Western Massachusetts Electric 10-Q 2 May 14 2014 FY Quarterly report Financial data

DOCUMENT_AND_ENTITY_INFORMATIO

DOCUMENT AND ENTITY INFORMATION (USD $)	3 Months Ended
	Mar. 31, 2014	Apr. 30, 2014
Document And Entity [Line Items]	'	'
Entity Registrant Name	'NORTHEAST UTILITIES	'
Document Period End Date	31-Mar-14	'
Document Type	'10-Q	'
Entity Central Index Key	'0000072741	'
Current Fiscal Year End Date	'--12-31	'
Entity Common Stock, Shares Outstanding	'	315,985,270
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	'2014	'
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 $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current Assets:	'	'
Cash	$89,150	$43,364
Receivables, Net	980,033	765,391
Unbilled Revenues	202,867	224,982
Fuel, Materials and Supplies	228,192	303,233
Regulatory Assets Current	573,028	535,791
Prepayments and Other Current Assets	292,539	214,288
Total Current Assets	2,365,809	2,087,049
Property, Plant and Equipment, Net	17,713,027	17,576,186
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	3,486,645	3,758,694
Goodwill	3,519,401	3,519,401
Marketable Securities	507,931	488,515
Other Long-Term Assets	504,057	365,692
Total Deferred Debits and Other Assets	8,018,034	8,132,302
Total Assets	28,096,870	27,795,537
Current Liabilities:	'	'
Notes Payable to Banks	571,147	1,093,000
Long-Term Debt - Current Portion	530,533	533,346
Accounts Payable - Current	711,594	742,251
Regulatory Liability Current	263,754	204,278
Other Liabilities - Current	713,116	702,776
Total Current Liabilities	2,790,144	3,275,651
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	4,209,969	4,029,026
Regulatory Liabilities Long-Term	591,468	502,984
Long-Term Derivative Liabilities	546,387	624,050
Accrued Pension, PBOP and SERP	890,019	896,844
Other Long-Term Liabilities	871,050	923,053
Total Deferred Credits and Other Liabilities	7,108,893	6,975,957
Capitalization:	'	'
Long-Term Debt	8,318,332	7,776,833
Noncontrolling Interest in Consolidated Subsidiary:	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:	'	'
Common Stock	1,666,580	1,665,351
Capital Surplus, Paid In	6,185,027	6,192,765
Retained Earnings	2,237,710	2,125,980
Accumulated Other Comprehensive Loss	-44,321	-46,031
Treasury Stock	-321,063	-326,537
Common Shareholders' Equity	9,723,933	9,611,528
Total Capitalization	18,197,833	17,543,929
Total Liabilities and Capitalization	28,096,870	27,795,537
The Connecticut Light And Power Company [Member]	'	'
Current Assets:	'	'
Cash	15,675	7,237
Receivables, Net	386,876	319,670
Accounts Receivable from Affiliated Companies	14,721	13,777
Unbilled Revenues	98,095	92,401
Regulatory Assets Current	175,926	150,943
Materials and Supplies	51,376	54,606
Prepayments and Other Current Assets	73,602	53,082
Total Current Assets	816,271	691,716
Property, Plant and Equipment, Net	6,506,245	6,451,259
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	1,580,609	1,663,147
Other Long-Term Assets	170,814	174,380
Total Deferred Debits and Other Assets	1,751,423	1,837,527
Total Assets	9,073,939	8,980,502
Current Liabilities:	'	'
Notes Payable To Affiliated Companies	351,600	287,300
Long-Term Debt - Current Portion	150,000	150,000
Accounts Payable - Current	186,792	201,047
Accounts Payable to Affiliated Companies	52,760	56,531
Obligations to Third Party Suppliers	76,236	73,914
Regulatory Liability Current	107,284	93,961
Derivative Liabilities - Current	92,040	92,233
Other Liabilities - Current	154,312	134,716
Total Current Liabilities	1,171,024	1,089,702
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	1,579,498	1,510,586
Regulatory Liabilities Long-Term	90,053	93,757
Long-Term Derivative Liabilities	539,444	617,072
Accrued Pension, PBOP and SERP	94,820	95,895
Other Long-Term Liabilities	152,920	163,588
Total Deferred Credits and Other Liabilities	2,456,735	2,480,898
Capitalization:	'	'
Long-Term Debt	2,591,405	2,591,208
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	1,682,900	1,682,047
Retained Earnings	996,591	961,482
Accumulated Other Comprehensive Loss	-1,268	-1,387
Common Shareholders' Equity	2,738,575	2,702,494
Total Capitalization	5,446,180	5,409,902
Total Liabilities and Capitalization	9,073,939	8,980,502
NSTAR Electric Company [Member]	'	'
Current Assets:	'	'
Cash	42,035	8,021
Receivables, Net	231,082	209,711
Accounts Receivable from Affiliated Companies	123,953	27,264
Unbilled Revenues	28,249	41,368
Fuel, Materials and Supplies	47,843	44,236
Regulatory Assets Current	222,598	204,144
Prepayments and Other Current Assets	5,686	36,710
Total Current Assets	701,446	571,454
Property, Plant and Equipment, Net	5,069,203	5,043,887
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	1,041,925	1,235,156
Other Long-Term Assets	65,983	60,624
Total Deferred Debits and Other Assets	1,107,908	1,295,780
Total Assets	6,878,557	6,911,121
Current Liabilities:	'	'
Notes Payable to Banks	0	103,500
Long-Term Debt - Current Portion	301,650	301,650
Accounts Payable - Current	264,834	207,559
Accounts Payable to Affiliated Companies	42,879	75,707
Deferred Tax Liabilities Current	55,763	50,128
Regulatory Liability Current	73,596	53,958
Other Liabilities - Current	140,146	118,410
Total Current Liabilities	878,868	910,912
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	1,400,532	1,466,835
Regulatory Liabilities Long-Term	257,101	253,108
Accrued Pension, PBOP and SERP	150,938	118,010
Other Long-Term Liabilities	132,679	142,214
DueToRelatedPartiesNoncurrent	0	64,172
Total Deferred Credits and Other Liabilities	1,941,250	2,044,339
Capitalization:	'	'
Long-Term Debt	1,797,389	1,499,417
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	1,225,425	1,420,828
Common Shareholders' Equity	2,218,050	2,413,453
Total Capitalization	4,058,439	3,955,870
Total Liabilities and Capitalization	6,878,557	6,911,121
Public Service Company Of New Hampshire [Member]	'	'
Current Assets:	'	'
Cash	4,284	130
Receivables, Net	88,143	76,331
Accounts Receivable from Affiliated Companies	479	90
Unbilled Revenues	38,327	38,344
Taxes Receivable	20,968	2,180
Fuel, Materials and Supplies	94,410	128,736
Regulatory Assets Current	83,832	92,194
Prepayments and Other Current Assets	7,270	21,920
Total Current Assets	337,713	359,925
Property, Plant and Equipment, Net	2,486,440	2,467,556
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	210,702	219,346
Other Long-Term Assets	40,621	39,891
Total Deferred Debits and Other Assets	251,323	259,237
Total Assets	3,075,476	3,086,718
Current Liabilities:	'	'
Notes Payable To Affiliated Companies	39,900	86,500
Long-Term Debt - Current Portion	50,000	50,000
Accounts Payable - Current	59,847	82,920
Accounts Payable to Affiliated Companies	28,009	22,040
Deferred Tax Liabilities Current	22,811	28,596
Regulatory Liability Current	27,333	20,643
Other Liabilities - Current	46,880	51,729
Total Current Liabilities	274,780	342,428
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	539,255	500,166
Regulatory Liabilities Long-Term	51,769	51,723
Accrued Pension, PBOP and SERP	15,321	15,272
Other Long-Term Liabilities	46,559	46,247
Total Deferred Credits and Other Liabilities	652,904	613,408
Capitalization:	'	'
Long-Term Debt	999,081	999,006
Common Shareholders' Equity:	'	'
Common Stock	0	0
Capital Surplus, Paid In	702,304	701,911
Retained Earnings	454,653	438,515
Accumulated Other Comprehensive Loss	-8,246	-8,550
Common Shareholders' Equity	1,148,711	1,131,876
Total Capitalization	2,147,792	2,130,882
Total Liabilities and Capitalization	3,075,476	3,086,718
Western Massachusetts Electric Company [Member]	'	'
Current Assets:	'	'
Cash	4,227	0
Receivables, Net	54,844	49,018
Accounts Receivable from Affiliated Companies	5,996	47,607
Unbilled Revenues	16,531	16,562
Taxes Receivable	12,845	432
Regulatory Assets Current	49,578	43,024
Marketable Securities - Current	19,194	26,628
Prepayments and Other Current Assets	9,663	10,479
Total Current Assets	172,878	193,750
Property, Plant and Equipment, Net	1,398,810	1,381,060
Deferred Debits and Other Assets:	'	'
Regulatory Assets Long Term	132,181	146,088
Marketable Securities	38,710	31,243
Other Long-Term Assets	40,956	40,679
Total Deferred Debits and Other Assets	211,847	218,010
Total Assets	1,783,535	1,792,820
Current Liabilities:	'	'
Notes Payable To Affiliated Companies	37,400	0
Accounts Payable - Current	38,407	62,961
Accounts Payable to Affiliated Companies	18,154	9,230
Accrued Interest	2,837	7,525
Deferred Tax Liabilities Current	15,361	13,098
Regulatory Liability Current	21,816	19,858
Other Liabilities - Current	15,563	20,629
CounterPartyDeposit	3,188	7,688
Total Current Liabilities	152,726	140,989
Deferred Credits and Other Liabilities:	'	'
Accumulated Deferred Income Taxes	409,493	396,933
Regulatory Liabilities Long-Term	10,445	13,873
Accrued Pension, PBOP and SERP	3,850	3,911
Other Long-Term Liabilities	29,411	28,619
Total Deferred Credits and Other Liabilities	453,199	443,336
Capitalization:	'	'
Long-Term Debt	629,162	629,389
Common Shareholders' Equity:	'	'
Common Stock	10,866	10,866
Capital Surplus, Paid In	390,895	390,743
Retained Earnings	150,117	181,014
Accumulated Other Comprehensive Loss	-3,430	-3,517
Common Shareholders' Equity	548,448	579,106
Total Capitalization	1,177,610	1,208,495
Total Liabilities and Capitalization	$1,783,535	$1,792,820

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Operating Revenues	$2,290,590	$1,995,023
Operating Expenses:	'	'
Purchased Power and Transmission	978,150	747,809
Operations and Maintenance	351,688	346,092
Depreciation	150,807	154,977
Amortization of Regulatory Assets/(Liabilities), Net	57,898	54,049
Amortization of Rate Reduction Bonds	0	34,499
Energy Efficiency Programs	138,825	105,771
Taxes Other Than Income Taxes	145,533	132,881
Total Operating Expenses	1,822,901	1,576,078
Operating Income	467,689	418,945
Interest Expense:	'	'
Interest on Long-Term Debt	87,377	85,906
Other Interest	2,598	-9,651
Total Interest Expense	89,975	76,255
Other Income/(Loss), Net	1,667	7,765
Income Before Income Tax Expense	379,381	350,455
Income Tax Expense	141,545	120,487
Net Income	237,836	229,968
Net Income Attributable to Noncontrolling Interests	1,879	1,879
Net Income Attributable to Controlling Interests	235,957	228,089
Diluted Earnings Per Common Share	$0.74	$0.72
Basic Earnings Per Common Share	$0.75	$0.72
Common Stock Dividends Per Share Declared	$0.39	$0.37
Weighted Average Common Shares Outstanding:	'	'
Basic	315,534,512	315,129,782
Diluted	316,892,119	316,002,538
The Connecticut Light And Power Company [Member]	'	'
Operating Revenues	734,614	624,097
Operating Expenses:	'	'
Purchased Power and Transmission	281,381	229,259
Operations and Maintenance	109,514	108,895
Depreciation	46,130	42,448
Amortization of Regulatory Assets/(Liabilities), Net	29,931	10,787
Energy Efficiency Programs	42,694	22,813
Taxes Other Than Income Taxes	66,953	60,192
Total Operating Expenses	576,603	474,394
Operating Income	158,011	149,703
Interest Expense:	'	'
Interest on Long-Term Debt	32,908	32,635
Other Interest	1,335	-2,941
Total Interest Expense	34,243	29,694
Other Income/(Loss), Net	1,072	4,187
Income Before Income Tax Expense	124,840	124,196
Income Tax Expense	45,541	39,188
Net Income	79,299	85,008
NSTAR Electric Company [Member]	'	'
Operating Revenues	666,188	592,257
Operating Expenses:	'	'
Purchased Power and Transmission	319,082	214,053
Operations and Maintenance	85,924	92,301
Depreciation	46,626	45,441
Amortization of Regulatory Assets/(Liabilities), Net	15,664	46,994
Amortization of Rate Reduction Bonds	0	15,054
Energy Efficiency Programs	48,329	51,703
Taxes Other Than Income Taxes	32,151	32,174
Total Operating Expenses	547,776	497,720
Operating Income	118,412	94,537
Interest Expense:	'	'
Interest on Long-Term Debt	20,756	19,991
Other Interest	304	-4,068
Total Interest Expense	21,060	15,923
Other Income/(Loss), Net	-31	773
Income Before Income Tax Expense	97,321	79,387
Income Tax Expense	39,234	31,265
Net Income	58,087	48,122
Public Service Company Of New Hampshire [Member]	'	'
Operating Revenues	299,833	273,829
Operating Expenses:	'	'
Purchased Power and Transmission	115,246	101,024
Operations and Maintenance	62,212	59,729
Depreciation	24,215	22,568
Amortization of Regulatory Assets/(Liabilities), Net	12,562	-3,051
Amortization of Rate Reduction Bonds	0	14,756
Energy Efficiency Programs	3,839	3,669
Taxes Other Than Income Taxes	17,715	17,016
Total Operating Expenses	235,789	215,711
Operating Income	64,044	58,118
Interest Expense:	'	'
Interest on Long-Term Debt	11,526	11,881
Other Interest	445	287
Total Interest Expense	11,971	12,168
Other Income/(Loss), Net	265	1,030
Income Before Income Tax Expense	52,338	46,980
Income Tax Expense	19,700	17,984
Net Income	32,638	28,996
Western Massachusetts Electric Company [Member]	'	'
Operating Revenues	137,409	124,953
Operating Expenses:	'	'
Purchased Power and Transmission	49,431	40,044
Operations and Maintenance	22,579	20,928
Depreciation	10,321	8,970
Amortization of Regulatory Assets/(Liabilities), Net	399	129
Amortization of Rate Reduction Bonds	0	4,689
Energy Efficiency Programs	11,865	8,315
Taxes Other Than Income Taxes	8,082	6,288
Total Operating Expenses	102,677	89,363
Operating Income	34,732	35,590
Interest Expense:	'	'
Interest on Long-Term Debt	6,062	6,082
Other Interest	-416	211
Total Interest Expense	5,646	6,293
Other Income/(Loss), Net	574	1,004
Income Before Income Tax Expense	29,660	30,301
Income Tax Expense	11,558	11,698
Net Income	$18,102	$18,603

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net Income	$237,836	$229,968
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	509	516
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	240	-181
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	961	1,621
Other Comprehensive Income (Loss), Net of Tax, Total	1,710	1,956
Comprehensive Income Attributable to Noncontrolling Interests	-1,879	-1,879
Comprehensive Income	237,667	230,045
The Connecticut Light And Power Company [Member]	'	'
Net Income	79,299	85,008
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111	111
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	8	-6
Other Comprehensive Income (Loss), Net of Tax, Total	119	105
Comprehensive Income	79,418	85,113
NSTAR Electric Company [Member]	'	'
Net Income	58,087	48,122
Public Service Company Of New Hampshire [Member]	'	'
Net Income	32,638	28,996
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	290	291
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	14	-11
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	-3
Other Comprehensive Income (Loss), Net of Tax, Total	304	277
Comprehensive Income	32,942	29,273
Western Massachusetts Electric Company [Member]	'	'
Net Income	18,102	18,603
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	85	85
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	2	-2
Other Comprehensive Income (Loss), Net of Tax, Total	87	83
Comprehensive Income	$18,189	$18,686

CONSOLIDATED_STATEMENT_OF_CASH

CONSOLIDATED STATEMENT OF CASH FLOWS (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Operating Activities:	'	'
Net Income	$237,836	$229,968
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'
Depreciation	150,807	154,977
Deferred Income Tax Expense (Benefit)	137,417	168,938
Pension and PBOP Expense, Net of PBOP Contributions	24,995	53,102
Pension and Other Postretirement Benefit Contributions	-6,622	-47,048
Regulatory (Underrecoveries)/Overrecoveries, Net	872	39,218
Amortization of Regulatory Assets/(Liabilities), Net	57,898	54,049
Amortization of Rate Reduction Bonds	0	34,499
Other Noncash Income (Expense)	-7,574	-51,106
Proceeds from DOE Damages Claim	163,300	77,936
CYAPC and YAEC Deferred DOE Proceeds	-163,300	'
Changes in Current Assets and Liabilities:	'	'
Receivables and Unbilled Revenues, Net	-182,221	-129,431
Inventory	75,041	28,487
Taxes Receivable/(Accrued)	-59,840	-21,295
Change in Accounts Payable	53,905	-86,916
Other Current Assets and Liabilities	11,282	-32,235
Net Cash Flows Provided by Operating Activities	493,796	473,143
Investing Activities:	'	'
Investments in Property, Plant and Equipment	-348,691	-388,950
Proceeds from Sales of Marketable Securities	128,505	98,070
Purchases of Marketable Securities	-132,605	-184,030
Other Investing Activities	1,637	27,997
Net Cash Flows Used in Investing Activities	-351,154	-446,913
Financing Activities:	'	'
Cash Dividends on Common Stock	-118,460	-116,431
Cash Dividends on Preferred Stock	-1,879	-1,879
Increase/(Decrease) in Short-Term Debt	-299,500	-228,000
Issuance of Long-Term Debt	400,000	400,000
Retirements of Long-Term Debt	-75,000	0
Retirements of Rate Reduction Bonds	0	-62,529
Other Financing Activities	-2,017	-2,322
Net Cash Flows Provided by/(Used in) Financing Activities	-96,856	-11,161
Net Increase/(Decrease) in Cash	45,786	15,069
Cash - Beginning of Year	43,364	45,748
Cash - End of Year	89,150	60,817
The Connecticut Light And Power Company [Member]	'	'
Operating Activities:	'	'
Net Income	79,299	85,008
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'
Depreciation	46,130	42,448
Deferred Income Tax Expense (Benefit)	59,334	65,475
Pension and PBOP Expense, Net of PBOP Contributions	4,086	8,183
Regulatory (Underrecoveries)/Overrecoveries, Net	-40,399	-15,835
Amortization of Regulatory Assets/(Liabilities), Net	29,931	10,787
Other Noncash Income (Expense)	4,536	3,653
Changes in Current Assets and Liabilities:	'	'
Receivables and Unbilled Revenues, Net	-82,833	-32,041
Taxes Receivable/(Accrued)	7,015	-12,777
Change in Accounts Payable	-2,872	-106,140
Other Current Assets and Liabilities	-8,730	-22,340
Net Cash Flows Provided by Operating Activities	95,497	26,421
Investing Activities:	'	'
Investments in Property, Plant and Equipment	-107,993	-89,360
Other Investing Activities	1,027	447
Net Cash Flows Used in Investing Activities	-106,966	-88,913
Financing Activities:	'	'
Cash Dividends on Common Stock	-42,800	-38,000
Cash Dividends on Preferred Stock	-1,390	-1,390
Increase/(Decrease) in Short-Term Debt	0	-89,000
Issuance of Long-Term Debt	0	400,000
Increase/(Decrease) in Notes Payable to Affiliate	64,300	-194,700
Other Financing Activities	-203	-6,112
Net Cash Flows Provided by/(Used in) Financing Activities	19,907	70,798
Net Increase/(Decrease) in Cash	8,438	8,306
Cash - Beginning of Year	7,237	1
Cash - End of Year	15,675	8,307
NSTAR Electric Company [Member]	'	'
Operating Activities:	'	'
Net Income	58,087	48,122
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'
Bad Debt Expense	6,096	5,523
Depreciation	46,626	45,441
Deferred Income Tax Expense (Benefit)	1,585	26,571
Pension and PBOP Expense, Net of PBOP Contributions	-4,908	6,420
Regulatory (Underrecoveries)/Overrecoveries, Net	6,423	-2,951
Amortization of Regulatory Assets/(Liabilities), Net	15,664	46,994
Amortization of Rate Reduction Bonds	0	15,054
Other Noncash Income (Expense)	-15,538	-23,969
Changes in Current Assets and Liabilities:	'	'
Receivables and Unbilled Revenues, Net	-14,348	-31,455
Inventory	-3,606	-7,060
Taxes Receivable/(Accrued)	21,504	-22,501
Change in Accounts Payable	86,309	1,867
Other Current Assets and Liabilities	31,112	18,916
IncreaseDecreaseInAccountsPayableRelatedParties	-43,654	-37,547
Net Cash Flows Provided by Operating Activities	191,352	89,425
Investing Activities:	'	'
Investments in Property, Plant and Equipment	-94,957	-107,573
DecreaseInRestrictedCash	-530	33,631
Other Investing Activities	41	-86
Net Cash Flows Used in Investing Activities	-95,446	-74,028
Financing Activities:	'	'
Cash Dividends on Common Stock	-253,000	0
Cash Dividends on Preferred Stock	-490	-490
Increase/(Decrease) in Short-Term Debt	-103,500	32,000
Issuance of Long-Term Debt	300,000	0
Retirements of Rate Reduction Bonds	0	-43,493
Other Financing Activities	-4,902	0
Net Cash Flows Provided by/(Used in) Financing Activities	-61,892	-11,983
Net Increase/(Decrease) in Cash	34,014	3,414
Cash - Beginning of Year	8,021	13,695
Cash - End of Year	42,035	17,109
Public Service Company Of New Hampshire [Member]	'	'
Operating Activities:	'	'
Net Income	32,638	28,996
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'
Depreciation	24,215	22,568
Deferred Income Tax Expense (Benefit)	33,667	10,143
Pension and PBOP Expense, Net of PBOP Contributions	1,961	8,022
Pension and Other Postretirement Benefit Contributions	-30	-35,146
Regulatory (Underrecoveries)/Overrecoveries, Net	6,827	-799
Amortization of Regulatory Assets/(Liabilities), Net	12,562	-3,051
Amortization of Rate Reduction Bonds	0	14,756
Other Noncash Income (Expense)	2,729	-1,505
Changes in Current Assets and Liabilities:	'	'
Receivables and Unbilled Revenues, Net	-14,268	-13,889
Inventory	34,326	562
Taxes Receivable/(Accrued)	-30,254	23,137
Change in Accounts Payable	3,403	31,257
Other Current Assets and Liabilities	21,505	22,152
Net Cash Flows Provided by Operating Activities	129,281	107,203
Investing Activities:	'	'
Investments in Property, Plant and Equipment	-61,864	-64,956
Other Investing Activities	-76	-17
Net Cash Flows Used in Investing Activities	-61,940	-64,973
Financing Activities:	'	'
Cash Dividends on Common Stock	-16,500	-17,000
Increase/(Decrease) in Short-Term Debt	-46,600	-9,900
Retirements of Rate Reduction Bonds	0	-14,320
Other Financing Activities	-87	-127
Net Cash Flows Provided by/(Used in) Financing Activities	-63,187	-41,347
Net Increase/(Decrease) in Cash	4,154	883
Cash - Beginning of Year	130	2,493
Cash - End of Year	4,284	3,376
Western Massachusetts Electric Company [Member]	'	'
Operating Activities:	'	'
Net Income	18,102	18,603
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:	'	'
Depreciation	10,321	8,970
Deferred Income Tax Expense (Benefit)	14,688	16,828
Regulatory (Underrecoveries)/Overrecoveries, Net	5,780	-2,357
Amortization of Regulatory Assets/(Liabilities), Net	399	129
Amortization of Rate Reduction Bonds	0	4,689
Other Noncash Income (Expense)	-1,351	-1,299
Changes in Current Assets and Liabilities:	'	'
Receivables and Unbilled Revenues, Net	34,905	-4,907
Taxes Receivable/(Accrued)	-17,126	21,600
Change in Accounts Payable	-10,516	17,667
Other Current Assets and Liabilities	-8,869	-8,931
Net Cash Flows Provided by Operating Activities	46,333	70,992
Investing Activities:	'	'
Investments in Property, Plant and Equipment	-30,347	-66,340
Proceeds from Sales of Marketable Securities	34,656	21,035
Purchases of Marketable Securities	-34,804	-21,191
Other Investing Activities	0	500
Net Cash Flows Used in Investing Activities	-30,495	-65,996
Financing Activities:	'	'
Cash Dividends on Common Stock	-49,000	-10,000
Increase/(Decrease) in Notes Payable to Affiliate	37,400	11,500
Retirements of Rate Reduction Bonds	0	-4,716
Other Financing Activities	-11	-13
Net Cash Flows Provided by/(Used in) Financing Activities	-11,611	-3,229
Net Increase/(Decrease) in Cash	4,227	1,767
Cash - Beginning of Year	0	1
Cash - End of Year	$4,227	$1,768

SUMMARY_OF_SIGNIFICANT_ACCOUNT

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2014
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 CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (Unaudited)
	Refer to the Glossary of Terms included in this combined Quarterly Report on Form 10-Q for abbreviations and acronyms used throughout the combined notes to the unaudited condensed consolidated financial statements.
	1.       SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	A.       Basis of Presentation
	NU is a public utility holding company primarily engaged through its wholly owned regulated utility subsidiaries in the energy delivery business. 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.
	The unaudited condensed 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 unaudited condensed consolidated financial statements of NU, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements."
	The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the entirety of this combined Quarterly Report on Form 10-Q and the 2013 combined Annual Report on Form 10-K of NU, CL&P, NSTAR Electric, PSNH and WMECO, which was filed with the SEC. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly NU's, CL&P's, NSTAR Electric's, PSNH's and WMECO's financial position as of March 31, 2014 and December 31, 2013, and the results of operations, comprehensive income and cash flows for the three months ended March 31, 2014 and 2013. The results of operations, comprehensive income and cash flows for the three months ended March 31, 2014 and 2013 are not necessarily indicative of the results expected for a full year. The demand for electricity and natural gas is affected by weather conditions, economic conditions, and consumer conservation (including company-sponsored energy efficiency programs). Electric energy sales and revenues are typically higher in the winter and summer months than in the spring and fall months. Natural gas sales and revenues are typically higher in the winter months than during other periods of the year.
	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.
	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 2, "Regulatory Accounting," for further information.
	Certain reclassifications of prior period data were made in the accompanying balance sheets for NU, CL&P and PSNH, statements of income for NU, NSTAR Electric, PSNH and WMECO, and statements of cash flows for CL&P, NSTAR Electric and WMECO. These reclassifications were made to conform to the current period's presentation.
	B.       Recently Adopted Accounting Standards
	On January 1, 2014, as required, NU prospectively adopted the Financial Accounting Standards Board's (FASB) final Accounting Standards Updates (ASU) that required presentation of certain unrecognized tax benefits as reductions to deferred tax assets. Implementation of this guidance had an immaterial impact on the balance sheets and no impact on the results of operations or cash flows of NU, CL&P, NSTAR Electric, PSNH and WMECO.
	C.       Provision for Uncollectible Accounts
	NU, including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at estimated net realizable value by maintaining a provision for uncollectible accounts. This provision is determined based upon a variety of factors, including the application of an estimated uncollectible percentage to each receivable aging category. The estimate is based upon historical collection and write-off experience and management's assessment of collectibility from individual customers. Management continuously assesses the collectibility of receivables, and adjusts collectibility estimates based on actual experience. Receivable balances are written off against the provision for uncollectible accounts when the accounts are terminated and these balances are deemed to be uncollectible. The provision for uncollectible accounts, which is included in Receivables, Net on the balance sheets, was as follows:
	(Millions of Dollars)			As of March 31, 2014			As of December 31, 2013
	NU			$	180		$	171.3
	CL&P				83.4			82
	NSTAR Electric				43.1			41.7
	PSNH				7.8			7.4
	WMECO				10.6			10
	D.       Fair Value Measurements
	Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases or normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to 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 4, "Derivative Instruments," Note 5, "Marketable Securities," and Note 9, "Fair Value of Financial Instruments," to the financial statements.
	E.       Other Income, Net
	Items included within Other Income, Net on the statements of income primarily consist of investment income/(loss), interest income, AFUDC related to equity funds, and equity in earnings. Investment income/(loss) primarily relates to debt and equity securities held in trust. For further information, see Note 5, "Marketable Securities," to the financial statements. For CL&P, NSTAR Electric, PSNH and WMECO, equity in earnings relate to investments in CYAPC, YAEC and MYAPC as well as NSTAR Electric's investment in two regional transmission companies, which are all accounted for on the equity method. On an NU consolidated basis, equity in earnings relate to the investment in MYAPC and NU's investment in two regional transmission companies.
	F.       Other Taxes
	Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respective customers. These gross receipts taxes are shown on a gross basis with collections in Operating Revenues and payments in Taxes Other Than Income Taxes on the statements of income as follows:
		For the Three Months Ended
	(Millions of Dollars)	31-Mar-14			31-Mar-13
	NU	$	44.4		$	38.4
	CL&P		35.6			32
	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.
	G.			Supplemental Cash Flow Information
	Non-cash investing activities include plant additions included in Accounts Payable as follows:
	(Millions of Dollars)				As of March 31, 2014			As of March 31, 2013
	NU				$	108.5		$	98.7
	CL&P					36.2			28.2
	NSTAR Electric					28			30.7
	PSNH					14.4			12.9
	WMECO					14.4			15.8
	H.       Severance Benefits
	In the first quarter of 2014, NU recorded severance benefit expenses of $4.3 million associated with the partial outsourcing of information technology functions and ongoing post-merger integration. As of March 31, 2014 and December 31, 2013, the severance accrual totaled $17.7 million and $14.7 million, respectively, and was included in Other Current Liabilities on the balance sheets.
	I.       Restricted Cash
	On March 28, 2014, CYAPC and YAEC received payment of $163.3 million of the DOE Phase II Damages proceeds. It is anticipated that in the second quarter of 2014, the Yankee Companies will complete the FERC review process and return these amounts to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, for the benefit of their respective customers. As a result of the consolidation of CYAPC and YAEC, the cash received is included in Other Long-Term Assets on the NU consolidated balance sheet pending refund. For further information, see Note 8B, “Commitments and Contingencies - Contractual Obligations - Yankee Companies.”

REGULATORY_ACCOUNTING

REGULATORY ACCOUNTING	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Public Utilities Disclosure [Text Block]	'
	2.       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 follow 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:
		As of March 31, 2014			As of December 31, 2013
	(Millions of Dollars)	NU			NU
	Benefit Costs	$	1,205.40		$	1,240.20
	Derivative Liabilities		564.9			638
	Income Taxes, Net		629.2			626.2
	Storm Restoration Costs		580.9			589.6
	Goodwill		520.8			525.9
	Regulatory Tracker Mechanisms		347.4			323.4
	Buy Out Agreements for Power Contracts		63.4			70.2
	Other Regulatory Assets		147.6			281
	Total Regulatory Assets		4,059.60			4,294.50
	Less: Current Portion		573			535.8
	Total Long-Term Regulatory Assets	$	3,486.60		$	3,758.70
			As of March 31, 2014									As of December 31, 2013
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Benefit Costs		$	287.1		$	321.3	$	96.7	$	55.1	$	297.7	$	496.7	$	100.6	$	57.3
	Derivative Liabilities			557			7.9		-		-		630.4		7.7		-		-
	Income Taxes, Net			419.7			82.5		39.4		43.5		415.5		84		40.3		43.7
	Storm Restoration Costs			395.3			109.2		40.3		36.1		397.8		109.3		43.7		38.8
	Goodwill			-			447.1		-		-		-		451.5		-		-
	Regulatory Tracker Mechanisms			33.3			182.7		75.2		31.6		8		169.5		83.3		32.6
	Buy Out Agreements for Power Contracts			-			58.3		5.1		-		-		64.7		5.5		-
	Other Regulatory Assets			64.1			55.5		37.8		15.5		64.6		55.9		38.1		16.7
	Total Regulatory Assets			1,756.50			1,264.50		294.5		181.8		1,814.00		1,439.30		311.5		189.1
	Less: Current Portion			175.9			222.6		83.8		49.6		150.9		204.1		92.2		43
	Total Long-Term Regulatory Assets		$	1,580.60		$	1,041.90	$	210.7	$	132.2	$	1,663.10	$	1,235.20	$	219.3	$	146.1
	Benefit Costs: For information related to the Regulated companies' pension and other postretirement benefits, see Note 7, "Pension Benefits and Postretirement Benefits Other Than Pensions."
	Storm Restoration Costs: From 2011 to 2013, CL&P, NSTAR Electric, PSNH and WMECO experienced several significant storm events. As a result of these storm events, each company suffered extensive damage to its distribution and transmission systems resulting in customer outages. Each company incurred significant costs to repair damage and restore customer service. The storm restoration cost regulatory asset balance at CL&P, NSTAR Electric, PSNH and WMECO reflects incremental 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 that recovery from customers is probable through the applicable regulatory recovery process.
	On March 12, 2014, the PURA issued a final decision on CL&P's request to recover storm restoration costs associated with five major storms, which occurred in 2011 and 2012. 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 recovered through depreciation expense in future rate proceedings. CL&P will recover the $365 million with carrying charges in its distribution rates over a six-year period beginning December 1, 2014. The remaining costs were either disallowed or we believe will be recovered from other sources. These costs did not have a material impact on CL&P's financial position, results of operations or cash flows.
	Regulatory Costs in Other Long-Term Assets: The Regulated companies had $71.7 million ($12.4 million for CL&P, $33.7 million for NSTAR Electric, and $10.2 million for WMECO) and $65.1 million ($7.3 million for CL&P, $33.4 million for NSTAR Electric, and $10.1 million for WMECO) of additional regulatory costs as of March 31, 2014 and December 31, 2013, 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.
	Regulatory Liabilities: The components of regulatory liabilities are as follows:
		As of March 31, 2014			As of December 31, 2013
	(Millions of Dollars)	NU			NU
	Cost of Removal	$	437.3		$	435.1
	Regulatory Tracker Mechanisms		203.6			151.2
	AFUDC - Transmission		67.8			68.1
	Contractual Obligations - Yankee Companies		93.3			-
	Other Regulatory Liabilities		53.3			52.9
	Total Regulatory Liabilities		855.3			707.3
	Less: Current Portion		263.8			204.3
	Total Long-Term Regulatory Liabilities	$	591.5		$	503
			As of March 31, 2014									As of December 31, 2013
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Cost of Removal		$	27.5		$	252.5	$	49.7	$	-	$	29.1	$	250	$	49.7	$	-
	Regulatory Tracker Mechanisms			105.6			43.8		27.5		22.4		95.6		21.9		21.6		21.1
	AFUDC - Transmission			54.5			4		-		9.3		54.7		4.1		-		9.3
	Other Regulatory Liabilities			9.8			30.4		1.9		0.5		8.4		31.1		1		3.4
	Total Regulatory Liabilities			197.4			330.7		79.1		32.2		187.8		307.1		72.3		33.8
	Less: Current Portion			107.3			73.6		27.3		21.8		94		54		20.6		19.9
	Total Long-Term Regulatory Liabilities		$	90.1		$	257.1	$	51.8	$	10.4	$	93.8	$	253.1	$	51.7	$	13.9
	For further information on matters related to the Yankee Companies, see Note 8B, "Commitments and Contingencies - Contractual Obligations - Yankee Companies," to the financial statements.

PROPERTY_PLANT_AND_ACCUMULATED

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Property Plant And Equipment Disclosure [Text Block]	'
	3.       PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION
	The following tables summarize the investments in utility property, plant and equipment by asset category:
				As of March 31, 2014			As of December 31, 2013
	(Millions of Dollars)			NU			NU
	Distribution - Electric			$	12,039.70		$	11,950.20
	Distribution - Natural Gas				2,447.90			2,425.90
	Transmission				6,423.50			6,412.50
	Generation				1,154.70			1,152.30
	Electric and Natural Gas Utility				22,065.80			21,940.90
	Other (1)				510.2			508.7
	Property, Plant and Equipment, Gross				22,576.00			22,449.60
	Less: Accumulated Depreciation
		Electric and Natural Gas Utility			-5,491.70			-5,387.00
		Other			-204.7			-196.2
	Total Accumulated Depreciation				-5,696.40			-5,583.20
	Property, Plant and Equipment, Net				16,879.60			16,866.40
	Construction Work in Progress				833.4			709.8
	Total Property, Plant and Equipment, Net			$	17,713.00		$	17,576.20
	(1)       These assets represent unregulated property and are primarily comprised of building improvements, computer software, hardware and equipment and telecommunications assets at NU's unregulated companies.
		As of March 31, 2014										As of December 31, 2013
					NSTAR									NSTAR
	(Millions of Dollars)	CL&P			Electric			PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Distribution	$	4,979.80		$	4,717.60		$	1,620.30	$	762	$	4,930.70	$	4,694.70	$	1,608.20	$	756.6
	Transmission		3,074.80			1,769.00			701.7		831.7		3,071.90		1,772.30		695.7		826.4
	Generation		-			-			1,133.60		21.1		-		-		1,131.20		21.1
	Property, Plant and
	Equipment, Gross		8,054.60			6,486.60			3,455.60		1,614.80		8,002.60		6,467.00		3,435.10		1,604.10
	Less: Accumulated Depreciation		-1,838.50			-1,664.60			-1,040.60		-278.4		-1,804.10		-1,631.30		-1,021.80		-271.5
	Property, Plant and Equipment, Net		6,216.10			4,822.00			2,415.00		1,336.40		6,198.50		4,835.70		2,413.30		1,332.60
	Construction Work in Progress		290.1			247.2			71.4		62.4		252.8		208.2		54.3		48.5
	Total Property, Plant and
	Equipment, Net	$	6,506.20		$	5,069.20		$	2,486.40	$	1,398.80	$	6,451.30	$	5,043.90	$	2,467.60	$	1,381.10
	As discussed in Note 2, "Regulatory Accounting," during the first quarter of 2014, as a result of a regulatory proceeding, CL&P reclassified approximately $18 million from Regulatory Assets to Property, Plant and Equipment, Net.

DERIVATIVE_INSTRUMENTS

DERIVATIVE INSTRUMENTS	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Derivative Instruments and Hedging Activities Disclosure [Text Block]	'
	4.       DERIVATIVE INSTRUMENTS
	The Regulated companies purchase and procure energy and energy-related products 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 March 31, 2014
			Commodity Supply and						Net Amount Recorded as
	(Millions of Dollars)		Price Risk Management			Netting (1)			Derivative Asset/(Liability)
	Current Derivative Assets:
	Level 2:
		NU (1)	$	1.2		$	-0.1		$	1.1
	Level 3:
		NU (1)		17.8			-9.7			8.1
		CL&P (1)		17			-9.7			7.3
		NSTAR Electric		0.8			-			0.8
	Long-Term Derivative Assets:
	Level 3:
		NU, CL&P (1)	$	98.8		$	-31.7		$	67.1
	Current Derivative Liabilities:
	Level 3:
		NU	$	-93.3		$	-		$	-93.3
		CL&P		-92			-			-92
		NSTAR Electric		-1.3			-			-1.3
	Long-Term Derivative Liabilities:
	Level 2:
		NU	$	-0.2		$	-		$	-0.2
	Level 3:
		NU		-546.2			-			-546.2
		CL&P		-539.4			-			-539.4
		NSTAR Electric		-6.8			-			-6.8
			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:
		NU (1)	$	1.9		$	-0.3		$	1.6
	Level 3:
		NU (1)		18.4			-9.8			8.6
		CL&P (1)		17.1			-9.8			7.3
		NSTAR Electric		1.2			-			1.2
	Long-Term Derivative Assets:
	Level 2:
		NU	$	0.2		$	-		$	0.2
	Level 3:
		NU (1)		116.2			-42.2			74
		CL&P (1)		113.6			-42.2			71.4
	Current Derivative Liabilities:
	Level 3:
		NU	$	-93.7		$	-		$	-93.7
		CL&P		-92.2			-			-92.2
		NSTAR Electric		-1.5			-			-1.5
	Long-Term Derivative Liabilities:
	Level 3:
		NU	$	-624.1		$	-		$	-624.1
		CL&P		-617.1			-			-617.1
		NSTAR Electric		-7			-			-7
	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.
	For further information on the fair value of derivative contracts, see Note 1D, "Summary of Significant Accounting Policies - Fair Value Measurements," to the financial statements.
	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.
	As of March 31, 2014 and December 31, 2013, NU had NYMEX future contracts in order to reduce variability associated with the purchase price of approximately 7.4 million and 9.1 million MMBtu of natural gas, respectively.
	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 Three Months Ended March 31,
(Millions of Dollars)			2014			2013
NU
Balance Sheets:
	Regulatory Assets and Liabilities		$	54.1		$	28
Statements of Income:
	Purchased Power, Fuel and Transmission			-			0.3
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 March 31, 2014 and December 31, 2013, there were no derivative contracts in a net liability position that were subject to credit risk contingent features.
Valuation of Derivative Instruments
Derivative contracts classified as Level 2 in the fair value hierarchy relate to the financial contracts for natural gas futures. Prices are obtained from broker quotes and are based on actual market activity. The contracts are valued using 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 and NSTAR Electric's, Level 3 derivative contracts and the range of the significant unobservable inputs utilized in the valuations over the duration of the contracts:
	As of March 31, 2014									As of December 31, 2013
		Range						Period Covered			Range					Period Covered
Energy Prices:
NU	$	57	-	60	per MWh			2018 - 2020		$	49	-	77	per MWh		2018 - 2029
CL&P	$	57	-	60	per MWh			2018 - 2020		$	56	-	58	per MWh		2018 - 2029
Capacity Prices:
NU	$	1.7	-	10.42		per kW-Month		2016 - 2026		$	5.07	-	11.82		per kW-Month	2017 - 2029
CL&P	$	5.23	-	10.42		per kW-Month		2018 - 2026		$	5.07	-	10.42		per kW-Month	2017 - 2026
NSTAR Electric	$	1.7	-	7.38		per kW-Month		2016 - 2019		$	5.07	-	7.38		per kW-Month	2017 - 2019
Forward Reserve:
NU, CL&P	$	3.3	-	3.3		per kW-Month		2014 - 2024		$	3.3	-	3.3		per kW-Month	2014 - 2024
REC Prices:
NU	$	38	-	70	per REC			2014 - 2018		$	36	-	87	per REC		2014 - 2029
NSTAR Electric	$	38	-	70	per REC			2014 - 2018		$	36	-	70	per REC		2014 - 2018
Exit price premiums of 9 percent through 26 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 three months ended March 31, 2014 and 2013 in the Level 3 category of derivative assets and derivative liabilities measured at fair value on a recurring basis. The derivative assets and liabilities are presented on a net basis.
		For the Three Months Ended March 31,
		2014			2013
(Millions of Dollars)		NU			NU
Derivatives, Net:
Fair Value as of Beginning of Period		$	-635.2		$	-878.6
Net Realized/Unrealized Gains Included in:
	Net Income (1)		-			5.7
	Regulatory Assets and Liabilities		49.2			26.2
Settlements			21.7			13.6
Fair Value as of End of Period		$	-564.3		$	-833.1
		For the Three Months Ended
		31-Mar-14							31-Mar-13
(Millions of Dollars)		CL&P			NSTAR Electric				CL&P			NSTAR Electric
Derivatives, Net:
Fair Value as of Beginning of Period		$	-630.6		$	-7.3			$	-866.2		$	-14.9
Net Realized/Unrealized Gains/(Losses)
	Included in Regulatory Assets and Liabilities		52			-0.1				24.3			0.7
Settlements			21.6			0.1				22.3			0.6
Fair Value as of End of Period		$	-557		$	-7.3			$	-819.6		$	-13.6
The Net Income impact for the three months ended March 31, 2013 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 $0.3 million as of March 31, 2013.

MARKETABLE_SECURITIES

MARKETABLE SECURITIES	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Marketable Securities [Text Block]	'
	5.       MARKETABLE SECURITIES
	NU maintains trusts to fund certain non-qualified executive benefits and WMECO maintains a spent nuclear fuel trust to fund WMECO's prior period spent nuclear fuel liability, 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.
	In accordance with applicable accounting guidance, the Company elected to record mutual funds designated as available-for-sale at fair value and certain other equity investments as trading securities, with the changes in fair values recorded in Other Income, Net on the statements of income. As of March 31, 2014, the mutual funds and equity investments were classified as Level 1 in the fair value hierarchy and totaled $57.4 million and $24 million, respectively. As of December 31, 2013, the mutual funds were classified as Level 1, and totaled $57.2 million. Net gains on the mutual funds were $0.2 million and $4.2 million for the three months ended March 31, 2014 and 2013, respectively, and net gains on the equity investments were $0.5 million for the three months ended March 31, 2014. 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 and WMECO's available-for-sale securities. These securities are recorded at fair value and included in current and long-term Marketable Securities on the balance sheets.
			As of March 31, 2014
						Pre-Tax			Pre-Tax
			Amortized			Unrealized			Unrealized
	(Millions of Dollars)		Cost			Gains(1)			Losses(1)			Fair Value
	NU
		Debt Securities (2)	$	300.6		$	4.8		$	-0.7		$	304.7
		Equity Securities (2)		163.3			65.6			-			228.9
	WMECO
		Debt Securities		58			-			-0.1			57.9
			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
	Unrealized gains and losses on debt securities held by WMECO are recorded in Other Long-Term Assets on the balance sheets.
	(2)       NU's amounts include CYAPC's and YAEC's marketable securities held in nuclear decommissioning trusts of $435.9 million and $424 million as of March 31, 2014 and December 31, 2013, 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. 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 statements 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 NU or WMECO. Factors considered in determining whether a credit loss exists include the duration and severity of the impairment, adverse conditions specifically affecting the issuer, and the payment history, ratings and rating changes of the security. For asset-backed debt securities, underlying collateral and expected future cash flows are also evaluated.
	Realized Gains and Losses: Realized gains and losses on available-for-sale securities are recorded in Other Income, Net for NU's benefit trust, Other Long-Term Assets for WMECO, and offset in Other Long-Term Liabilities for CYAPC and YAEC. NU utilizes the specific identification basis method for the NU benefit trust and the average cost basis method for the WMECO trust and the CYAPC and YAEC nuclear decommissioning trusts to compute the realized gains and losses on the sale of available-for-sale securities.
	Contractual Maturities: As of March 31, 2014, 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)		$	54.5		$	54.4		$	19.2		$	19.2
	One to five years			73.3			73.9			33.2			33.2
	Six to ten years			68.1			69.4			1.6			1.6
	Greater than ten years			104.7			107			4			3.9
	Total Debt Securities		$	300.6		$	304.7		$	58		$	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						As of
	(Millions of Dollars)				31-Mar-14			31-Dec-13			31-Mar-14			31-Dec-13
	Level 1:
		Mutual Funds and Equities			$	310.3		$	281.3		$	-		$	-
		Money Market Funds				22.5			32.9			4.3			10.9
	Total Level 1				$	332.8		$	314.2		$	4.3		$	10.9
	Level 2:
		U.S. Government Issued Debt Securities
			(Agency and Treasury)		$	56.7		$	61.4		$	-		$	6.8
		Corporate Debt Securities				56.3			53.6			14.1			15.1
		Asset-Backed Debt Securities				35.3			30.4			14			9
		Municipal Bonds				109.6			105.5			12.3			11.2
		Other Fixed Income Securities				24.3			15.8			13.2			4.9
	Total Level 2				$	282.2		$	266.7		$	53.6		$	47
	Total Marketable Securities				$	615		$	580.9		$	57.9		$	57.9
	U.S. government issued debt securities are valued using market approaches that incorporate transactions for the same or similar bonds and adjustments for yields and maturity dates. Corporate debt securities are valued using a market approach, utilizing recent trades of the same or similar instrument and also incorporating yield curves, credit spreads and specific bond terms and conditions. Asset-backed debt securities include collateralized mortgage obligations, commercial mortgage backed securities, and securities collateralized by auto loans, credit card loans or receivables. Asset-backed debt securities are valued using recent trades of similar instruments, prepayment assumptions, yield curves, issuance and maturity dates and tranche information. Municipal bonds are valued using a market approach that incorporates reported trades and benchmark yields. Other fixed income securities are valued using pricing models, quoted prices of securities with similar characteristics, and discounted cash flows.

SHORT_TERM_AND_LONG_TERM_DEBT

SHORT TERM AND LONG TERM DEBT	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Debt Disclosure	'
	6.       SHORT-TERM AND LONG-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 $1.45 billion revolving credit facility due to expire on September 6, 2018. The revolving credit facility is to be used primarily to backstop the $1.45 billion commercial paper program at NU. The commercial paper program allows NU parent to issue commercial paper as a form of short-term debt. As of March 31, 2014 and December 31, 2013, NU had approximately $818.5 million and $1.01 billion, respectively, in short-term borrowings outstanding under the NU parent commercial paper program, leaving $631.5 million and $435.5 million of available borrowing capacity as of March 31, 2014 and December 31, 2013, respectively. The weighted-average interest rate on these borrowings as of March 31, 2014 and December 31, 2013 was 0.23 percent and 0.24 percent, respectively, which is generally based on money market rates. As of March 31, 2014, there were intercompany loans from NU of $351.6 million to CL&P, $39.9 million to PSNH and $37.4 million to WMECO. As of December 31, 2013, there were intercompany loans from NU of $287.3 million to CL&P and $86.5 million to PSNH.
	NSTAR Electric has a five-year $450 million revolving credit facility due to expire on September 6, 2018. This facility serves to backstop NSTAR Electric's existing $450 million commercial paper program. As of March 31, 2014, NSTAR Electric had no borrowings outstanding under its commercial paper program. As of December 31, 2013, NSTAR Electric had $103.5 million in short-term borrowings outstanding under its commercial paper program, leaving $346.5 million of available borrowing capacity. The weighted-average interest rate on these borrowings as of December 31, 2013 was 0.13 percent, which is generally based on money market rates.
	Amounts outstanding under the commercial paper programs are generally included in Notes Payable for NU and NSTAR Electric and classified in current liabilities on the balance sheets as all borrowings are outstanding for no more than 364 days at one time. Intercompany loans from NU to CL&P, PSNH and WMECO are included in Notes Payable to NU Parent and classified in current liabilities on the balance sheets. See the Long-Term Debt portion of this Note for further information on the CL&P $250 million bond issuance and the Yankee Gas $100 million bond issuance and their impacts on the NU balance sheet as of March 31, 2014 and December 31, 2013, respectively.
	Long-Term Debt: 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 $75 million 4.80 percent Series G First Mortgage Bonds that matured on January 1, 2014 and to pay $25 million in short-term borrowings. 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 March 7, 2014, NSTAR Electric issued $300 million of 4.40 percent debentures, due to mature in 2044. The proceeds, net of issuance costs, were used to repay the $300 million of 4.875 percent debentures that matured on April 15, 2014.
	On April 24, 2014, CL&P issued $250 million of 4.30 percent 2014 Series A First Mortgage Bonds, due to mature in April 2044. The proceeds, net of issuance costs, were used to repay short-term borrowings. In accordance with applicable accounting guidance, Notes Payable of $247.4 million were classified as Long-Term Debt on NU's balance sheet as of March 31, 2014.
	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 their 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 $424 million, $355 million and $177 million at NU, CL&P and NSTAR Electric, respectively, as of March 31, 2014.
	As of March 31, 2014, $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, $28.8 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.

PENSION_BENEFITS_AND_POSTRETIR

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Pension and Other Postretirement Benefits Disclosure [Text Block]	'
	7.       Pension Benefits and Postretirement Benefits Other than Pensions
	The components of net periodic benefit expense for the Pension, SERP and PBOP Plans are detailed below. The net periodic benefit expense less the capitalized portion of pension and PBOP amounts is included in Operations and Maintenance on the statements of income. Capitalized pension and PBOP amounts relate to employees working on capital projects and are included in Property, Plant and Equipment, Net. Intercompany allocations are not included in the net periodic benefit expense amounts.
		Pension and SERP
		For the Three Months Ended
		31-Mar-14		31-Mar-13
	(Millions of Dollars)	NU		NU
	Service Cost	$	22.3	$	26.6
	Interest Cost		56.6		51.4
	Expected Return on Plan Assets		-77.7		-70.3
	Actuarial Loss		33		52.9
	Prior Service Cost		1.1		1.1
	Total Net Periodic Benefit Expense	$	35.3	$	61.7
	Capitalized Pension Expense	$	9.7	$	16.7
		PBOP
		For the Three Months Ended
		31-Mar-14		31-Mar-13
	(Millions of Dollars)	NU		NU
	Service Cost	$	3	$	4.8
	Interest Cost		12.6		12.8
	Expected Return on Plan Assets		-15.7		-13.8
	Actuarial Loss		3		8.2
	Prior Service Credit		-0.6		-0.6
	Total Net Periodic Benefit Expense	$	2.3	$	11.4
	Capitalized PBOP Expense	$	0.4	$	3.5
		Pension and SERP
		For the Three Months Ended March 31, 2014								For the Three Months Ended March 31, 2013
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric		PSNH		WMECO		CL&P		Electric(1)		PSNH		WMECO
	Service Cost	$	5.2	$	4.6	$	2.8	$	1	$	6.1	$	9.3	$	3.3	$	1.2
	Interest Cost		13.3		10.2		6.5		2.7		12.1		14.2		6		2.5
	Expected Return on Plan Assets		-19.4		-15.8		-10.2		-4.6		-18.5		-22		-7.7		-4.3
	Actuarial Loss		9.1		5.8		3.3		1.9		14.1		14.5		5.5		3
	Prior Service Cost		0.5		-		0.2		0.1		0.5		-		0.1		0.1
	Total Net Periodic Benefit Expense	$	8.7	$	4.8	$	2.6	$	1.1	$	14.3	$	16	$	7.2	$	2.5
	Intercompany Allocations	$	6.8	$	2.4	$	1.9	$	1.3	$	10.7	$	-2	$	2.6	$	1.8
	Capitalized Pension Expense	$	4.9	$	1.9	$	0.9	$	0.8	$	7	$	5.3	$	2.2	$	1.3
		PBOP
		For the Three Months Ended March 31, 2014								For the Three Months Ended March 31, 2013
	(Millions of Dollars)	CL&P			NSTAR Electric		PSNH		WMECO	CL&P		PSNH		WMECO
	Service Cost	$	0.6	$	0.7	$	0.4	$	0.1	$	0.9	$	0.6	$	0.2
	Interest Cost		2.1		4.9		1.1		0.5		2		1		0.4
	Expected Return on Plan Assets		-2.7		-6.4		-1.4		-0.6		-2.5		-1.3		-0.6
	Actuarial Loss/(Gain)		1.1		-0.1		0.5		0.1		1.7		0.9		0.3
	Prior Service Credit		-		-0.5		-		-		-		-		-
	Total Net Periodic Benefit Expense/(Income)	$	1.1	$	-1.4	$	0.6	$	0.1	$	2.1	$	1.2	$	0.3
	Intercompany Allocations	$	1.1	$	0.1	$	0.3	$	0.2	$	1.6	$	0.4	$	0.3
	Capitalized PBOP Expense/(Income)	$	0.5	$	-0.5	$	0.2	$	0.1	$	1.2	$	0.3	$	0.2
	NSTAR Electric's pension amounts for the three months ended March 31, 2013 do not include SERP expense.
	For the three months ended March 31, 2013, the net periodic PBOP expense allocated to NSTAR Electric was $4.3 million.
	As of December 31, 2013, the funded status of the NSTAR Pension Plan was recorded on NSTAR Electric's balance sheet while the total SERP obligation and PBOP Plan funded status were recorded on NSTAR Electric & Gas' balance sheet. As of December 31, 2013, all NSTAR employees were employed by NSTAR Electric & Gas. On January 1, 2014, NSTAR Electric & Gas was merged into NUSCO and, concurrently, all employees were transferred to the company they predominately provide services for: NUSCO, NSTAR Electric or NSTAR Gas. As a result of the employee transfers, the pension and PBOP assets and liabilities were attributed by participant and transferred to the respective company's balance sheets.
	As of March 31, 2014, the liabilities associated with the Pension, SERP and PBOP plans for NSTAR Electric were $74.8 million for the Pension Plan, $3.5 million for the SERP Plans ($0.4 million of which is included in other current liabilities) and $73 million for the PBOP Plan. As of December 31, 2013, the liability associated with the NSTAR Pension Plan for NSTAR Electric was $118 million. This change had no impact on the income statement or net assets of NSTAR Electric.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Commitments and Contingencies Disclosure [Text Block]	'
	8.       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.
	The number of environmental sites and reserves related to these sites for which remediation or long-term monitoring, preliminary site work or site assessment are being performed are as follows:
		As of March 31, 2014				As of December 31, 2013
				Reserve				Reserve
		Number of Sites		(in millions)		Number of Sites		(in millions)
	NU		66	$	35.4		68	$	35.4
	CL&P		18		3.4		18		3.4
	NSTAR Electric		12		1.2		12		1.2
	PSNH		13		5.4		15		5.4
	WMECO		5		0.4		5		0.4
	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 $30.9 million and $31.4 million as of March 31, 2014 and December 31, 2013, respectively, and relates primarily to the natural gas business segment.
	B.       Contractual Obligations – Yankee Companies
	Spent Nuclear Fuel Litigation - DOE Phase II Damages - On November 15, 2013, the Court of Federal Claims issued an award to CYAPC for $126.3 million, YAEC for $73.3 million and MYAPC for $35.8 million for lawsuits against the DOE seeking recovery of actual damages incurred in the years following 2001 and 2002 (DOE Phase II Damages). 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.
	On March 28, 2014, CYAPC, YAEC and MYAPC received payment of $90 million, $73.3 million and $35.8 million, respectively, of the DOE Phase II Damages proceeds. On April 28, 2014, the Yankee Companies made the required informational filing with FERC in accordance with the process and methodology outlined in the 2013 FERC order. It is anticipated that the Yankee Companies will receive FERC approval and return the DOE Phase II Damages proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, for the benefit of their respective customers, effective June 1, 2014.
	As of March 31, 2014, the CYAPC and YAEC proceeds received have been reflected as restricted cash in Other Long-Term Assets and the refund obligation to the member companies was reflected as Regulatory Liabilities on the NU consolidated balance sheet.
	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 U.S. Department of Justice was filed on November 18, 2013, and discovery has begun.
	C.       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 and the termination of an unregulated business, 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 March 31, 2014:
				Maximum Exposure
	Subsidiary		Description	(in millions)		Expiration Dates
	Various		Surety Bonds	$	66.7	2014 - 2016 (1)
	Various		New England Hydro Companies' Long-Term Debt	$	3	Unspecified
	NUSCO and RRR		Lease Payments for Vehicles and Real Estate	$	16.8	2019 and 2024
	(1)       Surety bond expiration dates reflect termination dates, the majority of which will be renewed or extended.
	Certain surety bonds contain credit ratings triggers that would require NU parent to post collateral in the event that the unsecured debt credit ratings of NU are downgraded.
	D. 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 the financial position, results of operations or cash flows.
	Management expects the CL&P, NSTAR Electric, PSNH, and WMECO aggregate shareholder equity invested in their transmission facilities will be approximately $2.4 billion at the end of 2014. As a result, each 10 basis point change in the prospective period authorized base ROE would change annual consolidated earnings by an approximate $2.4 million.
	E. 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.
	F. 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.

FAIR_VALUE_OF_FINANCIAL_INSTRU

FAIR VALUE OF FINANCIAL INSTRUMENTS	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Fair Value Disclosures [Text Block]	'
	9.       FAIR VALUE OF FINANCIAL INSTRUMENTS
	The following methods and assumptions were used to estimate the fair value of each of the following financial instruments:
	Preferred Stock and Long-Term Debt: The fair value of CL&P's and NSTAR Electric's preferred stock is based upon pricing models that incorporate interest rates and other market factors, valuations or trades of similar securities and cash flow projections. The fair value of fixed-rate long-term debt securities is based upon pricing models that incorporate quoted market prices for those issues or similar issues adjusted for market conditions, credit ratings of the respective companies and treasury benchmark yields. 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 March 31, 2014				As of December 31, 2013
			NU				NU
			Carrying		Fair		Carrying		Fair
	(Millions of Dollars)		Amount		Value		Amount		Value
	Preferred Stock Not
		Subject to Mandatory Redemption	$	155.6	$	152	$	155.6	$	152.7
	Long-Term Debt			8,848.90		9,177.70		8,310.20		8,443.10
			As of March 31, 2014
			CL&P				NSTAR Electric				PSNH				WMECO
			Carrying		Fair		Carrying		Fair		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)		Amount		Value		Amount		Value		Amount		Value		Amount		Value
	Preferred Stock Not
		Subject to Mandatory Redemption	$	116.2	$	110.9	$	43	$	41.1	$	-	$	-	$	-	$	-
	Long-Term Debt			2,741.40		3,033.10		2,099.00		2,224.00		1,049.10		1,096.50		629.2		661
			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
	Derivative Instruments: Derivative instruments are carried at fair value. For further information, see Note 4, "Derivative Instruments," to the financial statements.
	Other Financial Instruments: Investments in marketable securities are carried at fair value. For further information, see Note 1D, "Summary of Significant Accounting Policies - Fair Value Measurements," and Note 5, "Marketable Securities," to the financial statements. The carrying value of other financial instruments included in current assets and current liabilities, including cash and cash equivalents and special deposits, approximates their fair value due to the short-term nature of these instruments.

ACCUMULATED_OTHER_COMPREHENSIV

ACCUMULATED OTHER COMPREHENSIVE INCOME	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Comprehensive Income Note [Text Block]	'
	10.       ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)
	The changes in accumulated other comprehensive income/(loss) by component, net of tax, is as follows:
			For the Three Months Ended March 31, 2014										For the Three Months Ended March 31, 2013
						Unrealized			Pension,						Unrealized		Pension,
			Qualified			Gains/(Losses)			SERP and				Qualified		Gains/(Losses)		SERP and
			Cash Flow			on Available-			PBOP				Cash Flow		on Available-		PBOP
			Hedging			for-Sale			Benefit				Hedging		for-Sale		Benefit
	(Millions of Dollars)		Instruments			Securities			Plans		Total		Instruments		Securities		Plans		Total
	AOCI as of Beginning of Period		$	-14.4		$	0.4		$	-32	$	-46	$	-16.4	$	1.3	$	-57.8	$	-72.9
	OCI Before Reclassifications			-			0.2			-		0.2		-		-0.1		-		-0.1
	Amounts Reclassified from AOCI			0.5			-			1		1.5		0.5		-		1.6		2.1
	Net OCI			0.5			0.2			1		1.7		0.5		-0.1		1.6		2
	AOCI as of End of Period		$	-13.9		$	0.6		$	-31	$	-44.3	$	-15.9	$	1.2	$	-56.2	$	-70.9
	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 following table sets forth the amounts reclassified from AOCI by component and the impacted line item on the statements of income:
		For the Three Months Ended March 31,
		Amounts Reclassified from AOCI						Statements of Income Line Item Impacted
	(Millions of Dollars)	2014			2013
	Qualified Cash Flow Hedging Instruments	$	-0.8		$	-0.8		Interest Expense
	Tax Benefit		0.3			0.3		Income Tax Expense
	Qualified Cash Flow Hedging Instruments, Net of Tax	$	-0.5		$	-0.5
	Pension, SERP and PBOP Benefit Plan Costs:
	Amortization of Actuarial Losses	$	-1.7		$	-2.6		Operations and Maintenance (1)
	Tax Benefit		0.7			1		Income Tax Expense
	Pension, SERP and PBOP Benefit Plan Costs, Net of Tax	$	-1		$	-1.6
	Total Amount Reclassified from AOCI, Net of Tax	$	-1.5		$	-2.1
	These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 7, "Pension Benefits and Postretirement Benefits Other Than Pensions," for further information.

COMMON_SHARES

COMMON SHARES	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Stock by Class [Text Block]	'
	11.       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 as of
		Per Share		March 31, 2014 and	Issued as of
		Par Value		31-Dec-13	31-Mar-14	31-Dec-13
	NU	$	5	380,000,000	333,316,045	333,113,492
	CL&P	$	10	24,500,000	6,035,205	6,035,205
	NSTAR Electric	$	1	100,000,000	100	100
	PSNH	$	1	100,000,000	301	301
	WMECO	$	25	1,072,471	434,653	434,653
	As of March 31, 2014 and December 31, 2013, there were 17,498,327 and 17,796,672 NU common shares held as treasury shares, respectively. As of March 31, 2014 and December 31, 2013, NU common shares outstanding were 315,817,718 and 315,273,559, respectively.

COMMON_SHARESHOLDERS_EQUITY_AN

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Stockholders' Equity Note Disclosure [Text Block]	'
	12	COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS
	A summary of the changes in Common Shareholders' Equity and Noncontrolling Interests of NU is as follows:
			For the Three Months Ended
			31-Mar-14				31-Mar-13
					Noncontrolling				Noncontrolling
					Interest -				Interest -
			Common		Preferred		Common		Preferred
			Shareholders'		Stock of		Shareholders'		Stock of
	(Millions of Dollars)		Equity		Subsidiaries		Equity		Subsidiaries
	Balance as of Beginning of Period		$	9,611.50	$	155.6	$	9,237.10	$	155.6
	Net Income			237.8		-		230		-
	Dividends on Common Shares			-123.9		-		-116.4		-
	Dividends on Preferred Stock			-1.9		-1.9		-1.9		-1.9
	Issuance of Common Shares			5.2		-		8.4		-
	Other Transactions, Net			-6.5		-		-14		-
	Net Income Attributable to Noncontrolling Interests			-		1.9		-		1.9
	Other Comprehensive Income			1.7		-		2		-
	Balance as of End of Period		$	9,723.90	$	155.6	$	9,345.20	$	155.6

EARNINGS_PER_SHARE

EARNINGS PER SHARE	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Earnings Per Share [Text Block]	'
	13.       EARNINGS PER SHARE
	Basic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is computed on the basis of the weighted average number of common shares outstanding plus the potential dilutive effect of certain share-based compensation awards as if they were converted into common shares. There were no antidilutive share awards outstanding for the three months ended March 31, 2014. For the three months ended March 31, 2013, there were 6,299 antidilutive share awards excluded from the computation.
	The following table sets forth the components of basic and diluted EPS:
			For the Three Months Ended
	(Millions of Dollars, except share information)		31-Mar-14		31-Mar-13
	Net Income Attributable to Controlling Interest		$	236	$	228.1
	Weighted Average Common Shares Outstanding:
		Basic		315,534,512		315,129,782
		Dilutive Effect		1,357,607		872,756
		Diluted		316,892,119		316,002,538
	Basic EPS		$	0.75	$	0.72
	Diluted EPS		$	0.74	$	0.72
	RSUs and performance shares are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. The dilutive effect of unvested RSUs and performance shares is calculated using the treasury stock method. Assumed proceeds of these units under the treasury stock method consist of the remaining compensation cost to be recognized and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the units (the difference between the market value of the average units outstanding for the period, using the average market price during the period, and the grant date market value).
	The dilutive effect of stock options to purchase common shares is also calculated using the treasury stock method. Assumed proceeds for stock options consist of cash proceeds that would be received upon exercise, and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the stock options (the difference between the market value of the average stock options outstanding for the period, using the average market price during the period, and the exercise price).

SEGMENT_INFORMATION

SEGMENT INFORMATION	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Segment Reporting Disclosure [Text Block]	'
	14.       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 three months ended March 31, 2014 and 2013. 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 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.
	NU's segment information for the three months ended March 31, 2014 and 2013 is as follows:
		For the Three Months Ended March 31, 2014
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,585.90	$	432.8	$	252.1	$	172.2	$	-152.4	$	2,290.60
	Depreciation and Amortization		-148.8		-17.7		-37		-7		1.8		-208.7
	Other Operating Expenses		-1,210.90		-321.4		-66.4		-165.4		149.9		-1,614.20
	Operating Income/(Loss)		226.2		93.7		148.7		-0.2		-0.7		467.7
	Interest Expense		-47.4		-8.5		-25.5		-9.6		1		-90
	Other Income, Net		1.4		0.1		1.5		294.8		-296.1		1.7
	Net Income Attributable to Controlling Interest	$	112.2	$	52.1	$	74.9	$	291.7	$	-294.9	$	236
	Cash Flows Used for Investments in Plant	$	189.4	$	28.9	$	112.2	$	18.2	$	-	$	348.7
		For the Three Months Ended March 31, 2013
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,374.20	$	361.8	$	239.5	$	217.2	$	-197.7	$	1,995.00
	Depreciation and Amortization		-177		-17.4		-31.8		-19		1.7		-243.5
	Other Operating Expenses		-1,004.90		-267.2		-62.2		-197.4		199.2		-1,332.50
	Operating Income		192.3		77.2		145.5		0.8		3.2		419
	Interest Expense		-42.1		-7.4		-21.9		-6.4		1.5		-76.3
	Other Income, Net		4.8		0.2		2.8		321.9		-321.9		7.8
	Net Income Attributable to Controlling Interest	$	99.5	$	43.3	$	79.9	$	322.8	$	-317.4	$	228.1
	Cash Flows Used for Investments in Plant	$	157.8	$	31.2	$	185.4	$	14.6	$	-	$	389
	The following table summarizes NU's segmented total assets:
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	As of March 31, 2014	$	18,882.90	$	2,846.70	$	5,165.60	$	11,913.60	$	-10,711.90	$	28,096.90
	As of December 31, 2013		17,260.00		2,759.70		6,745.80		11,842.40		-10,812.40		27,795.50

SUBSEQUENT_EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Subsequent Events [Text Block]	'
	15.       SUBSEQUENT EVENT
	See Note 6, "Short-Term and Long-Term Debt," for information regarding the April 2014 CL&P long-term debt issuance.

SIGNIFCANT_ACCOUNTING_POLICIES

SIGNIFCANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Organization Consolidation And Presentation Of Financial Statements Disclosure Text Block	'
	A.       Basis of Presentation
	NU is a public utility holding company primarily engaged through its wholly owned regulated utility subsidiaries in the energy delivery business. 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.
	The unaudited condensed 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 unaudited condensed consolidated financial statements of NU, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements."
	The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the entirety of this combined Quarterly Report on Form 10-Q and the 2013 combined Annual Report on Form 10-K of NU, CL&P, NSTAR Electric, PSNH and WMECO, which was filed with the SEC. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly NU's, CL&P's, NSTAR Electric's, PSNH's and WMECO's financial position as of March 31, 2014 and December 31, 2013, and the results of operations, comprehensive income and cash flows for the three months ended March 31, 2014 and 2013. The results of operations, comprehensive income and cash flows for the three months ended March 31, 2014 and 2013 are not necessarily indicative of the results expected for a full year. The demand for electricity and natural gas is affected by weather conditions, economic conditions, and consumer conservation (including company-sponsored energy efficiency programs). Electric energy sales and revenues are typically higher in the winter and summer months than in the spring and fall months. Natural gas sales and revenues are typically higher in the winter months than during other periods of the year.
	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.
	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 2, "Regulatory Accounting," for further information.
	Certain reclassifications of prior period data were made in the accompanying balance sheets for NU, CL&P and PSNH, statements of income for NU, NSTAR Electric, PSNH and WMECO, and statements of cash flows for CL&P, NSTAR Electric and WMECO. These reclassifications were made to conform to the current period's presentation.
Receivables Policy Text Block	'
	NU, including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at estimated net realizable value by maintaining a provision for uncollectible accounts. This provision is determined based upon a variety of factors, including the application of an estimated uncollectible percentage to each receivable aging category. The estimate is based upon historical collection and write-off experience and management's assessment of collectibility from individual customers. Management continuously assesses the collectibility of receivables, and adjusts collectibility estimates based on actual experience. Receivable balances are written off against the provision for uncollectible accounts when the accounts are terminated and these balances are deemed to be uncollectible.
Fair Value Of Financial Instruments Policy	'
	Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases or normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to 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.
	The following methods and assumptions were used to estimate the fair value of each of the following financial instruments:
	Preferred Stock and Long-Term Debt: The fair value of CL&P's and NSTAR Electric's preferred stock is based upon pricing models that incorporate interest rates and other market factors, valuations or trades of similar securities and cash flow projections. The fair value of fixed-rate long-term debt securities is based upon pricing models that incorporate quoted market prices for those issues or similar issues adjusted for market conditions, credit ratings of the respective companies and treasury benchmark yields. 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.
Other Taxes Policy	'Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respective customers. These gross receipts taxes are shown on a gross basis with collections in Operating Revenues and payments in Taxes Other Than Income Taxes on the statements of income Certain sales taxes are 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 follow 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	'
	4.       DERIVATIVE INSTRUMENTS
Marketable Securities Policy	'
	5.       MARKETABLE SECURITIES
	NU maintains trusts to fund certain non-qualified executive benefits and WMECO maintains a spent nuclear fuel trust to fund WMECO's prior period spent nuclear fuel liability, 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.
	In accordance with applicable accounting guidance, the Company elected to record mutual funds designated as available-for-sale at fair value and certain other equity investments as trading securities, with the changes in fair values recorded in Other Income, Net on the statements of income. As of March 31, 2014, the mutual funds and equity investments were classified as Level 1 in the fair value hierarchy and totaled $57.4 million and $24 million, respectively. As of December 31, 2013, the mutual funds were classified as Level 1, and totaled $57.2 million. Net gains on the mutual funds were $0.2 million and $4.2 million for the three months ended March 31, 2014 and 2013, respectively, and net gains on the equity investments were $0.5 million for the three months ended March 31, 2014. 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 and WMECO's available-for-sale securities. These securities are recorded at fair value and included in current and long-term Marketable Securities on the balance sheets.
	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.
Earnings Per Share Policy Text Block	'
	Basic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is computed on the basis of the weighted average number of common shares outstanding plus the potential dilutive effect of certain share-based compensation awards as if they were converted into common shares.
	RSUs and performance shares are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. The dilutive effect of unvested RSUs and performance shares is calculated using the treasury stock method. Assumed proceeds of these units under the treasury stock method consist of the remaining compensation cost to be recognized and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the units (the difference between the market value of the average units outstanding for the period, using the average market price during the period, and the grant date market value).
	The dilutive effect of stock options to purchase common shares is also calculated using the treasury stock method. Assumed proceeds for stock options consist of cash proceeds that would be received upon exercise, and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the stock options (the difference between the market value of the average stock options outstanding for the period, using the average market price during the period, and the exercise price).
Segment Reporting Policy Policy Text Block	'
	SEGMENT INFORMATION
	Presentation: 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 three months ended March 31, 2014 and 2013. 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 the capitalized portions of pension expense.

Provision_for_Uncollectible_Ac

Provision for Uncollectible Accounts (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Accounts Notes Loans And Financing Receivable Text Block	'
	(Millions of Dollars)	As of March 31, 2014		As of December 31, 2013
	NU	$	180	$	171.3
	CL&P		83.4		82
	NSTAR Electric		43.1		41.7
	PSNH		7.8		7.4
	WMECO		10.6		10

Other_Taxes_Tables

Other Taxes (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
State Of Connecticut Gross Earnings Taxes [Table Text Block]	'
		For the Three Months Ended
	(Millions of Dollars)	31-Mar-14		31-Mar-13
	NU	$	44.4	$	38.4
	CL&P		35.6		32

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	'
	G.	Supplemental Cash Flow Information
	Non-cash investing activities include plant additions included in Accounts Payable as follows:
	(Millions of Dollars)		As of March 31, 2014		As of March 31, 2013
	NU		$	108.5	$	98.7
	CL&P			36.2		28.2
	NSTAR Electric			28		30.7
	PSNH			14.4		12.9
	WMECO			14.4		15.8

REGULATORY_ACCOUNTING_Tables

REGULATORY ACCOUNTING (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Regulatory Assets Text Block	'
		As of March 31, 2014			As of December 31, 2013
	(Millions of Dollars)	NU			NU
	Benefit Costs	$	1,205.40		$	1,240.20
	Derivative Liabilities		564.9			638
	Income Taxes, Net		629.2			626.2
	Storm Restoration Costs		580.9			589.6
	Goodwill		520.8			525.9
	Regulatory Tracker Mechanisms		347.4			323.4
	Buy Out Agreements for Power Contracts		63.4			70.2
	Other Regulatory Assets		147.6			281
	Total Regulatory Assets		4,059.60			4,294.50
	Less: Current Portion		573			535.8
	Total Long-Term Regulatory Assets	$	3,486.60		$	3,758.70
			As of March 31, 2014									As of December 31, 2013
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Benefit Costs		$	287.1		$	321.3	$	96.7	$	55.1	$	297.7	$	496.7	$	100.6	$	57.3
	Derivative Liabilities			557			7.9		-		-		630.4		7.7		-		-
	Income Taxes, Net			419.7			82.5		39.4		43.5		415.5		84		40.3		43.7
	Storm Restoration Costs			395.3			109.2		40.3		36.1		397.8		109.3		43.7		38.8
	Goodwill			-			447.1		-		-		-		451.5		-		-
	Regulatory Tracker Mechanisms			33.3			182.7		75.2		31.6		8		169.5		83.3		32.6
	Buy Out Agreements for Power Contracts			-			58.3		5.1		-		-		64.7		5.5		-
	Other Regulatory Assets			64.1			55.5		37.8		15.5		64.6		55.9		38.1		16.7
	Total Regulatory Assets			1,756.50			1,264.50		294.5		181.8		1,814.00		1,439.30		311.5		189.1
	Less: Current Portion			175.9			222.6		83.8		49.6		150.9		204.1		92.2		43
	Total Long-Term Regulatory Assets		$	1,580.60		$	1,041.90	$	210.7	$	132.2	$	1,663.10	$	1,235.20	$	219.3	$	146.1
Schedule Of Regulatory Liabilities Text Block	'
		As of March 31, 2014			As of December 31, 2013
	(Millions of Dollars)	NU			NU
	Cost of Removal	$	437.3		$	435.1
	Regulatory Tracker Mechanisms		203.6			151.2
	AFUDC - Transmission		67.8			68.1
	Contractual Obligations - Yankee Companies		93.3			-
	Other Regulatory Liabilities		53.3			52.9
	Total Regulatory Liabilities		855.3			707.3
	Less: Current Portion		263.8			204.3
	Total Long-Term Regulatory Liabilities	$	591.5		$	503
			As of March 31, 2014									As of December 31, 2013
						NSTAR								NSTAR
	(Millions of Dollars)		CL&P			Electric		PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Cost of Removal		$	27.5		$	252.5	$	49.7	$	-	$	29.1	$	250	$	49.7	$	-
	Regulatory Tracker Mechanisms			105.6			43.8		27.5		22.4		95.6		21.9		21.6		21.1
	AFUDC - Transmission			54.5			4		-		9.3		54.7		4.1		-		9.3
	Other Regulatory Liabilities			9.8			30.4		1.9		0.5		8.4		31.1		1		3.4
	Total Regulatory Liabilities			197.4			330.7		79.1		32.2		187.8		307.1		72.3		33.8
	Less: Current Portion			107.3			73.6		27.3		21.8		94		54		20.6		19.9
	Total Long-Term Regulatory Liabilities		$	90.1		$	257.1	$	51.8	$	10.4	$	93.8	$	253.1	$	51.7	$	13.9

PROPERTY_PLANT_AND_ACCUMULATED1

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Public Utility Property, Plant, and Equipment [Text Block]	'
				As of March 31, 2014			As of December 31, 2013
	(Millions of Dollars)			NU			NU
	Distribution - Electric			$	12,039.70		$	11,950.20
	Distribution - Natural Gas				2,447.90			2,425.90
	Transmission				6,423.50			6,412.50
	Generation				1,154.70			1,152.30
	Electric and Natural Gas Utility				22,065.80			21,940.90
	Other (1)				510.2			508.7
	Property, Plant and Equipment, Gross				22,576.00			22,449.60
	Less: Accumulated Depreciation
		Electric and Natural Gas Utility			-5,491.70			-5,387.00
		Other			-204.7			-196.2
	Total Accumulated Depreciation				-5,696.40			-5,583.20
	Property, Plant and Equipment, Net				16,879.60			16,866.40
	Construction Work in Progress				833.4			709.8
	Total Property, Plant and Equipment, Net			$	17,713.00		$	17,576.20
		As of March 31, 2014										As of December 31, 2013
					NSTAR									NSTAR
	(Millions of Dollars)	CL&P			Electric			PSNH		WMECO		CL&P		Electric		PSNH		WMECO
	Distribution	$	4,979.80		$	4,717.60		$	1,620.30	$	762	$	4,930.70	$	4,694.70	$	1,608.20	$	756.6
	Transmission		3,074.80			1,769.00			701.7		831.7		3,071.90		1,772.30		695.7		826.4
	Generation		-			-			1,133.60		21.1		-		-		1,131.20		21.1
	Property, Plant and
	Equipment, Gross		8,054.60			6,486.60			3,455.60		1,614.80		8,002.60		6,467.00		3,435.10		1,604.10
	Less: Accumulated Depreciation		-1,838.50			-1,664.60			-1,040.60		-278.4		-1,804.10		-1,631.30		-1,021.80		-271.5
	Property, Plant and Equipment, Net		6,216.10			4,822.00			2,415.00		1,336.40		6,198.50		4,835.70		2,413.30		1,332.60
	Construction Work in Progress		290.1			247.2			71.4		62.4		252.8		208.2		54.3		48.5
	Total Property, Plant and
	Equipment, Net	$	6,506.20		$	5,069.20		$	2,486.40	$	1,398.80	$	6,451.30	$	5,043.90	$	2,467.60	$	1,381.10

DERIVATIVE_INSTRUMENTS_Tables

DERIVATIVE INSTRUMENTS (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Derivative Instruments In Statement Of Financial Position Fair Value Text Block	'
			As of March 31, 2014
			Commodity Supply and						Net Amount Recorded as
	(Millions of Dollars)		Price Risk Management			Netting (1)			Derivative Asset/(Liability)
	Current Derivative Assets:
	Level 2:
		NU (1)	$	1.2		$	-0.1		$	1.1
	Level 3:
		NU (1)		17.8			-9.7			8.1
		CL&P (1)		17			-9.7			7.3
		NSTAR Electric		0.8			-			0.8
	Long-Term Derivative Assets:
	Level 3:
		NU, CL&P (1)	$	98.8		$	-31.7		$	67.1
	Current Derivative Liabilities:
	Level 3:
		NU	$	-93.3		$	-		$	-93.3
		CL&P		-92			-			-92
		NSTAR Electric		-1.3			-			-1.3
	Long-Term Derivative Liabilities:
	Level 2:
		NU	$	-0.2		$	-		$	-0.2
	Level 3:
		NU		-546.2			-			-546.2
		CL&P		-539.4			-			-539.4
		NSTAR Electric		-6.8			-			-6.8
			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:
		NU (1)	$	1.9		$	-0.3		$	1.6
	Level 3:
		NU (1)		18.4			-9.8			8.6
		CL&P (1)		17.1			-9.8			7.3
		NSTAR Electric		1.2			-			1.2
	Long-Term Derivative Assets:
	Level 2:
		NU	$	0.2		$	-		$	0.2
	Level 3:
		NU (1)		116.2			-42.2			74
		CL&P (1)		113.6			-42.2			71.4
	Current Derivative Liabilities:
	Level 3:
		NU	$	-93.7		$	-		$	-93.7
		CL&P		-92.2			-			-92.2
		NSTAR Electric		-1.5			-			-1.5
	Long-Term Derivative Liabilities:
	Level 3:
		NU	$	-624.1		$	-		$	-624.1
		CL&P		-617.1			-			-617.1
		NSTAR Electric		-7			-			-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 Three Months Ended March 31,
	(Millions of Dollars)			2014			2013
	NU
	Balance Sheets:
		Regulatory Assets and Liabilities		$	54.1		$	28
	Statements of Income:
		Purchased Power, Fuel and Transmission			-			0.3
Rollforward Of Net Derivative Asset Liabilities Valued Using Unobservable Inputs [Table Text Block]	'
			For the Three Months Ended March 31,
			2014			2013
	(Millions of Dollars)		NU			NU
	Derivatives, Net:
	Fair Value as of Beginning of Period		$	-635.2		$	-878.6
	Net Realized/Unrealized Gains Included in:
		Net Income (1)		-			5.7
		Regulatory Assets and Liabilities		49.2			26.2
	Settlements			21.7			13.6
	Fair Value as of End of Period		$	-564.3		$	-833.1
			For the Three Months Ended
			31-Mar-14							31-Mar-13
	(Millions of Dollars)		CL&P			NSTAR Electric				CL&P			NSTAR Electric
	Derivatives, Net:
	Fair Value as of Beginning of Period		$	-630.6		$	-7.3			$	-866.2		$	-14.9
	Net Realized/Unrealized Gains/(Losses)
		Included in Regulatory Assets and Liabilities		52			-0.1				24.3			0.7
	Settlements			21.6			0.1				22.3			0.6
	Fair Value as of End of Period		$	-557		$	-7.3			$	-819.6		$	-13.6
Fairvalueinputsliabilitiesquantitativeinformationtabletextblock	'
		As of March 31, 2014									As of December 31, 2013
			Range						Period Covered			Range					Period Covered
	Energy Prices:
	NU	$	57	-	60	per MWh			2018 - 2020		$	49	-	77	per MWh		2018 - 2029
	CL&P	$	57	-	60	per MWh			2018 - 2020		$	56	-	58	per MWh		2018 - 2029
	Capacity Prices:
	NU	$	1.7	-	10.42		per kW-Month		2016 - 2026		$	5.07	-	11.82		per kW-Month	2017 - 2029
	CL&P	$	5.23	-	10.42		per kW-Month		2018 - 2026		$	5.07	-	10.42		per kW-Month	2017 - 2026
	NSTAR Electric	$	1.7	-	7.38		per kW-Month		2016 - 2019		$	5.07	-	7.38		per kW-Month	2017 - 2019
	Forward Reserve:
	NU, CL&P	$	3.3	-	3.3		per kW-Month		2014 - 2024		$	3.3	-	3.3		per kW-Month	2014 - 2024
	REC Prices:
	NU	$	38	-	70	per REC			2014 - 2018		$	36	-	87	per REC		2014 - 2029
	NSTAR Electric	$	38	-	70	per REC			2014 - 2018		$	36	-	70	per REC		2014 - 2018

MARKETABLE_SECURITIES_Tables

MARKETABLE SECURITIES (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Available For Sale Securities Reconciliation [Table TextBlock]	'
			As of March 31, 2014
						Pre-Tax			Pre-Tax
			Amortized			Unrealized			Unrealized
	(Millions of Dollars)		Cost			Gains(1)			Losses(1)			Fair Value
	NU
		Debt Securities (2)	$	300.6		$	4.8		$	-0.7		$	304.7
		Equity Securities (2)		163.3			65.6			-			228.9
	WMECO
		Debt Securities		58			-			-0.1			57.9
			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
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)		$	54.5		$	54.4		$	19.2		$	19.2
	One to five years			73.3			73.9			33.2			33.2
	Six to ten years			68.1			69.4			1.6			1.6
	Greater than ten years			104.7			107			4			3.9
	Total Debt Securities		$	300.6		$	304.7		$	58		$	57.9
Fair Value Heirarchy [Table Text Block]	'
					NU						WMECO
					As of						As of
	(Millions of Dollars)				31-Mar-14			31-Dec-13			31-Mar-14			31-Dec-13
	Level 1:
		Mutual Funds and Equities			$	310.3		$	281.3		$	-		$	-
		Money Market Funds				22.5			32.9			4.3			10.9
	Total Level 1				$	332.8		$	314.2		$	4.3		$	10.9
	Level 2:
		U.S. Government Issued Debt Securities
			(Agency and Treasury)		$	56.7		$	61.4		$	-		$	6.8
		Corporate Debt Securities				56.3			53.6			14.1			15.1
		Asset-Backed Debt Securities				35.3			30.4			14			9
		Municipal Bonds				109.6			105.5			12.3			11.2
		Other Fixed Income Securities				24.3			15.8			13.2			4.9
	Total Level 2				$	282.2		$	266.7		$	53.6		$	47
	Total Marketable Securities				$	615		$	580.9		$	57.9		$	57.9

Recovered_Sheet1

Pension Benefits and Postretirement Benefits Other Than Pensions (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Net Benefit Costs [Table Text Block]	'
		Pension and SERP
		For the Three Months Ended
		31-Mar-14		31-Mar-13
	(Millions of Dollars)	NU		NU
	Service Cost	$	22.3	$	26.6
	Interest Cost		56.6		51.4
	Expected Return on Plan Assets		-77.7		-70.3
	Actuarial Loss		33		52.9
	Prior Service Cost		1.1		1.1
	Total Net Periodic Benefit Expense	$	35.3	$	61.7
	Capitalized Pension Expense	$	9.7	$	16.7
		PBOP
		For the Three Months Ended
		31-Mar-14		31-Mar-13
	(Millions of Dollars)	NU		NU
	Service Cost	$	3	$	4.8
	Interest Cost		12.6		12.8
	Expected Return on Plan Assets		-15.7		-13.8
	Actuarial Loss		3		8.2
	Prior Service Credit		-0.6		-0.6
	Total Net Periodic Benefit Expense	$	2.3	$	11.4
	Capitalized PBOP Expense	$	0.4	$	3.5
		Pension and SERP
		For the Three Months Ended March 31, 2014								For the Three Months Ended March 31, 2013
				NSTAR								NSTAR
	(Millions of Dollars)	CL&P		Electric		PSNH		WMECO		CL&P		Electric(1)		PSNH		WMECO
	Service Cost	$	5.2	$	4.6	$	2.8	$	1	$	6.1	$	9.3	$	3.3	$	1.2
	Interest Cost		13.3		10.2		6.5		2.7		12.1		14.2		6		2.5
	Expected Return on Plan Assets		-19.4		-15.8		-10.2		-4.6		-18.5		-22		-7.7		-4.3
	Actuarial Loss		9.1		5.8		3.3		1.9		14.1		14.5		5.5		3
	Prior Service Cost		0.5		-		0.2		0.1		0.5		-		0.1		0.1
	Total Net Periodic Benefit Expense	$	8.7	$	4.8	$	2.6	$	1.1	$	14.3	$	16	$	7.2	$	2.5
	Intercompany Allocations	$	6.8	$	2.4	$	1.9	$	1.3	$	10.7	$	-2	$	2.6	$	1.8
	Capitalized Pension Expense	$	4.9	$	1.9	$	0.9	$	0.8	$	7	$	5.3	$	2.2	$	1.3
		PBOP
		For the Three Months Ended March 31, 2014								For the Three Months Ended March 31, 2013
	(Millions of Dollars)	CL&P			NSTAR Electric		PSNH		WMECO	CL&P		PSNH		WMECO
	Service Cost	$	0.6	$	0.7	$	0.4	$	0.1	$	0.9	$	0.6	$	0.2
	Interest Cost		2.1		4.9		1.1		0.5		2		1		0.4
	Expected Return on Plan Assets		-2.7		-6.4		-1.4		-0.6		-2.5		-1.3		-0.6
	Actuarial Loss/(Gain)		1.1		-0.1		0.5		0.1		1.7		0.9		0.3
	Prior Service Credit		-		-0.5		-		-		-		-		-
	Total Net Periodic Benefit Expense/(Income)	$	1.1	$	-1.4	$	0.6	$	0.1	$	2.1	$	1.2	$	0.3
	Intercompany Allocations	$	1.1	$	0.1	$	0.3	$	0.2	$	1.6	$	0.4	$	0.3
	Capitalized PBOP Expense/(Income)	$	0.5	$	-0.5	$	0.2	$	0.1	$	1.2	$	0.3	$	0.2

Environmental_Matters_Tables

Environmental Matters (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Environmental Loss Contingencies By Site Text Block	'
		As of March 31, 2014				As of December 31, 2013
				Reserve				Reserve
		Number of Sites		(in millions)		Number of Sites		(in millions)
	NU		66	$	35.4		68	$	35.4
	CL&P		18		3.4		18		3.4
	NSTAR Electric		12		1.2		12		1.2
	PSNH		13		5.4		15		5.4
	WMECO		5		0.4		5		0.4

Guarantees_and_Indemnification

Guarantees and Indemnifications (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Guarantee Obligations Text Block	'
			Maximum Exposure
	Subsidiary	Description	(in millions)		Expiration Dates
	Various	Surety Bonds	$	66.7	2014 - 2016 (1)
	Various	New England Hydro Companies' Long-Term Debt	$	3	Unspecified
	NUSCO and RRR	Lease Payments for Vehicles and Real Estate	$	16.8	2019 and 2024

FAIR_VALUE_OF_FINANCIAL_INSTRU1

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Fair Value By Balance Sheet Grouping Text Block	'
			As of March 31, 2014				As of December 31, 2013
			NU				NU
			Carrying		Fair		Carrying		Fair
	(Millions of Dollars)		Amount		Value		Amount		Value
	Preferred Stock Not
		Subject to Mandatory Redemption	$	155.6	$	152	$	155.6	$	152.7
	Long-Term Debt			8,848.90		9,177.70		8,310.20		8,443.10
			As of March 31, 2014
			CL&P				NSTAR Electric				PSNH				WMECO
			Carrying		Fair		Carrying		Fair		Carrying		Fair		Carrying		Fair
	(Millions of Dollars)		Amount		Value		Amount		Value		Amount		Value		Amount		Value
	Preferred Stock Not
		Subject to Mandatory Redemption	$	116.2	$	110.9	$	43	$	41.1	$	-	$	-	$	-	$	-
	Long-Term Debt			2,741.40		3,033.10		2,099.00		2,224.00		1,049.10		1,096.50		629.2		661
			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

ACCUMULATED_OTHER_COMPREHENSIV1

ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Accumulated Other Comprehensive Income Loss Table Text Block	'
			For the Three Months Ended March 31, 2014										For the Three Months Ended March 31, 2013
						Unrealized			Pension,						Unrealized		Pension,
			Qualified			Gains/(Losses)			SERP and				Qualified		Gains/(Losses)		SERP and
			Cash Flow			on Available-			PBOP				Cash Flow		on Available-		PBOP
			Hedging			for-Sale			Benefit				Hedging		for-Sale		Benefit
	(Millions of Dollars)		Instruments			Securities			Plans		Total		Instruments		Securities		Plans		Total
	AOCI as of Beginning of Period		$	-14.4		$	0.4		$	-32	$	-46	$	-16.4	$	1.3	$	-57.8	$	-72.9
	OCI Before Reclassifications			-			0.2			-		0.2		-		-0.1		-		-0.1
	Amounts Reclassified from AOCI			0.5			-			1		1.5		0.5		-		1.6		2.1
	Net OCI			0.5			0.2			1		1.7		0.5		-0.1		1.6		2
	AOCI as of End of Period		$	-13.9		$	0.6		$	-31	$	-44.3	$	-15.9	$	1.2	$	-56.2	$	-70.9
		For the Three Months Ended March 31,
		Amounts Reclassified from AOCI						Statements of Income Line Item Impacted
	(Millions of Dollars)	2014			2013
	Qualified Cash Flow Hedging Instruments	$	-0.8		$	-0.8		Interest Expense
	Tax Benefit		0.3			0.3		Income Tax Expense
	Qualified Cash Flow Hedging Instruments, Net of Tax	$	-0.5		$	-0.5
	Pension, SERP and PBOP Benefit Plan Costs:
	Amortization of Actuarial Losses	$	-1.7		$	-2.6		Operations and Maintenance (1)
	Tax Benefit		0.7			1		Income Tax Expense
	Pension, SERP and PBOP Benefit Plan Costs, Net of Tax	$	-1		$	-1.6
	Total Amount Reclassified from AOCI, Net of Tax	$	-1.5		$	-2.1

COMMON_SHARES_Tables

COMMON SHARES (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule of Stock by Class [Text Block]	'
	11.       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 as of
		Per Share		March 31, 2014 and	Issued as of
		Par Value		31-Dec-13	31-Mar-14	31-Dec-13
	NU	$	5	380,000,000	333,316,045	333,113,492
	CL&P	$	10	24,500,000	6,035,205	6,035,205
	NSTAR Electric	$	1	100,000,000	100	100
	PSNH	$	1	100,000,000	301	301
	WMECO	$	25	1,072,471	434,653	434,653
	As of March 31, 2014 and December 31, 2013, there were 17,498,327 and 17,796,672 NU common shares held as treasury shares, respectively. As of March 31, 2014 and December 31, 2013, NU common shares outstanding were 315,817,718 and 315,273,559, respectively.

COMMON_SHARESHOLDERS_EQUITY_AN1

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Minority Interest Disclosure Text Block	'
	12	COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS
	A summary of the changes in Common Shareholders' Equity and Noncontrolling Interests of NU is as follows:
			For the Three Months Ended
			31-Mar-14				31-Mar-13
					Noncontrolling				Noncontrolling
					Interest -				Interest -
			Common		Preferred		Common		Preferred
			Shareholders'		Stock of		Shareholders'		Stock of
	(Millions of Dollars)		Equity		Subsidiaries		Equity		Subsidiaries
	Balance as of Beginning of Period		$	9,611.50	$	155.6	$	9,237.10	$	155.6
	Net Income			237.8		-		230		-
	Dividends on Common Shares			-123.9		-		-116.4		-
	Dividends on Preferred Stock			-1.9		-1.9		-1.9		-1.9
	Issuance of Common Shares			5.2		-		8.4		-
	Other Transactions, Net			-6.5		-		-14		-
	Net Income Attributable to Noncontrolling Interests			-		1.9		-		1.9
	Other Comprehensive Income			1.7		-		2		-
	Balance as of End of Period		$	9,723.90	$	155.6	$	9,345.20	$	155.6

EARNINGS_PER_SHARE_Tables

EARNINGS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2014
Notes To Consolidated Financial Statements [Abstract]	'
Schedule Of Earnings Per Share Basic And Diluted [Table Text Block]	'
			For the Three Months Ended
	(Millions of Dollars, except share information)		31-Mar-14		31-Mar-13
	Net Income Attributable to Controlling Interest		$	236	$	228.1
	Weighted Average Common Shares Outstanding:
		Basic		315,534,512		315,129,782
		Dilutive Effect		1,357,607		872,756
		Diluted		316,892,119		316,002,538
	Basic EPS		$	0.75	$	0.72
	Diluted EPS		$	0.74	$	0.72

SEGMENT_INFORMATION_Tables

SEGMENT INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2014
Segment Reporting Information [Line Items]	'
Schedule Of Segment Reporting Information By Segment Text Block	'
		For the Three Months Ended March 31, 2014
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,585.90	$	432.8	$	252.1	$	172.2	$	-152.4	$	2,290.60
	Depreciation and Amortization		-148.8		-17.7		-37		-7		1.8		-208.7
	Other Operating Expenses		-1,210.90		-321.4		-66.4		-165.4		149.9		-1,614.20
	Operating Income/(Loss)		226.2		93.7		148.7		-0.2		-0.7		467.7
	Interest Expense		-47.4		-8.5		-25.5		-9.6		1		-90
	Other Income, Net		1.4		0.1		1.5		294.8		-296.1		1.7
	Net Income Attributable to Controlling Interest	$	112.2	$	52.1	$	74.9	$	291.7	$	-294.9	$	236
	Cash Flows Used for Investments in Plant	$	189.4	$	28.9	$	112.2	$	18.2	$	-	$	348.7
		For the Three Months Ended March 31, 2013
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	Operating Revenues	$	1,374.20	$	361.8	$	239.5	$	217.2	$	-197.7	$	1,995.00
	Depreciation and Amortization		-177		-17.4		-31.8		-19		1.7		-243.5
	Other Operating Expenses		-1,004.90		-267.2		-62.2		-197.4		199.2		-1,332.50
	Operating Income		192.3		77.2		145.5		0.8		3.2		419
	Interest Expense		-42.1		-7.4		-21.9		-6.4		1.5		-76.3
	Other Income, Net		4.8		0.2		2.8		321.9		-321.9		7.8
	Net Income Attributable to Controlling Interest	$	99.5	$	43.3	$	79.9	$	322.8	$	-317.4	$	228.1
	Cash Flows Used for Investments in Plant	$	157.8	$	31.2	$	185.4	$	14.6	$	-	$	389
	The following table summarizes NU's segmented total assets:
		Electric		Natural Gas
	(Millions of Dollars)	Distribution		Distribution		Transmission		Other		Eliminations		Total
	As of March 31, 2014	$	18,882.90	$	2,846.70	$	5,165.60	$	11,913.60	$	-10,711.90	$	28,096.90
	As of December 31, 2013		17,260.00		2,759.70		6,745.80		11,842.40		-10,812.40		27,795.50

Basis_of_Presentation_Details

Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2014
Description of Consolidation of Yankee Companies	'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.

Provision_for_Uncollectible_Ac1

Provision for Uncollectible Accounts (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	$180	$171.30
The Connecticut Light And Power Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	83.4	82
NSTAR Electric Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	43.1	41.7
Public Service Company Of New Hampshire [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	7.8	7.4
Western Massachusetts Electric Company [Member]	'	'
Accounts Notes And Loans Receivable [Line Items]	'	'
Allowance For Doubtful Accounts Receivable Current	$10.60	$10

Restricted_Cash_and_Other_Depo

Restricted Cash and Other Deposits (Details) (USD $)	Mar. 31, 2014
In Millions, unless otherwise specified
Special Deposits [Line Items]	'
Restricted Cash And Cash Equivalents	$163.30

Other_Taxes_Details

Other Taxes (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Excise And Sales Taxes	$44.40	$38.40
The Connecticut Light And Power Company [Member]	'	'
Excise And Sales Taxes	$35.60	$32

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Capital Expenditures Incurred But Not Yet Paid	$108.50	$98.70
The Connecticut Light And Power Company [Member]	'	'
Capital Expenditures Incurred But Not Yet Paid	36.2	28.2
NSTAR Electric Company [Member]	'	'
Capital Expenditures Incurred But Not Yet Paid	28	30.7
Public Service Company Of New Hampshire [Member]	'	'
Capital Expenditures Incurred But Not Yet Paid	14.4	12.9
Western Massachusetts Electric Company [Member]	'	'
Capital Expenditures Incurred But Not Yet Paid	$14.40	$15.80

Severance_Benefits_Details

Severance Benefits (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'	'
Description Of Postemployment Benefits	'Severance Benefits In the first quarter of 2014, NU recorded severance benefit expenses of $4.3 million associated with the partial outsourcing of information technology functions and ongoing post-merger integration. As of March 31, 2014 and December 31, 2013, the severance accrual totaled $17.7 million and $14.7 million, respectively, and was included in Other Current Liabilities on the balance sheets.	'
Postemployment Benefits Period Expense	$4.30	'
Postemployment Benefits Liability Current And Noncurrent	$17.70	$14.70

REGULATORY_ACCOUNTING_Details

REGULATORY ACCOUNTING (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	$4,059,600,000	$4,294,500,000
Regulatory Assets Current	573,028,000	535,791,000
Regulatory Assets Long Term	3,486,645,000	3,758,694,000
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 $71.7 million ($12.4 million for CL&P, $33.7 million for NSTAR Electric, and $10.2 million for WMECO) and $65.1 million ($7.3 million for CL&P, $33.4 million for NSTAR Electric, and $10.1 million for WMECO) of additional regulatory costs as of March 31, 2014 and December 31, 2013, 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.	'
Description Of Regulatory Costs Recently Approved	'On March 12, 2014, the PURA issued a final decision on CL&P’s request to recover storm restoration costs associated with five major storms, which occurred in 2011 and 2012. 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 recovered through depreciation expense in future rate proceedings. CL&P will recover the $365 million with carrying charges in its distribution rates over a six-year period beginning December 1, 2014. The remaining costs were either disallowed or we believe will be recovered from other sources. These costs did not have a material impact on CL&P’s financial position, results of operations or cash flows. As discussed in Note 2, "Regulatory Accounting," during the first quarter of 2014, as a result of a regulatory proceeding, CL&P reclassified approximately $18 million from Regulatory Assets to Property, Plant and Equipment, Net.	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	855,300,000	707,300,000
Regulatory Liability Current	263,754,000	204,278,000
Regulatory Liabilities Long-Term	591,468,000	502,984,000
Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	437,300,000	435,100,000
Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	203,600,000	151,200,000
AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	67,800,000	68,100,000
Contractual Obligations [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	93,300,000	0
Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	53,300,000	52,900,000
The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	1,756,500,000	1,814,000,000
Regulatory Assets Current	175,926,000	150,943,000
Regulatory Assets Long Term	1,580,609,000	1,663,147,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	197,400,000	187,800,000
Regulatory Liability Current	107,284,000	93,961,000
Regulatory Liabilities Long-Term	90,053,000	93,757,000
The Connecticut Light And Power Company [Member] | Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	27,500,000	29,100,000
The Connecticut Light And Power Company [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	105,600,000	95,600,000
The Connecticut Light And Power Company [Member] | AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	54,500,000	54,700,000
The Connecticut Light And Power Company [Member] | Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	9,800,000	8,400,000
NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	1,264,500,000	1,439,300,000
Regulatory Assets Current	222,598,000	204,144,000
Regulatory Assets Long Term	1,041,925,000	1,235,156,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	330,700,000	307,100,000
Regulatory Liability Current	73,596,000	53,958,000
Regulatory Liabilities Long-Term	257,101,000	253,108,000
NSTAR Electric Company [Member] | Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	252,500,000	250,000,000
NSTAR Electric Company [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	43,800,000	21,900,000
NSTAR Electric Company [Member] | AFUDC Transmission Incentive [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	4,000,000	4,100,000
NSTAR Electric Company [Member] | Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	30,400,000	31,100,000
Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	294,500,000	311,500,000
Regulatory Assets Current	83,832,000	92,194,000
Regulatory Assets Long Term	210,702,000	219,346,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	79,100,000	72,300,000
Regulatory Liability Current	27,333,000	20,643,000
Regulatory Liabilities Long-Term	51,769,000	51,723,000
Public Service Company Of New Hampshire [Member] | Cost Of Removal [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	49,700,000	49,700,000
Public Service Company Of New Hampshire [Member] | Regulatory Tracker Deferrals Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	27,500,000	21,600,000
Public Service Company Of New Hampshire [Member] | Other Regulatory Liabilities [Member]	'	'
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	1,900,000	1,000,000
Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	181,800,000	189,100,000
Regulatory Assets Current	49,578,000	43,024,000
Regulatory Assets Long Term	132,181,000	146,088,000
Regulatory Liabilities [Line Items]	'	'
Regulatory Liabilities, Total	32,200,000	33,800,000
Regulatory Liability Current	21,816,000	19,858,000
Regulatory Liabilities Long-Term	10,445,000	13,873,000
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	22,400,000	21,100,000
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	500,000	3,400,000
Benefit Costs [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	1,205,400,000	1,240,200,000
Benefit Costs [Member] | The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	287,100,000	297,700,000
Benefit Costs [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	321,300,000	496,700,000
Benefit Costs [Member] | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	96,700,000	100,600,000
Benefit Costs [Member] | Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	55,100,000	57,300,000
Regulatory Assets Offsetting Derivative Liabilities [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	564,900,000	638,000,000
Regulatory Assets Offsetting Derivative Liabilities [Member] | The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	557,000,000	630,400,000
Regulatory Assets Offsetting Derivative Liabilities [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	7,900,000	7,700,000
Regulatory Assets Offsetting Derivative Liabilities [Member] | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	0
Regulatory Assets Offsetting Derivative Liabilities [Member] | Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	0	0
Deferred Income Tax Charges Member	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	629,200,000	626,200,000
Deferred Income Tax Charges Member | The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	419,700,000	415,500,000
Deferred Income Tax Charges Member | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	82,500,000	84,000,000
Deferred Income Tax Charges Member | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	39,400,000	40,300,000
Deferred Income Tax Charges Member | Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	43,500,000	43,700,000
Storm Restoration Costs [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	580,900,000	589,600,000
Storm Restoration Costs [Member] | The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	395,300,000	397,800,000
Storm Restoration Costs [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	109,200,000	109,300,000
Storm Restoration Costs [Member] | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	40,300,000	43,700,000
Storm Restoration Costs [Member] | Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	36,100,000	38,800,000
Goodwill Regulatory Asset [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	520,800,000	525,900,000
Goodwill Regulatory Asset [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	447,100,000	451,500,000
Regulatory Tracker Deferrals Regulatory Assets [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	347,400,000	323,400,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	33,300,000	8,000,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	182,700,000	169,500,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	75,200,000	83,300,000
Regulatory Tracker Deferrals Regulatory Assets [Member] | Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	31,600,000	32,600,000
Power Contracts Buy Out Agreements [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	63,400,000	70,200,000
Power Contracts Buy Out Agreements [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	58,300,000	64,700,000
Power Contracts Buy Out Agreements [Member] | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	5,100,000	5,500,000
Other Regulatory Assets [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	147,600,000	281,000,000
Other Regulatory Assets [Member] | The Connecticut Light And Power Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	64,100,000	64,600,000
Other Regulatory Assets [Member] | NSTAR Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	55,500,000	55,900,000
Other Regulatory Assets [Member] | Public Service Company Of New Hampshire [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	37,800,000	38,100,000
Other Regulatory Assets [Member] | Western Massachusetts Electric Company [Member]	'	'
Regulatory Asset [Line Items]	'	'
Regulatory Assets, Total	$15,500,000	$16,700,000

PROPERTY_PLANT_AND_ACCUMULATED2

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Public Utility Property Plant And Equipment [Line Items]	'	'
Public Utilities Property Plant And Equipment Distribution	$12,039,700,000	$11,950,200,000
Public Utilities Property Plant And Equipment Distribution Natural Gas	2,447,900,000	2,425,900,000
Public Utilities Property Plant And Equipment Transmission	6,423,500,000	6,412,500,000
Public Utilities Property Plant And Equipment Generation Or Processing	1,154,700,000	1,152,300,000
Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total	22,065,800,000	21,940,900,000
Public Utilities Property Plant And Equipment Other Property Plant And Equipment	510,200,000	508,700,000
Public Utilities Property Plant And Equipment Plant In Service	22,576,000,000	22,449,600,000
Electric And Natural Gas Utility Accumulated Depreciation	-5,491,700,000	-5,387,000,000
Other Accumulated Depreciation	-204,700,000	-196,200,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-5,696,400,000	-5,583,200,000
Property Plant And Equipment Net Excluding Construction Work In Progress	16,879,600,000	16,866,400,000
Public Utilities Property Plant And Equipment Construction Work In Progress	833,400,000	709,800,000
Property, Plant and Equipment, Net	17,713,027,000	17,576,186,000
Description Of Regulatory Costs Recently Approved	'On March 12, 2014, the PURA issued a final decision on CL&P’s request to recover storm restoration costs associated with five major storms, which occurred in 2011 and 2012. 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 recovered through depreciation expense in future rate proceedings. CL&P will recover the $365 million with carrying charges in its distribution rates over a six-year period beginning December 1, 2014. The remaining costs were either disallowed or we believe will be recovered from other sources. These costs did not have a material impact on CL&P’s financial position, results of operations or cash flows. As discussed in Note 2, "Regulatory Accounting," during the first quarter of 2014, as a result of a regulatory proceeding, CL&P reclassified approximately $18 million from Regulatory Assets to Property, Plant and Equipment, Net.	'
The Connecticut Light And Power Company [Member]	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'
Public Utilities Property Plant And Equipment Distribution	4,979,800,000	4,930,700,000
Public Utilities Property Plant And Equipment Transmission	3,074,800,000	3,071,900,000
Public Utilities Property Plant And Equipment Generation Or Processing	0	0
Public Utilities Property Plant And Equipment Plant In Service	8,054,600,000	8,002,600,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,838,500,000	-1,804,100,000
Property Plant And Equipment Net Excluding Construction Work In Progress	6,216,100,000	6,198,500,000
Public Utilities Property Plant And Equipment Construction Work In Progress	290,100,000	252,800,000
Property, Plant and Equipment, Net	6,506,245,000	6,451,259,000
NSTAR Electric Company [Member]	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'
Public Utilities Property Plant And Equipment Distribution	4,717,600,000	4,694,700,000
Public Utilities Property Plant And Equipment Transmission	1,769,000,000	1,772,300,000
Public Utilities Property Plant And Equipment Generation Or Processing	0	0
Public Utilities Property Plant And Equipment Plant In Service	6,486,600,000	6,467,000,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,664,600,000	-1,631,300,000
Property Plant And Equipment Net Excluding Construction Work In Progress	4,822,000,000	4,835,700,000
Public Utilities Property Plant And Equipment Construction Work In Progress	247,200,000	208,200,000
Property, Plant and Equipment, Net	5,069,203,000	5,043,887,000
Public Service Company Of New Hampshire [Member]	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'
Public Utilities Property Plant And Equipment Distribution	1,620,300,000	1,608,200,000
Public Utilities Property Plant And Equipment Transmission	701,700,000	695,700,000
Public Utilities Property Plant And Equipment Generation Or Processing	1,133,600,000	1,131,200,000
Public Utilities Property Plant And Equipment Plant In Service	3,455,600,000	3,435,100,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-1,040,600,000	-1,021,800,000
Property Plant And Equipment Net Excluding Construction Work In Progress	2,415,000,000	2,413,300,000
Public Utilities Property Plant And Equipment Construction Work In Progress	71,400,000	54,300,000
Property, Plant and Equipment, Net	2,486,440,000	2,467,556,000
Western Massachusetts Electric Company [Member]	'	'
Public Utility Property Plant And Equipment [Line Items]	'	'
Public Utilities Property Plant And Equipment Distribution	762,000,000	756,600,000
Public Utilities Property Plant And Equipment Transmission	831,700,000	826,400,000
Public Utilities Property Plant And Equipment Generation Or Processing	21,100,000	21,100,000
Public Utilities Property Plant And Equipment Plant In Service	1,614,800,000	1,604,100,000
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	-278,400,000	-271,500,000
Property Plant And Equipment Net Excluding Construction Work In Progress	1,336,400,000	1,332,600,000
Public Utilities Property Plant And Equipment Construction Work In Progress	62,400,000	48,500,000
Property, Plant and Equipment, Net	$1,398,810,000	$1,381,060,000

DERIVATIVE_INSTURMENTS_Details

DERIVATIVE INSTURMENTS (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative Instrument Detail Abstract	'	'	'
Derivative Liabilities, Noncurrent	($546,387,000)	'	($624,050,000)
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. NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity related contract to purchase up to 35 MW per year through 2019. As of March 31, 2014 and December 31, 2013, NU had NYMEX future contracts in order to reduce variability associated with the purchase price of approximately 7.4 million and 9.1 million MMBtu of natural gas, respectively.	'	'
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract	'	'	'
Derivative Gain Loss On Derivative Net	'	300,000	'
Derivative Instruments Gain Loss Recognized In Regulatory Asset Liability	54,100,000	28,000,000	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsExitPricePremium	'Exit price premiums of 9 percent through 26 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	-92,040,000	'	-92,233,000
Derivative Liabilities, Noncurrent	-539,444,000	'	-617,072,000
Fair Value Inputs Level 2 [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	1,100,000	'	1,600,000
Derivative Liabilities, Noncurrent	-200,000	'	'
Derivative Assets Noncurrent	'	'	200,000
Fair Value Inputs Level 3 [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	8,100,000	'	8,600,000
Derivative Liabilities - Current	-93,300,000	'	-93,700,000
Derivative Liabilities, Noncurrent	-546,200,000	'	-624,100,000
Derivative Assets Noncurrent	67,100,000	'	74,000,000
Fair Value Inputs Level 3 [Member] | MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	1.7	'	5.07
FairValueInputsEnergyPrices	57	'	49
FairValueInputsRenewableEnergyCreditPrices	38	'	36
FairValueInputsForwardReserve	3.3	'	3.3
Fair Value Inputs Level 3 [Member] | MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	10.42	'	11.82
FairValueInputsEnergyPrices	60	'	77
FairValueInputsRenewableEnergyCreditPrices	70	'	87
FairValueInputsForwardReserve	3.3	'	3.3
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	7,300,000	'	7,300,000
Derivative Liabilities - Current	-92,000,000	'	-92,200,000
Derivative Liabilities, Noncurrent	-539,400,000	'	-617,100,000
Derivative Assets Noncurrent	67,100,000	'	71,400,000
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member] | MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	5.23	'	5.07
FairValueInputsEnergyPrices	57	'	56
FairValueInputsForwardReserve	3.3	'	3.3
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member] | MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	10.42	'	10.42
FairValueInputsEnergyPrices	60	'	58
FairValueInputsForwardReserve	3.3	'	3.3
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	800,000	'	1,200,000
Derivative Liabilities - Current	-1,300,000	'	-1,500,000
Derivative Liabilities, Noncurrent	-6,800,000	'	-7,000,000
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member] | MinimumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	1.7	'	5.07
FairValueInputsRenewableEnergyCreditPrices	38	'	36
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member] | MaximumMember	'	'	'
FairValueInputsQuantitativeInformation[Abstract]	'	'	'
FairValueInputsCapacityPrices	7.38	'	7.38
FairValueInputsRenewableEnergyCreditPrices	70	'	70
Netting And Collateral [Member] | Fair Value Inputs Level 2 [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	-100,000	'	-300,000
Netting And Collateral [Member] | Fair Value Inputs Level 3 [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	-9,700,000	'	-9,800,000
Derivative Assets Noncurrent	-31,700,000	'	-42,200,000
Netting And Collateral [Member] | Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	-9,700,000	'	-9,800,000
Derivative Assets Noncurrent	-31,700,000	'	-42,200,000
Commodity [Member] | Fair Value Inputs Level 2 [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	1,200,000	'	1,900,000
Derivative Liabilities, Noncurrent	-200,000	'	'
Derivative Assets Noncurrent	'	'	200,000
Commodity [Member] | Fair Value Inputs Level 3 [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	17,800,000	'	18,400,000
Derivative Liabilities - Current	-93,300,000	'	-93,700,000
Derivative Liabilities, Noncurrent	-546,200,000	'	-624,100,000
Derivative Assets Noncurrent	98,800,000	'	116,200,000
Commodity [Member] | Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	17,000,000	'	17,100,000
Derivative Liabilities - Current	-92,000,000	'	-92,200,000
Derivative Liabilities, Noncurrent	-539,400,000	'	-617,100,000
Derivative Assets Noncurrent	98,800,000	'	113,600,000
Commodity [Member] | Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member]	'	'	'
Derivative Instrument Detail Abstract	'	'	'
Derivative Assets - Current	800,000	'	1,200,000
Derivative Liabilities - Current	-1,300,000	'	-1,500,000
Derivative Liabilities, Noncurrent	($6,800,000)	'	($7,000,000)

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	($635.20)	($878.60)
Net Realized/Unrealized Gains Losses included in Net Income	0	5.7
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	49.2	26.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	21.7	13.6
Ending Balance	-564.3	-833.1
The Connecticut Light And Power Company [Member]	'	'
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	-630.6	-866.2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	52	24.3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	21.6	22.3
Ending Balance	-557	-819.6
NSTAR Electric Company [Member]	'	'
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	-7.3	-14.9
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	-0.1	0.7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0.1	0.6
Ending Balance	($7.30)	($13.60)

MARKETABLE_SECURITIES_Details

MARKETABLE SECURITIES (Details) (USD $)

3 Months Ended

3 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Mar. 31, 2014

Mar. 31, 2013

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

US Government Debt Securities Member

US Government Debt Securities Member

US Government Debt Securities Member

US Government Debt Securities Member

Corporate Bond Securities Member

Corporate Bond Securities Member

Corporate Bond Securities Member

Corporate Bond Securities Member

Asset Backed Securities Member

Asset Backed Securities Member

Asset Backed Securities Member

Asset Backed Securities Member

Municipal Bonds Member

Municipal Bonds Member

Municipal Bonds Member

Municipal Bonds Member

Other Debt Securities Member

Other Debt Securities Member

Other Debt Securities Member

Other Debt Securities Member

Cash And Cash Equivalents Member

Cash And Cash Equivalents Member

Cash And Cash Equivalents Member

Cash And Cash Equivalents Member

Mutual Funds [Member]

Mutual Funds [Member]

Debt Securities

Debt Securities

Debt Securities

Debt Securities

Equity Securities

Equity Securities

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 2 [Member]

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Fair Value Inputs Level 1 Member

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Schedule Of Available For Sale Securities [Line Items]

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair Value Of Securities Under Fair Value Option

$57.40

'

$57.20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

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'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair Value, Option, Changes in Fair Value, Gain (Loss)

0.2

4.2

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'

'

'

'

'

'

'

'

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'

'

'

'

'

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'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Investments, Debt and Equity Securities [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

'

'

'

'

'

'

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'

'

'

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'

'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Fair Value Disclosure

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

304.7

299.6

57.9

57.9

228.9

224.1

Available-for-sale Securities, Gross Unrealized Gains

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.8

2.5

0

0

65.6

60.5

AvailableForSaleSecuritiesGrossUnrealizedLoss

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

'

'

'

'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-0.7

-2.1

-0.1

0

'

'

Available For Sale Securities Amortized Cost

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300.6

299.2

58

57.9

163.3

163.6

Marketable Securities, Restricted

435.9

'

424

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities Fair Value Abstract

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value

69.4

'

'

1.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

'

'

'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities After Ten Years Fair Value

107

'

'

3.9

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities After One Year Through Five Years Fair Value

73.9

'

'

33.2

'

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'

'

'

'

'

'

'

'

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'

'

'

'

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'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities Within One Year Fair Value

54.4

'

'

19.2

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'

'

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'

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'

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'

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'

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'

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'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities Fair Value

304.7

'

'

57.9

'

'

'

'

'

'

'

'

'

'

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'

'

'

'

'

'

'

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'

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'

'

Available For Sale Securities Debt Maturities Amortized Cost Abstract

'

'

'

'

'

'

'

'

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'

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'

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'

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'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost

73.3

'

'

33.2

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'

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'

'

Available For Sale Securities Debt Maturities Within One Year Amortized Cost

54.5

'

'

19.2

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'

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'

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'

'

Available For Sale Securities Debt Maturities After Ten Years Amortized Cost

104.7

'

'

4

'

'

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'

'

Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost

68.1

'

'

1.6

'

'

'

'

'

'

'

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'

'

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'

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'

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'

'

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'

'

'

'

'

'

'

'

'

'

Available For Sale Securities Debt Maturities Amortized Cost

300.6

'

'

58

'

'

'

'

'

'

'

'

'

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'

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'

'

'

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'

'

'

Fair Value Assets And Liabilities Measured On Recurring Basis Abstract

'

'

'

'

'

'

'

'

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'

'

'

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'

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'

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'

'

'

'

'

'

'

'

'

'

'

Investments Fair Value Disclosure

615

'

580.9

57.9

57.9

332.8

314.2

4.3

10.9

282.2

266.7

53.6

47

56.7

61.4

0

6.8

56.3

53.6

14.1

15.1

35.3

30.4

14

9

109.6

105.5

12.3

11.2

24.3

15.8

13.2

4.9

22.5

32.9

4.3

10.9

310.3

281.3

'

'

'

'

'

'

TradingSecuritiesEquity

24

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'

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'

'

'

'

'

'

'

'

'

'

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'

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'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

IncreaseDecreaseInTradingSecurities

$0.50

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

'

'

'

'

'

'

'

SHORT_TERM_AND_LONG_TERM_DEBT_

SHORT TERM AND LONG TERM DEBT (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]	'	'
Line of Credit Facility, Remaining Borrowing Capacity	$631,500,000	$435,500,000
Line of Credit Facility, Amount Outstanding	818,500,000	1,010,000,000
Short-term Debt, Weighted Average Interest Rate	0.23%	0.24%
Description of commercial paper program	'NU parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year $1.45 billion revolving credit facility due to expire on September 6, 2018. The revolving credit facility is to be used primarily to backstop the $1.45 billion commercial paper program at NU. The commercial paper program allows NU parent to issue commercial paper as a form of short-term debt. As of March 31, 2014 and December 31, 2013, NU had approximately $818.5 million and $1.01 billion, respectively, in short-term borrowings outstanding under the NU parent commercial paper program, leaving $631.5 million and $435.5 million of available borrowing capacity as of March 31, 2014 and December 31, 2013, respectively. The weighted-average interest rate on these borrowings as of March 31, 2014 and December 31, 2013 was 0.23 percent and 0.24 percent, respectively, which is generally based on money market rates. As of March 31, 2014, there were intercompany loans from NU of $351.6 million to CL&P, $39.9 million to PSNH and $37.4 million to WMECO. As of December 31, 2013, there were intercompany loans from NU of $287.3 million to CL&P and $86.5 million to PSNH. NSTAR Electric has a five-year $450 million revolving credit facility due to expire on September 6, 2018. This facility serves to backstop NSTAR Electric’s existing $450 million commercial paper program. As of March 31, 2014, NSTAR Electric had no borrowings outstanding under its commercial paper program. As of December 31, 2013, NSTAR Electric had $103.5 million in short-term borrowings outstanding under its commercial paper program, leaving $346.5 million of available borrowing capacity. The weighted-average interest rate on these borrowings as of December 31, 2013 was 0.13 percent, which is generally based on money market rates.	'
Description of Working Capital	'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 their 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 $424 million, $355 million and $177 million at NU, CL&P and NSTAR Electric, respectively, as of March 31, 2014. As of March 31, 2014, $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, $28.8 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 April 24, 2014, CL&P issued $250 million of 4.30 percent 2014 Series A First Mortgage Bonds, due to mature in April 2044. The proceeds, net of issuance costs, were used to repay short-term borrowings. In accordance with applicable accounting guidance, Notes Payable of $247.4 million were classified as Long-Term Debt on NU’s balance sheet as of March 31, 2014.	'
Notes Payable to Banks	571,147,000	1,093,000,000
Long-term Debt, Description	': 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 $75 million 4.80 percent Series G First Mortgage Bonds that matured on January 1, 2014 and to pay $25 million in short-term borrowings. 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 March 7, 2014, NSTAR Electric issued $300 million of 4.40 percent debentures, due to mature in 2044. The proceeds, net of issuance costs, were used to repay the $300 million of 4.875 percent debentures that matured on April 15, 2014. On April 24, 2014, CL&P issued $250 million of 4.30 percent 2014 Series A First Mortgage Bonds, due to mature in April 2044. The proceeds, net of issuance costs, were used to repay short-term borrowings. In accordance with applicable accounting guidance, Notes Payable of $247.4 million were classified as Long-Term Debt on NU’s balance sheet as of March 31, 2014.	'
The Connecticut Light And Power Company [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Notes Payable To Affiliated Companies	351,600,000	287,300,000
NSTAR Electric Company [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Line of Credit Facility, Remaining Borrowing Capacity	'	346,500,000
Line of Credit Facility, Amount Outstanding	'	103,500,000
Short-term Debt, Weighted Average Interest Rate	'	0.13%
Notes Payable to Banks	0	103,500,000
Public Service Company Of New Hampshire [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Notes Payable To Affiliated Companies	39,900,000	86,500,000
Western Massachusetts Electric Company [Member]	'	'
Line of Credit Facility [Line Items]	'	'
Notes Payable To Affiliated Companies	$37,400,000	$0

PENSION_BENEFITS_AND_POSTRETIR1

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) (USD $)

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Pension Plans Defined Benefit Member

Pension Plans Defined Benefit Member

PBOP Plan

PBOP Plan

The Connecticut Light And Power Company [Member]

The Connecticut Light And Power Company [Member]

The Connecticut Light And Power Company [Member]

The Connecticut Light And Power Company [Member]

The Connecticut Light And Power Company [Member]

The Connecticut Light And Power Company [Member]

NSTAR Electric Company [Member]

NSTAR Electric Company [Member]

NSTAR Electric Company [Member]

NSTAR Electric Company [Member]

NSTAR Electric Company [Member]

NSTAR Electric Company [Member]

NSTAR Electric Company [Member]

Public Service Company Of New Hampshire [Member]

Public Service Company Of New Hampshire [Member]

Public Service Company Of New Hampshire [Member]

Public Service Company Of New Hampshire [Member]

Public Service Company Of New Hampshire [Member]

Public Service Company Of New Hampshire [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Western Massachusetts Electric Company [Member]

Pension Plans Defined Benefit Member

Pension Plans Defined Benefit Member

PBOP Plan

PBOP Plan

Pension Plans Defined Benefit Member

Pension Plans Defined Benefit Member

PBOP Plan

PBOP Plan

Supplemental Employee Retirement Plans, Defined Benefit [Member]

Pension Plans Defined Benefit Member

Pension Plans Defined Benefit Member

PBOP Plan

PBOP Plan

Pension Plans Defined Benefit Member

Pension Plans Defined Benefit Member

PBOP Plan

PBOP Plan

Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Defined Benefit Plan Service Cost

'

'

$22,300,000

$26,600,000

$3,000,000

$4,800,000

'

'

$5,200,000

$6,100,000

$600,000

$900,000

'

'

$4,600,000

$9,300,000

$700,000

'

'

'

'

$2,800,000

$3,300,000

$400,000

$600,000

'

'

$1,000,000

$1,200,000

$100,000

$200,000

Defined Benefit Plan Interest Cost

'

'

56,600,000

51,400,000

12,600,000

12,800,000

'

'

13,300,000

12,100,000

2,100,000

2,000,000

'

'

10,200,000

14,200,000

4,900,000

'

'

'

'

6,500,000

6,000,000

1,100,000

1,000,000

'

'

2,700,000

2,500,000

500,000

400,000

Defined Benefit Plan, Expected Return on Plan Assets

'

'

-77,700,000

-70,300,000

-15,700,000

-13,800,000

'

'

-19,400,000

-18,500,000

-2,700,000

-2,500,000

'

'

-15,800,000

-22,000,000

-6,400,000

'

'

'

'

-10,200,000

-7,700,000

-1,400,000

-1,300,000

'

'

-4,600,000

-4,300,000

-600,000

-600,000

Defined Benefit Plan, Amortization of Gains (Losses)

'

'

33,000,000

52,900,000

3,000,000

8,200,000

'

'

9,100,000

14,100,000

1,100,000

1,700,000

'

'

5,800,000

14,500,000

-100,000

'

'

'

'

3,300,000

5,500,000

500,000

900,000

'

'

1,900,000

3,000,000

100,000

300,000

Defined Benefit Plan Amortization Of Prior Service Cost Credit

'

'

1,100,000

1,100,000

-600,000

-600,000

'

'

500,000

500,000

'

'

'

'

0

0

-500,000

'

'

'

'

200,000

100,000

'

'

'

'

100,000

100,000

'

'

Defined Benefit Plan Net Periodic Benefit Cost

'

'

35,300,000

61,700,000

2,300,000

11,400,000

'

'

8,700,000

14,300,000

1,100,000

2,100,000

'

'

4,800,000

16,000,000

-1,400,000

'

'

'

'

2,600,000

7,200,000

600,000

1,200,000

'

'

1,100,000

2,500,000

100,000

300,000

Related Intercompany Allocationsof Defined Benefit Expense

'

'

'

'

'

'

'

'

6,800,000

10,700,000

1,100,000

1,600,000

'

'

2,400,000

-2,000,000

100,000

4,300,000

'

'

'

1,900,000

2,600,000

300,000

400,000

'

'

1,300,000

1,800,000

200,000

300,000

Amount Capitalized Defined Benefit Expense

'

'

9,700,000

16,700,000

400,000

3,500,000

'

'

4,900,000

7,000,000

500,000

1,200,000

'

'

1,900,000

5,300,000

-500,000

'

'

'

'

900,000

2,200,000

200,000

300,000

'

'

800,000

1,300,000

100,000

200,000

Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Pension and Other Postretirement Defined Benefit Plans, Current Liabilities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

400,000

'

'

'

'

'

'

'

'

'

'

'

'

Accrued Pension, PBOP and SERP

$890,019,000

$896,844,000

'

'

'

'

$94,820,000

$95,895,000

'

'

'

'

$150,938,000

$118,010,000

$74,800,000

'

$73,000,000

'

$3,500,000

$15,321,000

$15,272,000

'

'

'

'

$3,850,000

$3,911,000

'

'

'

'

Environmental_Matters_Details

Environmental Matters (Details) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Site Contingency [Line Items]	'	'
Environmental Site Quantity	66	68
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	$35.40	'
Ending Balance	35.4	35.4
MGP Site accrual [Member]	'	'
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Ending Balance	30.9	31.4
The Connecticut Light And Power Company [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	18	18
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	3.4	'
Ending Balance	3.4	3.4
NSTAR Electric Company [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	12	12
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	1.2	'
Ending Balance	1.2	1.2
Public Service Company Of New Hampshire [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	13	15
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	5.4	'
Ending Balance	5.4	5.4
Western Massachusetts Electric Company [Member]	'	'
Site Contingency [Line Items]	'	'
Environmental Site Quantity	5	5
Accrual for Environmental Loss Contingencies [Roll Forward]	'	'
Beginning Balance	0.4	'
Ending Balance	$0.40	$0.40

Deferred_Contractual_Obligatio

Deferred Contractual Obligations (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Loss Contingency, Information about Litigation Matters [Abstract]	'	'
Court of Federal Claims Ruling To CYAPC	'	$126.30
Court Of Federal Claims Ruling To YAEC	'	73.3
Court Of Federal Claims Ruling To MYAPC	'	35.8
Connecticut Yankee Proceeds Received	90	'
Yankee Atomic Proceeds Received	73.3	'
Maine Yankee Proceeds Received	$35.80	'

Guarantees_and_Indemnification1

Guarantees and Indemnifications (Details) (USD $)	Mar. 31, 2014
In Millions, unless otherwise specified
Guarantee Of Financial Obligations Of Npt [Member]	'
Guarantee Obligations [Line Items]	'
Guarantee Obligations Maximum Exposure	$25
Various Subsidiary Surety Bonds And Performance Guarantees Expiring Between 2014 And 2016 [Member]	'
Guarantee Obligations [Line Items]	'
Guarantee Obligations Maximum Exposure	66.7
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	16.8
Guarantee Of Debt Of Ne Hydros [Member]	'
Guarantee Obligations [Line Items]	'
Guarantee Obligations Maximum Exposure	$3

Other_Contingencies_Details

Other Contingencies (Details) (Unfavorable Regulatory Action [Member])	3 Months Ended
	Mar. 31, 2014
Unfavorable Regulatory Action [Member]	'
Loss Contingencies Line Items	'
Loss Contingency, Description	'     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 the financial position, results of operations or cash flows. Management expects the CL&P, NSTAR Electric, PSNH, and WMECO aggregate shareholder equity invested in their transmission facilities will be approximately $2.4 billion at the end of 2014. As a result, each 10 basis point change in the prospective period authorized base ROE would change annual consolidated earnings by an approximate $2.4 million. E. 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. F. 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.

FAIR_VALUE_OF_FINANCIAL_INSTRU2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	$155,568,000	$155,568,000
Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,600,000	155,600,000
Other Long Term Debt	8,848,900,000	8,310,200,000
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	152,000,000	152,700,000
Other Long Term Debt	9,177,700,000	8,443,100,000
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	2,741,400,000	2,741,200,000
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	110,900,000	110,500,000
Other Long Term Debt	3,033,100,000	2,952,800,000
NSTAR Electric Company [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000,000	43,000,000
NSTAR Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000,000	43,000,000
Other Long Term Debt	2,099,000,000	1,801,100,000
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	41,100,000	42,200,000
Other Long Term Debt	2,224,000,000	1,888,000,000
Public Service Company Of New Hampshire [Member] | Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Other Long Term Debt	1,049,100,000	1,049,000,000
Public Service Company Of New Hampshire [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Other Long Term Debt	1,096,500,000	1,073,900,000
Western Massachusetts Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Other Long Term Debt	629,200,000	629,400,000
Western Massachusetts Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]	'	'
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]	'	'
Other Long Term Debt	$661,000,000	$640,100,000

ACCUMULATED_OTHER_COMPREHENSIV2

ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
AOCI Cash Flow Hedging Component [Abstract]	'	'
Beginning Balance -AOCI From CF Hedges Effect Net Of Tax	($14,400,000)	($16,400,000)
OCI Amortization of Cash Flow Hedge, Net of Tax	500,000	500,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	509,000	516,000
Ending Balance - AOCI From CFHedges Effect Net Of Tax	-13,900,000	-15,900,000
AOCI Unrealized GainLoss component [Abstract]	'	'
AOCI Unrealized Gains/Losses on Other Securities	400,000	1,300,000
OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax	200,000	-100,000
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	240,000	-181,000
AOCI Unrealized Gains/Losses on Other Securities-Ending Balance	600,000	1,200,000
AOCI Defined Benefit Component [Abstract]	'	'
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	-32,000,000	57,800,000
Reclassification of DB Plans	1,000,000	1,600,000
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	961,000	1,621,000
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	-31,000,000	-56,200,000
AOCI Rollforward [Abstract]	'	'
AOCI Beginning Balance	-46,031,000	-72,900,000
AmountReclassifiedFromAOCI	1,500,000	2,100,000
OtherComprehensiveIncomeBeforeReclassifications	200,000	-100,000
Other Comprehensive Income (Loss), Net of Tax, Total	1,710,000	1,956,000
AOCI ending Balance	-44,321,000	-70,900,000
Reclassication of Items out of AOCI [Abstract]	'	'
OCI Reclass CF Hedging Tax	300,000	300,000
OCI Amortization of Cash Flow Hedges, Before Tax	-800,000	-800,000
OCI Amortization of Cash Flow Hedge, Net of Tax	-500,000	-500,000
Amortization of actuarial gain or loss	-1,700,000	-2,600,000
OCI Defined Benefit Plan Tax	700,000	1,000,000
Reclassification of DB Plans	-1,000,000	-1,600,000
AmountReclassifiedFromAOCI	-1,500,000	-2,100,000
The Connecticut Light And Power Company [Member]	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111,000	111,000
AOCI Unrealized GainLoss component [Abstract]	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	8,000	-6,000
AOCI Rollforward [Abstract]	'	'
AOCI Beginning Balance	-1,387,000	'
Other Comprehensive Income (Loss), Net of Tax, Total	119,000	105,000
AOCI ending Balance	-1,268,000	'
Public Service Company Of New Hampshire [Member]	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	290,000	291,000
AOCI Unrealized GainLoss component [Abstract]	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	14,000	-11,000
AOCI Defined Benefit Component [Abstract]	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	-3,000
AOCI Rollforward [Abstract]	'	'
AOCI Beginning Balance	-8,550,000	'
Other Comprehensive Income (Loss), Net of Tax, Total	304,000	277,000
AOCI ending Balance	-8,246,000	'
Western Massachusetts Electric Company [Member]	'	'
AOCI Cash Flow Hedging Component [Abstract]	'	'
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	85,000	85,000
AOCI Unrealized GainLoss component [Abstract]	'	'
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	2,000	-2,000
AOCI Rollforward [Abstract]	'	'
AOCI Beginning Balance	-3,517,000	'
Other Comprehensive Income (Loss), Net of Tax, Total	87,000	83,000
AOCI ending Balance	($3,430,000)	'

COMMON_SHARES_Details

COMMON SHARES (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
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	333,316,045	333,113,492
Treasury Stock Shares	17,498,327	17,796,672
Common Stock, Shares, Outstanding	315,817,718	315,273,559
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

COMMON_SHAREHOLDER_EQUIT_AND_N

COMMON SHAREHOLDER EQUIT AND NCI (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Shareholders' Equity, Beginning Balance	$9,611,528,000	'
Net Income	237,836,000	229,968,000
Net Income Attributable to Noncontrolling Interests	1,879,000	1,879,000
Other Comprehensive Income (Loss), Net of Tax	1,710,000	1,956,000
Shareholders' Equity, Ending Balance	9,723,933,000	'
Common Shareholders Equity [Member]	'	'
Shareholders' Equity, Beginning Balance	9,611,500,000	9,237,100,000
Net Income	237,800,000	230,000,000
Dividends on Common Shares	-123,900,000	-116,400,000
Dividends, Preferred Stock	-1,900,000	-1,900,000
Issuance of Common Shares	5,200,000	8,400,000
Other Transcations, Net	-6,500,000	-14,000,000
Other Comprehensive Income (Loss), Net of Tax	1,700,000	2,000,000
Shareholders' Equity, Ending Balance	9,723,900,000	9,345,200,000
Preferred Stock Member	'	'
Shareholders' Equity, Beginning Balance	155,600,000	155,600,000
Dividends, Preferred Stock	-1,900,000	-1,900,000
Net Income Attributable to Noncontrolling Interests	1,900,000	1,900,000
Shareholders' Equity, Ending Balance	$155,600,000	$155,600,000

EARNINGS_PER_SHARE_Details

EARNINGS PER SHARE (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Notes To Consolidated Financial Statements [Abstract]	'	'
Net Income Attributable to Controlling Interests	$235,957	$228,089
Basic	315,534,512	315,129,782
Weighted Average Number Diluted Shares Outstanding Adjustment	1,357,607	872,756
Diluted	316,892,119	316,002,538
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	0	6,299
Basic Earnings Per Common Share	$0.75	$0.72
Diluted Earnings Per Common Share	$0.74	$0.72

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	$2,290,590,000	$1,995,023,000	'
Operating Income	467,689,000	418,945,000	'
Total Interest Expense	-89,975,000	-76,255,000	'
Other Income/(Loss), Net	1,667,000	7,765,000	'
Income Tax Expense	-141,545,000	-120,487,000	'
Net Income	237,836,000	229,968,000	'
Net Income Attributable to Noncontrolling Interests	-1,879,000	-1,879,000	'
Net Income Attributable to Controlling Interests	235,957,000	228,089,000	'
Total Assets	28,096,870,000	'	27,795,537,000
Investments in Property, Plant and Equipment	348,691,000	388,950,000	'
Electric Distribution Member	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	1,585,900,000	1,374,200,000	'
Depreciation And Amortization	-148,800,000	-177,000,000	'
Operating Expenses, Other	-1,210,900,000	-1,004,900,000	'
Operating Income	226,200,000	192,300,000	'
Total Interest Expense	47,400,000	42,100,000	'
Other Income/(Loss), Net	1,400,000	4,800,000	'
Net Income Attributable to Controlling Interests	112,200,000	99,500,000	'
Total Assets	18,882,900,000	'	17,260,000,000
Investments in Property, Plant and Equipment	189,400,000	157,800,000	'
Natural Gas Distribution [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	432,800,000	361,800,000	'
Depreciation And Amortization	-17,700,000	-17,400,000	'
Operating Expenses, Other	-321,400,000	-267,200,000	'
Operating Income	93,700,000	77,200,000	'
Total Interest Expense	8,500,000	7,400,000	'
Other Income/(Loss), Net	100,000	200,000	'
Net Income Attributable to Controlling Interests	52,100,000	43,300,000	'
Total Assets	2,846,700,000	'	2,759,700,000
Investments in Property, Plant and Equipment	28,900,000	31,200,000	'
Transmission [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	252,100,000	239,500,000	'
Depreciation And Amortization	-37,000,000	-31,800,000	'
Operating Expenses, Other	-66,400,000	-62,200,000	'
Operating Income	148,700,000	145,500,000	'
Total Interest Expense	25,500,000	21,900,000	'
Other Income/(Loss), Net	1,500,000	2,800,000	'
Net Income Attributable to Controlling Interests	74,900,000	79,900,000	'
Total Assets	5,165,600,000	'	6,745,800,000
Investments in Property, Plant and Equipment	112,200,000	185,400,000	'
Other Segment [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	172,200,000	217,200,000	'
Depreciation And Amortization	-7,000,000	-19,000,000	'
Operating Expenses, Other	-165,400,000	-197,400,000	'
Operating Income	-200,000	800,000	'
Total Interest Expense	9,600,000	6,400,000	'
Other Income/(Loss), Net	294,800,000	321,900,000	'
Net Income Attributable to Controlling Interests	291,700,000	322,800,000	'
Total Assets	11,913,600,000	'	11,842,400,000
Investments in Property, Plant and Equipment	18,200,000	14,600,000	'
Eliminations Segment [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	-152,400,000	-197,700,000	'
Depreciation And Amortization	1,800,000	1,700,000	'
Operating Expenses, Other	149,900,000	199,200,000	'
Operating Income	-700,000	3,200,000	'
Total Interest Expense	-1,000,000	-1,500,000	'
Other Income/(Loss), Net	-296,100,000	-321,900,000	'
Net Income Attributable to Controlling Interests	-294,900,000	-317,400,000	'
Total Assets	-10,711,900,000	'	-10,812,400,000
Investments in Property, Plant and Equipment	0	0	'
Total [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Operating Revenues	2,290,600,000	1,995,000,000	'
Depreciation And Amortization	-208,700,000	-243,500,000	'
Operating Expenses, Other	-1,614,200,000	-1,332,500,000	'
Operating Income	467,700,000	419,000,000	'
Total Interest Expense	90,000,000	76,300,000	'
Other Income/(Loss), Net	1,700,000	7,800,000	'
Net Income Attributable to Controlling Interests	236,000,000	228,100,000	'
Total Assets	28,096,900,000	'	27,795,500,000
Investments in Property, Plant and Equipment	$348,700,000	$389,000,000	'