Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1,913	$ 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	671
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	624
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	1,082
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	362
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	432
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	218
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	225
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	186
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	30
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	606
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	209
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	397
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0