Condensed Guarantor and Non-Guarantor Financial Information, Comprehensive Income Statements (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	$ 332.8	$ 320.6		$ 1,044.4	$ 998.7
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	267.2	254.7		822.7	767.1
Lower of cost or market inventory write-down	0.0	0.0	$ 4.9	0.0	4.9
Unrealized gain on derivative instruments	(10.8)	(2.0)		(14.0)	(16.9)
Depreciation and amortization	10.2	9.0		29.3	26.7
Selling, general, administrative, research and development	24.7	25.6		74.7	79.2
Net periodic postretirement benefit cost relating to Salaried VEBA	1.2	0.8		3.4	2.5
Gain on removal of Union VEBA net assets	0.5	0.0		(0.8)	(0.1)
Total selling, general, administrative, research and development	26.4	26.4		77.3	81.6
Goodwill impairment	0.0	0.0		18.4	0.0
Other operating charges, net	0.0	2.7		0.0	2.8
Total costs and expenses	293.0	290.8		933.7	866.2
Operating income	39.8	29.8		110.7	132.5
Other (expense) income:
Interest (expense) income	(5.3)	(5.5)		(16.4)	(14.7)
Other (expense) income, net	1.5	0.0		3.1	(10.4)
Income before income taxes	36.0	24.3		97.4	107.4
Income tax provision	(16.1)	(9.4)		(36.8)	(40.2)
Earnings in equity of subsidiaries	0.0	0.0		0.0	0.0
Net income	19.9	14.9		60.6	67.2
Comprehensive income	21.5	16.0		64.6	70.1
Consolidating Adjustments
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	(19.4)	(19.9)		(60.7)	(58.8)
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	(18.4)	(19.0)		(58.1)	(56.3)
Lower of cost or market inventory write-down					0.0
Unrealized 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	(0.6)	(0.6)		(1.6)	(2.0)
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	0.0
Total selling, general, administrative, research and development	(0.6)	(0.6)		(1.6)	(2.0)
Goodwill impairment				0.0
Other operating charges, net		0.0			0.0
Total costs and expenses	(19.0)	(19.6)		(59.7)	(58.3)
Operating income	(0.4)	(0.3)		(1.0)	(0.5)
Other (expense) income:
Interest (expense) income	0.1	0.1		0.1	0.1
Other (expense) income, net	(0.1)	(0.1)		(0.1)	(0.1)
Income before income taxes	(0.4)	(0.3)		(1.0)	(0.5)
Income tax provision	2.3	2.5		7.1	11.6
Earnings in equity of subsidiaries	(26.5)	(22.3)		(81.1)	(98.8)
Net income	(24.6)	(20.1)		(75.0)	(87.7)
Comprehensive income	(26.2)	(21.2)		(79.0)	(90.6)
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 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	1.0	0.9		3.4	3.3
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	0.0
Total selling, general, administrative, research and development	1.0	0.9		3.4	3.3
Goodwill impairment				0.0
Other operating charges, net		0.0			0.0
Total costs and expenses	1.0	0.9		3.4	3.3
Operating income	(1.0)	(0.9)		(3.4)	(3.3)
Other (expense) income:
Interest (expense) income	(5.0)	(5.7)		(15.3)	(15.9)
Other (expense) income, net	0.0	(0.1)		0.0	(11.1)
Income before income taxes	(6.0)	(6.7)		(18.7)	(30.3)
Income tax provision	0.0	0.0		0.0	0.0
Earnings in equity of subsidiaries	25.9	21.6		79.3	97.5
Net income	19.9	14.9		60.6	67.2
Comprehensive income	21.5	16.0		64.6	70.1
Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	325.9	313.9		1,019.7	976.9
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	261.6	250.0		805.8	753.1
Lower of cost or market inventory write-down					4.9
Unrealized gain on derivative instruments	(10.8)	(2.0)		(14.0)	(16.9)
Depreciation and amortization	9.7	8.5		27.7	25.2
Selling, general, administrative, research and development	23.5	24.0		67.2	71.4
Net periodic postretirement benefit cost relating to Salaried VEBA	1.2	0.8		3.4	2.5
Gain on removal of Union VEBA net assets	0.5			(0.8)	(0.1)
Total selling, general, administrative, research and development	25.2	24.8		69.8	73.8
Goodwill impairment				18.4
Other operating charges, net		2.7			2.8
Total costs and expenses	285.7	284.0		907.7	842.9
Operating income	40.2	29.9		112.0	134.0
Other (expense) income:
Interest (expense) income	(0.4)	0.1		(1.2)	1.1
Other (expense) income, net	1.3	0.1		2.7	0.6
Income before income taxes	41.1	30.1		113.5	135.7
Income tax provision	(18.0)	(11.6)		(43.0)	(51.1)
Earnings in equity of subsidiaries	0.6	0.7		1.8	1.3
Net income	23.7	19.2		72.3	85.9
Comprehensive income	25.3	20.3		76.3	88.7
Non-Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	26.3	26.6		85.4	80.6
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	24.0	23.7		75.0	70.3
Lower of cost or market inventory write-down					0.0
Unrealized gain on derivative instruments	0.0	0.0		0.0	0.0
Depreciation and amortization	0.5	0.5		1.6	1.5
Selling, general, administrative, research and development	0.8	1.3		5.7	6.5
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	0.0
Total selling, general, administrative, research and development	0.8	1.3		5.7	6.5
Goodwill impairment				0.0
Other operating charges, net		0.0			0.0
Total costs and expenses	25.3	25.5		82.3	78.3
Operating income	1.0	1.1		3.1	2.3
Other (expense) income:
Interest (expense) income	0.0	0.0		0.0	0.0
Other (expense) income, net	0.3	0.1		0.5	0.2
Income before income taxes	1.3	1.2		3.6	2.5
Income tax provision	(0.4)	(0.3)		(0.9)	(0.7)
Earnings in equity of subsidiaries	0.0	0.0		0.0	0.0
Net income	0.9	0.9		2.7	1.8
Comprehensive income	$ 0.9	$ 0.9		$ 2.7	$ 1.9