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Common Stock (Schedule of Weighted Average Fair Value per Share PSUs and Related Valuation Assumptions) (Details) - $ / shares
12 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
Share-based Payment Arrangement, Option [Member]      
Performance Share Units      
Weighted average fair value per share (usd per share) $ 24.80 $ 25.28 $ 22.50
Valuation assumptions:      
Risk-free interest rate 1.60% 3.00% 2.20%
Expected dividend yield 0.80% 0.80% 0.90%
Expected volatility 27.70% 30.50% 30.80%
Performance Shares [Member]      
Performance Share Units      
Weighted average fair value per share (usd per share) $ 110.53 $ 112.79 $ 87.42
Valuation assumptions:      
Risk-free interest rate 1.60% 3.00% 1.90%
Expected volatility 23.80% 22.80% 21.90%