Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	12.00%	21.00%
income tax benefit related to tax act	$ 12.1
excess tax benefit related to stock based compensation	$ 5.5	$ 6.2
Statutory federal rate	21.00%	35.00%
Tax Credit Carryforward, Amount			$ 67.9
Foreign Earnings Repatriated	$ 1,150.0
Deferred Tax Liabilities, Undistributed Foreign Earnings	60.7
Deferred Tax Liabilities, Gross, Noncurrent	93.6
Liabilities, Other than Long-term Debt, Noncurrent	$ 8.1