Employee Benefits, Net Periodic Benefit Costs and Charges Relating To Other Benefit Plans(Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income	[1]	$ 3.7	$ 2.8	$ (23.5)
Total		18.1	509.6	(10.4)
Fabricated Products
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Deferred Compensation Arrangement with Individual, Compensation Expense		0.2	0.1	0.2
Defined contribution plans		8.1	7.8	7.3
Total		13.3	12.7	11.8
All Other
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Deferred Compensation Arrangement with Individual, Compensation Expense		0.7	0.3	0.7
Defined contribution plans		0.8	0.8	0.8
Total		4.8	496.9	(22.2)
Canadian pension plan | Fabricated Products
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income		0.3	0.4	0.3
VEBAs | All Other
Net Periodic Benefit Costs and Charges Relating to Other Benefit Plans
Non-cash net periodic benefit income		$ 3.4	$ 2.4	$ (23.7)

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