Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Summary of Significant Accounting Policies - Reconciliation of Cash, Temporary Investments and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and temporary cash investments	$ 199	$ 797	$ 69
Restricted cash	46		41
Total cash, temporary cash investments and restricted cash	245	844	110	$ 830
CEB \| Cash Collateral Held for Project Finance Agreements
Cash and Cash Equivalents [Line Items]
Restricted cash	44		39
CECONY
Cash and Cash Equivalents [Line Items]
Cash and temporary cash investments	17	730	17
Restricted cash	0		0
Total cash, temporary cash investments and restricted cash	17	$ 730	17	$ 704
RECO \| Transition Bond
Cash and Cash Equivalents [Line Items]
Restricted cash	$ 2		$ 2