PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (DETAILS) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class Of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 155,600	$ 155,600
Cash Dividends on Preferred Stock	$ 7,519	7,519	$ 7,682
The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	2,324,000
Preferred Stock, Value, Outstanding	$ 116,200	116,200
Cash Dividends on Preferred Stock	$ 5,559	5,559	5,559
Preferred Stock Authorized Description	The CL&P and NSTAR Electric preferred stock is not subject to mandatory redemption and is presented as a noncontrolling interest of a subsidiary in Eversource’s financial statements. CL&P is authorized to issue up to 9,000,000 shares of preferred stock, par value $50 per share, and NSTAR Electric is authorized to issue 2,890,000 shares of preferred stock, par value $100 per share. Holders of preferred stock of CL&P and NSTAR Electric are entitled to receive cumulative dividends in preference to any payment of dividends on the common stock. Upon liquidation, holders of preferred stock of CL&P and NSTAR Electric are entitled to receive a liquidation preference before any distribution to holders of common stock in an amount equal to the par value of the preferred stock plus accrued and unpaid dividends. If the net assets were to be insufficient to pay the liquidation preference in full, then the net assets would be distributed ratably to all holders of preferred stock. The preferred stock of CL&P and NSTAR Electric is subject to optional redemption by the CL&P and NSTAR Electric Board of Directors at any time.
NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	430,000
Preferred Stock, Value, Outstanding	$ 43,000	43,000
Cash Dividends on Preferred Stock	$ 1,960	1,961	$ 2,123
Series 1947 $1.90 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	163,912
Preferred Stock, Redemption Price Per Share	$ 52.50
Preferred Stock, Value, Outstanding	$ 8,200	8,200
Series 1947 $2.00 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	336,088
Preferred Stock, Redemption Price Per Share	$ 54.00
Preferred Stock, Value, Outstanding	$ 16,800	16,800
Series 1949 $2.04 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	100,000
Preferred Stock, Redemption Price Per Share	$ 52.00
Preferred Stock, Value, Outstanding	$ 5,000	5,000
Series 1949 $2.20 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 52.50
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Series 1949 3.90% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	160,000
Preferred Stock, Redemption Price Per Share	$ 50.50
Preferred Stock, Value, Outstanding	$ 8,000	8,000
Series E 1954 $2.06 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 51.00
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Series F 1955 $2.09 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	100,000
Preferred Stock, Redemption Price Per Share	$ 51.00
Preferred Stock, Value, Outstanding	$ 5,000	5,000
Series 1956 4.5% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	104,000
Preferred Stock, Redemption Price Per Share	$ 50.75
Preferred Stock, Value, Outstanding	$ 5,200	5,200
Series 1958 4.96% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	100,000
Preferred Stock, Redemption Price Per Share	$ 50.50
Preferred Stock, Value, Outstanding	$ 5,000	5,000
Series 1963 4.5% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	160,000
Preferred Stock, Redemption Price Per Share	$ 50.50
Preferred Stock, Value, Outstanding	$ 8,000	8,000
Series 1967 5.28% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 51.43
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Series G of 1968 $3.24 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	300,000
Preferred Stock, Redemption Price Per Share	$ 51.84
Preferred Stock, Value, Outstanding	$ 15,000	15,000
Series 1968 6.56% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 51.44
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Preferred Stock 4.25% [Member] | NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	180,000
Preferred Stock, Redemption Price Per Share	$ 103.625
Preferred Stock, Value, Outstanding	$ 18,000	18,000
Preferred Stock 4.78% [Member] | NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	250,000
Preferred Stock, Redemption Price Per Share	$ 102.80
Preferred Stock, Value, Outstanding	$ 25,000	$ 25,000