Income Taxes - Impact of Tax Cuts and Jobs Act (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal Taxes on Mandatory Deemed Repatriation	$ 150.0
Impact Related to Federal Deferred Taxes	(210.0)
Other Adjustments	6.9
Provision (Benefit) for Income Taxes	$ 53.1	$ 0.0	$ 0.0