Income Tax Matters, Components of Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Deferred income tax assets:
Loss and credit carryforwards	$ 275.4		$ 321.8
VEBAs (see Note 6)	5.1		6.1
Other assets	35.0		34.4
Inventories and other	21.5		2.5
Valuation allowances	(19.2)		(19.9)
Total deferred income tax assets	317.8		344.9
Deferred income tax liabilities:
Property, plant and equipment	(74.1)		(73.0)
VEBAs (see Note 6)	(120.6)		(152.4)
Inventories	(6.7)		(14.9)
Total deferred income tax liabilities	(201.4)		(240.3)
Net deferred income tax assets	116.4	[1]	104.6	[1]
Net deferred income tax assets, current			36.7
Net deferred income tax assets, long term	30.9		69.1
Deferred tax liability, long term	$ (0.9)		$ (1.2)

[1] Of the total net deferred income tax assets of $116.4, $86.4 was included in Prepaid expenses and other current assets, $30.9 was presented as Deferred tax assets, net and $0.9 was presented as Deferred tax liabilities on the Consolidated Balance Sheet as of December 31, 2014. Of the total net deferred income tax assets of $104.6, $36.7 was included in Prepaid expenses and other current assets and $69.1 was presented as Deferred tax assets, net and $1.2 was presented as Deferred tax liabilities on the Consolidated Balance Sheet as of December 31, 2013.