Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jul. 15, 2019	Jan. 31, 2019
Stockholders Equity Note [Line Items]
Additional share repurchase program						$ 8,500
January 2019 share repurchase program remaining authorized funds	$ 6,200		$ 6,200
Cash dividends declared and paid, at a quarterly amount per Class A share	$ 565	$ 487	$ 1,706	$ 1,435
Subsequent Event | Class A common stock
Stockholders Equity Note [Line Items]
Quarterly cash dividend (in dollars per share)					$ 0.25