Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2012	Sep. 06, 2013	Jun. 30, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	UIL HOLDINGS CORP
Entity Central Index Key	0001082510
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,791,227,691
Entity Common Stock, Shares Outstanding		50,712,507
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY
Document Type	10-K/A
Amendment Flag	true
Amendment Description	UIL Holdings Corporation (the “Company”) is filing this Amendment No. 1 on Form 10-K/A to amend Item 15 of Part IV of its Annual Report on Form 10-K for the fiscal year ended December 31, 2012, as filed with the Securities and Exchange Commission on February 21, 2013 (the “Original Filing”).
Document Period End Date	Dec. 31, 2012