Capital Stock, Dividends and Common Stock Repurchase Program (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capital Stock, Dividends and Common Stock Repurchase Program
Common stock, shares authorized	1,500,000,000	1,500,000,000	1,500,000,000
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued	630,282,461	630,282,461	630,282,461
Number of common shares outstanding at year-end	433,300,000	433,300,000	439,300,000	447,200,000
Preferred stock shares authorized	10,000,000	10,000,000
Preferred stock par value per share	$ 0.01	$ 0.01
Preferred stock shares outstanding	0	0
Cash dividends		$ 750	$ 726	$ 695
Cash dividends declared and paid per common share		$ 1.70	$ 1.64	$ 1.54
Quarterly common stock dividend per share	0.425
Expected quarterly common stock dividend per share	$ 0.465