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Share-Based Compensation - Assumptions for Estimation of Fair Values of Stock Appreciation Rights Granted During Reporting Periods (Details) - Stock Appreciation Rights (SARs) - $ / shares
12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 4.24% 4.51% 3.78%
Expected volatility 21.00% 22.00% 21.00%
Expected dividend yield 1.86% 1.59% 1.53%
Expected life 7 years 7 years 7 years
Fair value derived (in USD per share) $ 54.39 $ 63.05 $ 57.80