Share-based Compensation - Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2025 USD ($) $ / shares shares	Sep. 30, 2024 USD ($) $ / shares	Sep. 30, 2023 USD ($) $ / shares
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of options issued under EIP (in years)	10 years
Vesting period from the date of grant (in years)	3 years
Total intrinsic value from options exercised	$ 237	$ 185	$ 134
Tax benefit from exercise of stock options	23	$ 28	$ 28
Unrecognized compensation cost	$ 29
Total unrecognized compensation cost related to non-vested options expected to be recognized over a weighted average period (in years)	5 months 8 days
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period from the date of grant (in years)	3 years
Unrecognized compensation cost	$ 824
Number of shares of common stock issued for each award	1
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 315.21	$ 253.29	$ 212.94
Total grant date fair value of shares vested and earned	$ 687	$ 616	$ 486
Weighted-average period (in years)	11 months 4 days
Performance-based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period from the date of grant (in years)	3 years
Unrecognized compensation cost	$ 67
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 345.65
Total grant date fair value of shares vested and earned	$ 101	81	44
Weighted-average period (in years)	7 months 20 days
2007 Equity Incentive Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of Class A Common Stock authorized for issuance under EIP or ESPP (in shares) | shares	198
Share-based compensation expense under EIP	$ 861	817	734
Tax benefit under EIP	$ 131	$ 128	$ 112