Regulatory Matters - Orange and Rockland Utilities, Inc. - Electric - Additional Information (Detail) (O & R [Member], USD $)	1 Months Ended	12 Months Ended
	May 31, 2010	Dec. 31, 2012	Dec. 31, 2012 July 2008 [Member]	Dec. 31, 2011 July 2008 [Member]	Dec. 31, 2010 July 2008 [Member]	Dec. 31, 2009 July 2008 [Member]	Mar. 31, 2007 March 2007 [Member]	Dec. 31, 2012 July 2008 [Member]	Dec. 31, 2012 July 2009 [Member]	Dec. 31, 2012 July 2010 [Member]	Dec. 31, 2012 July 2011[Member]	Dec. 31, 2012 June 30, 2013 [Member]	Dec. 31, 2012 June 30, 2014 [Member]	Dec. 31, 2012 June 30, 2015 [Member]	Dec. 31, 2012 July 2012 [Member]	Dec. 31, 2012 July 2013 [Member]	Dec. 31, 2012 July 2014 [Member]	Dec. 31, 2012 Maximum [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Electricity base rate increases	$ 9.8						$ 6.4	$ 15.6	$ 15.6	$ 5.7	$ 26.6				$ 19.4	$ 8.8	$ 15.2
Collection of additional electric cost										9,900,000
Annual return on common equity	10.30%		9.40%	9.40%			9.75%				9.20%	9.40%	9.50%	9.60%
Actual earnings on equity,percentage			10.20%
Average common equity ratio subject to a 50 percent maximum			50.00%
Recognition of deferred expenses				300,000		3,000,000
Recognition of deferred revenue					700,000
Company deferred revenue				7,000,000	12,000,000	8,000,000
Annual inflation rate				4.00%
Potential negative earnings adjustments			3,000,000
Reduction in company revenue					1,000,000
Accrued revenue				3,300,000	5,100,000	12,500,000
Electric base rate increase	9.8						6.4	15.6	15.6	5.7	26.6				19.4	8.8	15.2
Weighted average cost of capital											7.22%	7.61%	7.65%	7.48%
Annual return on common equity	10.30%		9.40%	9.40%			9.75%				9.20%	9.40%	9.50%	9.60%
Austerity measures											825,000
Cost of long-term debt,percentage											5.50%
Common equity ratio	50.00%						46.50%				48.00%	48.00%	48.00%	48.00%				50.00%
Average net utility plant rates											718	678	704	753
Potential operational penalties		3,000,000									3,000,000
Surcharge payment																	2,100,000
Increase rate															15,200,000	15,200,000	13,100,000
Cost of long term debt												6.07%	6.07%	5.64%
Average base rate												$ 671	$ 708	$ 759
Percentage of revenue allocated to customers												50.00%	75.00%	90.00%
Common equity basis points												80	180	280