Earnings Per Share - Reconciliation of the Earnings (Losses) and Number of Shares Used in Calculations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Computation of Basic Earnings Per Share
Net income	$ 392	$ 70	$ 1,171	$ 536
Shares for basic earnings per share (in shares)	372.3	266.2	378.5	258.3
Basic earnings per share (in USD per share)	$ 1.05	$ 0.26	$ 3.09	$ 2.08
Computation of Diluted Earnings Per Share
Net income	$ 392	$ 70	$ 1,171	$ 536
Shares for basic earnings per share (in shares)	372.3	266.2	378.5	258.3
Effect of dilutive securities
Share-based compensation (in shares)	4.3	4.3	4.7	4.4
Shares for diluted earnings per share (in shares)	376.6	270.5	383.2	262.7
Diluted earnings per share (in USD per share)	$ 1.04	$ 0.26	$ 3.06	$ 2.04