Other Material Contingencies - Total Guarantees (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 2,422	$ 2,856
Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	1,048
Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	783
Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	463
Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	128
0-3 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	1,826
0-3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	618
0-3 years | Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	635
0-3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	445
0-3 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	128
4-10 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	487
4-10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	430
4-10 years | Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	57
4-10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	0
4-10 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	0
Greater than 10 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	109
Greater than 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	0
Greater than 10 years | Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	91
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	18
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 0