Nature of Business (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) MW	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Power Generation Facilities
Current portion of long-term debt and capital leases	$ 1,220	$ 481
Cash and cash equivalents	1,973	1,518	$ 2,116	$ 2,254
Net Cash Provided by (Used in) Operating Activities	2,072	$ 1,309	$ 1,510
Genon [Member]
Power Generation Facilities
Cash and cash equivalents	$ 1,000
Percent of Total Assets	0.156
Percent of Total Liabilities	0.169
Net Cash Provided by (Used in) Operating Activities	$ 94
GenOn Mid-Atlantic, LLC [Member]
Power Generation Facilities
Cash and cash equivalents	471
REMA [Member]
Power Generation Facilities
Cash and cash equivalents	100
2017 [Member] | Genon [Member]
Power Generation Facilities
Current portion of long-term debt and capital leases	691
Debt Instrument, Unamortized Premium, Current	$ 8
Active [Member] | Approximation [Member]
Power Generation Facilities
Generation capacity (in MW) | MW	47,000
NRG Energy [Member] | Letter of Credit [Member] | Intercompany Credit Agreement [Member] | Genon [Member]
Power Generation Facilities
Line of Credit Facility, Remaining Borrowing Capacity	$ 228
Line of Credit Facility, Maximum Borrowing Capacity	$ 500