Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,251	$ 2,042
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	570
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	815
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	796
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	1,310
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	393
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	455
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	392
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	277
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	177
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	52
4 – 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	48
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	664
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	308
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	356
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0