Income Tax Matters, Components of Deferred Tax Assets and Liabilities Table (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets:
Loss and credit carryforwards	$ 48.7	$ 98.7
Salaried VEBA (see Note 4)	8.0	11.6
Other assets	27.2	21.0
Inventories	20.0	9.3
Valuation allowances	(8.4)	(13.0)
Total deferred income tax assets	95.5	127.6
Deferred income tax liabilities:
Property, plant and equipment	(62.0)	(57.7)
Undistributed foreign earnings	(1.8)	(2.2)
Total deferred income tax liabilities	(63.8)	(59.9)
Net deferred income tax assets	31.7	67.7
Net deferred income tax assets, long term	35.9	72.0
Deferred tax liability, long term	$ (4.2)	$ (4.3)