Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 3,959	$ 3,126
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 3,065	$ 2,410
Weighted- Average Shares Outstanding - Basic (in shares)	1,669	1,694
Earnings per Share - Basic (in dollars per share)	$ 1.84	$ 1.42
Income Allocation - Diluted	$ 3,959	$ 3,126
Weighted- Average Shares Outstanding - Diluted (in shares)	2,159	2,200
Earnings per Share - Diluted (in dollars per share)	$ 1.83	$ 1.42
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 732	$ 567
Weighted- Average Shares Outstanding - Basic (in shares)	245	245
Earnings per Share - Basic (in dollars per share)	$ 2.98	$ 2.31
Income Allocation - Diluted	$ 731	$ 566
Weighted- Average Shares Outstanding - Diluted (in shares)	245	245
Earnings per Share - Diluted (in dollars per share)	$ 2.98	$ 2.31
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 74	$ 61
Weighted- Average Shares Outstanding - Basic (in shares)	10	11
Earnings per Share - Basic (in dollars per share)	$ 7.35	$ 5.69
Income Allocation - Diluted	$ 74	$ 61
Weighted- Average Shares Outstanding - Diluted (in shares)	10	11
Earnings per Share - Diluted (in dollars per share)	$ 7.34	$ 5.68
Participating securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 88	$ 88
Income Allocation - Diluted	$ 88	$ 89