Income Tax Matters, Components of Deferred Tax Assets and Liabilities Table (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets:
Loss and credit carryforwards	$ 48.7	$ 48.7
Salaried VEBA (see Note 5)	8.7	8.0
Other assets	30.1	27.2
Leased asset	7.1	0.0
Inventories	9.4	20.0
Valuation allowances	(9.9)	(8.4)
Total deferred income tax assets	94.1	95.5
Deferred income tax liabilities:
Property, plant and equipment	(78.5)	(62.0)
Leased liability	(6.3)	0.0
Undistributed foreign earnings	(2.0)	(1.8)
Total deferred income tax liabilities	(86.8)	(63.8)
Net deferred income tax assets	7.3	31.7
Net deferred income tax assets, long term	11.8	35.9
Deferred tax liability, long term	$ (4.5)	$ (4.2)