Statements of Consolidated Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Net sales	$ 320.6	$ 336.4		$ 998.7	$ 1,075.3
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	254.7	267.3		767.1	864.4
Lower of cost or market inventory write-down	0.0	0.0	$ 4.9	4.9	0.0
Unrealized (gain) loss on derivative instruments	(2.0)	1.7		(16.9)	7.7
Depreciation and amortization	9.0	8.1		26.7	24.2
Selling, general, administrative, research and development	25.6	21.1		79.2	67.4
Net periodic postretirement benefit cost relating to Salaried VEBA	0.8	0.6		2.5	1.8
(Gain) loss on removal of Union VEBA net assets	0.0	(2.9)		(0.1)	490.9
Total selling, general, administrative, research and development	26.4	18.8		81.6	560.1
Other operating charges, net	2.7	0.0		2.8	0.0
Total costs and expenses	290.8	295.9		866.2	1,456.4
Operating income (loss)	29.8	40.5		132.5	(381.1)
Other expense:
Interest expense	(5.5)	(4.9)		(14.7)	(19.9)
Other expense, net	0.0	(0.9)		(10.4)	(0.1)
Income (loss) before income taxes	24.3	34.7		107.4	(401.1)
Income tax (provision) benefit	(9.4)	(12.6)		(40.2)	151.2
Net income (loss)	$ 14.9	$ 22.1		$ 67.2	$ (249.9)
Net income (loss) per common share:
Basic (in dollars per share)	$ 0.84	$ 1.29		$ 3.76	$ (14.55)
Diluted (in dollars per share)	$ 0.82	$ 1.21		$ 3.70	$ (14.55)
Weighted-average number of common shares outstanding (in thousands):
Basic (shares)	17,841	17,123		17,858	17,178
Diluted (shares)	18,175	18,172		18,181	17,178
Cash dividends declared (in dollars per share)	$ 0.45	$ 0.40		$ 1.35	$ 1.20