Other Material Contingencies - Total Guarantees (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 2,705	$ 2,856
Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	1,383
Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	838
Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	409
Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	75
0-3 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	1,961
0-3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	791
0-3 years | Energy transactions
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	707
0-3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	388
0-3 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	75
4-10 years
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	633
4-10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	592
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	90
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	21
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 0