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Share-Based Payments - Restricted stock unit, PEP unit, and Stock Option activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Stock options, Weighted average exercise price |  |  |
Recognized compensation expense | $ 45.9 | $ 38.5 | $ 44.7
Unrecognized compensation expense | 48.3 | 45.9 |
Other disclosures |  |  |
Compensation expense related to share-based payments | 45.9 | 38.5 | $ 44.7
Unrecognized compensation expense | $ 48.3 | $ 45.9 |
Recognition period of unrecognized compensation expense | 3 years | 3 years |
Restricted Stock Units |  |  |
Units |  |  |
Outstanding at beginning (in units) | 1.0 | 1.3 | 2.1
Granted (in units) | 0.3 | 0.3 | 0.4
Vested (in shares) | (0.4) | (0.5) | (0.9)
Cancelled (in shares) | (0.1) | (0.1) | (0.3)
Outstanding at ending (in units) | 0.8 | 1.0 | 1.3
Weighted Average Grant-Date Fair Value |  |  |
Outstanding at beginning (in USD per unit) | $ 53.05 | $ 38.88 | $ 35.56
Granted (in USD per unit) | 83.64 | 74.30 | 49.21
Vested (in USD per unit) | 44.35 | 29.44 | 36.24
Cancelled (in USD per unit) | 62.09 | 49.74 | 36.89
Outstanding at ending (in USD per unit) | $ 68.34 | $ 53.05 | $ 38.88
PEP Units |  |  |
Units |  |  |
Outstanding at beginning (in units) | 0.7 | 1.2 | 1.6
Granted (in units) | 0.2 | 0.2 | 0.3
PEP units earned (unearned) (in shares) | 0.2 | 0.6 | 0.1
Vested (in shares) | (0.4) | (1.3) | (0.6)
Cancelled (in shares) |  |  | (0.2)
Outstanding at ending (in units) | 0.7 | 0.7 | 1.2
Weighted Average Grant-Date Fair Value |  |  |
Outstanding at beginning (in USD per unit) | $ 60.60 | $ 37.22 | $ 33.86
Granted (in USD per unit) | 94.64 | 85.46 | 52.76
PEP units earned (unearned) (in USD per share) | 43.19 | 27.90 | 37.37
Vested (in USD per unit) | 43.19 | 27.90 | 38.13
Cancelled (in USD per unit) | 71.71 | 56.64 | 37.53
Outstanding at ending (in USD per unit) | $ 75.54 | $ 60.60 | $ 37.22
Stock Options |  |  |
Shares of stock under options |  |  |
Balance at the beginning of the period (in shares) | 0.3 | 0.3 | 0.4
Options exercised (in shares) | (0.2) |  | (0.1)
Balance at the end of the period (in shares) | 0.1 | 0.3 | 0.3
Stock options, Weighted average exercise price |  |  |
Balance at the beginning of the period (in dollars per share) | $ 38.72 | $ 38.72 | $ 36.41
Options exercised (in dollars per share) | 38.72 |  | 31.62
Balance at the end of the period (in dollars per share) | $ 38.72 | $ 38.72 | $ 38.72

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