Debtors' Financial Information (GenOn and GenOn Americas Generation) - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		4 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
Total operating revenues	$ 484	$ 532		$ 1,231	$ 1,509
Total operating costs and expenses	382	468		1,130	1,409
Operating (Loss)/Income	102	326		101	394
Other Expense
Total other expense	(1)	(42)		(100)	(126)
Income Before Reorganization Items and Income Taxes	101	284		1	268
Reorganization items, net	(29)	0		48	0
(Loss)/Income Before Income Taxes	72	284		49	268
Income tax expense	0	21		7	20
Net (Loss)/Income	72	$ 263		$ 42	$ 248
GenOn Energy, Inc. Debtors
Condensed Financial Statements, Captions [Line Items]
Total operating revenues	500		$ 594
Total operating costs and expenses	396		462
Operating (Loss)/Income	104		132
Other Expense
Total other expense	(3)		(4)
Income Before Reorganization Items and Income Taxes	101		128
Reorganization items, net	(29)		74
(Loss)/Income Before Income Taxes	72		202
Income tax expense	0		0
Net (Loss)/Income	72		202
GenOn Americas Generation Debtors
Condensed Financial Statements, Captions [Line Items]
Total operating revenues	446		511
Total operating costs and expenses	408		471
Operating (Loss)/Income	38		40
Other Expense
Total other expense	(5)		(6)
Income Before Reorganization Items and Income Taxes	33		34
Reorganization items, net	0		43
(Loss)/Income Before Income Taxes	33		77
Income tax expense	0		0
Net (Loss)/Income	$ 33		$ 77