Shareholders' Equity - Summary of Approved Authorized Shares for Repurchase Program (Detail) - USD ($)	Sep. 30, 2019	Dec. 11, 2015	Oct. 23, 2014	Jul. 25, 2013
Statement Of Stockholders Equity [Abstract]
Cost of treasury stock	$ 2,000,000,000	$ 500,000,000	$ 1,000,000,000	$ 500,000,000