Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1,954	$ 2,439
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	573
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	724
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	587
Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	70
0 – 3 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	857
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	162
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	501
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	124
0 – 3 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	70
4 – 10 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	449
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	411
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	29
4 – 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	9
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	648
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	194
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	454
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0