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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Computation of Basic Earnings Per Share
Net income	$ 414	$ 247	$ 779	$ 466
Shares for basic earnings per share (in shares)	378.5	254.3	381.7	254.3
Basic earnings per share (in USD per share)	$ 1.09	$ 0.97	$ 2.04	$ 1.83
Computation of Diluted Earnings Per Share
Net income	$ 414	$ 247	$ 779	$ 466
Shares for basic earnings per share (in shares)	378.5	254.3	381.7	254.3
Effect of dilutive securities
Effect of dilutive securities (in shares)	4.5	3.7	4.8	4.4
Shares for diluted earnings per share (in shares)	383.0	258.0	386.5	258.7
Diluted earnings per share (in USD per share)	$ 1.08	$ 0.96	$ 2.02	$ 1.80