CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Revenues	$ 2,105,135	$ 2,055,635
Operating Expenses:
Purchased Power, Fuel and Transmission	753,649	754,859
Operations and Maintenance	330,265	320,136
Depreciation	186,805	173,986
Amortization of Regulatory Assets, Net	24,017	20,997
Energy Efficiency Programs	146,158	137,175
Taxes Other Than Income Taxes	155,222	159,946
Total Operating Expenses	1,596,116	1,567,099
Operating Income/(Loss)	509,019	488,536
Interest Expense	103,429	98,212
Other Income/(Loss), Net	13,577	2,011
Income Before Income Tax Expense	419,167	392,335
Income Tax Expense	157,829	146,302
Net Income	261,338	246,033
Net Income Attributable to Noncontrolling Interests	1,880	1,880
Net Income Attributable to Common Shareholders	$ 259,458	$ 244,153
Dividends Declared Per Common Share (in dollars per share)	$ 0.48	$ 0.45
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,463,151	317,517,141
Diluted (in shares)	318,124,536	318,481,050
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 732,310	$ 735,317
Operating Expenses:
Purchased Power, Fuel and Transmission	244,938	272,600
Operations and Maintenance	128,226	110,843
Depreciation	59,751	56,969
Amortization of Regulatory Assets, Net	12,803	9,878
Energy Efficiency Programs	36,591	38,090
Taxes Other Than Income Taxes	73,979	75,465
Total Operating Expenses	556,288	563,845
Operating Income/(Loss)	176,022	171,472
Interest Expense	34,964	36,498
Other Income/(Loss), Net	2,756	936
Income Before Income Tax Expense	143,814	135,910
Income Tax Expense	53,606	48,863
Net Income	90,208	87,047
NSTAR Electric Company [Member]
Operating Revenues	603,779	614,216
Operating Expenses:
Purchased Power, Fuel and Transmission	233,093	254,336
Operations and Maintenance	88,351	94,696
Depreciation	55,216	51,886
Amortization of Regulatory Assets, Net	4,977	4,683
Energy Efficiency Programs	67,312	66,243
Taxes Other Than Income Taxes	27,393	32,555
Total Operating Expenses	476,342	504,399
Operating Income/(Loss)	127,437	109,817
Interest Expense	22,029	20,889
Other Income/(Loss), Net	3,249	(334)
Income Before Income Tax Expense	108,657	88,594
Income Tax Expense	42,495	34,101
Net Income	66,162	54,493
Public Service Company Of New Hampshire [Member]
Operating Revenues	253,157	242,290
Operating Expenses:
Purchased Power, Fuel and Transmission	61,747	50,214
Operations and Maintenance	62,351	59,213
Depreciation	30,735	28,235
Amortization of Regulatory Assets, Net	5,445	8,518
Energy Efficiency Programs	3,746	3,620
Taxes Other Than Income Taxes	20,881	21,795
Total Operating Expenses	184,905	171,595
Operating Income/(Loss)	68,252	70,695
Interest Expense	12,808	12,461
Other Income/(Loss), Net	1,198	150
Income Before Income Tax Expense	56,642	58,384
Income Tax Expense	22,330	22,326
Net Income	34,312	36,058
Western Massachusetts Electric Company [Member]
Operating Revenues	130,136	128,095
Operating Expenses:
Purchased Power, Fuel and Transmission	40,867	39,563
Operations and Maintenance	22,498	21,805
Depreciation	12,002	11,371
Amortization of Regulatory Asset (Liability)	(488)	1,212
Energy Efficiency Programs	10,664	10,856
Taxes Other Than Income Taxes	10,428	10,232
Total Operating Expenses	95,971	95,039
Operating Income/(Loss)	34,165	33,056
Interest Expense	6,249	6,004
Other Income/(Loss), Net	77	(149)
Income Before Income Tax Expense	27,993	26,903
Income Tax Expense	10,775	10,076
Net Income	$ 17,218	$ 16,827