Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended
	Mar. 31, 2018	Feb. 28, 2018	Sep. 30, 2017
Equity, Class of Treasury Stock [Line Items]
Authorized share-repurchase program		$ 3,000	$ 2,500
Accelerated Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase agreement amount	$ 1,400	$ 500
Shares repurchased	19.1	8.5
Price per share repurchased	$ 58.16	$ 58.82
Treasury Stock [Member] | Accelerated Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase agreement amount	$ 1,100
Paid-in Capital [Member] | Accelerated Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Accelerated share repurchase agreement amount	$ 332