PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (DETAILS) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Class Of Stock Line Items
Cash Dividends on Preferred Stock	$ 5,559,000	$ 5,559,000	$ 5,559,000
The Connecticut Light And Power Company [Member]
Class Of Stock Line Items
Preferred Stock, Shares Outstanding	2,324,000
Preferred Stock, Value, Outstanding	116,200,000	116,200,000
Dividends Declared	5,600,000	6,100,000	5,600,000
Cash Dividends on Preferred Stock	5,559,000	5,559,000	5,559,000
Preferred Stock Authorized Description	CL&P's charter authorizes it to issue up to 9 million shares of preferred stock ($50 par value per share) of which 2,324,000 shares were outstanding as of December 31, 2011 and 2010.
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	8,200,000	8,200,000
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	16,800,000	16,800,000
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	5,000,000	5,000,000
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	10,000,000	10,000,000
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	8,000,000	8,000,000
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	10,000,000	10,000,000
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	5,000,000	5,000,000
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	5,200,000	5,200,000
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	5,000,000	5,000,000
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	8,000,000	8,000,000
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	10,000,000	10,000,000
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	15,000,000	15,000,000
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	$ 10,000,000	$ 10,000,000