Schedule I - Condensed Financial Information - Condensed Statement of Cash Flows (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Cash Flow Information [Line Items]
CECONY	$ (709)	$ (693)	$ (629)
Net Income	1,138	1,051	992
Other - net	27	51	207
Net Cash Flows from Operating Activities	2,599	3,137	2,381
INVESTING ACTIVITIES
NET CASH FLOWS USED IN INVESTING ACTIVITIES	(2,523)	(2,150)	(2,175)
FINANCING ACTIVITIES
Net proceeds of short-term debt	539
Retirement of long-term debt	(305)	(4)	(1,011)
Issuance of common shares for stock plans, net of repurchases	(9)	31	133
Common stock dividends	(709)	(693)	(629)
NET CASH FLOWS USED IN FINANCING ACTIVITIES	(330)	(677)	(128)
Net Change for the Period	(254)	310	78
BALANCE AT BEGINNING OF PERIOD	648	338	260
Balance at End of Period	394	648	338
Parent Company [Member]
Supplemental Cash Flow Information [Line Items]
CECONY	(709)	(693)	(629)
Net Income	1,138	1,051	992
Equity in earnings of subsidiaries	(1,154)	(1,064)	(1,008)
Other - net	(208)	(67)	(4)
Net Cash Flows from Operating Activities	503	646	690
INVESTING ACTIVITIES
Contributions to subsidiaries	(100)		(355)
NET CASH FLOWS USED IN INVESTING ACTIVITIES	(100)		(355)
FINANCING ACTIVITIES
Net proceeds of short-term debt	115
Retirement of long-term debt	(1)	(1)	(3)
Issuance of common shares for stock plans, net of repurchases	(9)	31	439
Common stock dividends	(709)	(693)	(629)
NET CASH FLOWS USED IN FINANCING ACTIVITIES	(604)	(663)	(193)
Net Change for the Period	(201)	(17)	142
BALANCE AT BEGINNING OF PERIOD	205	222	80
Balance at End of Period	4	205	222
CECONY [Member]
Supplemental Cash Flow Information [Line Items]
Net Income	1,014	978	893
Other - net	(40)	170	11
Net Cash Flows from Operating Activities	2,346	2,933	2,205
INVESTING ACTIVITIES
Contributions to subsidiaries			355
NET CASH FLOWS USED IN INVESTING ACTIVITIES	(1,958)	(1,947)	(1,998)
FINANCING ACTIVITIES
Net proceeds of short-term debt	421
Retirement of long-term debt	(300)		(850)
NET CASH FLOWS USED IN FINANCING ACTIVITIES	(407)	(692)	(260)
Net Change for the Period	(19)	294	(53)
BALANCE AT BEGINNING OF PERIOD	372	78	131
Balance at End of Period	353	372	78
CECONY [Member] | Parent Company [Member]
Supplemental Cash Flow Information [Line Items]
CECONY	682	681	670
FINANCING ACTIVITIES
Common stock dividends	682	681	670
O&R [Member] | Parent Company [Member]
Supplemental Cash Flow Information [Line Items]
CECONY	34	33	32
FINANCING ACTIVITIES
Common stock dividends	34	33	32
Competitive energy businesses [Member] | Parent Company [Member]
Supplemental Cash Flow Information [Line Items]
CECONY	11	12	8
FINANCING ACTIVITIES
Common stock dividends	$ 11	$ 12	$ 8