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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Computation of Basic Earnings Per Share
Net income	$ 610	$ 489	$ 1,008	$ 860
Shares for basic earnings per share (in shares)	353.4	378.5	355.9	381.7
Basic earnings per share (in USD per share)	$ 1.73	$ 1.29	$ 2.83	$ 2.25
Computation of Diluted Earnings Per Share
Net income	$ 610	$ 489	$ 1,008	$ 860
Shares for basic earnings per share (in shares)	353.4	378.5	355.9	381.7
Effect of dilutive securities
Share-based compensation (in shares)	3.9	4.5	4.4	4.8
Shares for diluted earnings per share (in shares)	357.3	383.0	360.3	386.5
Diluted earnings per share (in USD per share)	$ 1.71	$ 1.28	$ 2.80	$ 2.23