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Share-Based Payments (Details 3) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Tax benefit and cash received from stock option |  |  |
Tax benefit realized for stock options | $ 3.4 | $ 4.0 | $ 11.9
Cash received from the exercise of stock options | $ 0.7 | $ 2.2 | $ 6.3

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