Other Material Contingencies - Total Guarantees (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,073	$ 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	669
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	234
Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	123
0 – 3 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,407
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	431
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	210
0 – 3 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	123
4 – 10 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	431
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	27
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	235
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	211
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	24
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0