Chapter 11 Cases (GenOn and GenOn Americas Generation) - Liabilities Subject to Compromise (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Reorganization [Line Items]
Accounts payable and accrued expenses	$ 46
Long-term debt, including current portion	2,616
Accrued interest	56
Pension and post-retirement liabilities	131
Other	13
Liabilities subject to compromise	2,862	$ 0
GenOn Americas Generation
Reorganization [Line Items]
Accounts payable and accrued expenses	9
Long-term debt, including current portion	695	0
Accrued interest	10
Pension and post-retirement liabilities	0
Other	7
Liabilities subject to compromise	$ 721	$ 0