Share-based Compensation - Summary of Performance-based Shares Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Aggregate Intrinsic Value
Stock price used to calculate aggregate intrinsic value (in dollars per share)	$ 274.95	$ 230.01
Performance-based Shares
Shares
Beginning balance (in shares)	998,502
Granted (in shares)	528,008
Vested and earned (in shares)	(406,009)
Unearned (in shares)	(28,691)
Forfeited (in shares)	(7,578)
Ending balance (in shares)	1,084,232	998,502
Weighted- Average Grant Date Fair Value
Beginning balance (in dollars per share)	$ 212.28
Granted (in dollars per share)	281.85
Vested and earned (in dollars per share)	198.79
Unearned (in dollars per share)	195.38
Forfeited (in dollars per share)	248.50
Ending balance (in dollars per share)	$ 251.41	$ 212.28
Weighted- Average Remaining Contractual Term (in years)
Outstanding as of September 30, 2024	10 months 17 days
Aggregate Intrinsic Value
Outstanding as of September 30, 2024	$ 298
Restricted Stock Units (RSUs)
Shares
Beginning balance (in shares)	6,417,397
Granted (in shares)	3,221,842
Vested and earned (in shares)	(2,953,860)
Forfeited (in shares)	(325,718)
Ending balance (in shares)	6,359,661	6,417,397
Weighted- Average Grant Date Fair Value
Beginning balance (in dollars per share)	$ 209.19
Granted (in dollars per share)	253.29	$ 212.94	$ 204.73
Vested and earned (in dollars per share)	208.69
Forfeited (in dollars per share)	224.82
Ending balance (in dollars per share)	$ 230.99	$ 209.19
Weighted- Average Remaining Contractual Term (in years)
Outstanding as of September 30, 2024	11 months 4 days
Aggregate Intrinsic Value
Outstanding as of September 30, 2024	$ 1,749