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Discontinued Operations and Dispositions - Summary of Results (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |
Loss from discontinued operations, net of tax | $ 0 | $ (34)
Discontinued Operations | GenOn |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |
Operating revenues |  | 381
Operating costs and expenses |  | (373)
Other expenses |  | (44)
Loss from operations of discontinued components, before tax |  | (36)
Income tax expense |  | 1
Loss from operations of discontinued components |  | (37)
Interest income - affiliate |  | 3
Loss from discontinued operations, net of tax |  | $ (34)

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