Regulatory Matters - Cecony - Electric - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Public Utilities, General Disclosures [Line Items]
Earnings sharing threshold limit	$ 17.5
Deferred net regulatory assets	126	126
Deferred net regulatory liability	2,294.0	2,061.0
Increase in current liabilities	9
Regulatory liability	40
Deferred costs amortization period	3 years
February 2014 [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Difference in property taxes	10.00%
February 2014 [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Difference in property taxes	90.00%
CECONY-Electric [Member]
Public Utilities, General Disclosures [Line Items]
Maximum impact on return on common equity and deferral of facility relocation expenses	Not more than a 10 basis point
Deferred net regulatory assets	42	140
Deferred net regulatory liability			39.0
Deferred revenues	34.0	59.0	90.0
Potential operations penalties	152
System reliability penalty	0	0	5
Expected recovery of charges in 2014	20
CECONY-Electric [Member] | 50% of earnings [Member]
Public Utilities, General Disclosures [Line Items]
Percentage of revenue allocated to customers	50.00%
Percentage of revenue requirement earnings	9.80%
CECONY-Electric [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Difference in property taxes	20.00%
CECONY-Electric [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Difference in property taxes	80.00%
CECONY-Electric [Member] | T&D [Member]
Public Utilities, General Disclosures [Line Items]
Capital expenditures	2,300
CECONY-Electric [Member] | Other [Member]
Public Utilities, General Disclosures [Line Items]
Capital expenditures	402
CECONY-Electric [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Weighted average cost of capital	7.76%
Return on common equity	10.15%
Long-term debt cost	5.65%
Common equity ratio	48.00%
CECONY-Electric [Member] | Sale of transmission rights [Member]
Public Utilities, General Disclosures [Line Items]
Accrued revenues	27.0	45.0	26.0
Revenues difference between actual and rate year, recoverable from customers	120
Decrease in annual revenue	120
CECONY-Electric [Member] | February 2014 [Member]
Public Utilities, General Disclosures [Line Items]
Return on common equity	9.20%
Common equity ratio	48.00%
Maximum impact on return on common equity and deferral of facility relocation expenses	Not more than a 10 basis point
Decrease in annual revenue	21
Revenue requirement	21
Percent of incremental costs charge against the reserve	98.00%
Potential operations penalties	176.0
CECONY-Electric [Member] | December 2014 [Member] | February 2014 [Member]
Public Utilities, General Disclosures [Line Items]
Weighted average cost of capital	7.05%
Capital expenditures	1,487
Decrease in annual revenue	76
Cost of long-term debt, percentage	5.17%
Average base rate	17,323
CECONY-Electric [Member] | December 2014 [Member] | February 2014 [Member] | Storm Hardening [Member]
Public Utilities, General Disclosures [Line Items]
Capital expenditures	180
CECONY-Electric [Member] | December 2015 [Member] | February 2014 [Member]
Public Utilities, General Disclosures [Line Items]
Weighted average cost of capital	7.08%
Capital expenditures	1,708
Increase in annual revenues	124
Regulatory liability	30
Cost of long-term debt, percentage	5.23%
Average base rate	18,113
CECONY-Electric [Member] | December 2015 [Member] | February 2014 [Member] | Storm Hardening [Member]
Public Utilities, General Disclosures [Line Items]
Capital expenditures	278
CECONY-Electric [Member] | December 2014 and 2015 [Member] | February 2014 [Member]
Public Utilities, General Disclosures [Line Items]
Revenue requirement	107
CECONY-Electric [Member] | February 2010 [Member]
Public Utilities, General Disclosures [Line Items]
Potential refund from customers	249
Increase in current liabilities	36
CECONY-Electric [Member] | April 2010 [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Electric base rate increase	420.0
CECONY-Electric [Member] | April 2011 [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Electric base rate increase	420.0
CECONY-Electric [Member] | April 2012 [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Electric base rate increase	287.0
CECONY-Electric [Member] | March 2013 [Member]
Public Utilities, General Disclosures [Line Items]
Surcharge collected from customers	134.0
Deferred regulatory liabilities	7
CECONY-Electric [Member] | March 2013 [Member] | 50% of earnings [Member]
Public Utilities, General Disclosures [Line Items]
Percentage of revenue requirement earnings	10.65%
CECONY-Electric [Member] | March 2013 [Member] | T&D [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	15,414
CECONY-Electric [Member] | March 2013 [Member] | Other [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	1,650
CECONY-Electric [Member] | March 2013 [Member] | ERP [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	115
CECONY-Electric [Member] | March 2013 [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Surcharge collected from customers	134.0
Operations and maintenance expenses	13
Average base rate	16,826
CECONY-Electric [Member] | March 2011 [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	8
CECONY-Electric [Member] | March 2011 [Member] | 50% of earnings [Member]
Public Utilities, General Disclosures [Line Items]
Percentage of revenue requirement earnings	11.15%
CECONY-Electric [Member] | March 2011 [Member] | T&D [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	13,818
Capital expenditures	1,200
CECONY-Electric [Member] | March 2011 [Member] | Other [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	1,487
Capital expenditures	220
CECONY-Electric [Member] | March 2011 [Member] | ERP [Member]
Public Utilities, General Disclosures [Line Items]
Capital expenditures	125
CECONY-Electric [Member] | March 2011 [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Operations and maintenance expenses	27
Average base rate	14,887
CECONY-Electric [Member] | March 2012 [Member] | 50% of earnings [Member]
Public Utilities, General Disclosures [Line Items]
Percentage of revenue requirement earnings	10.65%
CECONY-Electric [Member] | March 2012 [Member] | T&D [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	14,742
CECONY-Electric [Member] | March 2012 [Member] | Other [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	1,565
CECONY-Electric [Member] | March 2012 [Member] | ERP [Member]
Public Utilities, General Disclosures [Line Items]
Deferred regulatory liabilities	25
CECONY-Electric [Member] | March 2012 [Member] | November 2009 Joint Proposal [Member]
Public Utilities, General Disclosures [Line Items]
Operations and maintenance expenses	20
Average base rate	$ 15,987