| **Capital Shares (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                               |
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| **Equity [Abstract]**       |                                                                                                                                                                                                                                                                          |
| Capital Shares              | Common shares repurchased as part of publicly announced programs during 2020, 2019 and 2018 were as follows:YearNumberof SharesTotalAmountAverageper Share2020303 38,138 $125.70 2019949 114,790 $121.01 2018145 18,939 $130.21  |

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| - References
No definition available.
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| - Definition
Tabular disclosure of treasury stock, including, but not limited to, average cost per share, description of share repurchase program, shares repurchased, shares held for each class of treasury stock.
+ References
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