Financial Instruments (Realized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Proceeds from sales	$ 194.8	$ 273.6	$ 232.8	$ 319.4
Realized gross gains on sales	2.7	3.5	3.6	3.8
Realized gross losses on sales	$ 7.2	$ 1.5	$ 8.0	$ 2.0