v3.21.2
Share-based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Jan. 26, 2021
Jan. 25, 2021
Stock Option          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Expiration period of options issued under EIP 10 years        
Vesting period from the date of grant 3 years        
Total intrinsic value from options exercised $ 124 $ 146 $ 107    
Tax benefit from exercise of stock options 23 $ 31 $ 23    
Unrecognized compensation cost $ 23        
Total unrecognized compensation cost related to non-vested options expected to be recognized over a weighted average period (in years) 5 months 1 day        
Risk-free rate of return 0.30% 1.60% 2.90%    
Expected term (in years) 4 years 25 days 4 years 10 days 3 years 11 months 23 days    
Expected volatility 25.10% 18.70% 20.20%    
Expected dividend yield 0.60% 0.70% 0.70%    
Restricted Stock Units (RSUs)          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period from the date of grant 3 years        
Unrecognized compensation cost $ 452        
Weighted average grant date fair value (in dollars per share) $ 209.00 $ 183.61 $ 137.38    
Total grant date fair value of shares vested and earned $ 331 $ 284 $ 228    
Weighted-average period 10 months 13 days        
Performance-based Shares          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period from the date of grant 3 years        
Unrecognized compensation cost $ 40        
Weighted average grant date fair value (in dollars per share) $ 229.81 $ 211.08 $ 153.42    
Total grant date fair value of shares vested and earned $ 47 $ 65 $ 41    
Weighted-average period 9 months 25 days        
Risk-free rate of return 0.20%        
Expected term (in years) 2 years        
Expected volatility 27.20%        
Expected dividend yield 0.60%        
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)       198 236
Share-based compensation expense under EIP $ 518 393 388    
Tax benefit under EIP $ 73 $ 63 $ 59    
Employee Stock Purchase 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) 20        
ESPP discount from market price 15.00%