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 and Other Matters - Reconciliation of Cash, Temporary Investments and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and temporary cash investments	$ 153	$ 981	$ 78
Restricted cash	161		175
Total cash, temporary cash investments and restricted cash	314	1,217	253	$ 1,006
CEB \| Cash Collateral Held for Project Finance Agreements
Cash and Cash Equivalents [Line Items]
Restricted cash	161		174
CECONY
Cash and Cash Equivalents [Line Items]
Cash and temporary cash investments	23	933	15
Restricted cash	0		0
Total cash, temporary cash investments and restricted cash	$ 23	$ 933	15	$ 818
RECO \| Transition Bond
Cash and Cash Equivalents [Line Items]
Restricted cash			$ 1