CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current Assets:
Cash	$ 283,379	$ 6,559
Receivables, Net	485,770	488,002
Unbilled Revenues	135,887	175,207
Fuel, Materials and Supplies	219,091	248,958
Regulatory Assets Current	241,902	255,144
Marketable Securities - Current	62,700	70,970
Prepayments and Other Current Assets	94,737	112,632
Total Current Assets	1,523,466	1,357,472
Property, Plant and Equipment, Net	10,613,199	10,403,065
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,214,208	3,267,710
Goodwill	287,591	287,591
Marketable Securities	74,050	60,311
Derivative Assets Noncurrent	94,258	98,357
Other Long-Term Assets	171,582	172,560
Total Deferred Debits and Other Assets	3,841,689	3,886,529
Total Assets	15,978,354	15,647,066
Current Liabilities:
Notes Payable to Banks	660,000	317,000
Long-Term Debt - Current Portion	267,286	331,582
Accounts Payable - Current	412,884	633,282
Regulatory Liability Current	149,755	167,844
Derivative Liabilities - Current	108,253	107,558
Other Liabilities - Current	369,503	390,416
Total Current Liabilities	1,967,681	1,947,682
Rate Reduction Bonds	94,357	112,260
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,923,266	1,868,316
Regulatory Liabilities Long-Term	248,314	266,145
Long-Term Derivative Liabilities	924,308	959,876
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	1,241,433	1,326,037
Other Long-Term Liabilities	414,004	420,011
Total Deferred Credits and Other Liabilities	4,751,325	4,840,385
Capitalization:
Long-Term Debt	4,977,131	4,614,913
Noncontrolling Interest in Consolidated Subsidiary:
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
Common Shareholders' Equity:
Common Stock	981,592	980,264
Capital Surplus, Paid In	1,801,752	1,797,884
Retained Earnings	1,698,553	1,651,875
Accumulated Other Comprehensive Loss	(68,822)	(70,686)
Treasury Stock	(344,774)	(346,667)
Noncontrolling Interest	3,359	2,956
Common Shareholders' Equity	4,068,301	4,012,670
Total Equity	4,071,660	4,015,626
Total Capitalization	9,164,991	8,746,739
Total Liabilities and Capitalization	15,978,354	15,647,066
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	3,837	1
Receivables, Net	279,541	295,028
Accounts Receivable from Affiliated Companies	3,146	1,548
Unbilled Revenues	72,601	94,995
Regulatory Assets Current	172,277	170,197
Materials and Supplies	59,048	61,102
Prepayments and Other Current Assets	51,917	53,920
Total Current Assets	642,367	676,791
Property, Plant and Equipment, Net	5,908,385	5,827,384
Deferred Debits and Other Assets:
Regulatory Assets Long Term	2,070,122	2,103,830
Derivative Assets Noncurrent	90,614	93,755
Other Long-Term Assets	89,165	89,636
Total Deferred Debits and Other Assets	2,249,901	2,287,221
Total Assets	8,800,653	8,791,396
Current Liabilities:
Notes Payable to Banks	275,000	31,000
Notes Payable To Affiliated Companies	9,275	58,525
Long-Term Debt - Current Portion	0	62,000
Accounts Payable - Current	201,373	340,321
Accounts Payable to Affiliated Companies	50,681	53,439
Obligations to Third Party Suppliers	65,434	67,967
Accrued Taxes	71,182	59,046
Regulatory Liability Current	82,423	108,291
Derivative Liabilities - Current	97,483	95,881
Other Liabilities - Current	76,789	102,065
Total Current Liabilities	929,640	978,535
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,244,748	1,215,989
Regulatory Liabilities Long-Term	133,844	139,307
Long-Term Derivative Liabilities	898,850	935,849
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	259,814	260,571
Other Long-Term Liabilities	206,550	215,640
Total Deferred Credits and Other Liabilities	2,743,806	2,767,356
Capitalization:
Long-Term Debt	2,583,881	2,521,753
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	1,613,865	1,613,503
Retained Earnings	755,048	735,948
Accumulated Other Comprehensive Loss	(2,139)	(2,251)
Common Shareholders' Equity	2,427,126	2,407,552
Total Capitalization	5,127,207	5,045,505
Total Liabilities and Capitalization	8,800,653	8,791,396
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	2,251	56
Receivables, Net	89,551	87,545
Accounts Receivable from Affiliated Companies	1,176	1,294
Notes Receivable from Affiliated Companies	0	55,900
Unbilled Revenues	39,304	45,403
Fuel, Materials and Supplies	115,383	124,744
Regulatory Assets Current	33,362	34,178
Prepayments and Other Current Assets	15,066	35,261
Total Current Assets	296,093	384,381
Property, Plant and Equipment, Net	2,287,951	2,256,688
Deferred Debits and Other Assets:
Regulatory Assets Long Term	375,122	393,941
Other Long-Term Assets	79,954	81,531
Total Deferred Debits and Other Assets	455,076	475,472
Total Assets	3,039,120	3,116,541
Current Liabilities:
Notes Payable to Banks	45,000	0
Notes Payable To Affiliated Companies	7,900	0
Accounts Payable - Current	74,374	106,377
Accounts Payable to Affiliated Companies	16,489	18,895
Accrued Interest	14,454	9,670
Regulatory Liability Current	23,108	24,500
Other Liabilities - Current	42,139	36,497
Total Current Liabilities	223,464	195,939
Rate Reduction Bonds	71,905	85,368
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	405,834	392,712
Regulatory Liabilities Long-Term	54,212	54,415
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	172,802	258,718
Other Long-Term Liabilities	55,935	53,304
Total Deferred Credits and Other Liabilities	688,783	759,149
Capitalization:
Long-Term Debt	997,775	997,722
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	700,452	700,285
Retained Earnings	367,281	388,910
Accumulated Other Comprehensive Loss	(10,540)	(10,832)
Common Shareholders' Equity	1,057,193	1,078,363
Total Capitalization	2,054,968	2,076,085
Total Liabilities and Capitalization	3,039,120	3,116,541
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	126	1
Receivables, Net	46,083	42,757
Accounts Receivable from Affiliated Companies	1,975	633
Notes Receivable from Affiliated Companies	0	11,000
Unbilled Revenues	13,666	16,277
Regulatory Assets Current	33,525	35,520
Marketable Securities - Current	13,953	26,335
Prepayments and Other Current Assets	6,117	8,719
Total Current Assets	115,445	141,242
Property, Plant and Equipment, Net	1,152,976	1,077,833
Deferred Debits and Other Assets:
Regulatory Assets Long Term	242,181	233,247
Marketable Securities	43,443	30,794
Other Long-Term Assets	21,155	19,777
Total Deferred Debits and Other Assets	306,779	283,818
Total Assets	1,575,200	1,502,893
Current Liabilities:
Notes Payable to Banks	65,000
Notes Payable To Affiliated Companies	18,200
Accounts Payable - Current	86,599	111,566
Accounts Payable to Affiliated Companies	9,314	10,626
Regulatory Liability Current	30,389	33,056
Other Liabilities - Current	16,889	20,755
Total Current Liabilities	226,391	176,003
Rate Reduction Bonds	22,452	26,892
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	264,178	244,511
Regulatory Liabilities Long-Term	15,731	16,597
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	28,893	29,546
Other Long-Term Liabilities	50,757	47,498
Total Deferred Credits and Other Liabilities	359,559	338,152
Capitalization:
Long-Term Debt	499,594	499,545
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	340,179	340,115
Retained Earnings	120,260	115,506
Accumulated Other Comprehensive Loss	(4,101)	(4,186)
Common Shareholders' Equity	467,204	462,301
Total Capitalization	966,798	961,846
Total Liabilities and Capitalization	$ 1,575,200	$ 1,502,893