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, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Computation of Basic Earnings Per Share
Net income	$ 232	$ 375	$ 667	$ 420	$ 607	$ 1,087
Shares for basic earnings per share (in shares)	333.8		353.4		336.7	355.9
Basic earnings per share (in USD per share)	$ 0.70		$ 1.89		$ 1.80	$ 3.06
Computation of Diluted Earnings Per Share
Net income	$ 232	$ 375	$ 667	$ 420	$ 607	$ 1,087
Shares for basic earnings per share (in shares)	333.8		353.4		336.7	355.9
Effect of dilutive securities
Share-based compensation (in shares)	2.6		3.9		2.9	4.4
Shares for diluted earnings per share (in shares)	336.4		357.3		339.6	360.3
Diluted earnings per share (in USD per share)	$ 0.69		$ 1.87		$ 1.79	$ 3.02