Condensed Consolidated Statement of Stockholders' Equity Statement - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]
Balance at beginning of year (shares) at Dec. 31, 2018		(50.0)	(6.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.1
Balance at end of year (shares) at Mar. 31, 2019		(50.1)	(6.8)
Balance at beginning of year at Dec. 31, 2018		$ (125.0)	$ (117.0)	$ (194.2)	$ 96.4	$ (712.7)
Balance at end of year at Mar. 31, 2019	$ (895.3)	(125.3)	(117.5)	(198.4)	68.6	(757.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.3		0.7
Shares acquired on stock award exercises and vested restricted shares			$ (0.5)
Stock awards granted				3.5
Change in net unrealized holding (losses) gains, net of tax	27.2				27.2
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	0.6				0.6
Net income (loss)	$ 49.4					49.4
Cash dividends paid		$ (4.4)
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018						0.0
Document Fiscal Year Focus	2020
Balance at beginning of year (shares) at Dec. 31, 2019		(50.4)	(6.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.2
Balance at end of year (shares) at Mar. 31, 2020		(50.6)	(6.9)
Balance at beginning of year at Dec. 31, 2019	$ (959.9)	$ (125.9)	$ (117.5)	(206.7)	37.9	(782.7)
Balance at end of year at Mar. 31, 2020	(866.7)	(126.5)	(118.4)	(209.1)	13.7	(663.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.6		1.3
Shares acquired on stock award exercises and vested restricted shares			$ (0.9)
Stock awards granted				$ 1.1
Change in net unrealized holding (losses) gains, net of tax	22.6				22.6
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	1.6				$ 1.6
Net income (loss)	$ (114.6)					(114.6)
Cash dividends paid		$ (4.4)
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018						$ (0.5)