SHORT-TERM CREDIT ARRANGEMENTS (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Disclosure of short-term credit arrangements [Abstract]
Standby letter of credit outstanding	$ 4.4
Standby Letter of Credit Expiring January 2014 [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Expiration date	Jan. 31, 2014
Standby Letter of Credit Expiring June 2014 [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Expiration date	Jun. 16, 2014
Revolving Credit Facility [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Amounts outstanding under the Credit Agreement	44
Expiration date	Nov. 30, 2016
Available credit under the Credit Facility	351.6
Credit Agreement [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Amounts outstanding under the Credit Agreement	$ 100
Expiration date	Oct. 31, 2013