849,900,000	-791,300,000	-457,200,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	0	0
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	-849,900,000	-791,300,000	-457,200,000
Total Assets	-10,812,400,000	'	'	'	-17,482,200,000	'	'	'	-10,812,400,000	-17,482,200,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	0	0	0
Total [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	7,301,200,000	6,273,800,000	4,465,700,000
Depreciation And Amortization	'	'	'	'	'	'	'	'	-859,700,000	-740,800,000	-463,200,000
Operating Expenses, Other	'	'	'	'	'	'	'	'	-4,912,100,000	-4,414,800,000	-3,208,300,000
Operating Income	'	'	'	'	'	'	'	'	1,529,400,000	1,118,200,000	794,200,000
Total Interest Expense	'	'	'	'	'	'	'	'	-338,700,000	-329,900,000	-250,400,000
Interest Income	'	'	'	'	'	'	'	'	4,600,000	3,200,000	4,200,000
Other Income/(Loss)	'	'	'	'	'	'	'	'	25,300,000	16,500,000	23,500,000
Income Tax Expense	'	'	'	'	'	'	'	'	-426,900,000	-274,900,000	-171,000,000
Net Income	'	'	'	'	'	'	'	'	793,700,000	533,100,000	400,500,000
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	-7,700,000	-7,200,000	-5,800,000
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	786,000,000	525,900,000	394,700,000
Total Assets	27,795,500,000	'	'	'	28,302,800,000	'	'	'	27,795,500,000	28,302,800,000	'
Investments in Property, Plant and Equipment	'	'	'	'	'	'	'	'	$1,456,800,000	$1,472,300,000	$1,076,700,000

SUBSEQUENT_EVENTS_Details

SUBSEQUENT EVENTS (Details)	12 Months Ended
SUBSEQUENT EVENTS (Details)	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'
Subsequent Event, Description	'See Note 9, "Long-Term Debt," for information regarding the January 2014 Yankee Gas long-term debt issuance. See Note 3, "Regulatory Accounting," for information regarding the February 2014 PURA decision on CL&P’s request for approval to recover the restoration costs of the 2012 and 2011 major storms. See Note 12C, "Commitments and Contingencies - Contractual Obligations - Yankee Companies," for information regarding a January 2014 letter received from the U.S. Department of Justice stating that the DOE will not appeal the court's final judgment on the Yankee Companies' lawsuits against the DOE.

Recovered_Sheet2

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Revenues	$1,777,700	$1,892,600	$1,635,900	$1,995,000	$1,684,000	$1,861,500	$1,628,700	$1,099,600	$7,301,204	$6,273,787	$4,465,657
Operating Income	360,600	399,300	350,600	418,900	331,400	412,900	159,500	214,400	1,529,435	1,118,206	794,176
Net Income	179,200	211,400	173,100	230,000	176,600	209,500	46,200	100,800	793,689	533,077	400,513
Net Income Attributable to Controlling Interests	177,400	209,500	171,000	228,100	174,700	207,600	44,300	99,300	786,007	525,945	394,693
Basic Earnings Per Common Share	'	'	'	'	'	'	'	'	$2.49	$1.90	$2.22
Diluted Earnings Per Common Share	'	'	'	'	'	'	'	'	$2.49	$1.89	$2.22
Earnings Per Share Basic And Diluted	$0.56	$0.66	$0.54	$0.72	$0.55	$0.66	$0.15	$0.56	'	'	'
The Connecticut Light And Power Company [Member]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	600,500	648,400	569,300	624,100	595,200	658,100	562,100	592,000	2,442,341	2,407,449	2,548,387
Operating Income	119,200	133,900	136,800	149,700	135,000	139,700	40,400	111,900	539,576	426,989	463,183
Net Income	60,200	66,300	67,900	85,000	73,900	74,900	6,900	54,000	279,412	209,725	250,164
NSTAR Electric Company [Member]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	576,900	753,900	570,400	592,300	516,200	693,700	534,600	556,500	2,493,479	2,300,997	2,403,053
Operating Income	109,200	192,000	112,500	94,500	70,900	194,100	93,900	22,500	508,156	381,416	486,173
Net Income	55,400	107,000	58,000	48,100	34,000	106,800	45,500	3,900	268,546	190,242	252,494
Public Service Company Of New Hampshire [Member]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	226,900	218,600	216,100	273,800	233,000	256,900	255,100	243,000	935,402	988,013	1,013,003
Operating Income	56,200	56,600	54,300	58,100	51,400	61,300	47,000	45,400	225,219	205,095	180,104
Net Income	26,800	28,400	27,200	29,000	27,200	27,200	21,200	21,300	111,397	96,882	100,267
Western Massachusetts Electric Company [Member]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	110,900	121,800	115,000	125,000	107,900	112,500	106,800	114,000	472,724	441,164	417,315
Operating Income	22,400	28,900	32,400	35,600	28,900	28,100	25,100	28,700	119,347	110,774	88,363
Net Income	$10,400	$15,000	$16,400	$18,600	$15,100	$14,100	$11,100	$14,200	$60,438	$54,503	$43,054

SCHEDULE_I_Balance_Sheets_Deta

SCHEDULE I - Balance Sheets (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current Assets:	'	'	'	'
Cash	$43,364	$45,748	$6,559	$23,395
Receivables, Net	765,391	792,822	'	'
Prepayments and Other Current Assets	214,288	199,947	'	'
Total Current Assets	2,087,049	2,227,295	'	'
Deferred Debits and Other Assets:	'	'	'	'
Derivative Assets Noncurrent	74,155	90,612	'	'
Other Long-Term Assets	291,537	327,766	'	'
Total Deferred Debits and Other Assets	8,132,302	9,470,519	'	'
Goodwill	3,519,401	3,519,401	300,000	'
Total Assets	27,795,537	28,302,824	'	'
Current Liabilities:	'	'	'	'
Notes Payable to Banks	1,093,000	1,120,196	'	'
Long-Term Debt - Current Portion	533,346	763,338	'	'
Accounts Payable - Current	742,251	764,350	'	'
Other Liabilities - Current	702,776	861,691	'	'
Total Current Liabilities	3,275,651	3,643,690	'	'
Deferred Credits and Other Liabilities:	'	'	'	'
Other Long-Term Liabilities	923,053	967,561	'	'
Total Deferred Credits and Other Liabilities	6,975,957	7,984,221	'	'
Capitalization:	'	'	'	'
Long-Term Debt	7,776,833	7,200,156	'	'
Common Shareholders' Equity:	'	'	'	'
Common Stock	1,665,351	1,662,547	'	'
Capital Surplus, Paid In	6,192,765	6,183,267	'	'
Retained Earnings	2,125,980	1,802,714	'	'
Accumulated Other Comprehensive Loss	46,031	72,854	'	'
Treasury Stock	-326,537	-338,624	'	'
Common Shareholders' Equity	9,611,528	9,237,050	'	'
Total Capitalization	17,543,929	16,592,774	'	'
Total Liabilities and Capitalization	27,795,537	28,302,824	'	'
Nu Parent [Member]	'	'	'	'
Current Assets:	'	'	'	'
Cash	35	429	62	268
Notes Receivable from Affiliated Companies	871,050	914,025	'	'
Receivables, Net	1	1	'	'
Accounts Receivable from Affiliated Companies	95,513	110,217	'	'
Prepayments and Other Current Assets	59,904	72,514	'	'
Total Current Assets	1,026,503	1,097,186	'	'
Deferred Debits and Other Assets:	'	'	'	'
Equity Method Investments	7,733,051	7,173,961	'	'
Notes Receivable, Related Parties, Noncurrent	62,500	25,000	'	'
Deferred Tax Assets, Net, Noncurrent	205,779	215,683	'	'
Other Long-Term Assets	22,099	17,108	'	'
Total Deferred Debits and Other Assets	11,255,240	10,663,563	'	'
Goodwill	3,231,811	3,231,811	'	'
Total Assets	12,281,743	11,760,749	'	'
Current Liabilities:	'	'	'	'
Notes Payable to Banks	1,014,500	1,150,000	'	'
Long-Term Debt - Current Portion	31,696	581,688	'	'
Accounts Payable - Current	441	9,932	'	'
Accounts Payable to Affiliated Companies	144,026	47,593	'	'
Other Liabilities - Current	59,559	41,383	'	'
Total Current Liabilities	1,250,222	1,830,596	'	'
Deferred Credits and Other Liabilities:	'	'	'	'
Other Long-Term Liabilities	122,226	114,903	'	'
Total Deferred Credits and Other Liabilities	122,226	114,903	'	'
Capitalization:	'	'	'	'
Long-Term Debt	1,297,767	578,200	'	'
Common Shareholders' Equity:	'	'	'	'
Common Stock	1,665,351	1,662,547	'	'
Capital Surplus, Paid In	6,192,765	6,183,267	'	'
Retained Earnings	2,125,980	1,802,714	'	'
Accumulated Other Comprehensive Loss	-46,031	-72,854	'	'
Treasury Stock	-326,537	-338,624	'	'
Common Shareholders' Equity	9,611,528	9,237,050	'	'
Total Capitalization	10,909,295	9,815,250	'	'
Total Liabilities and Capitalization	$12,281,743	$11,760,749	'	'

SCHEDULE_I_Income_Statements_D

SCHEDULE I - Income Statements (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	$1,777,700	$1,892,600	$1,635,900	$1,995,000	$1,684,000	$1,861,500	$1,628,700	$1,099,600	$7,301,204	$6,273,787	$4,465,657
Operating Expenses:	'	'	'	'	'	'	'	'	'	'	'
Operating Income	360,600	399,300	350,600	418,900	331,400	412,900	159,500	214,400	1,529,435	1,118,206	794,176
Total Interest Expense	'	'	'	'	'	'	'	'	338,699	329,945	250,425
Other Income [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Income Before Income Tax Expense	'	'	'	'	'	'	'	'	1,220,630	808,003	571,466
Income Tax Expense	'	'	'	'	'	'	'	'	426,941	274,926	170,953
Net Income	179,200	211,400	173,100	230,000	176,600	209,500	46,200	100,800	793,689	533,077	400,513
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	7,682	7,132	5,820
Net Income Attributable to Controlling Interests	177,400	209,500	171,000	228,100	174,700	207,600	44,300	99,300	786,007	525,945	394,693
Basic Earnings Per Common Share	'	'	'	'	'	'	'	'	$2.49	$1.90	$2.22
Diluted Earnings Per Common Share	'	'	'	'	'	'	'	'	$2.49	$1.89	$2.22
Weighted Average Common Shares Outstanding:	'	'	'	'	'	'	'	'	'	'	'
Basic	'	'	'	'	'	'	'	'	315,311,387	277,209,819	177,410,167
Diluted	'	'	'	'	'	'	'	'	316,211,160	277,993,631	177,804,568
Nu Parent [Member]	'	'	'	'	'	'	'	'	'	'	'
Condensed Financial Statements, Captions [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating Revenues	'	'	'	'	'	'	'	'	8	2	0
Operating Expenses:	'	'	'	'	'	'	'	'	'	'	'
Other Operating Expenses	'	'	'	'	'	'	'	'	12,766	80,719	19,075
Operating Income	'	'	'	'	'	'	'	'	-12,758	-80,717	-19,075
Total Interest Expense	'	'	'	'	'	'	'	'	31,639	36,325	26,767
Other Income [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Equity In Earnings Of Subsidiaries	'	'	'	'	'	'	'	'	785,650	579,221	422,408
Other Income/(Loss)	'	'	'	'	'	'	'	'	5,062	6,080	4,247
Total Other Income	'	'	'	'	'	'	'	'	790,712	585,301	426,655
Income Before Income Tax Expense	'	'	'	'	'	'	'	'	746,315	468,259	380,813
Income Tax Expense	'	'	'	'	'	'	'	'	-39,692	-57,789	-14,142
Net Income	'	'	'	'	'	'	'	'	786,007	526,048	394,955
Net Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	103	262
Net Income Attributable to Controlling Interests	'	'	'	'	'	'	'	'	$786,007	$525,945	$394,693
Basic Earnings Per Common Share	'	'	'	'	'	'	'	'	$2.49	$1.90	$2.22
Diluted Earnings Per Common Share	'	'	'	'	'	'	'	'	$2.49	$1.89	$2.22
Weighted Average Common Shares Outstanding:	'	'	'	'	'	'	'	'	'	'	'
Basic	'	'	'	'	'	'	'	'	315,311,387	277,209,819	177,410,167
Diluted	'	'	'	'	'	'	'	'	316,211,160	277,993,631	177,804,568

SCHEDULE_I_Cash_Flows_Details

SCHEDULE I - Cash Flows (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities:	'	'	'	'	'	'	'	'	'	'	'
Net Income	$179,200	$211,400	$173,100	$230,000	$176,600	$209,500	$46,200	$100,800	$793,689	$533,077	$400,513
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'	'	'	'	'	'	'	'	'
Deferred Income Tax Expense (Benefit)	'	'	'	'	'	'	'	'	431,413	292,000	196,761
Other Noncash Income (Expense)	'	'	'	'	'	'	'	'	56,071	42,852	-48,772
Changes in Current Assets and Liabilities:	'	'	'	'	'	'	'	'	'	'	'
Receivables and Unbilled Revenues, Net	'	'	'	'	'	'	'	'	163,549	20,214	-17,570
Change in Accounts Payable	'	'	'	'	'	'	'	'	-54,619	-128,339	18,916
Taxes Receivable/(Accrued)	'	'	'	'	'	'	'	'	50,950	5,450	-49,642
Other Current Assets and Liabilities	'	'	'	'	'	'	'	'	22,623	-8,532	-12,569
Net Cash Flows Provided by Operating Activities	'	'	'	'	'	'	'	'	1,663,539	1,161,229	970,386
Investing Activities:	'	'	'	'	'	'	'	'	'	'	'
Other Investing Activities	'	'	'	'	'	'	'	'	-67,816	-35,683	-60,674
Net Cash Flows Used in Investing Activities	'	'	'	'	'	'	'	'	-1,441,223	-1,467,924	-1,018,587
Financing Activities:	'	'	'	'	'	'	'	'	'	'	'
Cash Dividends on Common Stock	'	'	'	'	'	'	'	'	462,741	375,047	194,555
Increase/(Decrease) in Short-Term Debt	'	'	'	'	'	'	'	'	-397,000	825,000	50,000
Issuance of Long-Term Debt	'	'	'	'	'	'	'	'	1,680,000	850,000	627,500
Retirements of Long-Term Debt	'	'	'	'	'	'	'	'	929,885	839,136	369,586
Other Financing Activities	'	'	'	'	'	'	'	'	-25,253	6,529	-7,123
Net Cash Flows Provided by/(Used in) Financing Activities	'	'	'	'	'	'	'	'	-224,700	345,884	31,365
Supplemental Cash Flow Information [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Interest Paid, Net of Amounts Capitalized	'	'	'	'	'	'	'	'	343,300	356,500	256,300
Income Taxes Paid	'	'	'	'	'	'	'	'	50,000	-12,800	-76,600
Net Increase/(Decrease) in Cash	'	'	'	'	'	'	'	'	-2,384	39,189	-16,836
Cash - Beginning of Year	'	'	'	45,748	'	'	'	6,559	45,748	6,559	23,395
Cash - End of Year	43,364	'	'	'	45,748	'	'	'	43,364	45,748	6,559
Nu Parent [Member]	'	'	'	'	'	'	'	'	'	'	'
Operating Activities:	'	'	'	'	'	'	'	'	'	'	'
Net Income	'	'	'	'	'	'	'	'	786,007	526,048	394,955
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'	'	'	'	'	'	'	'	'	'
Equity In Earnings of Subsidiaries	'	'	'	'	'	'	'	'	-785,650	-579,221	-422,408
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	'	'	'	'	'	'	'	'	407,837	374,584	389,292
Deferred Income Tax Expense (Benefit)	'	'	'	'	'	'	'	'	15,159	-15,350	-15,934
Other Noncash Income (Expense)	'	'	'	'	'	'	'	'	29,169	-3,755	33,238
Changes in Current Assets and Liabilities:	'	'	'	'	'	'	'	'	'	'	'
Receivables and Unbilled Revenues, Net	'	'	'	'	'	'	'	'	14,704	-18,321	-436
Change in Accounts Payable	'	'	'	'	'	'	'	'	-7,058	48,332	-183
Taxes Receivable/(Accrued)	'	'	'	'	'	'	'	'	13,295	-16,872	11,537
Other Current Assets and Liabilities	'	'	'	'	'	'	'	'	-1,411	60,182	484
Net Cash Flows Provided by Operating Activities	'	'	'	'	'	'	'	'	472,052	375,627	390,545
Investing Activities:	'	'	'	'	'	'	'	'	'	'	'
Capital Contributions To Subsidiaries	'	'	'	'	'	'	'	'	-65,400	-81,431	-233,349
Return Of Investment In Subsidiaries	'	'	'	'	'	'	'	'	0	8,207	0
(Increase) Decrease in Due from Related Parties	'	'	'	'	'	'	'	'	0	2,200	400
(Increase) Decrease In Notes Receivable From Affiliated Company	'	'	'	'	'	'	'	'	5,475	-704,475	19,000
Other Investing Activities	'	'	'	'	'	'	'	'	-1,862	-608	-2,585
Net Cash Flows Used in Investing Activities	'	'	'	'	'	'	'	'	-61,787	-776,107	-216,534
Financing Activities:	'	'	'	'	'	'	'	'	'	'	'
Cash Dividends on Common Stock	'	'	'	'	'	'	'	'	462,741	375,047	194,555
Increase/(Decrease) in Short-Term Debt	'	'	'	'	'	'	'	'	-135,500	733,500	19,000
Issuance of Long-Term Debt	'	'	'	'	'	'	'	'	750,000	300,000	0
Retirements of Long-Term Debt	'	'	'	'	'	'	'	'	-550,000	-263,000	0
Other Financing Activities	'	'	'	'	'	'	'	'	-12,418	5,394	1,338
Net Cash Flows Provided by/(Used in) Financing Activities	'	'	'	'	'	'	'	'	-410,659	400,847	-174,217
Supplemental Cash Flow Information [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Interest Paid, Net of Amounts Capitalized	'	'	'	'	'	'	'	'	33,822	50,144	24,951
Income Taxes Paid	'	'	'	'	'	'	'	'	-30,603	-27,126	-10,833
Net Increase/(Decrease) in Cash	'	'	'	'	'	'	'	'	-394	367	-206
Cash - Beginning of Year	'	'	'	429	'	'	'	62	429	62	268
Cash - End of Year	$35	'	'	'	$429	'	'	'	$35	$429	$62

SCHEDULE_I_Comprehensive_Incom

SCHEDULE I - Comprehensive Income (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Income	$179,200	$211,400	$173,100	$230,000	$176,600	$209,500	$46,200	$100,800	$793,689	$533,077	$400,513
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'	'	'	'	'	'	'	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	'	'	'	'	'	'	'	'	2,049	1,971	-14,177
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	'	'	'	'	'	'	'	'	-940	217	506
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	'	'	'	'	'	'	'	'	25,714	-4,356	-13,645
Other Comprehensive Income (Loss), Net of Tax	'	'	'	'	'	'	'	'	26,823	-2,168	-27,316
Comprehensive Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	7,682	7,132	5,820
Comprehensive Income	'	'	'	'	'	'	'	'	812,830	523,777	367,377
NSTAR Electric Company [Member]	'	'	'	'	'	'	'	'	'	'	'
Net Income	55,400	107,000	58,000	48,100	34,000	106,800	45,500	3,900	268,546	190,242	252,494
Nu Parent [Member]	'	'	'	'	'	'	'	'	'	'	'
Net Income	'	'	'	'	'	'	'	'	786,007	526,048	394,955
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'	'	'	'	'	'	'	'	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	'	'	'	'	'	'	'	'	2,049	1,971	-14,177
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	'	'	'	'	'	'	'	'	-940	217	506
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	'	'	'	'	'	'	'	'	25,714	-4,356	-13,645
Other Comprehensive Income (Loss), Net of Tax	'	'	'	'	'	'	'	'	26,823	-2,168	-27,316
Comprehensive Income Attributable to Noncontrolling Interests	'	'	'	'	'	'	'	'	0	-103	-262
Comprehensive Income	'	'	'	'	'	'	'	'	$812,830	$523,777	$367,377

SCHEDULE_II_VALUATION_AND_QUAL

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Valuation Allowances and Reserves, Beginning Balance	$165,549,000	$115,689,000	$119,190,000
Valuation Allowances and Reserves, Charged to Cost and Expense	55,465,000	36,275,000	16,420,000
Valuation Allowances and Reserves, Charged to Other Accounts	37,744,000	34,761,000	40,663,000
Valuation Allowances and Reserves, Deductions	87,507,000	80,462,000	60,584,000
Valuation Allowances and Reserves, Ending Balance	171,251,000	165,549,000	115,689,000
Uncollectible Hardship Accounts Receivable Reserves	'	68,600,000	'
Impact Related To Nstar Merger	0	59,286,000	'
The Connecticut Light And Power Company [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Valuation Allowances and Reserves, Beginning Balance	77,571,000	83,475,000	82,173,000
Valuation Allowances and Reserves, Charged to Cost and Expense	3,947,000	2,080,000	3,215,000
Valuation Allowances and Reserves, Charged to Other Accounts	27,258,000	27,084,000	33,911,000
Valuation Allowances and Reserves, Deductions	26,781,000	35,068,000	35,824,000
Valuation Allowances and Reserves, Ending Balance	81,995,000	77,571,000	83,475,000
NSTAR Electric Company [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Valuation Allowances and Reserves, Beginning Balance	44,115,000	27,118,000	29,033,000
Valuation Allowances and Reserves, Charged to Cost and Expense	28,108,000	40,301,000	22,582,000
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
Valuation Allowances and Reserves, Deductions	30,544,000	23,304,000	24,497,000
Valuation Allowances and Reserves, Ending Balance	41,679,000	44,115,000	27,118,000
Public Service Company Of New Hampshire [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Valuation Allowances and Reserves, Beginning Balance	6,760,000	7,190,000	6,824,000
Valuation Allowances and Reserves, Charged to Cost and Expense	6,608,000	6,457,000	7,035,000
Valuation Allowances and Reserves, Charged to Other Accounts	779,000	2,481,000	1,334,000
Valuation Allowances and Reserves, Deductions	6,783,000	9,368,000	8,003,000
Valuation Allowances and Reserves, Ending Balance	7,364,000	6,760,000	7,190,000
Western Massachusetts Electric Company [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Valuation Allowances and Reserves, Beginning Balance	8,501,000	10,018,000	12,891,000
Valuation Allowances and Reserves, Charged to Cost and Expense	2,580,000	2,294,000	3,133,000
Valuation Allowances and Reserves, Charged to Other Accounts	4,299,000	2,428,000	1,141,000
Valuation Allowances and Reserves, Deductions	5,396,000	6,239,000	7,147,000
Valuation Allowances and Reserves, Ending Balance	9,984,000	8,501,000	10,018,000
Uncollectible Hardship Accounts Receivable Reserves	'	5,400,000	'
Yankee Gas Services Company [Member]	'	'	'
Valuation and Qualifying Accounts Disclosure [Line Items]	'	'	'
Uncollectible Hardship Accounts Receivable Reserves	'	$6,800,000	'