Derivative Instruments (Net Cash Received (Paid) Related to Derivatives) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Operating activities	$ 179.0	$ 244.4	$ 6.8
Investing activities	0.0	0.0	(0.5)
Financing activities	331.5	112.8
Financing activities			(138.1)
Total	$ 510.5	$ 357.2	$ (131.8)