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Share-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Schedule of Recent Share-Based Compensation Expense | The following is a summary of share-based compensation expense:
Year |  | Share-Based Compensation Expense |  | Tax Benefit
2016 |  | $ | 39.2 |  |  | $ | 15.1 |
2017 |  | 40.4 |  |  | 13.6 |
2018 |  | 44.7 |  |  | 11.2 |
Schedule of Transactions of the Company's Stock Options | The following table summarizes the transactions in the Company’s stock options:
| Stock Options |  | Weighted Average Exercise Price |  | Weighted Average Remaining Contractual Life (years)
Unexercised options outstanding—December 31, 2017 | 0.6 |  |  | $ | 122.04 |  |  |
Options granted | 0.0 |  |  | 179.54 |  |  |
Options exercised | (0.1 | ) |  | 99.57 |  |  |
Options forfeited | (0.0 | ) |  | 122.40 |  |  |
Unexercised options outstanding—December 31, 2018 | 0.5 |  |  | 130.81 |  |  | 3.7
Exercisable at December 31, 2018 | 0.1 |  |  | 138.97 |  |  | 2.3
Schedule of Assumptions Used to Determine Fair Value of Options Granted | The fair value of options granted was estimated using the Black-Scholes option pricing model and were $39.02, $48.05 and $48.64, per option, for the years ended December 31, 2016, 2017 and 2018, respectively. The weighted average grant date assumptions used to estimate the fair value of options granted were as follows:
| For the Years Ended December 31,
| 2016 |  | 2017 |  | 2018
Dividend yield | 0.0 | % |  | 0.5 | % |  | 0.8 | %
Expected volatility(1) | 30.7 | % |  | 28.0 | % |  | 25.5 | %
Risk-free interest rate(2) | 1.6 | % |  | 2.1 | % |  | 2.8 | %
Expected life of options (in years)(3) | 5.7 |  |  | 5.7 |  |  | 5.7 |
Forfeiture rate | 0.0 | % |  | 0.0 | % |  | 0.0 | %
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(1) | Expected volatility is based on historical and implied volatility.
(2) | Risk-free interest rate is based on the U.S. Treasury yield curve in effect at the date of grant.
(3) | Expected life of options (in years) is based on the Company’s historical and expected exercise behavior.
Schedule of Transactions of the Company's Restricted Stock | The following table summarizes the transactions in the Company’s restricted stock units:
| Restricted Stock |  | Weighted Average Grant Date Value
Unvested units—December 31, 2017 | 0.4 |  |  | $ | 162.32 |
Units granted | 0.2 |  |  | 201.75 |
Units vested | (0.0 | ) |  | 188.93 |
Units forfeited | (0.0 | ) |  | 154.92 |
Unvested units—December 31, 2018 | 0.6 |  |  | 172.74 |

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- Definition Tabular disclosure of the changes in outstanding nonvested 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 (c)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure for share-based compensation plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + 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 (e) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: 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) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + 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) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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