Discontinued Operations and Dispositions - Summary of Results (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended		5 Months Ended	6 Months Ended
	Jun. 14, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 14, 2017	Jun. 30, 2017	Jun. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of assets					$ 22	$ (83)
Loss from discontinued operations, net of tax		$ (741)	$ (113)		$ (775)	(9)
Discontinued Operations | GenOn
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	$ 265		398	$ 646		977
Operating costs and expenses	(327)		(474)	(700)		(941)
Gain on sale of assets	0		0	0		32
Other expenses	(54)		(40)	(98)		(84)
Loss from operations of discontinued components, before tax	(116)		(116)	(152)		(16)
Income tax expense/(benefit)	8		0	9		(1)
Loss from operations of discontinued components	(124)		(116)	(161)		(15)
Interest income - affiliate	3		3	6		6
Net loss from discontinued operations	(121)		(113)	(155)		(9)
Pre-tax loss on deconsolidation	(208)		0	(208)		0
Settlement consideration and services credit	(289)		0	(289)		0
Pension liability assumption	(119)		0	(119)		0
Advisory and consulting fees	(4)		0	(4)		0
Loss on disposal of discontinued components, net of tax	(620)	$ (208)	0	(620)		0
Loss from discontinued operations, net of tax	$ (741)		$ (113)	$ (775)		$ (9)