CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash Flows from Operating Activities
Net (Loss)/Income	$ 42	$ 248
Adjustments to reconcile net (loss)/income to net cash (used)/provided by operating activities:
Depreciation and amortization	128	153
Amortization of debt premiums	(24)	(39)
Non-cash adjustment to write-off unamortized debt premiums	(107)	0
Loss on financing arrangement for 2022 Notes	18	0
Amortization of out-of-market contracts and emission allowances	(59)	(58)
Gain on sale of assets	0	(294)
Impairment losses	0	59
Changes in derivative instruments	(13)	175
Changes in collateral deposits supporting energy risk management activities	60	(112)
Proceeds from sale of emission allowances	0	36
Lower of cost or market inventory adjustments	2	0
Changes in other working capital	(100)	22
Net Cash (Used)/Provided by Operating Activities	(53)	190
Cash Flows from Investing Activities
Capital expenditures	(69)	(239)
Proceeds from sale of assets, net	0	563
Other	0	2
Net Cash (Used)/Provided by Investing Activities	(69)	326
Cash Flows from Financing Activities
Payment for credit support	(130)	0
Payments for financing costs	(94)	0
Proceeds from draw on intercompany secured revolving credit facility	125	0
Payments for current and long-term debt	(2)	(4)
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	1,228
Cash and Cash Equivalents at Beginning of Period	1,034
Cash and Cash Equivalents at End of Period	810
GenOn Americas Generation, LLC
Cash Flows from Operating Activities
Net (Loss)/Income	48	149
Adjustments to reconcile net (loss)/income to net cash (used)/provided by operating activities:
Depreciation and amortization	54	59
Amortization of debt premiums	(3)	(5)
Non-cash adjustment to write-off unamortized debt premiums	(47)	0
Amortization of out-of-market contracts and emission allowances	(21)	(20)
Gain on sale of assets	0	(77)
Changes in derivative instruments	(3)	182
Changes in collateral deposits supporting energy risk management activities	60	(119)
Lower of cost or market inventory adjustments	2	0
Changes in other working capital	(80)	(16)
Net Cash (Used)/Provided by Operating Activities	10	153
Cash Flows from Investing Activities
Capital expenditures	(33)	(44)
Proceeds from sale of assets, net	0	76
Net Cash (Used)/Provided by Investing Activities	(36)	32
Cash Flows from Financing Activities
Payment for amounts due to GenOn Energy, Inc.	(125)	0
Payment for credit support	(130)	0
Payments for financing costs	(16)	0
Net Cash Used by Financing Activities	(271)	0
Net (Decrease)/Increase in Cash, Cash Equivalents and Funds Deposited by Counterparties	(297)	185
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at Beginning of Period	471	297
Cash, Cash Equivalents, Restricted Cash and Funds Deposited by Counterparties at End of Period	174	482
Cash and Cash Equivalents at Beginning of Period	471
Cash and Cash Equivalents at End of Period	174
GenOn Americas Generation, LLC | Affiliated Entity
Cash Flows from Investing Activities
Increase in notes receivable — affiliate	(3)	0
GenOn Mid-Atlantic, LLC
Cash Flows from Operating Activities
Net (Loss)/Income	(33)	57
Adjustments to reconcile net (loss)/income to net cash (used)/provided by operating activities:
Depreciation and amortization	47	45
Amortization of out-of-market contracts and emission allowances	(21)	(21)
Changes in derivative instruments	4	160
Lower of cost or market inventory adjustments	2	0
Changes in other working capital	(9)	(17)
Net Cash (Used)/Provided by Operating Activities	(10)	224
Cash Flows from Investing Activities
Capital expenditures	(30)	(40)
Net Cash (Used)/Provided by Investing Activities	(30)	(40)
Cash Flows from Financing Activities
Payment for amounts due to GenOn Energy, Inc.	(125)	0
Payment for credit support	(130)	0
Payments for financing costs	(1)	0
Net Cash Used by Financing Activities	(256)
Net (Decrease)/Increase in Cash and Cash Equivalents	(296)	184
Cash and Cash Equivalents at Beginning of Period	471	299
Cash and Cash Equivalents at End of Period	$ 175	$ 483