Leases - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended											12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2012 Tax deficiency paid in December 2005 [Member]	Dec. 31, 2012 Interest in April 2006 [Member]	Dec. 31, 2012 Disallowance of tax 1998-2007 [Member]	Dec. 31, 2011 Disallowance of tax 2011 [Member]	Dec. 31, 2010 Disallowance of tax 2010 [Member]	Dec. 31, 2009 Disallowance of tax 2009 [Member]	Dec. 31, 2008 Disallowance of tax 2008 [Member]	Dec. 31, 2012 CECONY [Member]	Dec. 31, 2011 CECONY [Member]
Operating Leased Assets [Line Items]
Accumulated amortization	$ 1.0	$ 66.0										$ 0.4	$ 65.0
Lease in lease out total investment	259
Lease in lease out total financed by equity	93
Lease in lease out total financed by long-term debt	166
The company's investment in leverage leases	(76)	(55)
Gross investment in leverage leases	228	234
Deferred tax liabilities	304	289
Tax deficiency paid to IRS					0.3
Interest paid related to tax deficiency						0.2
Disallowed deduction							416	35	40	41	42
Estimated charge after-tax			150	170
Defray interest charges	447
Cash proceeds from negotiate termination of the transactions	$ 210