Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income by Component (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Jun. 30, 2013	Mar. 31, 2013
Amounts reclassified from accumulated OCI related to pension plan liabilities, Tax	$ 1	$ 1
CECONY [Member]
Amounts reclassified from accumulated OCI related to pension plan liabilities, Tax

Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

No definition available.

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration