Other Material Contingencies - Total Guarantees (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 2,544	$ 2,856
Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	1,202
Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	804
Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	463
Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	75
0-3 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	1,809
0-3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	619
0-3 years | Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	672
0-3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	443
0-3 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	75
4-10 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	624
4-10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	583
4-10 years | Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	41
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	111
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	20
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 0