Financial Instruments (Realized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Proceeds from sales	$ 63.3	$ 93.7
Realized gross gains on sales	11.6	2.5
Realized gross losses on sales	$ 0.8	$ 0.4