v3.21.2
Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Income allocation - basic earnings per share $ 12,311 $ 10,866 $ 12,080
Class A common stock      
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Income allocation - basic earnings per share $ 9,527 $ 8,310 $ 9,273
Weighted-average shares outstanding - basic (in shares) 1,691,000,000 1,697,000,000 1,742,000,000
Earnings per share - basic (in dollars per share) $ 5.63 $ 4.90 $ 5.32
Income allocation - diluted $ 12,311 $ 10,866 $ 12,080
Weighted-average shares outstanding - diluted (in shares) 2,188,000,000 2,223,000,000 2,272,000,000
Earnings per share - diluted (in dollars per share) $ 5.63 $ 4.89 $ 5.32
Class B common stock      
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Income allocation - basic earnings per share $ 2,244 $ 1,951 $ 2,130
Weighted-average shares outstanding - basic (in shares) 245,000,000 245,000,000 245,000,000
Earnings per share - basic (in dollars per share) $ 9.14 $ 7.94 $ 8.68
Income allocation - diluted $ 2,242 $ 1,948 $ 2,127
Weighted-average shares outstanding - diluted (in shares) 245,000,000 245,000,000 245,000,000
Earnings per share - diluted (in dollars per share) $ 9.13 $ 7.93 $ 8.66
Weighted average number shares as-converted basis (in shares) 398,000,000 398,000,000 400,000,000
Class C common stock      
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Income allocation - basic earnings per share $ 237 $ 214 $ 247
Weighted-average shares outstanding - basic (in shares) 10,000,000 11,000,000 12,000,000
Earnings per share - basic (in dollars per share) $ 22.53 $ 19.58 $ 21.30
Income allocation - diluted $ 236 $ 214 $ 246
Weighted-average shares outstanding - diluted (in shares) 10,000,000 11,000,000 12,000,000
Earnings per share - diluted (in dollars per share) $ 22.51 $ 19.56 $ 21.26
Weighted average number shares as-converted basis (in shares) 42,000,000 44,000,000 46,000,000
Participating Securities      
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Income allocation - basic earnings per share $ 303 $ 391 $ 430
Income allocation - diluted $ 303 $ 391 $ 429
Weighted average number shares as-converted basis (in shares) 12,000,000 1,000,000  
Series B Preferred Stock      
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Weighted average number shares as-converted basis (in shares) 16,000,000 32,000,000 32,000,000
Series C Preferred Stock      
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]      
Weighted average number shares as-converted basis (in shares) 22,000,000 43,000,000 44,000,000