Stockholders' Equity - Number of Shares of Class A Common Shares Outstanding on an As-Converted Basis (Detail) shares in Millions	Sep. 30, 2024 shares	Sep. 30, 2023 shares
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	5	5
As-converted Class A Common Stock (in shares)	1,983	2,047
Series A preferred stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, conversion rate into Class A Common Stock	100.0000	100.0000
As-converted Class A Common Stock (in shares)	9	7
Series B preferred stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	2	2
Preferred stock, conversion rate into Class A Common Stock	1.0030	2.9370
As-converted Class A Common Stock (in shares)	2	7
Series C preferred stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	3	3
Preferred stock, conversion rate into Class A Common Stock	1.7860	3.6290
As-converted Class A Common Stock (in shares)	6	11
Class A common stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)	1,733	1,594
Common stock, conversion rate	0	0
As-converted Class A Common Stock (in shares)	1,733	1,594
Class B-1 common stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)	5	245
Common stock, conversion rate	1.5653	1.5875
As-converted Class A Common Stock (in shares)	8	390
Class B-2 common stock
Class of Stock [Line Items]
Common stock, shares outstanding (in shares)	120	0
Common stock, conversion rate	1.5430	0
As-converted Class A Common Stock (in shares)	186	0
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	38