CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current Assets:
Cash	$ 28,483	$ 6,559
Receivables, Net	661,910	488,002
Unbilled Revenues	202,262	175,207
Fuel, Materials and Supplies	262,562	248,958
Regulatory Assets Current	624,397	255,144
Marketable Securities - Current	79,231	70,970
Prepayments and Other Current Assets	95,160	112,632
Total Current Assets	1,954,005	1,357,472
Property, Plant and Equipment, Net	16,054,913	10,403,065
Deferred Debits and Other Assets:
Regulatory Assets Long Term	5,201,154	3,267,710
Goodwill	3,518,454	287,591
Marketable Securities	372,302	60,311
Derivative Assets Noncurrent	93,616	98,357
Other Long-Term Assets	311,856	172,560
Total Deferred Debits and Other Assets	9,497,382	3,886,529
Total Assets	27,506,300	15,647,066
Current Liabilities:
Notes Payable to Banks	1,248,500	317,000
Long-Term Debt - Current Portion	683,208	331,582
Accounts Payable - Current	600,995	633,282
Regulatory Liability Current	203,767	167,844
Derivative Liabilities - Current	113,188	107,558
Other Liabilities - Current	640,809	390,416
Total Current Liabilities	3,490,467	1,947,682
Rate Reduction Bonds	160,133	112,260
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	3,249,323	1,868,316
Regulatory Liabilities Long-Term	551,690	266,145
Long-Term Derivative Liabilities	946,621	959,876
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	2,064,069	1,326,037
Other Long-Term Liabilities	884,317	420,011
Total Deferred Credits and Other Liabilities	7,696,020	4,840,385
Capitalization:
Long-Term Debt	6,936,473	4,614,913
Noncontrolling Interest in Consolidated Subsidiary:
Preferred Stock Not Subject to Mandatory Redemption	155,568	116,200
Common Shareholders' Equity:
Common Stock	1,662,251	980,264
Capital Surplus, Paid In	6,178,698	1,797,884
Retained Earnings	1,635,709	1,651,875
Accumulated Other Comprehensive Loss	(66,387)	(70,686)
Treasury Stock	(342,632)	(346,667)
Noncontrolling Interest	0	2,956
Common Shareholders' Equity	9,067,639	4,012,670
Total Equity	9,067,639	4,015,626
Total Capitalization	16,159,680	8,746,739
Total Liabilities and Capitalization	27,506,300	15,647,066
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	4,523	1
Receivables, Net	259,940	295,028
Accounts Receivable from Affiliated Companies	973	1,548
Unbilled Revenues	82,355	94,995
Regulatory Assets Current	196,145	170,197
Materials and Supplies	63,449	61,102
Prepayments and Other Current Assets	21,535	53,920
Total Current Assets	628,920	676,791
Property, Plant and Equipment, Net	6,000,783	5,827,384
Deferred Debits and Other Assets:
Regulatory Assets Long Term	2,025,569	2,103,830
Derivative Assets Noncurrent	91,146	93,755
Other Long-Term Assets	88,953	89,636
Total Deferred Debits and Other Assets	2,205,668	2,287,221
Total Assets	8,835,371	8,791,396
Current Liabilities:
Notes Payable to Banks	330,000	31,000
Notes Payable To Affiliated Companies	5,000	58,525
Long-Term Debt - Current Portion		62,000
Accounts Payable - Current	193,582	340,321
Accounts Payable to Affiliated Companies	44,666	53,439
Obligations to Third Party Suppliers	62,459	67,967
Accrued Taxes	91,297	59,046
Regulatory Liability Current	88,373	108,291
Derivative Liabilities - Current	97,704	95,881
Other Liabilities - Current	87,763	102,065
Total Current Liabilities	1,000,844	978,535
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,241,020	1,215,989
Regulatory Liabilities Long-Term	130,573	139,307
Long-Term Derivative Liabilities	910,115	935,849
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	248,624	260,571
Other Long-Term Liabilities	204,227	215,640
Total Deferred Credits and Other Liabilities	2,734,559	2,767,356
Capitalization:
Long-Term Debt	2,584,036	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	1,614,307	1,613,503
Retained Earnings	727,096	735,948
Accumulated Other Comprehensive Loss	(2,023)	(2,251)
Common Shareholders' Equity	2,399,732	2,407,552
Total Capitalization	5,099,968	5,045,505
Total Liabilities and Capitalization	8,835,371	8,791,396
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	203	56
Receivables, Net	83,335	87,545
Accounts Receivable from Affiliated Companies	616	1,294
Notes Receivable from Affiliated Companies	0	55,900
Unbilled Revenues	43,630	45,403
Fuel, Materials and Supplies	102,948	124,744
Regulatory Assets Current	28,912	34,178
Prepayments and Other Current Assets	37,235	35,261
Total Current Assets	296,879	384,381
Property, Plant and Equipment, Net	2,315,954	2,256,688
Deferred Debits and Other Assets:
Regulatory Assets Long Term	347,498	393,941
Other Long-Term Assets	76,466	81,531
Total Deferred Debits and Other Assets	423,964	475,472
Total Assets	3,036,797	3,116,541
Current Liabilities:
Notes Payable to Banks	65,000
Notes Payable To Affiliated Companies	13,500
Accounts Payable - Current	69,792	106,377
Accounts Payable to Affiliated Companies	16,532	18,895
Accrued Interest	9,517	9,670
Regulatory Liability Current	23,121	24,500
Other Liabilities - Current	29,365	36,497
Total Current Liabilities	226,827	195,939
Rate Reduction Bonds	57,742	85,368
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	410,763	392,712
Regulatory Liabilities Long-Term	53,272	54,415
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	168,428	258,718
Other Long-Term Liabilities	58,895	53,304
Total Deferred Credits and Other Liabilities	691,358	759,149
Capitalization:
Long-Term Debt	997,827	997,722
Common Shareholders' Equity:
Common Stock
Capital Surplus, Paid In	700,658	700,285
Retained Earnings	372,621	388,910
Accumulated Other Comprehensive Loss	(10,236)	(10,832)
Common Shareholders' Equity	1,063,043	1,078,363
Total Capitalization	2,060,870	2,076,085
Total Liabilities and Capitalization	3,036,797	3,116,541
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	1	1
Receivables, Net	42,580	42,757
Accounts Receivable from Affiliated Companies	82	633
Notes Receivable from Affiliated Companies	0	11,000
Unbilled Revenues	15,440	16,277
Regulatory Assets Current	40,587	35,520
Marketable Securities - Current	18,461	26,335
Prepayments and Other Current Assets	8,057	8,719
Total Current Assets	125,208	141,242
Property, Plant and Equipment, Net	1,216,370	1,077,833
Deferred Debits and Other Assets:
Regulatory Assets Long Term	232,001	233,247
Marketable Securities	39,032	30,794
Other Long-Term Assets	20,902	19,777
Total Deferred Debits and Other Assets	291,935	283,818
Total Assets	1,633,513	1,502,893
Current Liabilities:
Notes Payable to Banks	110,000	0
Notes Payable To Affiliated Companies	5,400	0
Accounts Payable - Current	109,164	111,566
Accounts Payable to Affiliated Companies	8,463	10,626
Regulatory Liability Current	19,400	33,056
Other Liabilities - Current	27,033	20,755
Total Current Liabilities	279,460	176,003
Rate Reduction Bonds	18,079	26,892
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	265,871	244,511
Regulatory Liabilities Long-Term	13,643	16,597
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	26,556	29,546
Other Long-Term Liabilities	51,748	47,498
Total Deferred Credits and Other Liabilities	357,818	338,152
Capitalization:
Long-Term Debt	499,648	499,545
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	340,259	340,115
Retained Earnings	131,398	115,506
Accumulated Other Comprehensive Loss	(4,015)	(4,186)
Common Shareholders' Equity	478,508	462,301
Total Capitalization	978,156	961,846
Total Liabilities and Capitalization	1,633,513	1,502,893
NSTAR Electric Company [Member]
Current Assets:
Cash	9,044	9,373
Receivables, Net	211,388	232,828
Accounts Receivable from Affiliated Companies	48,254	389,652
Unbilled Revenues	53,409	40,380
Taxes Receivable	35,642	5,664
Regulatory Assets Current	326,630	323,871
Prepayments and Other Current Assets	21,588	31,470
Total Current Assets	705,955	1,033,238
Property, Plant and Equipment, Net	4,555,454	4,447,258
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,594,571	1,680,595
Other Long-Term Assets	75,516	78,273
Total Deferred Debits and Other Assets	1,670,087	1,758,868
Total Assets	6,931,496	7,239,364
Current Liabilities:
Notes Payable to Banks	344,500	141,500
Long-Term Debt - Current Portion	401,513	400,688
Accounts Payable - Current	114,308	150,581
Accounts Payable to Affiliated Companies	146,858	514,377
Deferred Tax Liabilities Current	94,398	101,819
Regulatory Liability Current	52,636	41,579
Other Liabilities - Current	103,606	103,634
Total Current Liabilities	1,257,819	1,454,178
Rate Reduction Bonds	84,312	127,860
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,300,332	1,310,180
Regulatory Liabilities Long-Term	253,766	239,858
Other Long-Term Liabilities	189,803	195,606
Defined Benefit Pension Plan, Liabilities, Noncurrent	385,235	357,685
Due to Related Parties, Noncurrent	70,569	75,905
Total Deferred Credits and Other Liabilities	2,199,705	2,179,234
Capitalization:
Long-Term Debt	1,201,871	1,203,344
Noncontrolling Interest in Consolidated Subsidiary:
Preferred Stock Not Subject to Mandatory Redemption	43,000	43,000
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	992,625	992,625
Retained Earnings	1,152,164	1,239,123
Common Shareholders' Equity	2,144,789	2,231,748
Total Capitalization	3,389,660	3,478,092
Total Liabilities and Capitalization	$ 6,931,496	$ 7,239,364