Earnings Per Share - Additional Information (Detail) - shares	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]
Common stock equivalents included in the computation of diluted shares outstanding (in shares)	3,000,000	3,000,000	3,000,000	3,000,000
Antidilutive securities excluded from computation of earnings per share (less than for 2021) (in shares)	1,000,000	1,000,000	1,000,000	1,000,000
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)	398,000,000	398,000,000	398,000,000	398,000,000
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)	42,000,000	43,000,000	42,000,000	44,000,000
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)	9,000,000		14,000,000
UK&I 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)	16,000,000	32,000,000	16,000,000	32,000,000
Europe 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)	22,000,000	44,000,000	22,000,000	44,000,000