Condensed Guarantor and Non-Guarantor Financial Information, Comprehensive Income Statements (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	$ 356.3	$ 334.9		$ 711.6	$ 678.1
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	277.7	250.4		555.5	512.4
Lower of cost or market inventory write-down	0.0	0.0	$ 4.9	0.0	4.9
Unrealized loss (gain) on derivative instruments	11.9	(10.9)		(3.2)	(14.9)
Depreciation and amortization	9.5	9.0		19.1	17.7
Selling, general, administrative, research and development	26.3	27.5		50.0	53.6
Net periodic postretirement benefit cost relating to Salaried VEBA	1.1	0.9		2.2	1.7
Gain on removal of Union VEBA net assets	0.0	0.0		(1.3)	(0.1)
Total selling, general, administrative, research and development	27.4	28.4		50.9	55.2
Goodwill impairment	18.4	0.0		18.4	0.0	$ 0.0
Other operating charges, net	0.0	0.1		0.0	0.1
Total costs and expenses	344.9	277.0		640.7	575.4
Operating income	11.4	57.9		70.9	102.7
Other (expense) income:
Interest (expense) income	(5.5)	(5.5)		(11.1)	(9.2)
Other (expense) income, net	1.0	(10.7)		1.6	(10.4)
Income before income taxes	6.9	41.7		61.4	83.1
Income tax provision	(2.2)	(15.7)		(20.7)	(30.8)
Earnings in equity of subsidiaries	0.0	0.0		0.0	0.0
Net income	4.7	26.0		40.7	52.3
Comprehensive income	5.8	26.9		43.1	54.1
Consolidating Adjustments
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	(20.5)	(20.0)		(41.3)	(38.9)
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	(19.6)	(19.1)		(39.7)	(37.3)
Lower of cost or market inventory write-down					0.0
Unrealized loss (gain) 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	(0.5)	(0.9)		(1.0)	(1.4)
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0		0.0	0.0
Gain on removal of Union VEBA net assets				0.0	0.0
Total selling, general, administrative, research and development	(0.5)	(0.9)		(1.0)	(1.4)
Goodwill impairment	0.0			0.0
Other operating charges, net		0.0			0.0
Total costs and expenses	(20.1)	(20.0)		(40.7)	(38.7)
Operating income	(0.4)	0.0		(0.6)	(0.2)
Other (expense) income:
Interest (expense) income	0.0	0.0		0.0	0.0
Other (expense) income, net	0.0	0.0		0.0	0.0
Income before income taxes	(0.4)	0.0		(0.6)	(0.2)
Income tax provision	2.3	7.1		4.8	9.1
Earnings in equity of subsidiaries	(11.4)	(44.8)		(54.6)	(76.5)
Net income	(9.5)	(37.7)		(50.4)	(67.6)
Comprehensive income	(10.6)	(38.6)		(52.8)	(69.4)
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 loss (gain) 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	1.5	1.6		2.4	2.4
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0		0.0	0.0
Gain on removal of Union VEBA net assets				0.0	0.0
Total selling, general, administrative, research and development	1.5	1.6		2.4	2.4
Goodwill impairment	0.0			0.0
Other operating charges, net		0.0			0.0
Total costs and expenses	1.5	1.6		2.4	2.4
Operating income	(1.5)	(1.6)		(2.4)	(2.4)
Other (expense) income:
Interest (expense) income	(4.6)	(5.9)		(10.3)	(10.2)
Other (expense) income, net	0.0	(11.0)		0.0	(11.0)
Income before income taxes	(6.1)	(18.5)		(12.7)	(23.6)
Income tax provision	0.0	0.0		0.0	0.0
Earnings in equity of subsidiaries	10.8	44.5		53.4	75.9
Net income	4.7	26.0		40.7	52.3
Comprehensive income	5.8	26.9		43.1	54.1
Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	347.0	327.3		693.8	663.0
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	271.6	246.0		544.2	503.1
Lower of cost or market inventory write-down					4.9
Unrealized loss (gain) on derivative instruments	11.9	(10.9)		(3.2)	(14.9)
Depreciation and amortization	9.0	8.5		18.0	16.7
Selling, general, administrative, research and development	22.8	23.8		43.7	47.4
Net periodic postretirement benefit cost relating to Salaried VEBA	1.1	0.9		2.2	1.7
Gain on removal of Union VEBA net assets				(1.3)	(0.1)
Total selling, general, administrative, research and development	23.9	24.7		44.6	49.0
Goodwill impairment	18.4			18.4
Other operating charges, net		0.1			0.1
Total costs and expenses	334.8	268.4		622.0	558.9
Operating income	12.2	58.9		71.8	104.1
Other (expense) income:
Interest (expense) income	(0.9)	0.4		(0.8)	1.0
Other (expense) income, net	0.8	0.2		1.4	0.5
Income before income taxes	12.1	59.5		72.4	105.6
Income tax provision	(4.2)	(22.6)		(25.0)	(39.5)
Earnings in equity of subsidiaries	0.6	0.3		1.2	0.6
Net income	8.5	37.2		48.6	66.7
Comprehensive income	9.6	38.1		51.0	68.4
Non-Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	29.8	27.6		59.1	54.0
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	25.7	23.5		51.0	46.6
Lower of cost or market inventory write-down					0.0
Unrealized loss (gain) on derivative instruments	0.0	0.0		0.0	0.0
Depreciation and amortization	0.5	0.5		1.1	1.0
Selling, general, administrative, research and development	2.5	3.0		4.9	5.2
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0		0.0	0.0
Gain on removal of Union VEBA net assets				0.0	0.0
Total selling, general, administrative, research and development	2.5	3.0		4.9	5.2
Goodwill impairment	0.0			0.0
Other operating charges, net		0.0			0.0
Total costs and expenses	28.7	27.0		57.0	52.8
Operating income	1.1	0.6		2.1	1.2
Other (expense) income:
Interest (expense) income	0.0	0.0		0.0	0.0
Other (expense) income, net	0.2	0.1		0.2	0.1
Income before income taxes	1.3	0.7		2.3	1.3
Income tax provision	(0.3)	(0.2)		(0.5)	(0.4)
Earnings in equity of subsidiaries	0.0	0.0		0.0	0.0
Net income	1.0	0.5		1.8	0.9
Comprehensive income	$ 1.0	$ 0.5		$ 1.8	$ 1.0