Stock-Based Compensation - Summary of Stock Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining Contractual Life	2 years
Options Outstanding / Exercisable	606,475	927,025
Weighted Average Exercise Price	$ 43.008	$ 43.046
2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining Contractual Life	3 years
Options Outstanding / Exercisable	228,250
Weighted Average Exercise Price	$ 43.870
2005 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining Contractual Life	2 years
Options Outstanding / Exercisable	170,125
Weighted Average Exercise Price	$ 42.243
2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining Contractual Life	1 year
Options Outstanding / Exercisable	157,000
Weighted Average Exercise Price	$ 44.060
2003 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding / Exercisable	51,100
Weighted Average Exercise Price	$ 38.470
2003 [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining Contractual Life	1 year
CECONY [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding / Exercisable	481,175	740,875
Weighted Average Exercise Price	$ 42.973	$ 43.066
CECONY [Member] | 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding / Exercisable	188,150
Weighted Average Exercise Price	$ 43.841
CECONY [Member] | 2005 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding / Exercisable	139,025
Weighted Average Exercise Price	$ 42.258
CECONY [Member] | 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding / Exercisable	112,400
Weighted Average Exercise Price	$ 44.072
CECONY [Member] | 2003 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding / Exercisable	41,600
Weighted Average Exercise Price	$ 38.470