Schedule II - Valuation and Qualifying Accounts (Details) - Allowance For Uncollectible Accounts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 83	$ 96	$ 106
Charged To Costs And Expenses	64	63	77
Charged To Other Accounts	0	0	0
Deductions	77	76	87
Balance At End of Period	70	83	96
CECONY
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	78	91	98
Charged To Costs And Expenses	60	57	69
Charged To Other Accounts	0	0	0
Deductions	73	70	76
Balance At End of Period	$ 65	$ 78	$ 91