Debtors' Financial Information (GenOn and GenOn Americas Generation) - Statement of Cash Flows (Details) - USD ($) $ in Millions	4 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities		$ (53)	$ 190
Net cash used by investing activities		(69)	326
Net cash used by financing activities		(101)	(4)
Net (Decrease)/Increase in Cash, Cash Equivalents and Funds Deposited by Counterparties		(223)	512
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at Beginning of Period		1,034	716
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at End of Period	$ 811	811	$ 1,228
GenOn Energy, Inc. Debtors
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	97
Net cash used by investing activities	(9)
Net cash used by financing activities	(3)
Net (Decrease)/Increase in Cash, Cash Equivalents and Funds Deposited by Counterparties	85
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at Beginning of Period	484
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at End of Period	569	569
GenOn Americas Generation Debtors
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	4
Net cash used by investing activities	(4)
Net cash used by financing activities	0
Net (Decrease)/Increase in Cash, Cash Equivalents and Funds Deposited by Counterparties	0
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at Beginning of Period	0
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at End of Period	$ 0	$ 0

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. 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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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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