Debt (July 2020 Senior Notes Redemption) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Interest Paid	$ 474.0	$ 357.2	$ 254.7
Write off of financing fees	$ 3.2	$ 35.8	$ 99.6