Debtors' Financial Information (GenOn and GenOn Americas Generation) - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 810	$ 1,034
Restricted cash	1	0
Accounts receivable	124	109
Prepaid rent and other current assets	151	128
Total current assets	1,572	1,900
Property, plant and equipment, net	2,468	2,543
Other non-current assets	136	94
Total Assets	4,701	4,860
LIABILITIES AND STOCKHOLDER'S EQUITY
Accrued expenses and other current liabilities	128	191
Total current liabilities	270	1,191
Liabilities subject to compromise	2,862	0
Long-term debt	1	2,050
Other non-current liabilities	289	451
Total Liabilities	4,306	4,520
Stockholder's equity	395	340
Total Liabilities and Stockholder's Equity	4,701	4,860
Non-affiliated Entity
LIABILITIES AND STOCKHOLDER'S EQUITY
Accounts payable	79	113
Long-term debt	1	2,050
Affiliated Entity
LIABILITIES AND STOCKHOLDER'S EQUITY
Accounts payable	27	78
Long-term debt	125	$ 0
GenOn Energy, Inc. Debtors
ASSETS
Cash and cash equivalents	568
Restricted cash	1
Prepaid rent and other current assets	898
Total current assets	2,242
Property, plant and equipment, net	1,235
Investment in subsidiaries	(269)
Other non-current assets	144
Total Assets	3,896
LIABILITIES AND STOCKHOLDER'S EQUITY
Accrued expenses and other current liabilities	134
Total current liabilities	176
Liabilities subject to compromise	2,862
Other non-current liabilities	338
Total Liabilities	3,501
Stockholder's equity	395
Total Liabilities and Stockholder's Equity	3,896
GenOn Energy, Inc. Debtors | Non-affiliated Entity
ASSETS
Accounts receivable	117
LIABILITIES AND STOCKHOLDER'S EQUITY
Accounts payable	42
GenOn Energy, Inc. Debtors | Affiliated Entity
ASSETS
Accounts receivable	658
Note receivable	0
Notes receivable	544
LIABILITIES AND STOCKHOLDER'S EQUITY
Accounts payable	0
Long-term debt	125
GenOn Americas Generation Debtors
ASSETS
Cash and cash equivalents	0
Restricted cash	0
Prepaid rent and other current assets	274
Total current assets	702
Property, plant and equipment, net	155
Investment in subsidiaries	1,117
Other non-current assets	68
Total Assets	2,042
LIABILITIES AND STOCKHOLDER'S EQUITY
Accrued expenses and other current liabilities	93
Total current liabilities	139
Liabilities subject to compromise	721
Other non-current liabilities	81
Total Liabilities	941
Stockholder's equity	1,101
Total Liabilities and Stockholder's Equity	2,042
GenOn Americas Generation Debtors | Non-affiliated Entity
ASSETS
Accounts receivable	110
LIABILITIES AND STOCKHOLDER'S EQUITY
Accounts payable	20
GenOn Americas Generation Debtors | Affiliated Entity
ASSETS
Accounts receivable	0
Note receivable	318
Notes receivable	0
LIABILITIES AND STOCKHOLDER'S EQUITY
Accounts payable	26
Long-term debt	$ 0