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, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Computation of Basic Earnings Per Share
Net income	$ 387	$ 232	$ 375	$ 503	$ 667	$ 420	$ 994	$ 1,590
Shares for basic earnings per share (in shares)	329.9			346.7			334.4	352.8
Basic earnings per share (in USD per share)	$ 1.17			$ 1.45			$ 2.97	$ 4.51
Computation of Diluted Earnings Per Share
Net income	$ 387	$ 232	$ 375	$ 503	$ 667	$ 420	$ 994	$ 1,590
Shares for basic earnings per share (in shares)	329.9			346.7			334.4	352.8
Effect of dilutive securities
Share-based compensation (in shares)	2.6			3.9			2.8	4.3
Shares for diluted earnings per share (in shares)	332.5			350.6			337.2	357.1
Diluted earnings per share (in USD per share)	$ 1.16			$ 1.43			$ 2.95	$ 4.45