Income Taxes - Allocation of Total Income Taxes (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Tax Benefit/(Loss) Applicable To: [Abstract]
Income/(loss) from continuing operations, before income taxes	$ (3,261)	$ (998)	$ (5,626)	$ 5,937
Income tax benefit/(provision)	$ (27)	$ 206	$ (37)	$ 49
Effective tax rate	(0.80%)	20.60%	(0.70%)	(0.80%)
Discontinued operations, before income taxes	$ 3,973	$ 55	$ 4,091	$ 156
Income tax provision	$ (680)	$ (19)	$ (740)	$ (50)

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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