Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Common stock, shares authorized	4,500,000,000
Common stock, par value	$ 0.01
Common stock, shares outstanding	1,383,932,776	1,391,475,510
Preferred stock, shares authorized	200,000,000
Preferred stock, par value	$ 0.01
Preferred stock, issued	0
Other comprehensive income (loss)	$ 369	$ (85)	$ (352,000)