Consolidated Statement of Capitalization - Long-term Debt - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Schedule of Capitalization, Long-term Debt [Line Items]
Other long-term debt		$ 310	$ 317
Unamortized debt expense		(113)	(107)
Unamortized debt discount		(29)	(27)
TOTAL		16,029	14,774
Long-term debt - Variable rate term loan		0	400
Less: Long-term debt due within one year		1,298	39
TOTAL LONG-TERM DEBT		14,731	14,735
TOTAL CAPITALIZATION		30,149	29,033
CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Unamortized debt expense		(94)	(87)
Unamortized debt discount		(27)	(26)
TOTAL		13,265	12,073
Less: Long-term debt due within one year		1,200	0
TOTAL LONG-TERM DEBT		12,065	12,073
TOTAL CAPITALIZATION		24,504	23,902
Coram
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL PROJECT DEBT		$ 170	180
Coram | Maximum
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.52%
Texas Solar 4
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL PROJECT DEBT		$ 61	64
Texas Solar 4 | Minimum
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.95%
Texas Solar 4 | Maximum
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.25%
California Solar 2
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.94%
TOTAL PROJECT DEBT		$ 110	114
California Solar 3
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.07%
TOTAL PROJECT DEBT		$ 93	95
Texas Solar 5
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.53%
TOTAL PROJECT DEBT		$ 155	158
Texas Solar 7
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.21%
TOTAL PROJECT DEBT		$ 214	218
Upton County Solar
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.45%
TOTAL PROJECT DEBT		$ 97	0
Other project debt
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL PROJECT DEBT		15	16
Project Debt
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL PROJECT DEBT		915	845
Debentures
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL		13,860	12,260
Debentures | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL		$ 12,300	11,100
Debentures | Debenture Series 2008A, 5.85% Due 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.85%
TOTAL		$ 600	600
Debentures | Debenture Series 2008A, 5.85% Due 2018 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.85%
TOTAL		$ 600	600
Debentures | Debenture Series 2008A, 6.15% Due 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.15%
TOTAL		$ 50	50
Debentures | Debenture Series 2008C, 7.125% Due 2018
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		7.125%
TOTAL		$ 600	600
Debentures | Debenture Series 2008C, 7.125% Due 2018 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		7.125%
TOTAL		$ 600	600
Debentures | Debenture Series 2009A, 4.96% Due 2019
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.96%
TOTAL		$ 60	60
Debentures | Debenture Series 2009B, 6.65% Due 2019
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.65%
TOTAL		$ 475	475
Debentures | Debenture Series 2009B, 6.65% Due 2019 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.65%
TOTAL		$ 475	475
Debentures | Debenture Series 2010A, 4.45% Due 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.45%
TOTAL		$ 350	350
Debentures | Debenture Series 2010A, 4.45% Due 2020 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.45%
TOTAL		$ 350	350
Debentures | Debenture Series 2017A, 2.00% Due 2020
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		2.00%
TOTAL		$ 400	0
Debentures | Debenture Series 2016A, 2.00% Due 2021
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		2.00%
TOTAL		$ 500	500
Debentures | Debenture Series 2014B, 3.30% Due 2024
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.30%
TOTAL		$ 250	250
Debentures | Debenture Series 2014B, 3.30% Due 2024 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.30%
TOTAL		$ 250	250
Debentures | Debenture Series 2016B, 2.90% Due 2026
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		2.90%
TOTAL		$ 250	250
Debentures | Debenture Series 2016B, 2.90% Due 2026 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		2.90%
TOTAL		$ 250	250
Debentures | Debenture Series 1997F, 6.50% Due 2027
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.50%
TOTAL		$ 80	80
Debentures | Debenture Series 2017B, 3.125% Due 2027
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.125%
TOTAL		$ 350	0
Debentures | Debenture Series 2017B, 3.125% Due 2027 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.125%
TOTAL		$ 350	0
Debentures | Debenture Series 2003A, 5.875% Due 2033
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.875%
TOTAL		$ 175	175
Debentures | Debenture Series 2003A, 5.875% Due 2033 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.875%
TOTAL		$ 175	175
Debentures | Debenture Series 2003C, 5.10% Due 2033
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.10%
TOTAL		$ 200	200
Debentures | Debenture Series 2003C, 5.10% Due 2033 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.10%
TOTAL		$ 200	200
Debentures | Debenture Series 2004B, 5.70% Due 2034
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.70%
TOTAL		$ 200	200
Debentures | Debenture Series 2004B, 5.70% Due 2034 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.70%
TOTAL		$ 200	200
Debentures | Debenture Series 2005A, 5.30% Due 2035
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.30%
TOTAL		$ 350	350
Debentures | Debenture Series 2005A, 5.30% Due 2035 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.30%
TOTAL		$ 350	350
Debentures | Debenture Series 2005B, 5.25% Due 2035
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.25%
TOTAL		$ 125	125
Debentures | Debenture Series 2005B, 5.25% Due 2035 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.25%
TOTAL		$ 125	125
Debentures | Debenture Series 2006A, 5.85% Due 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.85%
TOTAL		$ 400	400
Debentures | Debenture Series 2006A, 5.85% Due 2036 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.85%
TOTAL		$ 400	400
Debentures | Debenture Series 2006B, 6.20% Due 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.20%
TOTAL		$ 400	400
Debentures | Debenture Series 2006B, 6.20% Due 2036 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.20%
TOTAL		$ 400	400
Debentures | Debenture Series 2006E, 5.70% Due 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.70%
TOTAL		$ 250	250
Debentures | Debenture Series 2006E, 5.70% Due 2036 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.70%
TOTAL		$ 250	250
Debentures | Debenture Series 2007A, 6.30% Due 2037
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.30%
TOTAL		$ 525	525
Debentures | Debenture Series 2007A, 6.30% Due 2037 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.30%
TOTAL		$ 525	525
Debentures | Debenture Series 2008B, 6.75% Due 2038
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.75%
TOTAL		$ 600	600
Debentures | Debenture Series 2008B, 6.75% Due 2038 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.75%
TOTAL		$ 600	600
Debentures | Debenture Series 2009B, 6.00% Due 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		6.00%
TOTAL		$ 60	60
Debentures | Debenture Series 2009C, 5.50% Due 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.50%
TOTAL		$ 600	600
Debentures | Debenture Series 2009C, 5.50% Due 2039 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.50%
TOTAL		$ 600	600
Debentures | Debenture Series 2010B, 5.70% Due 2040
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.70%
TOTAL		$ 350	350
Debentures | Debenture Series 2010B, 5.70% Due 2040 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.70%
TOTAL		$ 350	350
Debentures | Debenture Series 2010B, 5.50% Due 2040
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		5.50%
TOTAL		$ 115	115
Debentures | Debenture Series 2012A, 4.20% Due 2042
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.20%
TOTAL		$ 400	400
Debentures | Debenture Series 2012A, 4.20% Due 2042 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.20%
TOTAL		$ 400	400
Debentures | Debenture Series 2013A, 3.95% Due 2043
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.95%
TOTAL		$ 700	700
Debentures | Debenture Series 2013A, 3.95% Due 2043 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.95%
TOTAL		$ 700	700
Debentures | Debenture Series 2014A, 4.45% Due 2044
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.45%
TOTAL		$ 850	850
Debentures | Debenture Series 2014A, 4.45% Due 2044 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.45%
TOTAL		$ 850	850
Debentures | Debenture Series 2015A, 4.50% due 2045
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.50%
TOTAL		$ 650	650
Debentures | Debenture Series 2015A, 4.50% due 2045 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.50%
TOTAL		$ 650	650
Debentures | Debenture Series 2015A, 4.95% due 2045
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.95%
TOTAL		$ 120	120
Debentures | Debenture Series 2015B, 4.69% due 2045
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.69%
TOTAL		$ 100	100
Debentures | Debenture Series 2016A, 3.85% Due 2046
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.85%
TOTAL		$ 550	550
Debentures | Debenture Series 2016A, 3.85% Due 2046 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.85%
TOTAL		$ 550	550
Debentures | Debenture Series 2016A. 3.88% Due 2046
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.88%
TOTAL		$ 75	75
Debentures | Debenture Series 2017A, 3.875% Due 2047
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.875%
TOTAL		$ 500	0
Debentures | Debenture Series 2017A, 3.875% Due 2047 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		3.875%
TOTAL		$ 500	0
Debentures | Debenture Series 2014C, 4.625% Due 2054
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.625%
TOTAL		$ 750	750
Debentures | Debenture Series 2014C, 4.625% Due 2054 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.625%
TOTAL		$ 750	750
Debentures | Debenture Series 2016C, 4.30% Due 2056
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.30%
TOTAL		$ 500	500
Debentures | Debenture Series 2016C, 4.30% Due 2056 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.30%
TOTAL		$ 500	500
Debentures | Debenture Series 2017C, 4.00% Due 2057
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		4.00%
TOTAL		$ 350
Debentures | Debenture Series 2017C, 4.00% Due 2057 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		400.00%
TOTAL		$ 350	0
Tax-Exempt Debt
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL PROJECT DEBT	[1]	1,086	1,086
Tax-Exempt Debt | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
TOTAL		$ 1,086	1,086
Tax-Exempt Debt | Tax Exempt Debt Series 2004B Series 1, 2.45% Due 2032
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	2.45%
TOTAL PROJECT DEBT	[1]	$ 127	127
Tax-Exempt Debt | Tax Exempt Debt Series 2004B Series 1, 2.45% Due 2032 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		2.45%
TOTAL		$ 127	127
Tax-Exempt Debt | Tax Exempt Debt Series 1999A, 1.834% Due 2034
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.834%
TOTAL PROJECT DEBT	[1]	$ 293	293
Tax-Exempt Debt | Tax Exempt Debt Series 1999A, 1.834% Due 2034 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.834%
TOTAL		$ 293	293
Tax-Exempt Debt | Tax Exempt Debt Series 2004B Series 2, 1.68% Due 2035
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.68%
TOTAL PROJECT DEBT	[1]	$ 20	20
Tax-Exempt Debt | Tax Exempt Debt Series 2004B Series 2, 1.68% Due 2035 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.68%
TOTAL		$ 20	20
Tax-Exempt Debt | Tax Exempt Debt Series 2001B, 1.796% Due 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.796%
TOTAL PROJECT DEBT	[1]	$ 98	98
Tax-Exempt Debt | Tax Exempt Debt Series 2001B, 1.796% Due 2036 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.796%
TOTAL		$ 98	98
Tax-Exempt Debt | Tax Exempt Debt Series 2010A, 1.715% Due 2036
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.715%
TOTAL PROJECT DEBT	[1]	$ 225	225
Tax-Exempt Debt | Tax Exempt Debt Series 2010A, 1.715% Due 2036 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.715%
TOTAL		$ 225	225
Tax-Exempt Debt | Tax Exempt Debt Series 2004A, 1.943% Due 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.943%
TOTAL PROJECT DEBT	[1]	$ 98	98
Tax-Exempt Debt | Tax Exempt Debt Series 2004A, 1.943% Due 2039 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.943%
TOTAL		$ 98	98
Tax-Exempt Debt | Tax Exempt Debt Series 2004C, 1.663% Due 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.663%
TOTAL PROJECT DEBT	[1]	$ 99	99
Tax-Exempt Debt | Tax Exempt Debt Series 2004C, 1.663% Due 2039 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.663%
TOTAL		$ 99	99
Tax-Exempt Debt | Tax-Exempt Debt Series 2005A, 1.627% Due 2039
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate	[1]	1.627%
TOTAL PROJECT DEBT	[1]	$ 126	126
Tax-Exempt Debt | Tax-Exempt Debt Series 2005A, 1.627% Due 2039 | CECONY
Schedule of Capitalization, Long-term Debt [Line Items]
Interest Rate		1.627%
TOTAL		$ 126	$ 126

[1] Rates are to be reset weekly or by auction held every 35 days; December 31, 2017 rates shown.