Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1,895	$ 1,831
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	548
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	721
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	556
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	1,052
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	378
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	433
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	171
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	247
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	170
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	68
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	596
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	220
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	376
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0