CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Revenues	$ 4,465,657	$ 4,898,167	$ 5,439,430
Operating Expenses:
Fuel, Purchased and Net Interchange Power	1,580,683	1,985,634	2,629,619
Other Operating Expenses	1,026,192	958,417	1,001,190
Maintenance	271,779	210,283	234,173
Depreciation	302,192	300,737	309,618
Amortization of Regulatory Assets/(Liabilities), Net	97,113	95,593	13,315
Amortization of Rate Reduction Bonds	69,912	232,871	217,941
Taxes Other Than Income Taxes	323,610	314,741	282,199
Total Operating Expenses	3,671,481	4,098,276	4,688,055
Operating Income	794,176	799,891	751,375
Interest Expense:
Interest on Long-Term Debt	231,630	231,089	224,712
Interest on Rate Reduction Bonds	8,611	20,573	36,524
Other Interest	10,184	(14,371)	12,401
Total Interest Expense	250,425	237,291	273,637
Other Income/(Loss), Net	27,715	41,916	37,801
Income Before Income Tax Expense	571,466	604,516	515,539
Income Tax Expense	170,953	210,409	179,947
Net Income	400,513	394,107	335,592
Net Income Attributable to Noncontrolling Interests	5,820	6,158	5,559
Net Income Attributable to Controlling Interests	394,693	387,949	330,033
Diluted Earnings Per Common Share	$ 2.22	$ 2.19	$ 1.91
Basic Earnings Per Common Share	$ 2.22	$ 2.20	$ 1.91
Weighted Average Common Shares Outstanding:
Basic	177,410,167	176,636,086	172,567,928
Diluted	177,804,568	176,885,387	172,717,246
The Connecticut Light And Power Company [Member]
Operating Revenues	2,548,387	2,999,102	3,424,538
Operating Expenses:
Fuel, Purchased and Net Interchange Power	929,865	1,253,329	1,690,671
Other Operating Expenses	570,519	524,328	571,024
Maintenance	148,999	96,522	117,822
Depreciation	157,747	172,167	186,922
Amortization of Regulatory Assets/(Liabilities), Net	65,189	83,906	45,821
Amortization of Rate Reduction Bonds	0	167,021	155,938
Taxes Other Than Income Taxes	212,885	214,179	191,234
Total Operating Expenses	2,085,204	2,511,452	2,959,432
Operating Income	463,183	487,650	465,106
Interest Expense:
Interest on Long-Term Debt	131,918	134,553	133,422
Interest on Rate Reduction Bonds	0	7,542	19,061
Other Interest	809	(4,357)	3,334
Total Interest Expense	132,727	137,738	155,817
Other Income/(Loss), Net	9,741	26,669	25,874
Income Before Income Tax Expense	340,197	376,581	335,163
Income Tax Expense	90,033	132,438	118,847
Net Income	250,164	244,143	216,316
Public Service Company Of New Hampshire [Member]
Operating Revenues	1,013,003	1,033,439	1,109,591
Operating Expenses:
Fuel, Purchased and Net Interchange Power	308,777	363,147	520,529
Other Operating Expenses	217,119	230,210	239,650
Maintenance	93,079	82,384	87,026
Depreciation	76,167	67,237	61,961
Amortization of Regulatory Assets/(Liabilities), Net	25,383	11,232	(29,619)
Amortization of Rate Reduction Bonds	53,389	50,357	47,482
Taxes Other Than Income Taxes	58,985	52,686	47,975
Total Operating Expenses	832,899	857,253	975,004
Operating Income	180,104	176,186	134,587
Interest Expense:
Interest on Long-Term Debt	36,832	36,220	33,045
Interest on Rate Reduction Bonds	6,276	9,660	13,128
Other Interest	1,039	1,187	316
Total Interest Expense	44,147	47,067	46,489
Other Income/(Loss), Net	14,255	11,749	9,462
Income Before Income Tax Expense	150,212	140,868	97,560
Income Tax Expense	49,945	50,801	31,990
Net Income	100,267	90,067	65,570
Western Massachusetts Electric Company [Member]
Operating Revenues	417,315	395,161	402,413
Operating Expenses:
Fuel, Purchased and Net Interchange Power	145,594	157,276	192,177
Other Operating Expenses	98,328	102,053	85,591
Maintenance	17,734	19,196	17,895
Depreciation	26,455	23,561	22,454
Amortization of Regulatory Assets/(Liabilities), Net	6,361	2,395	(2,980)
Amortization of Rate Reduction Bonds	16,523	15,494	14,521
Taxes Other Than Income Taxes	17,957	16,529	14,174
Total Operating Expenses	328,952	336,504	343,832
Operating Income	88,363	58,657	58,581
Interest Expense:
Interest on Long-Term Debt	20,023	17,988	14,074
Interest on Rate Reduction Bonds	2,335	3,372	4,335
Other Interest	1,254	479	877
Total Interest Expense	23,612	21,839	19,286
Other Income/(Loss), Net	1,489	2,597	1,824
Income Before Income Tax Expense	66,240	39,415	41,119
Income Tax Expense	23,186	16,325	14,923
Net Income	$ 43,054	$ 23,090	$ 26,196