Schedule I - Condensed Financial Statements of Registrant, Notes (Details) (UIL Holdings Corporation [Member], USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
UIL Holdings Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends received from subsidiaries	$ 140,500,000	$ 73,100,000	$ 174,500,000
Information regarding maturities of long-term debt [Abstract]
2014	0
2015	0
2016	0
2017	0
2018 & thereafter	$ 450,000,000