CONSOLIDATED STATEMENT OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Operating Activities:
Net Income	$ 356,482	$ 285,734
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	24,249	12,435
Depreciation	369,798	222,784
Deferred Income Tax Expense (Benefit)	186,181	133,528
Pension, SERP, and PBOP Expense, Net of PBOP Contributions	160,209	103,106
Pension and PBOP Contributions	(237,123)	(159,220)
Regulatory (Underrecoveries)/Overrecoveries, Net	(26,236)	(24,245)
Amortization of Regulatory Assets/(Liabilities), Net	74,851	86,653
Amortization of Rate Reduction Bonds	102,144	52,047
Changes in Derivative Assets and Liabilities	(7,907)	(33,767)
Other Noncash Income (Expense)	(9,702)	(14,802)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(27,677)	61,657
Inventory	32,887	(4,072)
Taxes Receivable/(Accrued)	26,302	109,410
Change in Accounts Payable	(208,308)	66,618
Other Current Assets and Liabilities	(20,145)	(9,419)
Net Cash Flows (Used in)/ Provided by Operating Activities	796,005	888,447
Investing Activities:
Investments in Property, Plant and Equipment	(1,081,750)	(749,060)
Proceeds from Sales of Marketable Securities	232,911	116,463
Purchases of Marketable Securities	(252,762)	(118,251)
Proceeds From Sale Of Property Plant And Equipment	0	46,841
Other Investing Activities	40,265	(5,849)
Net Cash Flows Used in Investing Activities	(1,061,336)	(709,856)
Financing Activities:
Cash Dividends on Common Stock	(267,356)	(145,865)
Cash Dividends on Preferred Stock	(5,149)	(4,169)
Increase/(Decrease) in Short-Term Debt	654,250	(237,000)
Issuance of Long-Term Debt	300,000	382,000
Retirements of Long-Term Debt	(267,561)	(124,086)
Retirements of Rate Reduction Bonds	(95,225)	(51,198)
Other Financing Activities	13,262	(4,947)
Net Cash Flows Provided by/(Used in) Financing Activities	332,221	(185,265)
Net Increase/(Decrease) in Cash	66,890	(6,674)
Cash - Beginning of Year	6,559	23,395
Cash - End of Year	73,449	16,721
The Connecticut Light And Power Company [Member]
Operating Activities:
Net Income	135,804	183,500
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	1,420	2,115
Depreciation	124,451	117,629
Deferred Income Tax Expense (Benefit)	97,224	67,948
Pension, SERP, and PBOP Expense, Net of PBOP Contributions	18,394	10,473
Regulatory (Underrecoveries)/Overrecoveries, Net	(13,804)	(49,525)
Amortization of Regulatory Assets/(Liabilities), Net	19,912	48,027
Other Noncash Income (Expense)	(12,121)	(22,435)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(21,632)	26,164
Inventory	(1,017)	(12,669)
Taxes Receivable/(Accrued)	21,410	64,779
Change in Accounts Payable	(173,107)	73,809
Other Current Assets and Liabilities	(48,733)	(23,245)
Net Cash Flows (Used in)/ Provided by Operating Activities	148,201	486,570
Investing Activities:
Investments in Property, Plant and Equipment	(332,323)	(305,595)
Decrease/(Increase) in Notes Receivable from Affiliate	0	(6,925)
Proceeds From Sale Of Property Plant And Equipment	0	46,841
Other Investing Activities	13,707	(6,693)
Net Cash Flows Used in Investing Activities	(318,616)	(272,372)
Financing Activities:
Cash Dividends on Common Stock	(100,486)	(205,981)
Cash Dividends on Preferred Stock	(4,169)	(4,169)
Increase/(Decrease) in Short-Term Debt	(31,000)	0
Increase/(Decrease) in Notes Payable to Affiliate	314,275	(6,225)
Other Financing Activities	(1,636)	(349)
Net Cash Flows Provided by/(Used in) Financing Activities	176,984	(216,724)
Net Increase/(Decrease) in Cash	6,569	(2,526)
Cash - Beginning of Year	1	9,762
Cash - End of Year	6,570	7,236
Public Service Company Of New Hampshire [Member]
Operating Activities:
Net Income	69,726	74,763
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	4,975	5,202
Depreciation	65,282	54,432
Deferred Income Tax Expense (Benefit)	39,108	51,809
Pension, SERP, and PBOP Expense, Net of PBOP Contributions	19,508	21,568
Pension and PBOP Contributions	(94,169)	(99,780)
Regulatory (Underrecoveries)/Overrecoveries, Net	1,718	2,581
Amortization of Regulatory Assets/(Liabilities), Net	(6,179)	35,303
Amortization of Rate Reduction Bonds	43,855	39,748
Changes in Derivative Assets and Liabilities	0	(18,072)
Other Noncash Income (Expense)	13,724	(15,501)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(4,274)	9,332
Inventory	20,178	11,981
Taxes Receivable/(Accrued)	4,506	18,758
Change in Accounts Payable	(18,567)	(6,905)
Other Current Assets and Liabilities	18,358	14,613
Net Cash Flows (Used in)/ Provided by Operating Activities	177,749	199,832
Investing Activities:
Investments in Property, Plant and Equipment	(161,021)	(167,383)
Decrease/(Increase) in Notes Receivable from Affiliate	55,900	(50,300)
Other Investing Activities	2,500	1,026
Net Cash Flows Used in Investing Activities	(102,621)	(216,657)
Financing Activities:
Cash Dividends on Common Stock	(74,675)	(44,121)
Increase/(Decrease) in Short-Term Debt	0	(30,000)
Issuance of Long-Term Debt	0	282,000
Increase/(Decrease) in Notes Payable to Affiliate	44,200	(47,900)
Retirements of Long-Term Debt	0	(119,800)
Retirements of Rate Reduction Bonds	(41,265)	(38,881)
Capital Contributions from NU Parent	0	20,000
Other Financing Activities	(349)	(4,162)
Net Cash Flows Provided by/(Used in) Financing Activities	(72,089)	17,136
Net Increase/(Decrease) in Cash	3,039	311
Cash - Beginning of Year	56	2,559
Cash - End of Year	3,095	2,870
Western Massachusetts Electric Company [Member]
Operating Activities:
Net Income	39,408	26,571
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	1,522	2,352
Depreciation	22,154	19,644
Deferred Income Tax Expense (Benefit)	30,565	9,323
Regulatory (Underrecoveries)/Overrecoveries, Net	(8,733)	21,803
Amortization of Regulatory Assets/(Liabilities), Net	634	3,538
Amortization of Rate Reduction Bonds	13,127	12,299
Changes in Derivative Assets and Liabilities		(6,859)
Other Noncash Income (Expense)	233	(3,396)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(10,482)	(7,804)
Inventory	(2,333)	67
Taxes Receivable/(Accrued)	7,337	10,675
Change in Accounts Payable	(28,510)	4,294
Other Current Assets and Liabilities	(6,852)	(3,830)
Net Cash Flows (Used in)/ Provided by Operating Activities	58,070	88,677
Investing Activities:
Investments in Property, Plant and Equipment	(218,184)	(153,470)
Proceeds from Sales of Marketable Securities	65,131	96,134
Purchases of Marketable Securities	(65,664)	(96,312)
Decrease/(Increase) in Notes Receivable from Affiliate	11,000	(70,700)
Other Investing Activities	308	(1,664)
Net Cash Flows Used in Investing Activities	(207,409)	(226,012)
Financing Activities:
Cash Dividends on Common Stock	(9,431)	(19,729)
Issuance of Long-Term Debt	0	100,000
Increase/(Decrease) in Notes Payable to Affiliate	172,500	(20,400)
Retirements of Rate Reduction Bonds	(13,141)	(12,318)
Capital Contributions from NU Parent	0	91,812
Other Financing Activities	(54)	(1,761)
Net Cash Flows Provided by/(Used in) Financing Activities	149,874	137,604
Net Increase/(Decrease) in Cash	535	269
Cash - Beginning of Year	1	1
Cash - End of Year	536	270
NSTAR Electric Company [Member]
Operating Activities:
Net Income	156,184	203,367
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Bad Debt Expense	53,254	14,737
Depreciation	127,692	123,556
Deferred Income Tax Expense (Benefit)	(21,270)	5,063
Pension, SERP, and PBOP Expense, Net of PBOP Contributions	48,694	41,169
Pension and PBOP Contributions	(47,300)	(90,500)
Regulatory (Underrecoveries)/Overrecoveries, Net	62,075	112,554
Amortization of Regulatory Assets/(Liabilities), Net	87,912	56,734
Amortization of Rate Reduction Bonds	67,742	67,742
Other Noncash Income (Expense)	(28,134)	3,096
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(61,528)	(72,112)
Inventory	7,264	(4,670)
Taxes Receivable/(Accrued)	44,142	214,475
Change in Accounts Payable	(81,292)	(92,721)
Other Current Assets and Liabilities	17,130	(557)
Net Cash Flows (Used in)/ Provided by Operating Activities	432,565	581,933
Investing Activities:
Investments in Property, Plant and Equipment	(298,424)	(234,172)
Other Investing Activities	25,609	41,971
Net Cash Flows Used in Investing Activities	(272,815)	(192,201)
Financing Activities:
Cash Dividends on Common Stock	(188,700)	(141,600)
Cash Dividends on Preferred Stock	(1,470)	(1,470)
Increase/(Decrease) in Short-Term Debt	104,500	(145,000)
Retirements of Long-Term Debt	(688)	(16,237)
Retirements of Rate Reduction Bonds	(84,367)	(84,346)
Other Financing Activities	13,336	0
Net Cash Flows Provided by/(Used in) Financing Activities	(157,389)	(388,653)
Net Increase/(Decrease) in Cash	2,361	1,079
Cash - Beginning of Year	9,373	8,964
Cash - End of Year	$ 11,734	$ 10,043