Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 4,663	$ 4,257	$ 9,553	$ 8,436
Class A common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 3,616	$ 3,307	$ 7,408	$ 6,549
Weighted- Average Shares Outstanding - Basic (in shares)	1,579	1,624	1,582	1,627
Earnings per Share - Basic (in dollars per share)	$ 2.29	$ 2.04	$ 4.68	$ 4.03
Income Allocation - Diluted	$ 4,663	$ 4,257	$ 9,553	$ 8,436
Weighted- Average Shares Outstanding - Diluted (in shares)	2,039	2,093	2,042	2,098
Earnings per Share - Diluted (in dollars per share)	$ 2.29	$ 2.03	$ 4.68	$ 4.02
Class B-1 common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 892	$ 800	$ 1,825	$ 1,584
Weighted- Average Shares Outstanding - Basic (in shares)	245	245	245	245
Earnings per Share - Basic (in dollars per share)	$ 3.63	$ 3.26	$ 7.44	$ 6.45
Income Allocation - Diluted	$ 891	$ 799	$ 1,823	$ 1,582
Weighted- Average Shares Outstanding - Diluted (in shares)	245	245	245	245
Earnings per Share - Diluted (in dollars per share)	$ 3.63	$ 3.25	$ 7.43	$ 6.44
Weighted-average as-converted common stock used in income allocation (in shares)	390	393	390	393
Class C common stock
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 85	$ 79	$ 176	$ 157
Weighted- Average Shares Outstanding - Basic (in shares)	9	10	9	10
Earnings per Share - Basic (in dollars per share)	$ 9.16	$ 8.15	$ 18.73	$ 16.10
Income Allocation - Diluted	$ 85	$ 79	$ 176	$ 156
Weighted- Average Shares Outstanding - Diluted (in shares)	9	10	9	10
Earnings per Share - Diluted (in dollars per share)	$ 9.15	$ 8.14	$ 18.71	$ 16.09
Weighted-average as-converted common stock used in income allocation (in shares)	37	39	38	39
Participating securities
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income Allocation - Basic	$ 70	$ 71	$ 144	$ 146
Income Allocation - Diluted	$ 70	$ 71	$ 144	$ 146
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	10	6	11
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