Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		6 Months Ended	9 Months Ended
	Mar. 31, 2018	Feb. 28, 2018	Jun. 30, 2018	Jun. 30, 2018	Jul. 31, 2018	Sep. 30, 2017
Equity, Class of Treasury Stock [Line Items]
Authorized share-repurchase program		$ 3,000				$ 2,500
Amount of share repurchase program completed				$ 3,000
Accelerated Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Amount	$ 1,441	$ 500	$ 1,941	$ 1,941
Average Price per Share (in usd per share)	$ 65.28	$ 58.82
Initial Shares Delivered	19.1	7.0	26.1
Additional Shares Delivered	3.0	1.5	4.5
Total Shares Delivered	22.1	8.5	30.6
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Authorized share-repurchase program					$ 4,000