Income Taxes - Allocation of Total Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Benefit/(Loss) Applicable To: [Abstract]
Loss from continuing operations, before income taxes	$ (1,395)	$ (2,065)	$ (1,847)	$ (2,365)
Income tax provision	$ (31)	$ (3)	$ (103)	$ (10)
Effective tax rate	(2.20%)	(0.10%)	(5.60%)	(0.40%)
Discontinued operations, before income taxes	$ 0	$ 53	$ 0	$ 119
Income tax provision	$ 0	$ (28)	$ 0	$ (61)

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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