Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 102.1	$ 114.8
Effective tax rate	21.10%	29.40%
Provision for income taxes, change in accounting method	$ 22.6
Provision for income taxes, adjustments to initial estimate impact of TCJA	$ (15.8)