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New Accounting Pronouncements (Narrative) (Details) - ASU No. 2016-09 [Member] - USD ($) $ in Millions | 9 Months Ended
--- | ---
Sep. 30, 2017 | Sep. 30, 2016
Reclassification from Operating Activities to Financing Activities [Member] |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |
Shares withheld from employee awards for tax withholding purposes |  | $ 47.5
Incentive Stock Award Plans [Member] |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |
Provision for income tax expense (benefit) | $ (17.4) |

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