Employee Benefits, Net Periodic Benefit Costs and Charges Relating To Other Benefit Plans(Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income	[1]	$ 2.8	$ (23.5)	$ (22.0)
Total		505.2	(14.4)	(12.9)
Fabricated Products
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Deferred Compensation Arrangement with Individual, Compensation Expense		0.1	0.2	0.3
Defined contribution plans		7.8	7.3	7.2
Total		8.3	7.8	8.0
All Other
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Deferred Compensation Arrangement with Individual, Compensation Expense		0.3	0.7	0.9
Defined contribution plans		0.8	0.8	0.7
Total		496.9	(22.2)	(20.9)
Canadian pension plan | Fabricated Products
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income		0.4	0.3	0.5
VEBAs | All Other
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income		$ 2.4	$ (23.7)	$ (22.5)

[1] See Note 6 for the impact of removing the Union VEBA (defined in Note 6) net assets.