Income Taxes - Income Tax Expense (Benefit) Table (Detail) - 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]
Current income tax expense (benefit)	$ 430	$ 64	$ 670	$ 212
Deferred income tax expense (benefit)	(855)	(324)	(1,036)	(1,169)
Total income tax expense (benefit)	(425)	(260)	(366)	(957)
Income (loss) before income taxes	$ (1,066)	$ (1,007)	$ (1,616)	$ (3,313)
Effective tax rate	40.00%	26.00%	23.00%	29.00%