Derivative Instruments And Hedging Activities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 112				$ 112
Makeup of net credit exposure, with investment-grade counterparties	37				37
Makeup of net credit exposure with commodity exchange brokers	34				34
Makeup of net credit exposure independent system operators	39
Makeup of net credit exposure non-rated counterparties	2
Number of contracts, considered derivatives					1483
Unrealized gain (loss) on derivatives	18	[1]	97	[1]	(72)	[1]	80	[1]
Increase in the fair value of interest swap	1				1
CECONY
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	12				12
Makeup of net credit exposure, with investment-grade counterparties	1				1
Makeup of net credit exposure with commodity exchange brokers	11				11
Number of contracts, considered derivatives					706
Interest Rate Swap [Member]
Investment Holdings [Line Items]
Unrealized gain (loss) on derivatives					$ (7)
Derivative, fixed interest rate	6.09%				6.09%

[1] Qualifying derivative contracts, which have been designated as normal purchases or normal sales contracts, are not reported at fair value under the accounting rules for derivatives and hedging and, therefore, are excluded from the table.