Earnings Per Share - Schedule of Earnings Per Share, Basic and Diluted (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic		$ 4,872	$ 4,156	$ 14,425	$ 12,592
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic		$ 3,870	$ 3,228	$ 11,276	$ 9,778
Weighted- Average Shares Outstanding - Basic (in shares)		1,610	1,614	1,591	1,623
Earnings per Share - Basic (in dollars per share)		$ 2.40	$ 2.00	$ 7.09	$ 6.03
Income Allocation - Diluted		$ 4,872	$ 4,156	$ 14,425	$ 12,592
Weighted- Average Shares Outstanding - Diluted (in shares)		2,029	2,080	2,038	2,092
Earnings per Share - Diluted (in dollars per share)		$ 2.40	$ 2.00	$ 7.08	$ 6.02
Class B-1 common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic		$ 372	$ 785	$ 2,209	$ 2,369
Weighted- Average Shares Outstanding - Basic (in shares)		97	245	196	245
Earnings per Share - Basic (in dollars per share)		$ 3.82	$ 3.20	$ 11.25	$ 9.65
Income Allocation - Diluted		$ 371	$ 784	$ 2,206	$ 2,366
Weighted- Average Shares Outstanding - Diluted (in shares)		97	245	196	245
Earnings per Share - Diluted (in dollars per share)		$ 3.81	$ 3.19	$ 11.24	$ 9.64
Weighted-average as-converted common stock used in income allocation (in shares)		155	393	312	393
Class B-2 common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic		$ 283		$ 277
Weighted- Average Shares Outstanding - Basic (in shares)	[1]	74	0	25	0
Earnings per Share - Basic (in dollars per share)	[1]	$ 3.82	$ 0	$ 11.25	$ 0
Income Allocation - Diluted		$ 282		$ 276
Weighted- Average Shares Outstanding - Diluted (in shares)	[1]	74	0	25	0
Earnings per Share - Diluted (in dollars per share)	[1]	$ 3.81	$ 0	$ 11.24	$ 0
Weighted-average as-converted common stock used in income allocation (in shares)		118	0	39	0
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic		$ 275	$ 77	$ 447	$ 233
Weighted- Average Shares Outstanding - Basic (in shares)		29	10	16	10
Earnings per Share - Basic (in dollars per share)		$ 9.62	$ 8.00	$ 28.35	$ 24.10
Income Allocation - Diluted		$ 275	$ 76	$ 447	$ 233
Weighted- Average Shares Outstanding - Diluted (in shares)		29	10	16	10
Earnings per Share - Diluted (in dollars per share)		$ 9.60	$ 7.99	$ 28.31	$ 24.08
Weighted-average as-converted common stock used in income allocation (in shares)		114	38	63	39
Participating securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic		$ 72	$ 66	$ 216	$ 212
Income Allocation - Diluted		$ 72	$ 66	$ 216	$ 211
Series A preferred stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation (in shares)		6	8	6	10
Series B preferred stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation (in shares)		7	7	7	7
Series C preferred stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Weighted-average as-converted common stock used in income allocation (in shares)		11	11	11	11

[1] No shares of class B-2 common stock were outstanding prior to the class B-1 common stock exchange offer. See Note 9—Stockholders’ Equity for further details.