Material Contingencies - Total Guarantees (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,042	$ 1,831
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	753
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	649
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	1,228
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	480
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	285
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	237
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	51
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
> 10 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	577
> 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	0
> 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	222
> 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	355
> 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0