Employee Benefits, Net Periodic Benefit Costs and Charges Relating To Other Benefit Plans(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income	$ 4.8	$ 3.7	$ 2.8
Total	20.1	18.1	509.6
Fabricated Products
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Deferred Compensation Arrangement with Individual, Compensation Expense	0.4	0.2	0.1
Defined contribution plans	8.1	8.1	7.8
Total	13.4	13.3	12.7
All Other
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Deferred Compensation Arrangement with Individual, Compensation Expense	1.4	0.7	0.3
Defined contribution plans	0.8	0.8	0.8
Total	6.7	4.8	496.9
VEBAs | All Other
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income	$ 4.5	$ 3.4	$ 2.4