Capital Stock - Net Income (loss) Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic:
Income (loss) attributable to common stock	$ 572	$ (244)	$ 785	$ (616)
Income (loss) attributable to common stock, shares	381	379	380	379
Basic net income (loss) per share (in USD per share)	$ 1.50	$ (0.65)	$ 2.06	$ (1.63)
Effect of Dilutive Securities:
Stock options and other, shares	2	0	3	0
Stock options and other (in USD per share)			$ (0.01)
Diluted:
Income (loss) attributable to common stock	$ 572	$ (244)	$ 785	$ (616)
Income (loss) attributable to common stock, shares	383	379	383	379
Diluted net income (loss) per share (in USD per share)	$ 1.50	$ (0.65)	$ 2.05	$ (1.63)