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Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022 | Mar. 31, 2021 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Target Performance Shares Outstanding |  |  |  |  |  |
Beginning of period (in shares) |  |  |  | 39,449 | 40,828 | 42,458
Shares paid or expired (in shares) |  |  |  | (13,350) | (14,625) | (14,336)
Grants in period (in shares) |  |  |  | 10,895 | 13,225 | 13,475
Forfeitures and cancellations (in shares) |  |  |  | 37 | 21 | (769)
End of period (in shares) |  |  |  | 37,031 | 39,449 | 40,828
Accrued Expense |  |  |  |  |  |
Beginning of period |  |  |  | $ 67.5 | $ 42.2 | $ 56.3
Shares paid or expired |  |  |  | (40.8) | (26.4) | (35.2)
New grants |  |  |  | 0.0 | 0.0 | 0.0
Forfeitures and cancellations |  |  |  | (0.1) | (0.4) | 0.4
Expense recognized |  |  |  | 42.8 | 52.1 | 20.7
End of period |  |  |  | $ 69.4 | $ 67.5 | $ 42.2
Performance Shares |  |  |  |  |  |
Accrued Expense |  |  |  |  |  |
Percentage of target payout - minimum actual | 200.00% | 172.00% | 200.00% |  |  |

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- Definition The amount of performance shares that were paid out (including deposits into a deferred compensation plan) or that expired due to failure to meet performance criteria. + References No definition available. + Details
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