CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current Assets:
Cash	$ 36,055	$ 45,748
Receivables, Net	789,410	792,822
Unbilled Revenues	193,534	216,040
Fuel, Materials and Supplies	280,600	267,713
Regulatory Assets Current	577,010	705,025
Prepayments and Other Current Assets	174,484	199,947
Total Current Assets	2,051,093	2,227,295
Property, Plant and Equipment, Net	16,931,448	16,605,010
Deferred Debits and Other Assets:
Regulatory Assets Long Term	4,817,305	5,132,411
Goodwill	3,519,401	3,519,401
Marketable Securities	501,876	400,329
Derivative Assets Noncurrent	89,309	90,612
Other Long-Term Assets	286,460	327,766
Total Deferred Debits and Other Assets	9,214,351	9,470,519
Total Assets	28,196,892	28,302,824
Current Liabilities:
Notes Payable to Banks	794,500	1,120,196
Long-Term Debt - Current Portion	888,346	763,338
Accounts Payable - Current	532,036	764,350
Regulatory Liability Current	216,422	134,115
Other Liabilities - Current	650,206	861,691
Total Current Liabilities	3,081,510	3,643,690
Rate Reduction Bonds	0	82,139
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	3,745,144	3,463,347
Regulatory Liabilities Long-Term	511,737	540,162
Long-Term Derivative Liabilities	788,929	882,654
Accrued Pension, PBOP and SERP	1,956,726	2,130,497
Other Long-Term Liabilities	899,270	967,561
Total Deferred Credits and Other Liabilities	7,901,806	7,984,221
Capitalization:
Long-Term Debt	7,651,396	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	1,664,833	1,662,547
Capital Surplus, Paid In	6,176,366	6,183,267
Retained Earnings	1,969,755	1,802,714
Accumulated Other Comprehensive Loss	(69,469)	(72,854)
Treasury Stock	(334,873)	(338,624)
Common Shareholders' Equity	9,406,612	9,237,050
Total Capitalization	17,213,576	16,592,774
Total Liabilities and Capitalization	28,196,892	28,302,824
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	4,267	1
Receivables, Net	329,090	284,787
Accounts Receivable from Affiliated Companies	1,152	6,641
Unbilled Revenues	82,807	85,353
Regulatory Assets Current	173,484	185,858
Materials and Supplies	60,382	64,603
Prepayments and Other Current Assets	16,578	26,413
Total Current Assets	667,760	653,656
Property, Plant and Equipment, Net	6,251,908	6,152,959
Deferred Debits and Other Assets:
Regulatory Assets Long Term	2,055,333	2,158,363
Derivative Assets Noncurrent	89,309	90,612
Other Long-Term Assets	92,777	86,498
Total Deferred Debits and Other Assets	2,237,419	2,335,473
Total Assets	9,157,087	9,142,088
Current Liabilities:
Notes Payable To Affiliated Companies	189,300	99,296
Long-Term Debt - Current Portion	125,000	125,000
Accounts Payable - Current	169,254	262,857
Accounts Payable to Affiliated Companies	46,042	52,326
Obligations to Third Party Suppliers	65,206	67,344
Accrued Taxes	44,658	60,109
Regulatory Liability Current	64,007	32,119
Derivative Liabilities - Current	95,183	96,931
Other Liabilities - Current	100,044	125,662
Total Current Liabilities	898,694	921,644
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,451,287	1,336,105
Regulatory Liabilities Long-Term	99,863	124,319
Long-Term Derivative Liabilities	777,144	865,571
Accrued Pension, PBOP and SERP	297,059	304,696
Other Long-Term Liabilities	162,495	197,434
Total Deferred Credits and Other Liabilities	2,787,848	2,828,125
Capitalization:
Long-Term Debt	2,740,819	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	1,641,065	1,640,149
Retained Earnings	913,713	839,628
Accumulated Other Comprehensive Loss	(1,604)	(1,800)
Common Shareholders' Equity	2,613,526	2,538,329
Total Capitalization	5,470,545	5,392,319
Total Liabilities and Capitalization	9,157,087	9,142,088
NSTAR Electric Company [Member]
Current Assets:
Cash	11,165	13,695
Receivables, Net	246,292	202,025
Accounts Receivable from Affiliated Companies	394,242	160,176
Unbilled Revenues	52,637	41,377
Regulatory Assets Current	270,813	347,081
Prepayments and Other Current Assets	71,624	28,086
Total Current Assets	1,046,773	792,440
Property, Plant and Equipment, Net	4,839,707	4,735,297
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,461,875	1,444,870
Other Long-Term Assets	59,998	87,382
Total Deferred Debits and Other Assets	1,521,873	1,532,252
Total Assets	7,408,353	7,059,989
Current Liabilities:
Notes Payable to Banks	253,000	276,000
Long-Term Debt - Current Portion	301,650	1,650
Accounts Payable - Current	148,210	168,611
Accounts Payable to Affiliated Companies	423,758	247,061
Deferred Tax Liabilities Current	67,567	104,668
Regulatory Liability Current	74,435	47,539
Other Liabilities - Current	116,473	144,433
Total Current Liabilities	1,385,093	989,962
Rate Reduction Bonds	0	43,493
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,384,219	1,321,026
Regulatory Liabilities Long-Term	249,862	244,224
Accrued Pension, PBOP and SERP	379,015	360,932
Other Long-Term Liabilities	151,033	183,190
DueToRelatedPartiesNoncurrent	64,752	70,221
Total Deferred Credits and Other Liabilities	2,228,881	2,179,593
Capitalization:
Long-Term Debt	1,499,339	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	1,259,415	1,210,405
Common Shareholders' Equity	2,252,040	2,203,030
Total Capitalization	3,794,379	3,846,941
Total Liabilities and Capitalization	7,408,353	7,059,989
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	65	2,493
Receivables, Net	83,024	87,164
Accounts Receivable from Affiliated Companies	690	723
Unbilled Revenues	36,443	39,982
Taxes Receivable	2,500	17,177
Fuel, Materials and Supplies	108,634	95,345
Regulatory Assets Current	55,836	62,882
Prepayments and Other Current Assets	19,035	22,205
Total Current Assets	306,227	327,971
Property, Plant and Equipment, Net	2,383,167	2,352,515
Deferred Debits and Other Assets:
Regulatory Assets Long Term	311,442	351,059
Other Long-Term Assets	58,992	83,052
Total Deferred Debits and Other Assets	370,434	434,111
Total Assets	3,059,828	3,114,597
Current Liabilities:
Notes Payable To Affiliated Companies	182,200	63,300
Accounts Payable - Current	57,657	62,864
Accounts Payable to Affiliated Companies	17,111	21,337
Regulatory Liability Current	21,913	23,002
Other Liabilities - Current	49,369	50,950
Renewable Portfolio Standards Compliance Obligation	4,500	17,383
Total Current Liabilities	332,750	238,836
Rate Reduction Bonds	0	29,294
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	461,976	441,577
Regulatory Liabilities Long-Term	51,039	52,418
Accrued Pension, PBOP and SERP	171,622	220,129
Other Long-Term Liabilities	43,736	47,896
Total Deferred Credits and Other Liabilities	728,373	762,020
Capitalization:
Long-Term Debt	889,051	997,932
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	701,468	701,052
Retained Earnings	417,307	395,118
Accumulated Other Comprehensive Loss	(9,121)	(9,655)
Common Shareholders' Equity	1,109,654	1,086,515
Total Capitalization	1,998,705	2,084,447
Total Liabilities and Capitalization	3,059,828	3,114,597
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	1,419	1
Receivables, Net	53,676	47,297
Accounts Receivable from Affiliated Companies	530	164
Unbilled Revenues	15,540	16,192
Taxes Receivable	3	15,513
Regulatory Assets Current	45,036	42,370
Marketable Securities - Current	25,112	27,352
Prepayments and Other Current Assets	9,779	7,963
Total Current Assets	151,095	156,852
Property, Plant and Equipment, Net	1,330,207	1,290,498
Deferred Debits and Other Assets:
Regulatory Assets Long Term	192,231	221,752
Marketable Securities	32,579	30,342
Other Long-Term Assets	19,346	23,625
Total Deferred Debits and Other Assets	244,156	275,719
Total Assets	1,725,458	1,723,069
Current Liabilities:
Notes Payable To Affiliated Companies	35,200	31,900
Long-Term Debt - Current Portion	55,000	55,000
Accounts Payable - Current	44,789	68,141
Accounts Payable to Affiliated Companies	7,452	7,103
Deferred Tax Liabilities Current	12,838	8,404
Regulatory Liability Current	19,885	21,037
Other Liabilities - Current	25,740	24,809
Total Current Liabilities	200,904	216,394
Rate Reduction Bonds	0	9,352
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	332,628	303,111
Regulatory Liabilities Long-Term	11,058	9,686
Accrued Pension, PBOP and SERP	32,204	36,099
Other Long-Term Liabilities	25,477	40,148
Total Deferred Credits and Other Liabilities	401,367	389,044
Capitalization:
Long-Term Debt	549,840	550,270
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	390,573	390,412
Retained Earnings	175,593	160,577
Accumulated Other Comprehensive Loss	(3,685)	(3,846)
Common Shareholders' Equity	573,347	558,009
Total Capitalization	1,123,187	1,108,279
Total Liabilities and Capitalization	$ 1,725,458	$ 1,723,069