Discontinued Operations and Dispositions - Major Classes of Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other current assets	$ 0	$ 1,919
Current assets - discontinued operations	33	9
Other non-current assets	10	10
Non-current assets - discontinued operations	0	2,961
Current liabilities - discontinued operations	0	1,210
Other non-current liabilities	0	3,209
Non-current liabilities - discontinued operations	$ 13	11
GenOn | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents		1,034
Other current assets		885
Current assets - discontinued operations		1,919
Property, plant and equipment, net		2,543
Other non-current assets		418
Non-current assets - discontinued operations		2,961
Current portion of long term debt and capital leases		704
Other current liabilities		506
Current liabilities - discontinued operations		1,210
Long-term debt and capital leases		2,050
Out-of-market contracts		811
Other non-current liabilities		348
Non-current liabilities - discontinued operations		$ 3,209