CONSOLIDATED STATEMENT OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Activities:
Net Income	$ 400,513	$ 394,107	$ 335,592
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	16,420	31,352	53,947
Depreciation	302,192	300,737	309,618
Deferred Income Tax Expense (Benefit)	196,761	210,939	125,890
Pension and PBOP Expense, Net of PBOP Contributions	133,000	103,861	58,732
Pension Contribution	(191,101)	(90,633)	(37,160)
Regulatory (Underrecoveries)/Overrecoveries, Net	(76,896)	20,750	37,868
Amortization of Regulatory Assets/(Liabilities), Net	97,113	95,593	13,315
Amortization of Rate Reduction Bonds	69,912	232,871	217,941
Changes in Derivative Assets and Liabilities	(35,441)	(11,812)	(18,798)
Other Noncash Income (Expense)	(29,751)	(72,151)	(26,003)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	17,570	(51,285)	91,081
Inventory	(11,033)	38,126	25,957
Taxes Receivable/(Accrued)	49,642	(82,103)	16,194
Change in Accounts Payable	18,916	(44,355)	(208,180)
Other Current Assets and Liabilities	12,569	17,466	(6,876)
Net Cash Flows Provided by Operating Activities	970,386	1,093,463	989,118
Investing Activities:
Investments in Property, Plant and Equipment	(1,076,730)	(954,472)	(908,146)
Proceeds from Sales of Marketable Securities	149,441	174,865	208,947
Purchases of Marketable Securities	(151,972)	(177,204)	(211,243)
Proceeds From Sale Of Property Plant And Equipment	46,841	0	0
Other Investing Activities	13,833	(1,157)	7,963
Net Cash Flows Used in Investing Activities	(1,018,587)	(957,968)	(902,479)
Financing Activities:
Issuance of Common Stock	0	0	383,295
Cash Dividends on Common Stock	(194,555)	(180,542)	(162,381)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
Increase/(Decrease) in Short-Term Debt	50,000	166,687	(518,584)
Issuance of Long-Term Debt	627,500	145,000	462,000
Retirements of Long-Term Debt	(369,586)	(4,286)	(54,286)
Retirements of Rate Reduction Bonds	(69,312)	(260,864)	(244,075)
Other Financing Activities	(7,123)	512	(9,913)
Net Cash Flows Provided by/(Used in) Financing Activities	31,365	(139,052)	(149,503)
Net Increase/(Decrease) in Cash	(16,836)	(3,557)	(62,864)
Cash - Beginning of Year	23,395	26,952	89,816
Cash - End of Year	6,559	23,395	26,952
The Connecticut Light And Power Company [Member]
Operating Activities:
Net Income	250,164	244,143	216,316
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	3,215	7,484	15,276
Depreciation	157,747	172,167	186,922
Deferred Income Tax Expense (Benefit)	112,620	115,069	52,900
Pension and PBOP Expense, Net of PBOP Contributions	10,664	1,595	(10,709)
Regulatory (Underrecoveries)/Overrecoveries, Net	(86,666)	32,492	51,292
Amortization of Regulatory Assets/(Liabilities), Net	65,189	83,906	45,821
Amortization of Rate Reduction Bonds	0	167,021	155,938
Other Noncash Income (Expense)	(36,928)	(55,515)	(38,731)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	14,610	1,895	50,327
Inventory	(2,206)	3,377	(6,339)
Taxes Receivable/(Accrued)	2,719	(56,002)	25,823
Change in Accounts Payable	8,864	(35,976)	(85,773)
Other Current Assets and Liabilities	13,291	15,649	5,718
Net Cash Flows Provided by Operating Activities	513,283	697,305	664,781
Investing Activities:
Investments in Property, Plant and Equipment	(424,865)	(380,304)	(435,723)
Decrease/(Increase) in NU Money Pool Lending	0	97,775	(97,775)
Proceeds From Sale Of Property Plant And Equipment	46,841	0	0
Other Investing Activities	16,001	5,385	4,888
Net Cash Flows Used in Investing Activities	(362,023)	(277,144)	(528,610)
Financing Activities:
Cash Dividends on Common Stock	(243,218)	(217,691)	(113,848)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
Increase/(Decrease) in Short-Term Debt	31,000	0	(187,973)
Issuance of Long-Term Debt	245,500	0	312,000
Increase/(Decrease) in NU Money Pool Borrowings	52,300	6,225	(102,725)
Retirements of Long-Term Debt	(245,500)	0	0
Retirements of Rate Reduction Bonds	0	(195,587)	(182,608)
Capital Contributions from NU Parent	6,748	2,513	147,591
Other Financing Activities	(2,292)	(345)	(3,004)
Net Cash Flows Provided by/(Used in) Financing Activities	(161,021)	(410,444)	(136,126)
Net Increase/(Decrease) in Cash	(9,761)	9,717	45
Cash - Beginning of Year	9,762	45	0
Cash - End of Year	1	9,762	45
Public Service Company Of New Hampshire [Member]
Operating Activities:
Net Income	100,267	90,067	65,570
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	7,035	8,858	10,084
Depreciation	76,167	67,237	61,961
Deferred Income Tax Expense (Benefit)	75,628	39,225	35,270
Pension and PBOP Expense, Net of PBOP Contributions	27,298	29,112	22,494
Pension Contribution	(121,178)	(53,689)	(6,975)
Regulatory (Underrecoveries)/Overrecoveries, Net	6,079	(2,834)	(4,392)
Amortization of Regulatory Assets/(Liabilities), Net	25,383	11,232	(29,619)
Amortization of Rate Reduction Bonds	53,389	50,357	47,482
Changes in Derivative Assets and Liabilities	(18,072)	0	0
Insurance Proceeds	0	10,000	10,066
Other Noncash Income (Expense)	(20,958)	(41,590)	(7,526)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	7,833	(24,497)	1,505
Inventory	(9,873)	14,891	59
Taxes Receivable/(Accrued)	5,139	10,037	(13,791)
Change in Accounts Payable	(4,517)	(14,427)	(77,738)
Other Current Assets and Liabilities	(4,915)	1,294	(9,192)
Net Cash Flows Provided by Operating Activities	204,705	195,273	105,258
Investing Activities:
Investments in Property, Plant and Equipment	(241,772)	(296,335)	(266,440)
Decrease/(Increase) in NU Money Pool Lending	(55,900)	0	53,800
Other Investing Activities	2,089	(7,819)	(1,278)
Net Cash Flows Used in Investing Activities	(295,583)	(304,154)	(213,918)
Financing Activities:
Cash Dividends on Common Stock	(58,828)	(50,584)	(40,844)
Increase/(Decrease) in Short-Term Debt	(30,000)	30,000	(45,227)
Issuance of Long-Term Debt	282,000	0	150,000
Increase/(Decrease) in NU Money Pool Borrowings	(47,900)	21,200	26,700
Retirements of Long-Term Debt	(119,800)	0	0
Retirements of Rate Reduction Bonds	(52,879)	(49,867)	(47,026)
Capital Contributions from NU Parent	120,030	158,969	68,946
Other Financing Activities	(4,248)	(252)	(2,110)
Net Cash Flows Provided by/(Used in) Financing Activities	88,375	109,466	110,439
Net Increase/(Decrease) in Cash	(2,503)	585	1,779
Cash - Beginning of Year	2,559	1,974	195
Cash - End of Year	56	2,559	1,974
Western Massachusetts Electric Company [Member]
Operating Activities:
Net Income	43,054	23,090	26,196
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	3,133	9,747	7,590
Depreciation	26,455	23,561	22,454
Deferred Income Tax Expense (Benefit)	23,056	10,963	22,908
Pension and PBOP Expense, Net of PBOP Contributions	1,722	(535)	(2,630)
Regulatory (Underrecoveries)/Overrecoveries, Net	1,459	(11,551)	589
Amortization of Regulatory Assets/(Liabilities), Net	6,361	2,395	(2,980)
Amortization of Rate Reduction Bonds	16,523	15,494	14,521
Changes in Derivative Assets and Liabilities	(6,859)	0	0
Other Noncash Income (Expense)	(5,441)	(7,032)	(5,547)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(7,263)	(6,838)	3,757
Inventory	331	4,650	(4,489)
Taxes Receivable/(Accrued)	5,084	(393)	1,307
Change in Accounts Payable	12,956	(92)	(19,397)
Other Current Assets and Liabilities	3,824	2,406	(2,150)
Net Cash Flows Provided by Operating Activities	124,395	65,865	62,129
Investing Activities:
Investments in Property, Plant and Equipment	(237,996)	(115,178)	(105,440)
Proceeds from Sales of Marketable Securities	125,157	114,191	106,308
Purchases of Marketable Securities	(125,453)	(114,587)	(106,937)
Decrease/(Increase) in NU Money Pool Lending	(11,000)	0	0
Other Investing Activities	(1,919)	(888)	1,298
Net Cash Flows Used in Investing Activities	(251,211)	(116,462)	(104,771)
Financing Activities:
Cash Dividends on Common Stock	(26,305)	(14,882)	(18,203)
Increase/(Decrease) in Short-Term Debt	0	0	(29,850)
Issuance of Long-Term Debt	100,000	95,000	0
Increase/(Decrease) in NU Money Pool Borrowings	(20,400)	(115,700)	104,500
Retirements of Rate Reduction Bonds	(16,433)	(15,410)	(14,441)
Capital Contributions from NU Parent	91,812	102,479	863
Other Financing Activities	(1,858)	(890)	(226)
Net Cash Flows Provided by/(Used in) Financing Activities	126,816	50,597	42,643
Net Increase/(Decrease) in Cash	0	0	1
Cash - Beginning of Year	1	1	0
Cash - End of Year	$ 1	$ 1	$ 1