Segment Information, Financial Information by Operating Segment Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Net sales:
Net Sales	$ 343.2	$ 371.7
Segment operating income (loss):
Operating income (loss)	44.8	(458.6)
Interest expense	(3.7)	(9.8)
Other (expense) income, net	0.3	0.4
Income (loss) before income taxes	41.4	(468.0)
Depreciation and amortization:
Depreciation and amortization	8.7	8.0
Capital expenditures:
Capital expenditures	25.9	11.3
Assets:
Assets	1,236.6		$ 1,247.6
Unrealized Gain (Loss) on Derivatives	4.0	(4.5)
Non-cash defined benefit net periodic benefit cost relating to Salaried VEBA	0.8	0.6
(Gain) loss on removal of Union VEBA net assets	(0.1)	492.2
Fabricated Products
Net sales:
Net Sales	343.2	371.7
Segment operating income (loss):
Operating income (loss)	57.9	44.9
Depreciation and amortization:
Depreciation and amortization	8.6	7.9
Capital expenditures:
Capital expenditures	25.8	11.2
Assets:
Assets	932.5		904.7
Unrealized Gain (Loss) on Derivatives	4.0	(4.5)
All Other
Segment operating income (loss):
Operating income (loss)	(13.1)	(503.5)
Depreciation and amortization:
Depreciation and amortization	0.1	0.1
Capital expenditures:
Capital expenditures	0.1	0.1
Assets:
Assets	304.1		$ 342.9
VEBAs
Assets:
Non-cash defined benefit net periodic benefit cost relating to Salaried VEBA	0.8	0.6
(Gain) loss on removal of Union VEBA net assets	$ (0.1)	$ 492.2