Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	May 31, 2016	Jan. 31, 2016	Dec. 31, 2014
Related Party Transaction [Line Items]
Ownership interest, percentage							45.70%
Costs of gas purchased	$ 81	$ 89	$ 239	$ 351
CECONY
Related Party Transaction [Line Items]
Costs of gas purchased	$ 51	$ 54	183	$ 252
CET Electric
Related Party Transaction [Line Items]
Ownership interest, percentage					45.70%	45.70%
Stagecoach Gas Services LLC | CECONY | Equity Method Investee | Purchased Power Costs
Related Party Transaction [Line Items]
Costs of gas purchased			$ 3