Stockholders' Equity - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Sep. 20, 2016	Sep. 16, 2013
Share Repurchase Program 2013
Share Repurchases [Line Items]
Amount available for repurchase under the share repurchase program approved by the company's Board of Directors			$ 40,000,000,000
Share Repurchase Program 2016
Share Repurchases [Line Items]
Amount available for repurchase under the share repurchase program approved by the company's Board of Directors		$ 40,000,000,000
Unused amount of share repurchase program	$ 35,200,000,000