Pension Benefits (Companies' Net Periodic Benefit Costs) (Details) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 190		$ 168		$ 159
Interest cost on projected benefit obligation	560		556		525
Expected return on plan assets	(734)		(704)		(691)
Amortization of net actuarial loss	530		425		299
Amortization of prior service cost	8		8		8
NET PERIODIC BENEFIT COST	554		453		300
Amortization of regulatory asset	2	[1]	2	[1]	3	[1]
TOTAL PERIODIC BENEFIT COST	556		455		303
Cost capitalized	(185)		(157)		(109)
Cost deferred	(65)		(115)		(38)
Cost charged to operating expenses	$ 306		$ 183		$ 156

[1] Relates to an increase in CECONY's pension obligation of $45 million from a 1999 special retirement program.