Income Taxes - Income Tax Expense (Benefit) Table (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Current income tax expense (benefit)	$ 147	$ (522)	$ 237	$ 240
Deferred income tax expense (benefit)	(22)	484	14	(181)
Total income tax expense (benefit)	125	(38)	251	59
Income (loss) before income taxes	$ 142	$ (372)	$ 442	$ (550)
Effective tax rate	88.00%	10.00%	57.00%	(11.00%)

Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

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Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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