Consolidated Statement of Capitalization - Long term Debt (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL DEBENTURE	$ 9,310		$ 9,210
TOTAL TRANSITION BONDS	25		29
TOTAL TAX-EXEMPT DEBT	1,130		1,130
Other long-term debt	319		321
Unamortized debt discount	(16)		(17)
TOTAL	10,768		10,673
Less: long-term debt due within one year	706		530
TOTAL LONG-TERM DEBT	10,062		10,143
TOTAL CAPITALIZATION	21,931		21,792
Debenture Series 2002A, 5.625% Due 2012 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value			300
Interest Rate	5.625%
Maturity Date	2012
Debenture Series 2002B, 4.875% Due 2013 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	500		500
Interest Rate	4.875%
Maturity Date	2013
Debenture Series 2003B, 3.85% Due 2013 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	3.85%
Maturity Date	2013
Debenture Series 2004A, 4.70% Due 2014 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	4.70%
Maturity Date	2014
Debenture Series 2009A, 5.55% Due 2014 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	275		275
Interest Rate	5.55%
Maturity Date	2014
Debenture Series 2005C, 5.375% Due 2015 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	5.375%
Maturity Date	2015
Debenture Series 2006C, 5.50% Due 2016 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400		400
Interest Rate	5.50%
Maturity Date	2016
Debenture Series 2006D, 5.30% Due 2016 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	250		250
Interest Rate	5.30%
Maturity Date	2016
Debenture Series 2008A, 5.85% Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	5.85%
Maturity Date	2018
Debenture Series 2008C, 7.125% Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	7.125%
Maturity Date	2018
Debenture Series 2009B, 6.65% Due 2019 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	475		475
Interest Rate	6.65%
Maturity Date	2019
Debenture Series 2010A, 4.45% Due 2020 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	4.45%
Maturity Date	2020
Debenture Series 2003A, 5.875% Due 2033 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	175		175
Interest Rate	5.875%
Maturity Date	2033
Debenture Series 2003C, 5.10% Due 2033 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	5.10%
Maturity Date	2033
Debenture Series 2004B, 5.70% Due 2034 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	5.70%
Maturity Date	2034
Debenture Series 2005A, 5.30% Due 2035 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	5.30%
Maturity Date	2035
Debenture Series 2005B, 5.25% Due 2035 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	125		125
Interest Rate	5.25%
Maturity Date	2035
Debenture Series 2006A, 5.85% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400		400
Interest Rate	5.85%
Maturity Date	2036
Debenture Series 2006B, 6.20% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400		400
Interest Rate	6.20%
Maturity Date	2036
Debenture Series 2006E, 5.70% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	250		250
Interest Rate	5.70%
Maturity Date	2036
Debenture Series 2007A, 6.30% Due 2037 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	525		525
Interest Rate	6.30%
Maturity Date	2037
Debenture Series 2008B, 6.75% Due 2038 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	6.75%
Maturity Date	2038
Debenture Series 2009C, 5.50% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	5.50%
Maturity Date	2039
Debenture Series 2010B, 5.70% Due 2040 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	5.70%
Maturity Date	2040
Debenture Series 2012A, 4.20% Due 2042 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400
Interest Rate	4.20%
Maturity Date	2042
Tax Exempt Debt Series 2004B-1, 0.32% Due 2032 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	127	[1]	127	[1]
Interest Rate	0.32%	[1]
Maturity Date	2032	[1]
Tax-Exempt Debt Series 1999A, 0.27% Due 2034 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	293	[1]	293	[1]
Interest Rate	0.27%	[1]
Maturity Date	2034	[1]
Tax Exempt Debt Series 2004B-2, 0.28% Due 2035 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	20	[1]	20	[1]
Interest Rate	0.28%	[1]
Maturity Date	2035	[1]
Tax-Exempt Debt Series 2001B, 0.23% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	98	[1]	98	[1]
Interest Rate	0.23%	[1]
Maturity Date	2036	[1]
Tax-Exempt Debt Series 2010A, 0.13% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	225	[1]	225	[1]
Interest Rate	0.13%	[1]
Maturity Date	2036	[1]
Tax-Exempt Debt Series 2004A, 0.23% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	98	[1]	98	[1]
Interest Rate	0.23%	[1]
Maturity Date	2039	[1]
Tax-Exempt Debt Series 2004C, 0.13% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	99	[1]	99	[1]
Interest Rate	0.13%	[1]
Maturity Date	2039	[1]
Tax-Exempt Debt Series 2005A, 0.11% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	126	[1]	126	[1]
Interest Rate	0.11%	[1]
Maturity Date	2039	[1]
Debenture Series 2005A, 5.30% Due 2015 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	40		40
Interest Rate	5.30%
Maturity Date	2015
Debenture Series 2010A, 2.50% Due 2015 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	55		55
Interest Rate	2.50%
Maturity Date	2015
Debenture Series 2006A, 5.45% Due 2016 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	75		75
Interest Rate	5.45%
Maturity Date	2016
Debenture Series 2008A, 6.15% Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	50		50
Interest Rate	6.15%
Maturity Date	2018
Debenture Series 2009A, 4.96% Due 2019 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	60		60
Interest Rate	4.96%
Maturity Date	2019
Debenture Series 1997F, 6.50% Due 2027 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	80		80
Interest Rate	6.50%
Maturity Date	2027
Debenture Series 2009B, 6.00% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	60		60
Interest Rate	6.00%
Maturity Date	2039
Debenture Series 2010B, 5.50% Due 2040 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	115		115
Interest Rate	5.50%
Maturity Date	2040
Debenture Series 2004-1, 5.22% Due 2019 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	25	[2]	29	[2]
Interest Rate	5.22%	[2]
Maturity Date	2019	[2]
Debenture Series 1995, 0.21% Due 2015 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	44	[1],[3]	44	[1],[3]
Interest Rate	0.21%	[1],[3]
Maturity Date	2015	[1],[3]
CECONY [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL DEBENTURE	8,775		8,675
TOTAL TAX-EXEMPT DEBT	1,086		1,086
Unamortized debt discount	(16)		(16)
TOTAL	9,845		9,745
Less: long-term debt due within one year	700		525
TOTAL LONG-TERM DEBT	9,145		9,220
TOTAL CAPITALIZATION	19,697		19,651
CECONY [Member] | Debenture Series 2002A, 5.625% Due 2012 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value			300
Interest Rate	5.625%
Maturity Date	2012
CECONY [Member] | Debenture Series 2002B, 4.875% Due 2013 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	500		500
Interest Rate	4.875%
Maturity Date	2013
CECONY [Member] | Debenture Series 2003B, 3.85% Due 2013 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	3.85%
Maturity Date	2013
CECONY [Member] | Debenture Series 2004A, 4.70% Due 2014 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	4.70%
Maturity Date	2014
CECONY [Member] | Debenture Series 2009A, 5.55% Due 2014 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	275		275
Interest Rate	5.55%
Maturity Date	2014
CECONY [Member] | Debenture Series 2005C, 5.375% Due 2015 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	5.375%
Maturity Date	2015
CECONY [Member] | Debenture Series 2006C, 5.50% Due 2016 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400		400
Interest Rate	5.50%
Maturity Date	2016
CECONY [Member] | Debenture Series 2006D, 5.30% Due 2016 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	250		250
Interest Rate	5.30%
Maturity Date	2016
CECONY [Member] | Debenture Series 2008A, 5.85% Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	5.85%
Maturity Date	2018
CECONY [Member] | Debenture Series 2008C, 7.125% Due 2018 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	7.125%
Maturity Date	2018
CECONY [Member] | Debenture Series 2009B, 6.65% Due 2019 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	475		475
Interest Rate	6.65%
Maturity Date	2019
CECONY [Member] | Debenture Series 2010A, 4.45% Due 2020 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	4.45%
Maturity Date	2020
CECONY [Member] | Debenture Series 2003A, 5.875% Due 2033 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	175		175
Interest Rate	5.875%
Maturity Date	2033
CECONY [Member] | Debenture Series 2003C, 5.10% Due 2033 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	5.10%
Maturity Date	2033
CECONY [Member] | Debenture Series 2004B, 5.70% Due 2034 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	200		200
Interest Rate	5.70%
Maturity Date	2034
CECONY [Member] | Debenture Series 2005A, 5.30% Due 2035 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	5.30%
Maturity Date	2035
CECONY [Member] | Debenture Series 2005B, 5.25% Due 2035 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	125		125
Interest Rate	5.25%
Maturity Date	2035
CECONY [Member] | Debenture Series 2006A, 5.85% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400		400
Interest Rate	5.85%
Maturity Date	2036
CECONY [Member] | Debenture Series 2006B, 6.20% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400		400
Interest Rate	6.20%
Maturity Date	2036
CECONY [Member] | Debenture Series 2006E, 5.70% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	250		250
Interest Rate	5.70%
Maturity Date	2036
CECONY [Member] | Debenture Series 2007A, 6.30% Due 2037 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	525		525
Interest Rate	6.30%
Maturity Date	2037
CECONY [Member] | Debenture Series 2008B, 6.75% Due 2038 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	6.75%
Maturity Date	2038
CECONY [Member] | Debenture Series 2009C, 5.50% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	600		600
Interest Rate	5.50%
Maturity Date	2039
CECONY [Member] | Debenture Series 2010B, 5.70% Due 2040 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	350		350
Interest Rate	5.70%
Maturity Date	2040
CECONY [Member] | Debenture Series 2012A, 4.20% Due 2042 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	400
Interest Rate	4.20%
Maturity Date	2042
CECONY [Member] | Tax Exempt Debt Series 2004B-1, 0.32% Due 2032 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	127	[1]	127	[1]
Interest Rate	0.32%	[1]
Maturity Date	2032	[1]
CECONY [Member] | Tax-Exempt Debt Series 1999A, 0.27% Due 2034 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	293	[1]	293	[1]
Interest Rate	0.27%	[1]
Maturity Date	2034	[1]
CECONY [Member] | Tax Exempt Debt Series 2004B-2, 0.28% Due 2035 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	20	[1]	20	[1]
Interest Rate	0.28%	[1]
Maturity Date	2035	[1]
CECONY [Member] | Tax-Exempt Debt Series 2001B, 0.23% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	98	[1]	98	[1]
Interest Rate	0.23%	[1]
Maturity Date	2036	[1]
CECONY [Member] | Tax-Exempt Debt Series 2010A, 0.13% Due 2036 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	225	[1]	225	[1]
Interest Rate	0.13%	[1]
Maturity Date	2036	[1]
CECONY [Member] | Tax-Exempt Debt Series 2004A, 0.23% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	98	[1]	98	[1]
Interest Rate	0.23%	[1]
Maturity Date	2039	[1]
CECONY [Member] | Tax-Exempt Debt Series 2004C, 0.13% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	99	[1]	99	[1]
Interest Rate	0.13%	[1]
Maturity Date	2039	[1]
CECONY [Member] | Tax-Exempt Debt Series 2005A, 0.11% Due 2039 [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Debt Instrument, Fair Value	$ 126	[1]	$ 126	[1]
Interest Rate	0.11%	[1]
Maturity Date	2039	[1]

[1] Rates reset weekly or by auction held every 35 days; December 31, 2012 rates shown.

[2] The final date to pay the entire remaining unpaid principal balance, if any, of all outstanding bonds is May 17, 2021.

[3] Issued for O&R pollution control financing.