v3.21.2
Stockholders' Equity - Number of Shares of Class A Common Shares Outstanding on an As-Converted Basis (Detail)
shares in Millions
Sep. 30, 2021
shares
Sep. 30, 2020
shares
Class of Stock [Line Items]    
As-converted Class A Common Stock (in shares) 2,161 2,197
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) 7 35
Series B Preferred Stock    
Class of Stock [Line Items]    
Preferred stock, shares outstanding (in shares) 2 2
Preferred stock conversion rate 6.3210 6.3870
As-converted Class A Common Stock (in shares) 16 16
Series C Preferred Stock    
Class of Stock [Line Items]    
Preferred stock, shares outstanding (in shares) 3 3
Preferred stock conversion rate 6.8340 6.8610
As-converted Class A Common Stock (in shares) 22 22
Class A common stock    
Class of Stock [Line Items]    
Common stock, shares, outstanding (in shares) 1,677 1,683
As-converted Class A Common Stock (in shares) 1,677 1,683
Class B common stock    
Class of Stock [Line Items]    
Common stock, shares, outstanding (in shares) 245 245
Common stock, conversion rate 1.6228 1.6228
As-converted Class A Common Stock (in shares) 398 398
Class C common stock    
Class of Stock [Line Items]    
Common stock, shares, outstanding (in shares) 10 11
Common stock, conversion rate 4.0000 4.0000
As-converted Class A Common Stock (in shares) 41 43