PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) (USD $)			3 Months Ended						3 Months Ended						3 Months Ended							3 Months Ended						3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Pension Plans Defined Benefit Member	Mar. 31, 2013 Pension Plans Defined Benefit Member	Mar. 31, 2014 PBOP Plan	Mar. 31, 2013 PBOP Plan	Mar. 31, 2014 The Connecticut Light And Power Company [Member]	Dec. 31, 2013 The Connecticut Light And Power Company [Member]	Mar. 31, 2014 The Connecticut Light And Power Company [Member] Pension Plans Defined Benefit Member	Mar. 31, 2013 The Connecticut Light And Power Company [Member] Pension Plans Defined Benefit Member	Mar. 31, 2014 The Connecticut Light And Power Company [Member] PBOP Plan	Mar. 31, 2013 The Connecticut Light And Power Company [Member] PBOP Plan	Mar. 31, 2014 NSTAR Electric Company [Member]	Dec. 31, 2013 NSTAR Electric Company [Member]	Mar. 31, 2014 NSTAR Electric Company [Member] Pension Plans Defined Benefit Member	Mar. 31, 2013 NSTAR Electric Company [Member] Pension Plans Defined Benefit Member	Mar. 31, 2014 NSTAR Electric Company [Member] PBOP Plan	Mar. 31, 2013 NSTAR Electric Company [Member] PBOP Plan	Mar. 31, 2014 NSTAR Electric Company [Member] Supplemental Employee Retirement Plans, Defined Benefit [Member]	Mar. 31, 2014 Public Service Company Of New Hampshire [Member]	Dec. 31, 2013 Public Service Company Of New Hampshire [Member]	Mar. 31, 2014 Public Service Company Of New Hampshire [Member] Pension Plans Defined Benefit Member	Mar. 31, 2013 Public Service Company Of New Hampshire [Member] Pension Plans Defined Benefit Member	Mar. 31, 2014 Public Service Company Of New Hampshire [Member] PBOP Plan	Mar. 31, 2013 Public Service Company Of New Hampshire [Member] PBOP Plan	Mar. 31, 2014 Western Massachusetts Electric Company [Member]	Dec. 31, 2013 Western Massachusetts Electric Company [Member]	Mar. 31, 2014 Western Massachusetts Electric Company [Member] Pension Plans Defined Benefit Member	Mar. 31, 2013 Western Massachusetts Electric Company [Member] Pension Plans Defined Benefit Member	Mar. 31, 2014 Western Massachusetts Electric Company [Member] PBOP Plan	Mar. 31, 2013 Western Massachusetts Electric Company [Member] PBOP Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost			$ 22,300,000	$ 26,600,000	$ 3,000,000	$ 4,800,000			$ 5,200,000	$ 6,100,000	$ 600,000	$ 900,000			$ 4,600,000	$ 9,300,000	$ 700,000					$ 2,800,000	$ 3,300,000	$ 400,000	$ 600,000			$ 1,000,000	$ 1,200,000	$ 100,000	$ 200,000
Defined Benefit Plan Interest Cost			56,600,000	51,400,000	12,600,000	12,800,000			13,300,000	12,100,000	2,100,000	2,000,000			10,200,000	14,200,000	4,900,000					6,500,000	6,000,000	1,100,000	1,000,000			2,700,000	2,500,000	500,000	400,000
Defined Benefit Plan, Expected Return on Plan Assets			(77,700,000)	(70,300,000)	(15,700,000)	(13,800,000)			(19,400,000)	(18,500,000)	(2,700,000)	(2,500,000)			(15,800,000)	(22,000,000)	(6,400,000)					(10,200,000)	(7,700,000)	(1,400,000)	(1,300,000)			(4,600,000)	(4,300,000)	(600,000)	(600,000)
Defined Benefit Plan, Amortization of Gains (Losses)			33,000,000	52,900,000	3,000,000	8,200,000			9,100,000	14,100,000	1,100,000	1,700,000			5,800,000	14,500,000	(100,000)					3,300,000	5,500,000	500,000	900,000			1,900,000	3,000,000	100,000	300,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit			1,100,000	1,100,000	(600,000)	(600,000)			500,000	500,000					0	0	(500,000)					200,000	100,000					100,000	100,000
Defined Benefit Plan Net Periodic Benefit Cost			35,300,000	61,700,000	2,300,000	11,400,000			8,700,000	14,300,000	1,100,000	2,100,000			4,800,000	16,000,000	(1,400,000)					2,600,000	7,200,000	600,000	1,200,000			1,100,000	2,500,000	100,000	300,000
Related Intercompany Allocationsof Defined Benefit Expense									6,800,000	10,700,000	1,100,000	1,600,000			2,400,000	(2,000,000)	100,000	4,300,000				1,900,000	2,600,000	300,000	400,000			1,300,000	1,800,000	200,000	300,000
Amount Capitalized Defined Benefit Expense			9,700,000	16,700,000	400,000	3,500,000			4,900,000	7,000,000	500,000	1,200,000			1,900,000	5,300,000	(500,000)					900,000	2,200,000	200,000	300,000			800,000	1,300,000	100,000	200,000
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities																			400,000
Accrued Pension, PBOP and SERP	$ 890,019,000	$ 896,844,000					$ 94,820,000	$ 95,895,000					$ 150,938,000	$ 118,010,000	$ 74,800,000		$ 73,000,000		$ 3,500,000	$ 15,321,000	$ 15,272,000					$ 3,850,000	$ 3,911,000