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Share-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Summary of Recent Share-Based Compensation Expense | The following is a summary of share-based compensation expense:
Period |  | Share-Based Compensation Expense |  | Tax Benefit
2013 |  | $ | 27.5 |  |  | $ | 10.6 |
2014 |  | 29.3 |  |  | 11.3 |
2015 |  | 34.2 |  |  | 13.2 |
Schedule of Transactions of the Company's Stock Options | The following table summarizes the transactions of the Company’s stock options:
| Stock Options |  | Weighted Average Exercise Price |  | Weighted Average Remaining Contractual Life (years)
Unexercised options outstanding—January 1, 2015 | 2.3 |  |  | $ | 83.42 |  |  |
Options granted | 0.0 |  |  | 207.61 |  |  |
Options exercised | (0.9 | ) |  | 65.95 |  |  |
Options forfeited | (0.0 | ) |  | 101.29 |  |  |
Unexercised options outstanding—December 31, 2015 | 1.4 |  |  | 96.18 |  |  | 2.2
Exercisable at December 31, 2015 | 1.3 |  |  | 94.43 |  |  | 2.1
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. The weighted average fair value of options granted during the years ended December 31, 2013, 2014 and 2015 was $61.82, $60.20, and $54.92 per option, respectively, based on the weighted-average grant date assumptions stated below.
| For the Years Ended December 31,
| 2013 |  | 2014 |  | 2015
Dividend yield | 0.0 | % |  | 0.0 | % |  | 0.0 | %
Expected volatility(1) | 34.4 | % |  | 29.7 | % |  | 26.7 | %
Risk-free interest rate(2) | 1.5 | % |  | 1.8 | % |  | 1.5 | %
Expected life of options (in years)(3) | 5.0 |  |  | 5.0 |  |  | 5.0 |
Forfeiture rate(3) | 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 data and expected exercise behavior.
Summary of Transactions of the Company's Restricted Stock | The following table summarizes the transactions of the Company’s restricted stock:
| Restricted Stock |  | Weighted Average Grant Date Value
Unvested units—January 1, 2015 | 0.4 |  |  | $ | 182.83 |
Units granted | 0.3 |  |  | 197.59 |
Units vested | (0.1 | ) |  | 174.19 |
Units forfeited | (0.0 | ) |  | 190.23 |
Unvested units—December 31, 2015 | 0.6 |  |  | 192.04 |

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- Definition Tabular disclosure of the changes in outstanding nonvested shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of share-based compensation plans that may be presented in a single table for outstanding, vested and expected to vest, and exercisable awards. The information that may be disclosed in this table may include, but is not limited to, number of shares, weighted average exercise price, weighted average remaining contractual life, and aggregate intrinsic value. + References No definition available. + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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