Income Tax - Schedule of Differences on Deferred Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation	$ 4,210	$ 3,652
Regulatory asset - future income tax	2,061.0	1,971.0
Unrecognized pension and other postretirement costs	2,472	2,554
State income tax	1,060	920
Capitalized overheads	565	536
Pension	736	682
Investment tax credits	49	55
Other	931	743
Total deferred tax liabilities	12,084	11,113
Unrecognized pension and other postretirement costs	2,472	2,554
State income tax	382	336
Regulatory liability - future income tax	126	173
Other	1,028	753
Total deferred tax assets	4,008	3,816
Net deferred tax liabilities and investment tax credits	8,076	7,297
Deferred income taxes and investment tax credits - Noncurrent	8,372	7,563
Deferred tax assets - Current	(296)	(266)
Net deferred tax liabilities and investment tax credits	8,076	7,297
CECONY [Member]
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Depreciation	3,909	3,464
Regulatory asset - future income tax	1,962.0	1,891.0
Unrecognized pension and other postretirement costs	2,202	2,255
State income tax	897	811
Capitalized overheads	496	470
Pension	730	709
Investment tax credits	47	52
Other	528	467
Total deferred tax liabilities	10,771	10,119
Unrecognized pension and other postretirement costs	2,202	2,255
State income tax	357	309
Regulatory liability - future income tax	117	167
Other	836	624
Total deferred tax assets	3,512	3,355
Net deferred tax liabilities and investment tax credits	7,259	6,764
Deferred income taxes and investment tax credits - Noncurrent	7,452	6,921
Deferred tax assets - Current	(193)	(157)
Net deferred tax liabilities and investment tax credits	$ 7,259	$ 6,764