Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Summary of Significant Accounting Policies (Recently Adopted Accounting Principles) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Employee service share-based compensation, tax benefit from exercise of stock options	$ 8.4	$ 9.2
Subsequent Event \| Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset			$ 24.5
Operating lease, liability			$ 24.5