Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,210	$ 2,042
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	547
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	831
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	762
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	1,412
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	547
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	475
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	320
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	97
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	33
4 – 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	64
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	701
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	323
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	378
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0