CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current Assets:
Cash	$ 57,941	$ 45,748
Receivables, Net	784,498	792,822
Unbilled Revenues	174,097	216,040
Fuel, Materials and Supplies	304,698	267,713
Regulatory Assets Current	474,198	705,025
Prepayments and Other Current Assets	222,700	199,947
Total Current Assets	2,018,132	2,227,295
Property, Plant and Equipment, Net	17,187,896	16,605,010
Deferred Debits and Other Assets:
Regulatory Assets Long Term	4,882,381	5,132,411
Goodwill	3,519,401	3,519,401
Marketable Securities	468,094	400,329
Derivative Assets Noncurrent	88,887	90,612
Other Long-Term Assets	279,527	327,766
Total Deferred Debits and Other Assets	9,238,290	9,470,519
Total Assets	28,444,318	28,302,824
Current Liabilities:
Notes Payable to Banks	1,343,000	1,120,196
Long-Term Debt - Current Portion	608,346	763,338
Accounts Payable - Current	554,010	764,350
Regulatory Liability Current	224,416	134,115
Other Liabilities - Current	648,658	861,691
Total Current Liabilities	3,378,430	3,643,690
Rate Reduction Bonds	0	82,139
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	3,954,246	3,463,347
Regulatory Liabilities Long-Term	520,732	540,162
Long-Term Derivative Liabilities	766,804	882,654
Accrued Pension, PBOP and SERP	1,808,896	2,130,497
Other Long-Term Liabilities	897,997	967,561
Total Deferred Credits and Other Liabilities	7,948,675	7,984,221
Capitalization:
Long-Term Debt	7,444,192	7,200,156
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:
Common Stock	1,665,098	1,662,547
Capital Surplus, Paid In	6,185,805	6,183,267
Retained Earnings	2,064,401	1,802,714
Accumulated Other Comprehensive Loss	(67,387)	(72,854)
Treasury Stock	(330,464)	(338,624)
Common Shareholders' Equity	9,517,453	9,237,050
Total Capitalization	17,117,213	16,592,774
Total Liabilities and Capitalization	28,444,318	28,302,824
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	15,253	1
Receivables, Net	341,749	284,787
Accounts Receivable from Affiliated Companies	1,733	6,641
Unbilled Revenues	73,687	85,353
Regulatory Assets Current	147,076	185,858
Materials and Supplies	58,124	64,603
Prepayments and Other Current Assets	61,277	26,413
Total Current Assets	698,899	653,656
Property, Plant and Equipment, Net	6,326,225	6,152,959
Deferred Debits and Other Assets:
Regulatory Assets Long Term	2,021,974	2,158,363
Derivative Assets Noncurrent	88,018	90,612
Other Long-Term Assets	91,499	86,498
Total Deferred Debits and Other Assets	2,201,491	2,335,473
Total Assets	9,226,615	9,142,088
Current Liabilities:
Notes Payable To Affiliated Companies	342,900	99,296
Long-Term Debt - Current Portion	150,000	125,000
Accounts Payable - Current	170,683	262,857
Accounts Payable to Affiliated Companies	46,401	52,326
Obligations to Third Party Suppliers	65,580	67,344
Accrued Taxes	60,643	60,109
Regulatory Liability Current	81,988	32,119
Derivative Liabilities - Current	94,123	96,931
Other Liabilities - Current	78,520	125,662
Total Current Liabilities	1,090,838	921,644
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,471,547	1,336,105
Regulatory Liabilities Long-Term	107,964	124,319
Long-Term Derivative Liabilities	756,437	865,571
Accrued Pension, PBOP and SERP	291,257	304,696
Other Long-Term Liabilities	160,368	197,434
Total Deferred Credits and Other Liabilities	2,787,573	2,828,125
Capitalization:
Long-Term Debt	2,591,012	2,737,790
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200	116,200
Common Shareholders' Equity:
Common Stock	60,352	60,352
Capital Surplus, Paid In	1,641,487	1,640,149
Retained Earnings	940,647	839,628
Accumulated Other Comprehensive Loss	(1,494)	(1,800)
Common Shareholders' Equity	2,640,992	2,538,329
Total Capitalization	5,348,204	5,392,319
Total Liabilities and Capitalization	9,226,615	9,142,088
NSTAR Electric Company [Member]
Current Assets:
Cash	15,470	13,695
Receivables, Net	263,055	202,025
Accounts Receivable from Affiliated Companies	70,279	160,176
Unbilled Revenues	48,570	41,377
Regulatory Assets Current	189,754	347,081
Prepayments and Other Current Assets	54,105	28,086
Total Current Assets	641,233	792,440
Property, Plant and Equipment, Net	4,923,410	4,735,297
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,538,222	1,444,870
Other Long-Term Assets	59,267	87,382
Total Deferred Debits and Other Assets	1,597,489	1,532,252
Total Assets	7,162,132	7,059,989
Current Liabilities:
Notes Payable to Banks	156,000	276,000
Long-Term Debt - Current Portion	301,650	1,650
Accounts Payable - Current	157,375	168,611
Accounts Payable to Affiliated Companies	97,992	247,061
Deferred Tax Liabilities Current	32,049	104,668
Regulatory Liability Current	82,521	47,539
Other Liabilities - Current	128,846	144,433
Total Current Liabilities	956,433	989,962
Rate Reduction Bonds	0	43,493
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,463,285	1,321,026
Regulatory Liabilities Long-Term	251,005	244,224
Accrued Pension, PBOP and SERP	380,688	360,932
Other Long-Term Liabilities	145,032	183,190
DueToRelatedPartiesNoncurrent	64,752	70,221
Total Deferred Credits and Other Liabilities	2,304,762	2,179,593
Capitalization:
Long-Term Debt	1,499,378	1,600,911
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	43,000
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	992,625	992,625
Retained Earnings	1,365,934	1,210,405
Common Shareholders' Equity	2,358,559	2,203,030
Total Capitalization	3,900,937	3,846,941
Total Liabilities and Capitalization	7,162,132	7,059,989
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	5,604	2,493
Receivables, Net	78,464	87,164
Accounts Receivable from Affiliated Companies	1,182	723
Unbilled Revenues	31,081	39,982
Taxes Receivable	12,074	17,177
Fuel, Materials and Supplies	125,801	95,345
Regulatory Assets Current	67,716	62,882
Prepayments and Other Current Assets	6,464	22,205
Total Current Assets	328,386	327,971
Property, Plant and Equipment, Net	2,409,039	2,352,515
Deferred Debits and Other Assets:
Regulatory Assets Long Term	301,368	351,059
Other Long-Term Assets	55,953	83,052
Total Deferred Debits and Other Assets	357,321	434,111
Total Assets	3,094,746	3,114,597
Current Liabilities:
Notes Payable To Affiliated Companies	228,500	63,300
Long-Term Debt - Current Portion	50,000
Accounts Payable - Current	60,814	62,864
Accounts Payable to Affiliated Companies	18,279	21,337
Regulatory Liability Current	23,394	23,002
Other Liabilities - Current	54,315	50,950
Renewable Portfolio Standards Compliance Obligation	6,701	17,383
Total Current Liabilities	442,003	238,836
Rate Reduction Bonds	0	29,294
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	490,863	441,577
Regulatory Liabilities Long-Term	52,867	52,418
Accrued Pension, PBOP and SERP	104,557	220,129
Other Long-Term Liabilities	43,866	47,896
Total Deferred Credits and Other Liabilities	692,153	762,020
Capitalization:
Long-Term Debt	839,104	997,932
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	701,659	701,052
Retained Earnings	428,660	395,118
Accumulated Other Comprehensive Loss	(8,833)	(9,655)
Common Shareholders' Equity	1,121,486	1,086,515
Total Capitalization	1,960,590	2,084,447
Total Liabilities and Capitalization	3,094,746	3,114,597
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	3,157	1
Receivables, Net	49,056	47,297
Accounts Receivable from Affiliated Companies	29,231	164
Unbilled Revenues	13,046	16,192
Taxes Receivable	2	15,513
Regulatory Assets Current	37,854	42,370
Marketable Securities - Current	24,570	27,352
Prepayments and Other Current Assets	10,195	7,963
Total Current Assets	167,111	156,852
Property, Plant and Equipment, Net	1,352,705	1,290,498
Deferred Debits and Other Assets:
Regulatory Assets Long Term	194,744	221,752
Marketable Securities	33,195	30,342
Other Long-Term Assets	20,246	23,625
Total Deferred Debits and Other Assets	248,185	275,719
Total Assets	1,768,001	1,723,069
Current Liabilities:
Notes Payable To Affiliated Companies	79,800	31,900
Long-Term Debt - Current Portion	0	55,000
Accounts Payable - Current	40,432	68,141
Accounts Payable to Affiliated Companies	7,521	7,103
Deferred Tax Liabilities Current	9,416	8,404
Regulatory Liability Current	22,400	21,037
Other Liabilities - Current	18,718	24,809
Total Current Liabilities	178,287	216,394
Rate Reduction Bonds	0	9,352
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	392,360	303,111
Regulatory Liabilities Long-Term	11,914	9,686
Accrued Pension, PBOP and SERP	30,791	36,099
Other Long-Term Liabilities	26,503	40,148
Total Deferred Credits and Other Liabilities	461,568	389,044
Capitalization:
Long-Term Debt	549,617	550,270
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	390,645	390,412
Retained Earnings	180,618	160,577
Accumulated Other Comprehensive Loss	(3,600)	(3,846)
Common Shareholders' Equity	578,529	558,009
Total Capitalization	1,128,146	1,108,279
Total Liabilities and Capitalization	$ 1,768,001	$ 1,723,069