Related Party Transactions - Service Agreement with GenOn (Details) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	Jun. 14, 2017	Jun. 12, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Related Party Transaction [Line Items]
Other income - affiliate			$ 42	$ 48	$ 90	$ 96
GenOn | Services Agreement
Related Party Transaction [Line Items]
Service fees					$ 193
Shared services, annualized rate		$ 84
Credit applied		28
Restructuring Support Agreement | Services Agreement
Related Party Transaction [Line Items]
Shared services, annualized rate		84
Monthly shared services	$ 5
Credit applied		$ 28