Regulatory Matters - Schedule of Regulatory Liability Revenue Requirement Impact (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
March 2011 [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	$ 8.0
March 2011 [Member] | T&D [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	13,818
March 2011 [Member] | Other [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	1,487
March 2011 [Member] | Production [Member] | CECONY - Steam [Member]
Regulatory Assets [Line Items]
ERP	415
March 2011 [Member] | Distribution [Member] | CECONY - Steam [Member]
Regulatory Assets [Line Items]
ERP	521
March 2012 [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	0.1
March 2012 [Member] | T&D [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	14,742
March 2012 [Member] | Other [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	1,565
March 2012 [Member] | ERP [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	25
March 2012 [Member] | Production [Member] | CECONY - Steam [Member]
Regulatory Assets [Line Items]
ERP	426
March 2012 [Member] | Distribution [Member] | CECONY - Steam [Member]
Regulatory Assets [Line Items]
ERP	534
March 2013 [Member] | T&D [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	15,414
March 2013 [Member] | Other [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	1,650
March 2013 [Member] | ERP [Member] | CECONY - Electric [Member]
Regulatory Assets [Line Items]
ERP	115
March 2013 [Member] | Production [Member] | CECONY - Steam [Member]
Regulatory Assets [Line Items]
ERP	433
March 2013 [Member] | Distribution [Member] | CECONY - Steam [Member]
Regulatory Assets [Line Items]
ERP	$ 543