Other Material Contingencies - Total Guarantees (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 2,193	$ 2,370
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,047
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	732
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	286
Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	128
0 – 3 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,367
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	460
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	512
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	267
0 – 3 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	128
4 – 10 years
Guarantor Obligations [Line Items]
Total guarantees, by type and term	622
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	587
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	35
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	204
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	185
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	19
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 0