Other Material Contingencies - Total Guarantees (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,329	$ 2,370
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,047
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	743
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	411
Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	128
0 – 3 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,660
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	643
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	497
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	392
0 – 3 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	128
4 – 10 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	435
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	404
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	31
4 – 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	0
4 – 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	0
Greater than 10 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	234
Greater than 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	0
Greater than 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	215
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	19
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0