Financial Instruments (Realized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Proceeds from sales	$ 49.6	$ 14.0	$ 137.3	$ 246.8
Realized gross gains on sales	0.4	0.4	2.2	4.0
Realized gross losses on sales	$ 0.3	$ 0.2	$ 1.1	$ 8.2