Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,199	$ 2,439
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	876
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	709
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	544
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	1,241
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	539
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	490
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	142
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	356
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	337
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	19
4 – 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	0
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	602
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	200
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	402
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0