Earnings Per Share - Schedule of Weighted Average Number of Shares (Detail) - shares shares in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
Mar. 31, 2025 |
Mar. 31, 2024 |
|
| Class B-1 common 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) | 8 | 390 | 8 | 390 |
| Class B-2 common 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) | 186 | 0 | 186 | 0 |
| Class C common 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) | 37 | 37 | 37 | 38 |
| Participating securities | ||||
| 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) | 20 | 31 | 21 | 31 |