Stockholders' Equity - Number of Shares of Class A Common Shares Outstanding on an As-Converted Basis (Detail) shares in Millions	Sep. 30, 2022 shares	Sep. 30, 2021 shares
Class of Stock [Line Items]
As-converted Class A Common Stock (in shares)	2,103	2,161
Series A preferred stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock conversion rate	100.0000	100.0000
As-converted Class A Common Stock (in shares)	16	7
Series B
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	2	2
Preferred stock conversion rate	2.9710	6.3210
As-converted Class A Common Stock (in shares)	7	16
Series C
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	3	3
Preferred stock conversion rate	3.6450	6.8340
As-converted Class A Common Stock (in shares)	12	22
Class A common stock
Class of Stock [Line Items]
Common stock, shares, outstanding (in shares)	1,635	1,677
As-converted Class A Common Stock (in shares)	1,635	1,677
Class B common stock
Class of Stock [Line Items]
Common stock, shares, outstanding (in shares)	245	245
Common stock, conversion rate	1.6059	1.6228
As-converted Class A Common Stock (in shares)	394	398
Class C common stock
Class of Stock [Line Items]
Common stock, shares, outstanding (in shares)	10	10
Common stock, conversion rate	4.0000	4.0000
As-converted Class A Common Stock (in shares)	39	41