Employee Benefits, Net Periodic Benefit Costs and Charges Relating To All Other Employee Benefit Plans(Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Salaried VEBA:
Total net periodic postretirement benefit cost relating to Salaried VEBA	$ 0.8	$ 0.6	$ 2.5	$ 1.8
(Gain) loss on removal of Union VEBA net assets	0.0	(2.9)	(0.1)	490.9
Total VEBAs	0.8	(2.3)	2.4	492.7
Deferred compensation plan	0.5	(0.4)	0.8	0.1
Defined contribution plans	1.7	1.4	7.4	7.1
Multiemployer pension plans	1.2	1.1	3.5	2.9
Charges Relating To Other Benefit Plans	3.4	2.1	11.7	10.1
Total other employee benefit plans	4.2	(0.2)	14.1	502.8
Fabricated Products
Salaried VEBA:
Total other employee benefit plans	2.9	2.4	10.4	9.4
All Other
Salaried VEBA:
Total other employee benefit plans	1.3	(2.6)	3.7	493.4
VEBAs
Salaried VEBA:
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.7	0.7	2.2	2.1
Expected return on plan assets	(1.0)	(1.1)	(3.0)	(3.3)
Amortization of prior service cost	1.0	0.7	3.0	2.2
Amortization of net actuarial loss	0.1	0.3	0.3	0.8
Total net periodic postretirement benefit cost relating to Salaried VEBA	0.8	0.6	2.5	1.8
(Gain) loss on removal of Union VEBA net assets	$ 0.0	$ (2.9)	$ (0.1)	$ 490.9