Earnings Per Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Class B 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)	398	398
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)	40	43
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)	7	21
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)	16	16
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)	22	22