EQUITY METHOD INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 2,100	$ 2,000
The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	1,400	1,300
Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	400	400
Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	300	300
Equity Method Investment, Ownership Percentage	7.00%
CYAPC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%
CYAPC [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	34.50%
CYAPC [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	9.50%
CYAPC [Member] | Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	5.00%
YAEC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	38.50%
YAEC [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	24.50%
YAEC [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	7.00%
MYAPC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
MYAPC [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	12.00%
MYAPC [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	3.00%
MYAPC [Member] | Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	5.00%
Regional Transmission Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	4,600	5,600
Equity Method Investment, Ownership Percentage	22.70%
Energy Investment Fund [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 4,200