Condensed Guarantor and Non-Guarantor Financial Statements, Comprehensive Income Statements (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
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 (loss) income	29.8	40.5		132.5	(381.1)
Other expense:
Interest expense	(5.5)	(4.9)		(14.7)	(19.9)
Other (expense) income, net	0.0	(0.9)		(10.4)	(0.1)
(Loss) income before income taxes	24.3	34.7		107.4	(401.1)
Income tax (provision) benefit	(9.4)	(12.6)		(40.2)	151.2
Earnings (loss) in equity of subsidiaries	0.0	0.0		0.0	0.0
Net income (loss)	14.9	22.1		67.2	(249.9)
Comprehensive income (loss)	16.0	22.2		70.1	(182.5)
Consolidating Adjustments
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	(19.9)	(22.5)		(58.8)	(73.5)
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	(19.0)	(21.1)		(56.3)	(70.3)
Lower of cost or market inventory write-down				0.0
Unrealized (gain) loss on derivative instruments	0.0	0.0		0.0	0.0
Depreciation and amortization	0.0	0.0		0.0	0.0
Selling, general, administrative, research and development	(0.6)	(0.6)		(2.0)	(1.7)
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0		0.0	0.0
(Gain) loss on removal of Union VEBA net assets		0.0		0.0	0.0
Total selling, general, administrative, research and development	(0.6)	(0.6)		(2.0)	(1.7)
Other operating charges, net	0.0			0.0
Total costs and expenses	(19.6)	(21.7)		(58.3)	(72.0)
Operating (loss) income	(0.3)	(0.8)		(0.5)	(1.5)
Other expense:
Interest expense	0.1	0.1		0.1	0.3
Other (expense) income, net	(0.1)	(0.1)		(0.1)	(0.3)
(Loss) income before income taxes	(0.3)	(0.8)		(0.5)	(1.5)
Income tax (provision) benefit	2.5	2.2		11.6	8.5
Earnings (loss) in equity of subsidiaries	(22.3)	(27.3)		(98.8)	224.7
Net income (loss)	(20.1)	(25.9)		(87.7)	231.7
Comprehensive income (loss)	(21.2)	(26.0)		(90.6)	164.3
Parent
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	0.0	0.0		0.0	0.0
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	0.0	0.0		0.0	0.0
Lower of cost or market inventory write-down				0.0
Unrealized (gain) loss on derivative instruments	0.0	0.0		0.0	0.0
Depreciation and amortization	0.0	0.0		0.0	0.0
Selling, general, administrative, research and development	0.9	0.9		3.3	3.3
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0		0.0	0.0
(Gain) loss on removal of Union VEBA net assets		0.0		0.0	0.0
Total selling, general, administrative, research and development	0.9	0.9		3.3	3.3
Other operating charges, net	0.0			0.0
Total costs and expenses	0.9	0.9		3.3	3.3
Operating (loss) income	(0.9)	(0.9)		(3.3)	(3.3)
Other expense:
Interest expense	(5.7)	(4.7)		(15.9)	(19.1)
Other (expense) income, net	(0.1)	(0.6)		(11.1)	(0.6)
(Loss) income before income taxes	(6.7)	(6.2)		(30.3)	(23.0)
Income tax (provision) benefit	0.0	0.0		0.0	0.0
Earnings (loss) in equity of subsidiaries	21.6	28.3		97.5	(226.9)
Net income (loss)	14.9	22.1		67.2	(249.9)
Comprehensive income (loss)	16.0	22.2		70.1	(182.5)
Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	313.9	329.5		976.9	1,051.2
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	250.0	263.1		753.1	848.9
Lower of cost or market inventory write-down				4.9
Unrealized (gain) loss on derivative instruments	(2.0)	1.7		(16.9)	7.7
Depreciation and amortization	8.5	7.8		25.2	23.3
Selling, general, administrative, research and development	24.0	18.4		71.4	58.6
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		(2.9)		(0.1)	490.9
Total selling, general, administrative, research and development	24.8	16.1		73.8	551.3
Other operating charges, net	2.7			2.8
Total costs and expenses	284.0	288.7		842.9	1,431.2
Operating (loss) income	29.9	40.8		134.0	(380.0)
Other expense:
Interest expense	0.1	(0.3)		1.1	(1.1)
Other (expense) income, net	0.1	2.2		0.6	3.0
(Loss) income before income taxes	30.1	42.7		135.7	(378.1)
Income tax (provision) benefit	(11.6)	(15.6)		(51.1)	140.5
Earnings (loss) in equity of subsidiaries	0.7	(1.0)		1.3	2.2
Net income (loss)	19.2	26.1		85.9	(235.4)
Comprehensive income (loss)	20.3	26.5		88.7	(167.8)
Non-Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	26.6	29.4		80.6	97.6
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	23.7	25.3		70.3	85.8
Lower of cost or market inventory write-down				0.0
Unrealized (gain) loss on derivative instruments	0.0	0.0		0.0	0.0
Depreciation and amortization	0.5	0.3		1.5	0.9
Selling, general, administrative, research and development	1.3	2.4		6.5	7.2
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0		0.0	0.0
(Gain) loss on removal of Union VEBA net assets		0.0		0.0	0.0
Total selling, general, administrative, research and development	1.3	2.4		6.5	7.2
Other operating charges, net	0.0			0.0
Total costs and expenses	25.5	28.0		78.3	93.9
Operating (loss) income	1.1	1.4		2.3	3.7
Other expense:
Interest expense	0.0	0.0		0.0	0.0
Other (expense) income, net	0.1	(2.4)		0.2	(2.2)
(Loss) income before income taxes	1.2	(1.0)		2.5	1.5
Income tax (provision) benefit	(0.3)	0.8		(0.7)	2.2
Earnings (loss) in equity of subsidiaries	0.0	0.0		0.0	0.0
Net income (loss)	0.9	(0.2)		1.8	3.7
Comprehensive income (loss)	$ 0.9	$ (0.5)		$ 1.9	$ 3.5