Income Taxes - Income Tax Allocation (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Loss from continuing operations, before income taxes	$ (480)	$ (3,261)	$ (2,327)	$ (5,626)
Income tax benefit/(provision)	$ 20	$ (27)	$ (83)	$ (37)
Effective tax rate	4.20%	(0.80%)	(3.60%)	(0.70%)
Discontinued operations, before income taxes	$ 0	$ 3,973	$ 0	$ 4,091
Income tax provision	$ 0	$ (680)	$ 0	$ (740)

Amount before tax of income (loss) from a discontinued operation. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

Amount of tax expense (benefit) related to a discontinued operation. Includes, but is not limited to, tax expense (benefit) related to income (loss) from operations during the phase-out period, tax expense (benefit) related to gain (loss) on disposal, tax expense (benefit) related to gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and tax expense (benefit) related to adjustments of a prior period gain (loss) on disposal.

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