CONDENSED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Accounts receivable, reserves (in dollars)	$ 10.0	$ 4.2
Property, plant, and equipment, accumulated depreciation (in dollars)	$ 1,730.3	$ 1,672.1
Common stock, par value (in dollars per share)	$ 4	$ 4
Common stock, shares authorized	32,000,000	32,000,000
Common stock, shares, issued	23,896,962	23,896,962
Common stock, shares outstanding	23,896,962	23,896,962