CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating Revenues	$ 2,055,635	$ 2,513,431
Operating Expenses:
Purchased Power and Transmission	754,859	1,162,049
Operations and Maintenance	320,136	333,382
Depreciation	173,986	163,837
Amortization of Regulatory Assets/(Liabilities), Net	20,997	60,604
Energy Efficiency Programs	137,175	146,603
Taxes Other Than Income Taxes	159,946	149,481
Total Operating Expenses	1,567,099	2,015,956
Operating Income	488,536	497,475
Interest Expense:
Total Interest Expense	98,212	94,843
Other Income [Abstract]
Other Income/(Loss), Net	2,011	5,727
Income Before Income Tax Expense	392,335	408,359
Income Tax Expense	146,302	153,226
Net Income	246,033	255,133
Net Income Attributable to Noncontrolling Interests	1,880	1,879
Net Income Attributable to Controlling Interests	$ 244,153	$ 253,254
Earnings Per Share Basic And Diluted	$ 0.77	$ 0.80
Common Stock Dividends Per Share Declared	$ 0.45	$ 0.42
Weighted Average Common Shares Outstanding:
Basic	317,517,141	317,090,841
Diluted	318,481,050	318,491,188
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 735,317	$ 804,917
Operating Expenses:
Purchased Power and Transmission	272,600	333,619
Operations and Maintenance	110,843	117,357
Depreciation	56,969	52,902
Amortization of Regulatory Assets/(Liabilities), Net	9,878	48,306
Energy Efficiency Programs	38,090	42,807
Taxes Other Than Income Taxes	75,465	68,080
Total Operating Expenses	563,845	663,071
Operating Income	171,472	141,846
Interest Expense:
Total Interest Expense	36,498	36,624
Other Income [Abstract]
Other Income/(Loss), Net	936	2,159
Income Before Income Tax Expense	135,910	107,381
Income Tax Expense	48,863	38,147
Net Income	87,047	69,234
NSTAR Electric Company [Member]
Operating Revenues	614,216	766,808
Operating Expenses:
Purchased Power and Transmission	254,336	401,867
Operations and Maintenance	94,696	75,824
Depreciation	51,886	48,768
Amortization of Regulatory Assets/(Liabilities), Net	4,683	(5,565)
Energy Efficiency Programs	66,243	55,417
Taxes Other Than Income Taxes	32,555	30,962
Total Operating Expenses	504,399	607,273
Operating Income	109,817	159,535
Interest Expense:
Total Interest Expense	20,889	20,446
Other Income [Abstract]
Other Income/(Loss), Net	(334)	602
Income Before Income Tax Expense	88,594	139,691
Income Tax Expense	34,101	56,130
Net Income	54,493	83,561
Public Service Company Of New Hampshire [Member]
Operating Revenues	242,290	284,847
Operating Expenses:
Purchased Power and Transmission	50,214	99,579
Operations and Maintenance	59,213	58,428
Depreciation	28,235	25,646
Amortization of Regulatory Assets/(Liabilities), Net	8,518	15,132
Energy Efficiency Programs	3,620	3,772
Taxes Other Than Income Taxes	21,795	19,079
Total Operating Expenses	171,595	221,636
Operating Income	70,695	63,211
Interest Expense:
Total Interest Expense	12,461	11,272
Other Income [Abstract]
Other Income/(Loss), Net	150	382
Income Before Income Tax Expense	58,384	52,321
Income Tax Expense	22,326	20,276
Net Income	36,058	32,045
Western Massachusetts Electric Company [Member]
Operating Revenues	128,095	152,864
Operating Expenses:
Purchased Power and Transmission	39,563	69,661
Operations and Maintenance	21,805	19,784
Depreciation	11,371	10,375
Amortization of Regulatory Assets/(Liabilities), Net	1,212	3,927
Energy Efficiency Programs	10,856	11,075
Taxes Other Than Income Taxes	10,232	9,437
Total Operating Expenses	95,039	124,259
Operating Income	33,056	28,605
Interest Expense:
Total Interest Expense	6,004	6,823
Other Income [Abstract]
Other Income/(Loss), Net	(149)	575
Income Before Income Tax Expense	26,903	22,357
Income Tax Expense	10,076	9,113
Net Income	$ 16,827	$ 13,244