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Employee Benefits Employee Benefits, Defined Benefit Plans Narrative (Details) | 3 Months Ended | 12 Months Ended |
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Mar. 31, 2015 USD ($) | Dec. 31, 2016 USD ($) trustrees | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Mar. 31, 2016 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Accrued Annual Veba Contribution |  | $ 20,000,000 | $ 19,600,000 |  |
Long-term portion of contingent contribution to Union VEBA |  | 12,800,000 | 29,900,000 |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 69,600,000 | 69,100,000 |  |
(Gain) loss on removal of Union VEBA net assets – Note 6 |  | (100,000) | 493,400,000 | $ 0 |
Canadian pension plan |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Defined Benefit Plan, Benefit Obligation |  | 7,000,000 | 6,100,000 | 7,000,000 |
Defined Benefit Plan, Fair Value of Plan Assets |  | 6,100,000 | 5,700,000 | 6,300,000 |
Defined Benefit Plan, Accumulated Benefit Obligation |  | 6,400,000 | 5,400,000 |  |
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year |  | $ 400,000 |  |  |
Union VEBA |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Number of Trustees | trustrees |  | 4 |  |  |
Percent allocation of total contribution between VEBAs |  | 85.50% |  |  |
Accrued Annual Veba Contribution |  | $ 17,100,000 | 16,800,000 |  | $ 16,700,000
Long-term portion of contingent contribution to Union VEBA |  | $ 12,800,000 |  |  |
Accrued Veba contingent contribution - total | $ 46,700,000 |  |  |  |
Loss on settlement of Union VEBA - net of tax | 307,800,000 |  |  |  |
Income tax benefit on removal of Union VEBA net assets | $ 184,400,000 |  |  |  |
Salaried VEBA |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Percent allocation of total contribution between VEBAs |  | 14.50% |  |  |
Accrued Annual Veba Contribution |  | $ 2,900,000 | 2,800,000 |  |
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit) |  | 4,000,000 |  |  |
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year |  | 4,500,000 |  |  |
Defined Benefit Plan, Future Amortization of Gain (Loss) |  | 500,000 |  |  |
VEBAs |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Cash flow in determining VEBA obligation |  | 20,000,000 |  |  |
Minimum liquidity requirement in determining VEBA obligation |  | 50,000,000 |  |  |
Defined Benefit Plan, Benefit Obligation |  | 86,800,000 | 77,900,000 | 470,900,000 |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 58,200,000 | $ 58,900,000 | $ 793,800,000 |
Fixed Income Securities | London Ontario Facility | Canadian pension plan |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Defined Benefit Plan, Actual Plan Asset Allocations |  | 32.00% |  |  |
Defined Benefit Plan, Target Plan Asset Allocations |  | 30.00% |  |  |
Equity Securities | London Ontario Facility | Canadian pension plan |  |  |  |  |
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, Target Plan Asset Allocations |  | 65.00% |  |  |
Company Appointed | Union VEBA |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Number of Trustees | trustrees |  | 2 |  |  |
Usw Appointed | Union VEBA |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Number of Trustees | trustrees |  | 2 |  |  |
Annual Cash Flows up to $20 Million | VEBAs |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Postretirement Medical Plan Contribution Obligation Percentage |  | 10.00% |  |  |
Annual Cash Flows in Excess of $20 Million | VEBAs |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Postretirement Medical Plan Contribution Obligation Percentage |  | 20.00% |  |  |
Maximum | VEBAs |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Postretirement Medical Plan Contribution Obligation |  | $ 20,000,000 |  |  |
Variable cash contribution | VEBAs |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Annual VEBA contribution paid |  | $ 19,500,000 |  |  |

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- Definition For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503844 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition 1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Projected Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6522206 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Postretirement Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503904 + Details
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