Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock Issued [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock at Cost [Member]
Beginning balance at Dec. 31, 2017	$ 50.1	$ 0.9	$ 1,061.5	$ 1,575.9	$ (157.4)	$ (2,430.8)
Beginning balance, Treasury shares at Dec. 31, 2017						45,400,000
Stockholders' Equity [Roll Forward]
Net income	359.0			359.0
Dividends	(98.2)			(98.2)
Foreign currency translation adjustments, net	11.0				11.0
Pension and postretirement liability changes, net of tax expense (benefit)	(2.8)				(2.8)
Pension and post-retirement liability changes, net of tax benefit	0.0			1.8	(1.8)
Sale of marketable equity securities	26.3		26.3
Change in cash flow hedges, net of tax expense (benefit)	(15.1)				(15.1)
Treasury shares reissued for common stock	3.4		9.0			$ 12.4
Treasury shares reissued for common stock, shares						(400,000)
Additional investment in subsidiary	(477.1)					$ (477.1)
Treasury stock purchases, shares						2,300,000
Ending balance at Dec. 31, 2018	(149.6)	0.9	1,078.8	1,855.0	(188.8)	$ (2,895.5)
Ending balance, Treasury shares at Dec. 31, 2018						47,300,000
Stockholders' Equity [Roll Forward]
Cumulative Effect Period Of Adoption	$ (6.2)			16.5	(22.7)
Dividends per share (in usd per share)	$ 2.43
Net income	$ 408.7			408.7
Dividends	(114.7)			(114.7)
Foreign currency translation adjustments, net	5.8				5.8
Pension and postretirement liability changes, net of tax expense (benefit)	73.0				73.0
Pension and post-retirement liability changes, net of tax benefit				0.0
Sale of marketable equity securities	21.3		21.3
Change in cash flow hedges, net of tax expense (benefit)	6.2				6.2
Treasury shares reissued for common stock	3.4		6.6			$ 10.0
Treasury shares reissued for common stock, shares						(300,000)
Additional investment in subsidiary	(424.0)					$ (424.0)
Treasury stock purchases, shares						1,600,000
Ending balance at Dec. 31, 2019	(170.2)	0.9	1,093.5	2,148.7	(103.8)	$ (3,309.5)
Ending balance, Treasury shares at Dec. 31, 2019						48,600,000
Stockholders' Equity [Roll Forward]
Cumulative Effect Period Of Adoption	$ (0.3)			(0.3)
Dividends per share (in usd per share)	$ 2.95
Net income	$ 356.3			356.3
Dividends	(117.9)			(117.9)
Foreign currency translation adjustments, net	0.8				0.8
Pension and postretirement liability changes, net of tax expense (benefit)	(1.2)				(1.2)
Share of equity method investments other comprehensive income	(1.2)				(1.2)
Sale of marketable equity securities	24.3		24.3
Change in cash flow hedges, net of tax expense (benefit)	8.2				8.2
Treasury shares reissued for common stock	3.0		4.6			$ 7.6
Treasury shares reissued for common stock, shares						(300,000)
Additional investment in subsidiary	(117.9)					$ (117.9)
Treasury stock purchases, shares						500,000
Ending balance at Dec. 31, 2020	$ (17.1)	$ 0.9	$ 1,113.2	2,385.8	$ (97.2)	$ (3,419.8)
Ending balance, Treasury shares at Dec. 31, 2020	48,820,969					48,800,000
Stockholders' Equity [Roll Forward]
Cumulative Effect Period Of Adoption	$ (1.3)			$ (1.3)
Dividends per share (in usd per share)	$ 3.08