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, 2012	Dec. 31, 2011	Dec. 31, 2010
Balance at Beginning of Period	$ 97	$ 84	$ 75
Charged To Costs And Expenses	96	99	91
Charged To Other Accounts
Deductions	88	86	82
Balance At End of Period	105	97	84
CECONY [Member]
Balance at Beginning of Period	88	75	67
Charged To Costs And Expenses	90	91	82
Charged To Other Accounts
Deductions	82	78	74
Balance At End of Period	$ 96	$ 88	$ 75