Other Material Contingencies - Guarantees (Details) - USD ($) $ in Millions	1 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Total guarantees, by type and term	$ 1,991	$ 2,073
Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	1,148
Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	659
Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	114
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	1,341
0 – 3 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	744
0 – 3 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	434
0 – 3 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	93
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	428
4 – 10 years | Con Edison Transmission
Guarantor Obligations [Line Items]
Total guarantees, by type and term	404
4 – 10 years | Energy transactions
Guarantor Obligations [Line Items]
Total guarantees, by type and term	24
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	222
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	201
Greater than 10 years | Renewable electric production projects
Guarantor Obligations [Line Items]
Total guarantees, by type and term	21
Greater than 10 years | Other
Guarantor Obligations [Line Items]
Total guarantees, by type and term	0
Sempra Solar Holdings, LLC
Guarantor Obligations [Line Items]
Purchase price	$ 1,540