CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
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