Statements of Consolidated Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Net sales	$ 316.6	$ 336.4	$ 367.2	$ 371.7	$ 338.0	$ 338.9	$ 344.1	$ 335.1	$ 1,391.9	$ 1,356.1	$ 1,297.5
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	251.0	267.3	294.8	302.3	278.7	280.4	275.5	282.9	1,115.4	1,117.5	1,038.9
Lower of cost or market inventory write-down	2.6	0.0	0.0	0.0					2.6	0.0	0.0
Unrealized loss (gain) on derivative instruments	(4.3)	1.7	1.5	4.5	10.4	3.6	(1.6)	(2.0)	3.4	10.4	(0.7)
Depreciation and amortization									32.4	31.1	28.1
Selling, general, administrative, research and development									88.1	81.4	80.4
Net periodic postretirement benefit cost (income) relating to VEBAs – Note 6									2.4	(23.7)	(22.5)
Loss on removal of Union VEBA net assets – Note 6									493.4	0.0	0.0
Total selling, general, administrative, research and development									583.9	57.7	57.9
Other operating charges, net									0.1	1.5	0.0
Total costs and expenses									1,737.8	1,218.2	1,124.2
Operating (loss) income	35.2	40.5	37.0	(458.6)	26.8	32.6	46.4	32.1	(345.9)	137.9	173.3
Other (expense) income:
Interest expense									(24.1)	(37.5)	(35.7)
Other (expense) income, net – Note 15									(1.8)	6.7	5.6
(Loss) income before income taxes									(371.8)	107.1	143.2
Income tax benefit (provision)									135.2	(35.3)	(38.4)
Net (loss) income	$ 13.3	$ 22.1	$ 20.2	$ (292.2)	$ 15.6	$ 15.9	$ 24.5	$ 15.8	$ (236.6)	$ 71.8	$ 104.8
Net (loss) income per common share:
Basic (in dollars per share)	$ 0.76	$ 1.29	$ 1.19	$ (16.85)	$ 0.88	$ 0.90	$ 1.38	$ 0.88	$ (13.76)	$ 4.02	$ 5.56
Diluted (in dollars per share)	$ 0.73	$ 1.21	$ 1.11	$ (16.85)	$ 0.85	$ 0.85	$ 1.33	$ 0.85	$ (13.76)	$ 3.86	$ 5.44
Weighted-average number of common shares outstanding (in thousands):
Basic (in shares)									17,201	17,818	18,827
Diluted (in shares)									17,201	18,593	19,246
Dividends declared per common share (in dollars per share)									$ 1.6	$ 1.4	$ 1.2