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Acquisitions, Discontinued Operations and Dispositions - Summary of Results (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gain/(loss) on disposal of discontinued operations, net of tax |  |  |  |  |  |  |  |  | $ 0 | $ (13) | $ 0
Income/(loss) from discontinued operations, net of income tax | $ (78) | $ (2) | $ 13 | $ 388 | $ 80 | $ (336) | $ 69 | $ (5) | 321 | (192) | (992)
Discontinued Operations | South Central Portfolio |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenue |  |  |  |  |  |  |  |  | 31 | 410 | 422
Operating costs and expenses |  |  |  |  |  |  |  |  | (23) | (346) | (335)
Other income |  |  |  |  |  |  |  |  | 0 | 2 | 0
(Loss)/gain from operations of discontinued components, before tax |  |  |  |  |  |  |  |  | 8 | 66 | 87
(Loss)/income on disposal of discontinued operations, net of tax |  |  |  |  |  |  |  |  | 20 | 0 | 0
Income/(loss) from discontinued operations, net of income tax |  |  |  |  |  |  |  |  | 28 | 66 | 87
Discontinued Operations | Carlsbad Energy Holdings LLC |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenue |  |  |  |  |  |  |  |  | 19 | 909 | 1,164
Operating costs and expenses |  |  |  |  |  |  |  |  | (9) | (661) | (1,114)
Other expenses |  |  |  |  |  |  |  |  | (5) | (174) | (288)
(Loss)/gain from operations of discontinued components, before tax |  |  |  |  |  |  |  |  | 5 | 74 | (238)
Income tax expense |  |  |  |  |  |  |  |  | 0 | 4 | 52
Income/(loss) from discontinued operations, net of tax |  |  |  |  |  |  |  |  | 5 | 70 | (290)
Gain/(loss) on disposal of discontinued operations, net of tax |  |  |  |  |  |  |  |  | 265 | (134) | 0
Income/(expense) from California property tax indemnification |  |  |  |  |  |  |  |  | 22 | (153) | 0
Income/(expense) from other commitments, indemnification and fees |  |  |  |  |  |  |  |  | 4 | (75) | 0
(Loss)/income on disposal of discontinued operations, net of tax |  |  |  |  |  |  |  |  | 291 | (362) | 0
Income/(loss) from discontinued operations, net of income tax |  |  |  |  |  |  |  |  | 296 | (292) | (290)
Discontinued Operations | GenOn |  |  |  |  |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenue |  |  |  |  |  |  |  |  | 0 | 0 | 646
Operating costs and expenses |  |  |  |  |  |  |  |  | 0 | 0 | (702)
Other expenses |  |  |  |  |  |  |  |  | 0 | 0 | (98)
(Loss)/gain from operations of discontinued components, before tax |  |  |  |  |  |  |  |  | 0 | 0 | (154)
Income tax expense |  |  |  |  |  |  |  |  | 0 | 0 | 9
(Loss)/gain from discontinued operations |  |  |  |  |  |  |  |  | 0 | 0 | (163)
Interest income-affiliate |  |  |  |  |  |  |  |  | 0 | 3 | 8
Income/(loss) from discontinued operations, net of tax |  |  |  |  |  |  |  |  | 0 | 3 | (155)
Gain/(loss) on disposal of discontinued operations, net of tax |  |  |  |  |  |  |  |  | 0 | 0 | (208)
Settlement consideration, insurance and services credit |  |  |  |  |  |  |  |  | 0 | 63 | (289)
Pension and post-retirement liability assumptions |  |  |  |  |  |  |  |  | 0 | 21 | (131)
Income/(expense) from other commitments, indemnification and fees |  |  |  |  |  |  |  |  | (3) | (53) | (6)
(Loss)/income on disposal of discontinued operations, net of tax |  |  |  |  |  |  |  |  | (3) | 31 | (634)
Income/(loss) from discontinued operations, net of income tax |  |  |  |  |  |  |  |  | $ (3) | $ 34 | $ (789)

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