Stockholders' Equity - Share Repurchases in the Open Market (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Equity, Class of Treasury Stock [Line Items]
Total cost	$ 2,200	$ 1,069	$ 5,709	$ 6,572
Class A common stock
Equity, Class of Treasury Stock [Line Items]
Shares repurchased in the open market (in shares)	10	6	27	37
Average repurchase price per share (in dollars per share)	$ 227.11	$ 177.86	$ 213.02	$ 179.91
Total cost	$ 2,200	$ 1,069	$ 5,709	$ 6,572