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Share and Unit-based Plans - Schedule LTIP Units Valuation Assumptions (Details) - LTIP units | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
January 1, 2017 |  |  |
Share and unit-based plans |  |  |
Risk Free Interest Rate |  |  | 1.49%
Expected Volatility |  |  | 20.75%
June 1, 2017 |  |  |
Share and unit-based plans |  |  |
Risk Free Interest Rate |  |  | 1.45%
Expected Volatility |  |  | 21.40%
January 1, 2018 |  |  |
Share and unit-based plans |  |  |
Risk Free Interest Rate |  | 1.98% |
Expected Volatility |  | 23.38% |
January 29, 2018 |  |  |
Share and unit-based plans |  |  |
Risk Free Interest Rate |  | 2.25% |
Expected Volatility |  | 23.86% |
January 1, 2019 |  |  |
Share and unit-based plans |  |  |
Risk Free Interest Rate | 2.46% |  |
Expected Volatility | 23.52% |  |
September 1, 2019 |  |  |
Share and unit-based plans |  |  |
Risk Free Interest Rate | 1.42% |  |
Expected Volatility | 24.91% |  |

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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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