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Share-Based Payments - Assumptions Used in Valuation of Market Based Stock Units (Details) - Market stock units - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |
Expected dividend yield | 0.00% |  | 0.00% | 0.00%
Minimum range of risk-free interest rates | 1.41% |  | 2.46% | 1.90%
Maximum range of risk-free interest rates | 1.48% |  | 2.53% | 2.30%
Average stock price on grant date minimum | $ 257.83 |  | $ 228.59 | $ 279.47
Average stock price on grant date maximum | $ 325.40 |  | $ 331.18 | $ 346.76
Granted (in dollars per share) | $ 398.61 | [1] | $ 378.08 | $ 378.85
Minimum |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |
Range of expected stock price volatility | 37.80% |  | 31.20% | 27.50%
Maximum |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |
Range of expected stock price volatility | 44.10% |  | 33.60% | 32.40%
[1] | MSUs granted during 2020 include awards granted in conjunction with our annual awards made in February 2020 and MSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant. MSUs granted in 2020 also reflect an adjustment based upon the final performance multiplier in relation to shares granted in 2019, 2018 and 2017.

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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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 (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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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=120381028&loc=d3e5070-113901 + Details
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- Definition The maximum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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