CONSOLIDATED BALANCE SHEETS (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Current Assets:
Cash	$ 15,107	$ 23,395
Receivables, Net	470,921	523,644
Unbilled Revenues	154,370	208,834
Taxes Receivable	49,130	89,638
Fuel, Materials and Supplies	230,754	244,043
Regulatory Assets Current	242,137	238,699
Marketable Securities - Current	74,680	78,306
Prepayments and Other Current Assets	100,763	100,441
Total Current Assets	1,337,862	1,507,000
Property, Plant and Equipment, Net	9,863,789	9,567,726
Deferred Debits and Other Assets:
Regulatory Assets Long Term	2,656,093	2,756,580
Goodwill	287,591	287,591
Marketable Securities	58,154	51,201
Derivative Assets Noncurrent	86,730	123,242
Other Long-Term Assets	152,127	179,261
Total Deferred Debits and Other Assets	3,240,695	3,397,875
Total Assets	14,442,346	14,472,601
Current Liabilities:
Notes Payable to Banks	137,000	267,000
Long-Term Debt - Current Portion	336,991	66,286
Accounts Payable - Current	373,799	417,285
Obligations to Third Party Suppliers	74,522	74,659
Accrued Taxes	104,125	107,067
Accrued Interest	69,582	74,740
Regulatory Liability Current	152,956	99,403
Derivative Liabilities - Current	105,583	71,501
Other Liabilities - Current	121,469	167,206
Total Current Liabilities	1,476,027	1,345,147
Rate Reduction Bonds	147,252	181,572
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,777,163	1,636,750
Regulatory Liabilities Long-Term	273,909	339,655
Long-Term Derivative Liabilities	884,283	909,668
Accrued Pension	798,467	802,195
Other Long-Term Liabilities	696,040	695,915
Total Deferred Credits and Other Liabilities	4,429,862	4,384,183
Capitalization:
Long-Term Debt	4,356,052	4,632,866
Noncontrolling Interest in Consolidated Subsidiary:
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
Common Shareholders' Equity:
Common Stock	979,884	978,909
Capital Surplus, Paid In	1,785,907	1,777,592
Retained Earnings	1,546,493	1,452,777
Accumulated Other Comprehensive Loss	(45,791)	(43,370)
Treasury Stock	(351,387)	(354,732)
Noncontrolling Interest	1,847	1,457
Common Shareholders' Equity	3,915,106	3,811,176
Total Equity	3,916,953	3,812,633
Total Capitalization	8,389,205	8,561,699
Total Liabilities and Capitalization	14,442,346	14,472,601
The Connecticut Light and Power Company [Member]
Current Assets:
Cash	5,078	9,762
Receivables, Net	295,688	317,530
Accounts Receivable from Affiliated Companies	3,678	822
Notes Receivable from Affiliated Companies	24,125
Unbilled Revenues	87,486	116,392
Taxes Receivable	24,121	48,360
Regulatory Assets Current	163,917	157,530
Materials and Supplies	73,063	63,811
Accumulated Deferred Income Tax Asset	21,366
Prepayments and Other Current Assets	20,180	27,466
Total Current Assets	718,702	741,673
Property, Plant and Equipment, Net	5,655,205	5,586,504
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,668,232	1,721,416
Derivative Assets Noncurrent	82,902	115,870
Other Long-Term Assets	96,981	89,729
Total Deferred Debits and Other Assets	1,848,115	1,927,015
Total Assets	8,222,022	8,255,192
Current Liabilities:
Notes Payable To Affiliated Companies	0	6,225
Long-Term Debt - Current Portion	62,000	62,000
Accounts Payable - Current	173,098	204,868
Accounts Payable to Affiliated Companies	46,911	53,207
Obligations to Third Party Suppliers	67,026	68,692
Accrued Taxes	94,841	92,061
Accrued Interest	38,774	42,548
Regulatory Liability Current	102,869	75,716
Derivative Liabilities - Current	83,442	46,781
Other Liabilities - Current	49,042	46,209
Total Current Liabilities	718,003	698,307
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,165,269	1,068,344
Regulatory Liabilities Long-Term	141,635	206,394
Long-Term Derivative Liabilities	863,292	883,091
Accrued Pension	36,364	42,486
Other Long-Term Liabilities	315,912	321,793
Total Deferred Credits and Other Liabilities	2,522,472	2,522,108
Capitalization:
Long-Term Debt	2,521,457	2,521,102
Noncontrolling Interest in Consolidated Subsidiary:
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
Common Shareholders' Equity:
Common Stock	60,352	60,352
Capital Surplus, Paid In	1,606,014	1,605,275
Retained Earnings	680,010	734,561
Accumulated Other Comprehensive Loss	(2,486)	(2,713)
Common Shareholders' Equity	2,343,890	2,397,475
Total Capitalization	4,981,547	5,034,777
Total Liabilities and Capitalization	8,222,022	8,255,192
Public Service Company of New Hampshire [Member]
Current Assets:
Cash	2,413	2,559
Receivables, Net	87,958	105,070
Accounts Receivable from Affiliated Companies	646	858
Unbilled Revenues	44,358	48,691
Taxes Receivable	2,796	12,564
Fuel, Materials and Supplies	106,371	116,074
Regulatory Assets Current	38,705	39,215
Prepayments and Other Current Assets	29,879	20,098
Total Current Assets	313,126	345,129
Property, Plant and Equipment, Net	2,135,883	2,053,281
Deferred Debits and Other Assets:
Regulatory Assets Long Term	375,551	395,203
Other Long-Term Assets	59,932	85,508
Total Deferred Debits and Other Assets	435,483	480,711
Total Assets	2,884,492	2,879,121
Current Liabilities:
Notes Payable to Banks	22,000	30,000
Notes Payable To Affiliated Companies	43,800	47,900
Accounts Payable - Current	71,278	85,324
Accounts Payable to Affiliated Companies	19,854	20,007
Accrued Interest	8,463	10,231
Regulatory Liability Current	22,369	8,365
Derivative Liabilities - Current	9,097	12,834
Other Liabilities - Current	25,371	36,726
Total Current Liabilities	222,232	251,387
Rate Reduction Bonds	112,195	138,247
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	336,877	314,996
Regulatory Liabilities Long-Term	57,104	58,631
Accrued Pension	253,824	261,096
Other Long-Term Liabilities	100,518	91,952
Total Deferred Credits and Other Liabilities	748,323	726,675
Capitalization:
Long-Term Debt	838,304	836,365
Common Shareholders' Equity:
Common Stock	0
Capital Surplus, Paid In	599,917	579,577
Retained Earnings	367,186	347,471
Accumulated Other Comprehensive Loss	(3,665)	(601)
Common Shareholders' Equity	963,438	926,447
Total Capitalization	1,801,742	1,762,812
Total Liabilities and Capitalization	2,884,492	2,879,121
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	1	1
Receivables, Net	37,948	37,585
Accounts Receivable from Affiliated Companies	585	505
Unbilled Revenues	14,539	16,578
Taxes Receivable	8	7,346
Regulatory Assets Current	19,454	19,531
Materials and Supplies	4,062	3,664
Marketable Securities - Current	28,033	33,194
Prepayments and Other Current Assets	1,624	1,968
Total Current Assets	106,254	120,372
Property, Plant and Equipment, Net	908,654	817,146
Deferred Debits and Other Assets:
Regulatory Assets Long Term	191,939	207,584
Marketable Securities	29,085	23,860
Other Long-Term Assets	29,931	30,597
Total Deferred Debits and Other Assets	250,955	262,041
Total Assets	1,265,863	1,199,559
Current Liabilities:
Notes Payable to Banks	20,000	0
Notes Payable To Affiliated Companies	28,100	20,400
Accounts Payable - Current	65,344	48,344
Accounts Payable to Affiliated Companies	10,832	7,848
Accrued Interest	6,736	6,787
Deferred Tax Liabilities Current	2,818	5,902
Regulatory Liability Current	16,579	7,959
Other Liabilities - Current	10,957	9,842
Total Current Liabilities	161,366	107,082
Rate Reduction Bonds	35,057	43,325
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	229,399	218,063
Regulatory Liabilities Long-Term	16,904	15,048
Other Long-Term Liabilities	55,834	58,169
Total Deferred Credits and Other Liabilities	302,137	291,280
Capitalization:
Long-Term Debt	400,362	400,288
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	253,360	248,044
Retained Earnings	103,741	98,757
Accumulated Other Comprehensive Loss	(1,026)	(83)
Common Shareholders' Equity	366,941	357,584
Total Capitalization	767,303	757,872
Total Liabilities and Capitalization	$ 1,265,863	$ 1,199,559