Employee Benefits Employee Benefits, Defined Benefit Plans Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued Annual Veba Contribution		$ 15.7	$ 20.0
Long-term portion of contingent contribution to Union VEBA		0.0	12.8
Defined Benefit Plan, Fair Value of Plan Assets		72.3	69.6
(Gain) loss on removal of Union VEBA net assets – Note 4		0.0	(0.1)	$ 493.4
Union VEBA
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued Annual Veba Contribution		12.8	17.1
Loss on settlement of Union VEBA - net of tax	$ 307.8
Income tax benefit on removal of Union VEBA net assets	$ 184.4
Salaried VEBA
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued Annual Veba Contribution		2.9	2.9
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year		5.4
Defined Benefit Plan, Expected Amortization, Next Fiscal Year		6.2
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		0.8
VEBAs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		90.0	86.8	77.9
Defined Benefit Plan, Fair Value of Plan Assets		58.1	58.2	58.9
Salaried and certain hourly employee | Canadian pension plan | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated annual contribution to pension and other postretirement benefit plans		2.9
Canadian pension plan | Canadian pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		8.5	7.0	6.1
Defined Benefit Plan, Fair Value of Plan Assets		7.3	6.1	$ 5.7
Defined Benefit Plan, Accumulated Benefit Obligation		7.9	$ 6.4
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 0.5
London Ontario Facility | Canadian pension plan | Canadian pension plan | Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations		33.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		30.00%
London Ontario Facility | Canadian pension plan | Canadian pension plan | Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations		63.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		65.00%