Schedule II - Valuation and Qualifying Accounts - Valuation and Qualifying Accounts (Detail) (Allowance For Uncollectible Accounts [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 103	$ 105	$ 97
Charged To Costs And Expenses	98	86	96
Charged To Other Accounts	0	0	0
Deductions	95	88	88
Balance At End of Period	106	103	105
CECONY [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	95	96	88
Charged To Costs And Expenses	91	82	90
Charged To Other Accounts	0	0	0
Deductions	88	83	82
Balance At End of Period	$ 98	$ 95	$ 96