Condensed Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Balance at Dec. 31, 2019		$ 157.7	$ 2,122.1	$ (803.4)	$ 941.1
Common stock issued for stock options exercised	$ 0.5	0.0	0.5
Common stock issued for other transactions		0.1	2.8
Stock-based compensation			(2.6)
Other comprehensive income (loss)	(17.7)			(17.7)
Net income (loss)	(80.0)				(80.0)
Common stock dividends paid					(31.5)
Balance at Mar. 31, 2020	2,289.1	$ 157.8	2,122.8	(821.1)	829.6
Dividends declared per share of common stock		$ 0.20
Balance at Dec. 31, 2020	1,450.8	$ 158.0	2,137.8	(689.9)	(155.1)
Common stock issued for stock options exercised	25.7	1.2	24.5
Common stock issued for other transactions		0.0	1.4
Stock-based compensation			0.6
Other comprehensive income (loss)	6.2			6.2
Net income (loss)	243.6				243.6
Common stock dividends paid					(31.7)
Balance at Mar. 31, 2021	$ 1,696.6	$ 159.2	$ 2,164.3	$ (683.7)	$ 56.8
Dividends declared per share of common stock		$ 0.20