Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income	$ 2,575	$ 2,373	$ 8,727	$ 8,729
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 1,996	$ 1,814	$ 6,748	$ 6,679
Weighted- Average Shares Outstanding - Basic (in shares)	1,691	1,690	1,693	1,702
Earnings per Share - Basic (in dollars per share)	$ 1.18	$ 1.07	$ 3.99	$ 3.92
Income Allocation - Diluted	$ 2,575	$ 2,373	$ 8,727	$ 8,729
Weighted- Average Shares Outstanding - Diluted (in shares)	2,184	2,214	2,192	2,227
Earnings per Share - Diluted (in dollars per share)	$ 1.18	$ 1.07	$ 3.98	$ 3.92
Class B common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 470	$ 428	$ 1,588	$ 1,564
Weighted- Average Shares Outstanding - Basic (in shares)	245	245	245	245
Earnings per Share - Basic (in dollars per share)	$ 1.92	$ 1.74	$ 6.47	$ 6.37
Income Allocation - Diluted	$ 470	$ 427	$ 1,586	$ 1,561
Weighted- Average Shares Outstanding - Diluted (in shares)	245	245	245	245
Earnings per Share - Diluted (in dollars per share)	$ 1.91	$ 1.74	$ 6.46	$ 6.36
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 49	$ 46	$ 169	$ 172
Weighted- Average Shares Outstanding - Basic (in shares)	10	11	11	11
Earnings per Share - Basic (in dollars per share)	$ 4.72	$ 4.29	$ 15.94	$ 15.70
Income Allocation - Diluted	$ 49	$ 47	$ 169	$ 172
Weighted- Average Shares Outstanding - Diluted (in shares)	10	11	11	11
Earnings per Share - Diluted (in dollars per share)	$ 4.72	$ 4.29	$ 15.92	$ 15.68
Participating securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 60	$ 85	$ 222	$ 314
Income Allocation - Diluted	$ 60	$ 85	$ 221	$ 314