Income Tax - Schedule of Components of Income Tax (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax [Line Items]
State - Current	$ 29	$ 56	$ 23
State - Deferred	97	63	106
Federal - Current	(13)	53	(144)
Federal - Deferred	493	434	569
Amortization of investment tax credits	(6)	(6)	(6)
Total charge to income tax expense	600	600	548
CECONY [Member]
Income Tax [Line Items]
State - Current	53	53	13
State - Deferred	53	55	100
Federal - Current	110	43	(139)
Federal - Deferred	318	413	527
Amortization of investment tax credits	(5)	(6)	(6)
Total charge to income tax expense	$ 529	$ 558	$ 495