Income Tax - Schedule of Differences on Deferred Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Depreciation	$ 4,602	$ 4,210
Regulatory asset - future income tax	2,294.0	2,061.0
State income tax	1,111	1,060
Unrecognized pension and other postretirement costs	1,109	2,312
Pension	674	736
Capitalized overheads	566	565
Unamortized investment tax credits	43	49
Other	1,048	931
Total deferred tax liabilities	11,447	11,924
Unrecognized pension and other postretirement costs	1,109	2,312
Regulatory liability - future income tax	126	126
State income tax	555	382
Loss carryforwards	12	252
Loss carryforwards, valuation reserve	(12)	(15)
Other	1,313	791
Total deferred tax assets	3,103	3,848
Net deferred tax liabilities and investment tax credits	8,344	8,076
Deferred income taxes and investment tax credits - noncurrent	8,466	8,372
Deferred tax assets - current	(122)	(296)
Net deferred tax liabilities and investment tax credits	8,344	8,076
CECONY [Member]
Income Tax Contingency [Line Items]
Depreciation	4,277	3,909
Regulatory asset - future income tax	2,165.0	1,962.0
State income tax	1,008	897
Unrecognized pension and other postretirement costs	1,060	2,202
Pension	667	730
Capitalized overheads	501	496
Unamortized investment tax credits	42	47
Other	869	528
Total deferred tax liabilities	10,589	10,771
Unrecognized pension and other postretirement costs	1,060	2,202
Regulatory liability - future income tax	112	117
State income tax	500	357
Loss carryforwards		136
Other	1,185	700
Total deferred tax assets	2,857	3,512
Net deferred tax liabilities and investment tax credits	7,732	7,259
Deferred income taxes and investment tax credits - noncurrent	7,832	7,452
Deferred tax assets - current	(100)	(193)
Net deferred tax liabilities and investment tax credits	$ 7,732	$ 7,259