Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock Par	Common Stock Additional Paid-In Capital	Common Stock Accumulated Retained Earnings	Common Stock Accumulated Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock
Balance at Dec. 31, 2017	$ 1,495.1	$ 3.8	$ 1.1	$ 774.3	$ 1,496.1	$ 2.2	$ (45.0)	$ 1.6	$ (731.4)
Increase (Decrease) in Stockholders' Equity
Net income	276.6				276.6
Dividends paid on common stock	(48.4)				(48.4)
Change in other comprehensive income – net of tax	(64.6)						(64.6)
Stock-based compensation	24.0			24.0
Acquisition of treasury stock	(364.5)								(364.5)
Balance at Dec. 31, 2018	1,322.0		1.1	798.3	1,726.5		(108.0)		(1,095.9)
Increase (Decrease) in Stockholders' Equity
Net income	306.6				306.6
Dividends paid on common stock	(54.2)				(54.2)
Change in other comprehensive income – net of tax	(10.7)						(10.7)
Stock-based compensation	31.6			31.6
Acquisition of treasury stock	(149.2)								(149.2)
Balance at Dec. 31, 2019	1,446.1		1.1	829.9	1,978.9		(118.7)		(1,245.1)
Increase (Decrease) in Stockholders' Equity
Net income	31.7				31.7
Dividends paid on common stock	(14.2)				(14.2)
Change in other comprehensive income – net of tax	59.1						59.1
Stock-based compensation	19.8			19.8
Acquisition of treasury stock	(32.3)								(32.3)
Balance at Dec. 31, 2020	$ 1,510.2		$ 1.1	$ 849.7	$ 1,996.4		$ (59.6)		$ (1,277.4)