CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current Assets:
Cash	$ 6,559	$ 23,395
Receivables, Net	488,002	523,644
Unbilled Revenues	175,207	208,834
Taxes Receivable	4,931	89,638
Fuel, Materials and Supplies	248,958	244,043
Regulatory Assets Current	255,144	238,699
Marketable Securities - Current	70,970	78,306
Prepayments and Other Current Assets	107,701	100,441
Total Current Assets	1,357,472	1,507,000
Property, Plant and Equipment, Net	10,403,065	9,567,726
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,267,710	2,756,580
Goodwill	287,591	287,591
Marketable Securities	60,311	51,201
Derivative Assets Noncurrent	98,357	123,242
Other Long-Term Assets	172,560	179,261
Total Deferred Debits and Other Assets	3,886,529	3,397,875
Total Assets	15,647,066	14,472,601
Current Liabilities:
Notes Payable to Banks	317,000	267,000
Long-Term Debt - Current Portion	331,582	66,286
Accounts Payable - Current	633,282	417,285
Obligations to Third Party Suppliers	75,068	74,659
Accrued Taxes	69,592	107,067
Accrued Interest	69,198	74,740
Regulatory Liability Current	167,844	99,403
Derivative Liabilities - Current	107,558	71,501
Other Liabilities - Current	176,558	167,206
Total Current Liabilities	1,947,682	1,345,147
Rate Reduction Bonds	112,260	181,572
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,868,316	1,636,750
Regulatory Liabilities Long-Term	266,145	339,655
Long-Term Derivative Liabilities	959,876	909,668
Accrued Pension, PBOP and SERP	1,326,037	1,050,614
Other Long-Term Liabilities	420,011	447,496
Total Deferred Credits and Other Liabilities	4,840,385	4,384,183
Capitalization:
Long-Term Debt	4,614,913	4,632,866
Noncontrolling Interest in Consolidated Subsidiary:
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
Common Shareholders' Equity:
Common Stock	980,264	978,909
Capital Surplus, Paid In	1,797,884	1,777,592
Retained Earnings	1,651,875	1,452,777
Accumulated Other Comprehensive Loss	(70,686)	(43,370)
Treasury Stock	(346,667)	(354,732)
Noncontrolling Interest	2,956	1,457
Common Shareholders' Equity	4,012,670	3,811,176
Total Equity	4,015,626	3,812,633
Total Capitalization	8,746,739	8,561,699
Total Liabilities and Capitalization	15,647,066	14,472,601
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	1	9,762
Receivables, Net	295,028	317,530
Accounts Receivable from Affiliated Companies	1,548	822
Unbilled Revenues	94,995	116,392
Taxes Receivable	6,988	48,360
Regulatory Assets Current	170,197	157,530
Materials and Supplies	61,102	63,811
Prepayments and Other Current Assets	46,932	27,466
Total Current Assets	676,791	741,673
Property, Plant and Equipment, Net	5,827,384	5,586,504
Deferred Debits and Other Assets:
Regulatory Assets Long Term	2,103,830	1,721,416
Derivative Assets Noncurrent	93,755	115,870
Other Long-Term Assets	89,636	89,729
Total Deferred Debits and Other Assets	2,287,221	1,927,015
Total Assets	8,791,396	8,255,192
Current Liabilities:
Notes Payable to Banks	31,000
Notes Payable To Affiliated Companies	58,525	6,225
Long-Term Debt - Current Portion	62,000	62,000
Accounts Payable - Current	340,321	204,868
Accounts Payable to Affiliated Companies	53,439	53,207
Obligations to Third Party Suppliers	67,967	68,692
Accrued Taxes	59,046	92,061
Accrued Interest	35,279	42,548
Regulatory Liability Current	108,291	75,716
Derivative Liabilities - Current	95,881	46,781
Other Liabilities - Current	66,786	46,209
Total Current Liabilities	978,535	698,307
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,215,989	1,068,344
Regulatory Liabilities Long-Term	139,307	206,394
Long-Term Derivative Liabilities	935,849	883,091
Accrued Pension, PBOP and SERP	260,571	127,116
Other Long-Term Liabilities	215,640	237,163
Total Deferred Credits and Other Liabilities	2,767,356	2,522,108
Capitalization:
Long-Term Debt	2,521,753	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	1,613,503	1,605,275
Retained Earnings	735,948	734,561
Accumulated Other Comprehensive Loss	(2,251)	(2,713)
Common Shareholders' Equity	2,407,552	2,397,475
Total Capitalization	5,045,505	5,034,777
Total Liabilities and Capitalization	8,791,396	8,255,192
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	56	2,559
Receivables, Net	87,545	105,070
Accounts Receivable from Affiliated Companies	1,294	858
Notes Receivable from Affiliated Companies	55,900
Unbilled Revenues	45,403	48,691
Taxes Receivable	7,424	12,564
Fuel, Materials and Supplies	124,744	116,074
Regulatory Assets Current	34,178	39,215
Prepayments and Other Current Assets	27,837	20,098
Total Current Assets	384,381	345,129
Property, Plant and Equipment, Net	2,256,688	2,053,281
Deferred Debits and Other Assets:
Regulatory Assets Long Term	393,941	395,203
Other Long-Term Assets	81,531	85,508
Total Deferred Debits and Other Assets	475,472	480,711
Total Assets	3,116,541	2,879,121
Current Liabilities:
Notes Payable to Banks	0	30,000
Notes Payable To Affiliated Companies	0	47,900
Accounts Payable - Current	106,377	85,324
Accounts Payable to Affiliated Companies	18,895	20,007
Accrued Interest	9,670	10,231
Regulatory Liability Current	24,500	8,365
Derivative Liabilities - Current	0	12,834
Other Liabilities - Current	36,497	36,726
Total Current Liabilities	195,939	251,387
Rate Reduction Bonds	85,368	138,247
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	392,712	314,996
Regulatory Liabilities Long-Term	54,415	58,631
Accrued Pension, PBOP and SERP	258,718	296,102
Other Long-Term Liabilities	53,304	56,946
Total Deferred Credits and Other Liabilities	759,149	726,675
Capitalization:
Long-Term Debt	997,722	836,365
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	700,285	579,577
Retained Earnings	388,910	347,471
Accumulated Other Comprehensive Loss	(10,832)	(601)
Common Shareholders' Equity	1,078,363	926,447
Total Capitalization	2,076,085	1,762,812
Total Liabilities and Capitalization	3,116,541	2,879,121
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	1	1
Receivables, Net	42,757	37,585
Accounts Receivable from Affiliated Companies	633	505
Notes Receivable from Affiliated Companies	11,000
Unbilled Revenues	16,277	16,578
Taxes Receivable	2,263	7,346
Regulatory Assets Current	35,520	19,531
Materials and Supplies	3,333	3,664
Marketable Securities - Current	26,335	33,194
Prepayments and Other Current Assets	3,123	1,968
Total Current Assets	141,242	120,372
Property, Plant and Equipment, Net	1,077,833	817,146
Deferred Debits and Other Assets:
Regulatory Assets Long Term	233,247	207,584
Marketable Securities	30,794	23,860
Other Long-Term Assets	19,777	30,597
Total Deferred Debits and Other Assets	283,818	262,041
Total Assets	1,502,893	1,199,559
Current Liabilities:
Notes Payable To Affiliated Companies	0	20,400
Accounts Payable - Current	111,566	48,344
Accounts Payable to Affiliated Companies	10,626	7,848
Accrued Interest	7,714	6,787
Deferred Tax Liabilities Current	0	5,902
Regulatory Liability Current	33,056	7,959
Other Liabilities - Current	13,041	9,842
Total Current Liabilities	176,003	107,082
Rate Reduction Bonds	26,892	43,325
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	244,511	218,063
Regulatory Liabilities Long-Term	16,597	15,048
Accrued Pension, PBOP and SERP	29,546	15,315
Other Long-Term Liabilities	47,498	42,854
Total Deferred Credits and Other Liabilities	338,152	291,280
Capitalization:
Long-Term Debt	499,545	400,288
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	340,115	248,044
Retained Earnings	115,506	98,757
Accumulated Other Comprehensive Loss	(4,186)	(83)
Common Shareholders' Equity	462,301	357,584
Total Capitalization	961,846	757,872
Total Liabilities and Capitalization	$ 1,502,893	$ 1,199,559