Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Income allocation - basic earnings per share	$ 14,957	$ 12,311	$ 10,866
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	$ 11,569	$ 9,527	$ 8,310
Weighted-average shares outstanding - basic (in shares)	1,651	1,691	1,697
Earnings per share - basic (in dollars per share)	$ 7.01	$ 5.63	$ 4.90
Income allocation - diluted earnings per share	$ 14,957	$ 12,311	$ 10,866
Weighted-average shares outstanding - diluted (in shares)	2,136	2,188	2,223
Earnings per share - diluted (in dollars per share)	$ 7.00	$ 5.63	$ 4.89
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	$ 2,781	$ 2,244	$ 1,951
Weighted-average shares outstanding - basic (in shares)	245	245	245
Earnings per share - basic (in dollars per share)	$ 11.33	$ 9.14	$ 7.94
Income allocation - diluted earnings per share	$ 2,778	$ 2,242	$ 1,948
Weighted-average shares outstanding - diluted (in shares)	245	245	245
Earnings per share - diluted (in dollars per share)	$ 11.31	$ 9.13	$ 7.93
Weighted average number shares as-converted basis (in shares)	397	398	398
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	$ 280	$ 237	$ 214
Weighted-average shares outstanding - basic (in shares)	10	10	11
Earnings per share - basic (in dollars per share)	$ 28.03	$ 22.53	$ 19.58
Income allocation - diluted earnings per share	$ 280	$ 236	$ 214
Weighted-average shares outstanding - diluted (in shares)	10	10	11
Earnings per share - diluted (in dollars per share)	$ 28.00	$ 22.51	$ 19.56
Weighted average number shares as-converted basis (in shares)	40	42	44
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	$ 327	$ 303	$ 391
Income allocation - diluted earnings per share	$ 326	$ 303	$ 391
Weighted average number shares as-converted basis (in shares)	8	12	1
Series B
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)	14	16	32
Series C
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)	20	22	43