Income Tax - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating Loss Carryforwards [Line Items]
INCOME TAX EXPENSE	$ 250			$ 261	$ 373	$ 501
Effective tax rate	35.00%			37.00%	31.00%	35.00%
Estimated federal and state uncertain tax positions	8		72		8
Decrease in estimated prior year liabilities		238
Interest charges related to uncertain tax positions			126
Reduced interest expenses	5
Interest charges related to uncertain tax position, LILO transaction			131
Unrecognized tax benefits amount	5				5
Federal and State [Member]
Operating Loss Carryforwards [Line Items]
Estimated federal and state uncertain tax positions			238
CECONY [Member]
Operating Loss Carryforwards [Line Items]
INCOME TAX EXPENSE	222			227	431	436
Effective tax rate	36.00%			37.00%	34.00%	35.00%
Federal income tax benefits	7
Estimated federal and state uncertain tax positions			66
Reduced interest expenses	3		5
Con Edison [Member]
Operating Loss Carryforwards [Line Items]
INCOME TAX EXPENSE	$ 6				$ 6