Ak Steel Holding (AKS) 10-K 15 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 13, 2019	Jun. 30, 2018
Entity Information [Line Items]
Entity Registrant Name	AK STEEL HOLDING CORPORATION
Entity Central Index Key	918,160
Trading Symbol	AKS
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Small Business	false
Amendment Flag	false
Entity Common Stock, Shares Outstanding		316,308,531
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 1,359,812,849

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net sales	$ 1,677.1	$ 1,735.6	$ 1,746.6	$ 1,658.9	$ 1,495.6	$ 1,494.3	$ 1,557.2	$ 1,533.4	$ 6,818.2	$ 6,080.5	$ 5,882.5
Cost of products sold (exclusive of items shown separately below)									5,911	5,253.1	5,099.7
Selling and administrative expenses									322.6	284.9	279.1
Depreciation									220.2	226	216.6
Charge (credit) for termination of pellet agreement and related transportation costs									0	(19.3)	69.5
Asset impairment charge									0	75.6	0
Total operating costs									6,453.8	5,820.3	5,664.9
Operating profit	86.5	114.8	99.5	63.6	(52.3)	66.3	116.5	129.7	364.4	260.2	217.6
Interest expense									151.6	152.3	163.9
Pension and OPEB (income) expense									(19.2)	(71.9)	16.5
Other (income) expense									(5.9)	17.1	4.9
Income before income taxes									237.9	162.7	32.3
Income tax expense (benefit)									(6.2)	(2.2)	(16.9)
Net income									244.1	164.9	49.2
Less: Net income attributable to noncontrolling interests									58.1	61.4	66
Net income (loss) attributable to AK Steel Holding Corporation	$ 33.5	$ 67.2	$ 56.6	$ 28.7	$ (80.4)	$ 22.3	$ 77.2	$ 84.4	$ 186	$ 103.5	$ (16.8)
Basic and diluted earnings per share:
Earnings Per Share, Basic					$ (0.26)	$ 0.07	$ 0.25	$ 0.27	$ 0.59	$ 0.33	$ (0.07)
Earnings Per Share, Diluted					$ (0.26)	$ 0.07	$ 0.24	$ 0.26	$ 0.59	$ 0.32	$ (0.07)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income	$ 244.1	$ 164.9	$ 49.2
Other comprehensive income, before tax:
Foreign currency translation gain (loss)	(1.7)	4.7	(1.5)
Cash flow hedges:
Gains (losses) arising in period	(5.6)	(11.5)	56.1
Reclassification of losses (gains) to net income	(10.3)	(6.1)	39.1
Pension and OPEB plans:
Prior service credit (cost) arising in period	11.1	4.7	(8.3)
Gains (losses) arising in period	(63.6)	94.2	11.6
Reclassification of prior service cost (credits) included in net income	(9.8)	(53.8)	(54.8)
Reclassification of losses (gains) included in net income	29.3	6.3	97.9
Other comprehensive income (loss), before tax	(50.6)	38.5	140.1
Income tax expense in other comprehensive income	0	0	15.5
Other comprehensive income (loss)	(50.6)	38.5	124.6
Comprehensive income	193.5	203.4	173.8
Less: Comprehensive income attributable to noncontrolling interests	58.1	61.4	66
Comprehensive income attributable to AK Steel Holding Corporation	$ 135.4	$ 142	$ 107.8

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 48.6	$ 38
Accounts receivable, net	635.8	517.8
Inventory	1,419.9	1,385
Other current assets	97	130.3
Total current assets	2,201.3	2,071.1
Property, plant and equipment	6,969.2	6,831.8
Accumulated depreciation	(5,057.6)	(4,845.6)
Property, plant and equipment, net	1,911.6	1,986.2
Other non-current assets:
Goodwill and intangible assets	298.9	306.7
Other non-current assets	103.9	110.8
TOTAL ASSETS	4,515.7	4,474.8
Current liabilities:
Accounts payable	801	690.4
Accrued liabilities	288.9	270.5
Current portion of pension and other postretirement benefit obligations	38.7	40.1
Total current liabilities	1,128.6	1,001
Non-current liabilities:
Long-term debt	1,993.7	2,110.1
Pension and other postretirement benefit obligations	829.9	894.2
Other non-current liabilities	134	168.9
TOTAL LIABILITIES	4,086.2	4,174.2
Equity:
Common stock, authorized 450,000,000 shares of $.01 par value each; issued 316,595,613 and 315,782,764 shares in 2018 and 2017; outstanding 315,535,765 and 314,884,569 shares in 2018 and 2017	3.2	3.2
Additional paid-in capital	2,894.9	2,884.8
Treasury stock, common shares at cost, 1,059,848 and 898,195 shares in 2018 and 2017	(6.4)	(5.4)
Accumulated deficit	(2,691.8)	(2,877)
Accumulated other comprehensive loss	(100)	(50.2)
Total stockholders’ equity (deficit)	99.9	(44.6)
Noncontrolling interests	329.6	345.2
TOTAL EQUITY	429.5	300.6
TOTAL LIABILITIES AND EQUITY	4,515.7	4,474.8
SunCoke Middletown [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets:
Cash and cash equivalents	1.1	0.1
Inventory	21.1	18.4
Property, plant and equipment	427.8	425.9
Accumulated depreciation	(106.9)	(88.6)
Other non-current assets:
Other assets (liabilities), net	(1.2)	(1)
Current liabilities:
Accounts payable	13.7	11.3
Equity:
Noncontrolling interests	328.2	343.5
Other Variable Interest Entities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Current assets:
Cash and cash equivalents	0.5	0.7
Property, plant and equipment	11.7	11.7
Accumulated depreciation	(9.8)	(9.6)
Other non-current assets:
Other assets (liabilities), net	0.5	0.8
Equity:
Noncontrolling interests	$ 1.4	$ 1.7

CONSOLIDATED BALANCE SHEETS Par

CONSOLIDATED BALANCE SHEETS Parentheticals - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, shares authorized	450,000,000	450,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued	316,595,613	315,782,764
Common stock, shares outstanding	315,535,765	314,884,569
Treasury stock, shares	1,059,848	898,195

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 244.1	$ 164.9	$ 49.2
Adjustments to reconcile net income to cash flows from operating activities:
Depreciation	220.2	226	216.6
Amortization	32	24.1	18.4
Asset impairment charge	0	75.6	0
Charge (credit) for transportation costs affected by termination of pellet agreement	0	(19.3)	32.9
Deferred income taxes	(8)	(9)	(4.1)
Contributions to pension trust	(49.9)	(44.1)	0
Pension and OPEB (income) expense	(11.6)	(64.4)	24.3
(Gains) losses on retirement of debt	(2)	21.3	9.2
Mark-to-market (gains) losses on derivative contracts	(8.9)	(45.7)	1.2
Other operating items, net	2.4	20.1	3
Changes in assets and liabilities, net of effect of acquired business:
Accounts receivable	(125)	(34.4)	0.1
Inventory	(34.8)	(116.7)	129.6
Accounts payable and other current liabilities	119.6	46.2	(143.2)
Other assets	52.9	(6.5)	40.9
Other pension payments	(1)	(1.1)	(33)
OPEB payments	(35.6)	(39.6)	(34.4)
Other liabilities	(29.7)	1.4	(6.1)
Net cash flows from operating activities	364.7	198.8	304.6
Cash flows from investing activities:
Capital investments	(152)	(152.5)	(127.6)
Investment in acquired business, net of cash acquired	0	(360.4)	0
Other investing items, net	0.1	4.2	2.3
Net cash flows from investing activities	(151.9)	(508.7)	(125.3)
Cash flows from financing activities:
Net borrowings (repayments) under credit facility	(115)	450	(550)
Proceeds from issuance of long-term debt	0	680	380
Redemption of long-term debt	(12.6)	(848.4)	(392.8)
Proceeds from issuance of common stock	0	0	600.4
Debt issuance costs	0	(25.3)	(20.4)
SunCoke Middletown distributions to noncontrolling interest owners	(73.7)	(79.1)	(85.1)
Other financing items, net	(0.9)	(2.5)	5.2
Net cash flows from financing activities	(202.2)	174.7	(62.7)
Net increase (decrease) in cash and cash equivalents	10.6	(135.2)	116.6
Cash and cash equivalents, beginning of year	38	173.2	56.6
Cash and cash equivalents, end of year	48.6	38	173.2
Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Adjustments to reconcile net income to cash flows from operating activities:
Depreciation	201.6	209.8	201.7
SunCoke Middletown [Member]
Adjustments to reconcile net income to cash flows from operating activities:
Depreciation	18.6	16.2	14.9
Cash flows from financing activities:
SunCoke Middletown distributions to noncontrolling interest owners	$ (73.7)	$ (79.1)	$ (85.1)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adopting new hedging standard	$ 0				$ 0	$ 0
Balance at beginning of period at Dec. 31, 2015		$ 1.8	$ 2,266.8	$ (2)	(2,963.7)	(213.3)	$ 382
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock		1.3	599.1
Share-based compensation		0
Share-based compensation			5.4
Stock options exercised			5.4
Exchangeable notes exchange feature			(21.3)
Purchase of treasury stock				(0.4)
Net income attributable to AK Steel Holding Corporation	(16.8)				(16.8)
Change in accumulated other comprehensive loss	124.6					124.6
Net income attributable to noncontrolling interests	66						66
Net distributions to noncontrolling interests							(85.1)
Balance at end of period at Dec. 31, 2016	149.8	3.1	2,855.4	(2.4)	(2,980.5)	(88.7)	362.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adopting new hedging standard	0				0	0
Issuance of common stock		0	0
Share-based compensation		0.1
Share-based compensation			7.6
Stock options exercised			0.5
Exchangeable notes exchange feature			21.3
Purchase of treasury stock				(3)
Net income attributable to AK Steel Holding Corporation	103.5				103.5
Change in accumulated other comprehensive loss	38.5					38.5
Net income attributable to noncontrolling interests	61.4						61.4
Net distributions to noncontrolling interests							(79.1)
Balance at end of period at Dec. 31, 2017	300.6	3.2	2,884.8	(5.4)	(2,877)	(50.2)	345.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adopting new hedging standard	0.8				(0.8)	0.8
Issuance of common stock		0	0
Share-based compensation		0
Share-based compensation			9.2
Stock options exercised			0.9
Exchangeable notes exchange feature			0
Purchase of treasury stock				(1)
Net income attributable to AK Steel Holding Corporation	186				186
Change in accumulated other comprehensive loss	(50.6)					(50.6)
Net income attributable to noncontrolling interests	58.1						58.1
Net distributions to noncontrolling interests							(73.7)
Balance at end of period at Dec. 31, 2018	$ 429.5	$ 3.2	$ 2,894.9	$ (6.4)	$ (2,691.8)	$ (100)	$ 329.6

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation— These financial statements consolidate the operations and accounts of AK Steel Holding Corporation (“AK Holding”), its wholly owned subsidiary AK Steel Corporation (“AK Steel”), all subsidiaries in which AK Holding has a controlling interest, and two variable interest entities for which AK Steel is the primary beneficiary. Unless the context indicates otherwise, references to “we,” “us” and “our” refer to AK Holding and its subsidiaries. We also operate Mexican and European trading companies that buy and sell steel and steel products and other materials. We manage operations on a consolidated, integrated basis so that we can use the most appropriate equipment and facilities for the production of a product, regardless of product line. Therefore, we conclude that we operate in a single business segment. All intercompany transactions and balances have been eliminated. Use of Estimates— The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires the use of estimates and assumptions that affect the amounts reported. We base these estimates on historical experience and information available to us about current events and actions we may take in the future. Estimates and assumptions affect significant items that include the carrying value of long-lived assets, including investments and goodwill; valuation allowances for receivables, inventories and deferred income tax assets; legal and environmental liabilities; workers compensation and asbestos liabilities; share-based compensation; and assets and obligations of employee benefit plans. There can be no assurance that actual results will not differ from these estimates. Revenue Recognition— We generate our revenue through product sales, and shipping terms generally indicate when we have fulfilled our performance obligations and passed control of products to our customer. Our revenue transactions consist of a single performance obligation to transfer promised goods. We have contracts with a substantial portion of our customers. These contracts usually define the mechanism for determining the sales price, but the contracts do not impose a specific quantity on either party. Quantities to be delivered to the customer are determined at a point near the date of delivery through purchase orders or other written instructions we receive from the customer. Spot market sales are made through purchase orders or other written instructions. We recognize revenue when we have fulfilled a performance obligation, which is typically when we have shipped products at the customer’s instructions. For sales with shipping terms that transfer title and control at the destination point, we recognize revenue when the customer receives the goods and our performance obligation is complete. For sales with shipping terms that transfer title and control at the shipping point with us bearing responsibility for freight costs to the destination, we determine that we have fulfilled a single performance obligation and recognize revenue when we ship the goods. For our tooling solutions, we record progress payments that we receive from a customer as accrued liabilities until we recognize the revenue when the customer provides written acceptance that our performance obligation has been fulfilled. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring product. We reduce the amount of revenue recognized for estimated returns and other customer credits, such as discounts and volume rebates, based on the expected value to be realized. Payment terms are consistent with terms standard to the markets we serve. We maintain an allowance for doubtful accounts for the loss that would be incurred if a customer is unable to pay amounts due. We initially estimate the allowance required at the time of revenue recognition based on historical experience and make changes to the allowance based on various factors, including changes in the customer’s financial condition or payment patterns. Sales taxes collected from customers are excluded from revenues. Cost of Products Sold— Cost of products sold consists primarily of raw materials, energy costs, supplies consumed in the manufacturing process, manufacturing labor, contract labor and direct overhead expense necessary to manufacture the finished steel product, as well as distribution and warehousing costs. Our share of the income (loss) of investments in associated companies accounted for under the equity method is included in costs of products sold since these operations are integrated with our overall steelmaking operations. Share-Based Compensation— Compensation costs for stock awards granted under our Stock Incentive Plan are recognized over their vesting period using the straight-line method. We estimate stock award forfeitures expected to occur to determine the compensation cost we recognize each period. Legal Fees— Legal fees associated with litigation and similar proceedings that are not expected to provide a benefit in future periods are expensed as incurred. Legal fees associated with activities that are expected to provide a benefit in future periods, such as costs associated with the issuance of debt, are capitalized as incurred. Income Taxes— Interest and penalties from uncertain tax positions are included in income tax expense. Earnings per Share— Earnings per share is calculated using the “two-class” method. Under the “two-class” method, undistributed earnings are allocated to both common shares and participating securities. We divide the sum of distributed earnings to common stockholders and undistributed earnings allocated to common stockholders by the weighted-average number of common shares outstanding during the period. The restricted stock granted by AK Holding is entitled to non-forfeitable dividends before vesting and meets the criteria of a participating security. Cash Equivalents— Cash equivalents include short-term, highly liquid investments that are readily convertible to known amounts of cash and have an original maturity of three months or less. Inventory— Inventories are valued at the lower of cost or net realizable value. We measure the cost of inventories using the average cost method. See Note 2 for information on the change to the average cost method effective January 1, 2018. Property, Plant and Equipment— Plant and equipment are depreciated under the straight-line method over their estimated lives. Estimated lives are as follows: land improvements over 20 years , leaseholds over the life of the related operating lease term, buildings over 40 years and machinery and equipment over two to 20 years . The estimated weighted-average life of our machinery and equipment is 13 years at the end of 2018 . Amortization expense for assets recorded under capital leases is included in depreciation expense. Costs incurred to develop coal mines are capitalized when incurred. We use the units-of-production method utilizing only proven and probable reserves in the depletion base to compute the depletion of coal reserves and mine development costs. We expense costs for major maintenance activities at our operating facilities when the activities occur. We review the carrying value of long-lived assets to be held and used and long-lived assets to be disposed of when events and circumstances warrant such a review. If the carrying value of a long-lived asset exceeds its fair value, an impairment has occurred and a loss is recognized based on the amount by which the carrying value exceeds the fair value, less cost to dispose, for assets to be sold or abandoned. We determine fair value by using quoted market prices, estimates based on prices of similar assets or anticipated cash flows discounted at a rate commensurate with risk. Investments— Investments in associated companies are accounted for under the equity method. We review investments for impairment when circumstances indicate that a loss in value below its carrying amount is other than temporary. Goodwill and Intangible Assets— Goodwill relates to our tubular and Precision Partners’ businesses. Intangible assets are recorded at cost, and those with finite lives are amortized over their estimated useful lives. We review goodwill for potential impairment at least annually on October 1 each year and whenever events or circumstances make it more likely than not that impairment may have occurred. Considering operating results and the estimated fair value of the businesses, the most recent annual goodwill impairment tests indicated that the fair value of each of our business reporting units was in excess of its carrying value. No goodwill impairment was recorded as a result of the annual impairment tests in the past three years. Debt Issuance Costs— Debt issuance costs for the revolving credit facility are included in other non-current assets and all other debt issuance costs reduce the carrying amount of long-term debt. Pension and Other Postretirement Benefits— We recognize, as of a measurement date, any unrecognized actuarial net gains or losses that exceed 10% of the larger of the projected benefit obligations or the plan assets, defined as the “corridor.” Amounts inside the corridor are amortized over the plan participants’ life expectancy. We determine the expected return on assets using the fair value of plan assets. Concentrations of Credit Risk— We are primarily a producer of carbon, stainless and electrical steels and steel products, which are sold to a number of markets, including automotive, infrastructure and manufacturing, and distributors and converters. We had two customers that accounted for 11% and 10% of net sales in 2018 , one customer that accounted for 12% of net sales in 2017 , and two customers that accounted for 12% and 11% of net sales in 2016 . Approximately 52% and 55% of accounts receivable outstanding at December 31, 2018 and 2017 , are due from businesses associated with the U.S. automotive industry, including 13% of receivables due from one automotive customer as of December 31, 2018 , and 18% due from one automotive customer as of December 31, 2017 . Labor Agreements— At December 31, 2018 , we employed approximately 9,500 people, of which approximately 5,700 are represented by labor unions under various agreements that expire between 2019 and 2021 . In March 2018, members of the International Association of Machinists and Aerospace Workers, Local 1943 , ratified a labor agreement covering approximately 1,760 production employees at Middletown Works. The new agreement expires March 15, 2020 . With our January 28, 2019, announcement of plans to permanently close the Ashland Works facility by the end of 2019, over the coming months we expect to engage in negotiations with the United Steelworkers, Local 1865 , regarding the plant closure in accordance with applicable law and the terms and conditions of the labor agreement. The labor agreement, with an original expiration date of September 1, 2018 , is by mutual agreement being extended on a rolling 60-day basis, subject to further notification of termination by either party. Other agreements that expire within the next twelve months include an agreement with the United Steelworkers, Local 1190 , which governs approximately 230 production employees at Mountain State Carbon LLC, is scheduled to expire on March 1, 2019 . An agreement with the United Auto Workers, Local 3303 , which governs approximately 1,170 production employees at Butler Works, was originally scheduled to expire on April 1, 2019 . By mutual agreement, the labor agreement has been extended and is now scheduled to expire on April 16, 2019 . An agreement with the United Auto Workers, Local 4104 , which governs approximately 100 production employees at Zanesville Works, is scheduled to expire on May 31, 2019 . An agreement with the United Auto Workers, Local 3462 , which governs approximately 300 production employees at Coshocton Works, is scheduled to expire on September 30, 2019 . Financial Instruments— We are a party to derivative instruments that are designated and qualify as hedges for accounting purposes. We may also use derivative instruments to which we do not apply hedge accounting treatment. Our objective in using these instruments is to limit operating cash flow exposure to fluctuations in the fair value of selected commodities and currencies. Fluctuations in the price of certain commodities we use in production processes may affect our income and cash flows. We have implemented raw material and energy surcharges for some contract customers. For certain commodities where such exposure exists, we may use cash-settled commodity price swaps, collars and purchase options, with a duration of up to two years , to hedge the price of a portion of our natural gas, iron ore, electricity, zinc and nickel requirements. We may designate some of these instruments as cash flow hedges and changes in their fair value and settlements are recorded in accumulated other comprehensive income. We subsequently reclassify gains and losses from accumulated other comprehensive income to cost of products sold in the same period we recognize the earnings associated with the underlying transaction. The change in fair value for other instruments is immediately recorded in cost of products sold with the offset recorded as assets or liabilities. Exchange rate fluctuations affect a portion of revenues and operating costs that are denominated in foreign currencies, and we use currency forwards and options to reduce our exposure to these currency price fluctuations. These derivative contracts are entered into with durations up to three years . Contracts that sell euros have not been designated as hedges for accounting purposes and gains or losses are reported in earnings immediately in other income (expense). Contracts that purchase Canadian dollars are designated as hedges for accounting purposes, which requires us to record the gains and losses for the derivatives in accumulated other comprehensive income and reclassify them into cost of products sold in the same period we recognize costs for the associated underlying operations. We formally document all relationships between hedging instruments and hedged items, as well as risk management objectives and strategies for undertaking various hedge transactions. In this documentation, we specifically identify the asset, liability, firm commitment or forecasted transaction that has been designated as a hedged item, and state how the hedging instrument is expected to hedge the risks from that item. We formally measure effectiveness of hedging relationships both at the hedge inception and on an ongoing basis. We discontinue hedge accounting prospectively when we determine that the derivative is no longer effective in offsetting changes in the fair value or cash flows of a hedged item; when the derivative expires or is sold, terminated or exercised; when it is probable that the forecasted transaction will not occur; when a hedged firm commitment no longer meets the definition of a firm commitment; or when we determine that designation of the derivative as a hedge instrument is no longer appropriate. Our derivative contracts may contain collateral funding requirements. We have master netting arrangements with counterparties, giving us the right to offset amounts owed under the derivative instruments and the collateral. We do not offset derivative assets and liabilities or collateral on our consolidated balance sheets. Cash flows associated with purchasing and settling derivative contracts are classified as operating cash flows. Asbestos and Environmental Accruals— For a number of years, we have been remediating sites where hazardous materials may have been released, including sites no longer owned by us. In addition, a number of lawsuits alleging asbestos exposure have been filed and continue to be filed against us. We have established accruals for estimated probable costs from asbestos claim settlements and environmental investigation, monitoring and remediation. If the accruals are not adequate to meet future claims, operating results and cash flows may be negatively affected. Our accruals do not consider the potential for insurance recoveries, for which we have partial insurance coverage for some future asbestos claims. In addition, some existing insurance policies covering asbestos and environmental contingencies may serve to partially reduce future covered expenditures. Adoption of New Accounting Principles— On January 1, 2018, we adopted the following new accounting principles, both of which have been applied retrospectively to all periods presented. On January 1, 2018, we adopted Accounting Standards Update No. 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . Under this standard, the service cost component of periodic pension and other postretirement benefit expense is included in cost of products sold and selling and administrative expenses, consistent with our treatment of other employee compensation costs. The remainder of periodic pension and other postretirement benefit (income) expense of $(19.2) , $(71.9) and $16.5 for the years ended December 31, 2018, 2017 and 2016, is recorded separately in the consolidated statements of operations below operating profit. We have retrospectively applied the change in accounting principle to all periods presented. The adoption of this standard update had no other effect on our consolidated financial statements. On January 1, 2018, we changed our accounting method for valuing inventories to the average cost method for inventories previously valued using the last-in, first-out (LIFO) method. The effects of this change in accounting principle from LIFO to average cost have been retrospectively applied to all periods presented. See Note 2 for additional information. Other New Accounting Pronouncements Adopted— We adopted Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) , as of January 1, 2018, through the modified retrospective method applied to those contracts that were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018, are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with our historic accounting under ASC Topic 605. There was no adjustment required to adopt Topic 606 since our revenue recognition under Topic 606 is substantially the same as under Topic 605. In August 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities , to better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. Among other amendments, the update allows entities to designate the variability in cash flows attributable to changes in a contractually specified component stated in the contract as the hedged risk in a cash flow hedge of a forecasted purchase or sale of a nonfinancial asset. We adopted the standard update effective as of January 1, 2018, and have applied the new hedge guidance for certain hedges entered since adoption. The effect of adoption of the new guidance was not significant. In February 2018, FASB issued Accounting Standards Update 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted in December 2017. We early adopted this standard update as of December 31, 2018. We elected to not reclassify the income tax effects of the Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. Recent Accounting Pronouncements Not Yet Adopted— FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) , during the first quarter of 2016. Topic 842 requires entities to recognize lease assets and lease liabilities for substantially all leases, with the exception of short-term leases, and disclose key information about leasing arrangements for certain leases. We intend to recognize and measure leases beginning at the adoption date using a modified retrospective approach. Under the modified retrospective approach, we will not adjust our comparative period financial information or make the new lease disclosures for periods before the effective date. Topic 842 is effective for us beginning January 1, 2019. The new guidance provides a number of optional practical expedients in transition and we have determined to use certain of these practical expedients. We have designed new processes and controls, cataloged and entered our leases into a recently implemented software solution and evaluated our population of leased assets to assess the effect of the new guidance on our consolidated financial statements. We currently expect that the adoption of the standard will result in a material increase to the assets and liabilities on our consolidated balance sheets, but will not have a material effect on our results of operations or cash flows. We expect adoption of the standard will result in the recognition of additional lease assets and lease liabilities between $250.0 and $350.0 as of January 1, 2019. The range reflects our current best estimates as we are still evaluating whether to separate lease and non-lease components for certain asset types, particularly for leases embedded within service contracts. In June 2016, FASB issued Accounting Standards Update 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , to replace the incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. In connection with recognizing credit losses on receivables and other financial instruments, we will be required to use a forward-looking expected loss model rather than the incurred loss model. The new standard will be effective for us beginning January 1, 2020, with early adoption permitted beginning January 1, 2019. Adoption of this standard is through a cumulative-effect adjustment to retained earnings as of the effective date. We are currently evaluating the effect of this standard on our consolidated financial position and results of operations. Reclassifications—

Supplementary Financial Stateme

Supplementary Financial Statement Information (Notes)	12 Months Ended
	Dec. 31, 2018
Supplementary Financial Statement Information [Abstract]
Supplementary Financial Statement Information	Supplementary Financial Statement Information Revenue Net sales by market are presented below: 2018 2017 2016 Automotive $ 4,284.7 $ 3,951.5 $ 3,906.8 Infrastructure and Manufacturing 1,049.1 948.0 936.7 Distributors and Converters 1,484.4 1,181.0 1,039.0 Total $ 6,818.2 $ 6,080.5 $ 5,882.5 Net sales by product line are presented below: 2018 2017 2016 Carbon steel $ 4,409.1 $ 4,034.5 $ 4,014.5 Stainless and electrical steel 1,793.8 1,687.6 1,654.1 Tubular products, components and other 615.3 358.4 213.9 Total $ 6,818.2 $ 6,080.5 $ 5,882.5 We sell domestically to customers located primarily in the Midwestern and Eastern United States and to foreign customers, primarily in Canada, Mexico and Western Europe. Net sales to customers located outside the United States totaled $634.8 , $627.1 and $655.6 for 2018 , 2017 and 2016 . Research and Development Costs We conduct a broad range of research and development activities aimed at improving existing products and manufacturing processes and developing new products and processes. Research and development costs, which are recorded as cost of products sold when incurred, totaled $29.4 , $28.1 and $28.3 in 2018 , 2017 and 2016 . Allowance for Doubtful Accounts Changes in the allowance for doubtful accounts for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 Balance at beginning of year $ 6.8 $ 7.8 $ 6.0 Increase (decrease) in allowance 0.3 (1.0 ) 2.4 Receivables written off (0.5 ) — (0.6 ) Balance at end of year $ 6.6 $ 6.8 $ 7.8 Inventory Inventories as of December 31, 2018 and 2017 , consist of: 2018 2017 Finished and semi-finished $ 1,054.4 $ 996.8 Raw materials 365.5 388.2 Inventory $ 1,419.9 $ 1,385.0 Adoption of New Accounting Principle In the first quarter of 2018, we changed our accounting method for valuing certain inventories from the LIFO method to the average cost method. This method values inventory using average costs for materials and most recent production costs for labor and overhead. We believe that using the average cost method is preferable since it improves comparability with our peers, more closely tracks the physical flow of our inventory, better matches revenue with expenses and aligns with how we internally manage our business. The effects of the change in accounting principle from LIFO to average cost have been retrospectively applied to all periods presented. As a result of the retrospective application of the change in accounting principle, certain financial statement line items in our consolidated balance sheet as of December 31, 2017 and our consolidated statements of operations, comprehensive income and cash flows for years ended December 31, 2017 and 2016 were adjusted as follows: As Originally Reported Effect of Change As Adjusted Consolidated statement of operations for the year ended December 31, 2017: Cost of products sold (a) $ 5,365.2 $ (112.1 ) $ 5,253.1 Income tax expense (benefit) (17.0 ) 14.8 (2.2 ) Net income 67.6 97.3 164.9 Net income attributable to AK Steel Holding Corporation 6.2 97.3 103.5 Net income per share attributable to AK Steel Holding Corporation common stockholders: Basic $ 0.02 $ 0.31 $ 0.33 Diluted 0.02 0.30 0.32 Consolidated statement of comprehensive income for the year ended December 31, 2017: Cash flow hedges—Reclassification of losses (gains) to net income $ (12.5 ) $ 6.4 $ (6.1 ) Comprehensive income 91.1 112.3 203.4 Comprehensive income attributable to AK Steel Holding Corporation 29.7 112.3 142.0 Consolidated balance sheet as of December 31, 2017: Inventory $ 1,147.8 $ 237.2 $ 1,385.0 Other non-current assets 169.3 (58.5 ) 110.8 Other non-current liabilities 161.6 7.3 168.9 Accumulated deficit (3,058.6 ) 181.6 (2,877.0 ) Accumulated other comprehensive loss (40.0 ) (10.2 ) (50.2 ) Consolidated statement of cash flows for the year ended December 31, 2017: Net income $ 67.6 $ 97.3 $ 164.9 Deferred income taxes (15.2 ) 6.2 (9.0 ) Changes in working capital 1.8 (118.5 ) (116.7 ) Other operating items, net 5.1 15.0 20.1 Consolidated statement of operations for the year ended December 31, 2016: Cost of products sold (a) $ 5,070.6 $ 29.1 $ 5,099.7 Income tax expense (benefit) 3.2 (20.1 ) (16.9 ) Net income 58.2 (9.0 ) 49.2 Net income attributable to AK Steel Holding Corporation (7.8 ) (9.0 ) (16.8 ) Net income per share attributable to AK Steel Holding Corporation common stockholders: Basic $ (0.03 ) $ (0.04 ) $ (0.07 ) Diluted (0.03 ) (0.04 ) (0.07 ) Consolidated statement of comprehensive income for the year ended December 31, 2016: Cash flow hedges—Reclassification of losses (gains) to net income $ 27.2 $ 11.9 $ 39.1 Comprehensive income 181.9 (8.1 ) 173.8 As Originally Reported Effect of Change As Adjusted Comprehensive income attributable to AK Steel Holding Corporation 115.9 (8.1 ) 107.8 Consolidated statement of cash flows for the year ended December 31, 2016: Net income $ 58.2 $ (9.0 ) $ 49.2 Deferred income taxes 5.0 (9.1 ) (4.1 ) Changes in working capital 112.4 17.2 129.6 Other operating items, net 2.1 0.9 3.0 (a) Cost of products sold as originally reported reflects the change in presentation of pension and OPEB (income) expense further described in Note 1 . The following table shows the effects of the change in accounting principle from LIFO to average cost as of December 31, 2018 and for the year ended December 31, 2018 : As Computed under LIFO As Reported under Average Cost Effect of Change Consolidated statement of operations for the year ended December 31, 2018: Cost of products sold $ 5,966.7 $ 5,911.0 $ (55.7 ) Income tax expense (benefit) (19.4 ) (6.2 ) 13.2 Net income 201.6 244.1 42.5 Net income attributable to AK Steel Holding Corporation 143.5 186.0 42.5 Net income per share attributable to AK Steel Holding Corporation common stockholders: Basic $ 0.46 $ 0.59 $ 0.13 Diluted 0.45 0.59 0.14 Consolidated statement of comprehensive income for the year ended December 31, 2018: Comprehensive income $ 151.0 $ 193.5 $ 42.5 Comprehensive income attributable to AK Steel Holding Corporation 92.9 135.4 42.5 Consolidated balance sheet as of December 31, 2018: Inventory $ 1,128.7 $ 1,419.9 $ 291.2 Other non-current assets 180.9 103.9 (77.0 ) Other non-current liabilities 132.0 134.0 2.0 Accumulated deficit (2,915.9 ) (2,691.8 ) 224.1 Consolidated statement of cash flows for the year ended December 31, 2018: Net income $ 201.6 $ 244.1 $ 42.5 Deferred income taxes (21.2 ) (8.0 ) 13.2 Changes in working capital 66.7 12.7 (54.0 ) Other operating items, net 4.1 2.4 (1.7 ) Property, Plant and Equipment Property, plant and equipment as of December 31, 2018 and 2017 , consist of: 2018 2017 Land, land improvements and leaseholds $ 272.1 $ 275.3 Buildings 509.7 509.0 Machinery and equipment 6,061.6 5,958.2 Construction in progress 125.8 89.3 Total 6,969.2 6,831.8 Less accumulated depreciation (5,057.6 ) (4,845.6 ) Property, plant and equipment, net $ 1,911.6 $ 1,986.2 Interest on capital projects capitalized in 2018 , 2017 and 2016 was $1.6 , $1.9 and $3.1 . Asset retirement obligations were $8.5 and $7.8 at December 31, 2018 and 2017 . Goodwill and Intangible Assets Changes in goodwill for the years ended December 31, 2018 , 2017 and 2016 are presented below: 2018 2017 2016 Balance at beginning of year $ 253.8 $ 32.8 $ 32.8 Acquisition 1.2 221.0 — Balance at end of year $ 255.0 $ 253.8 $ 32.8 Intangible assets at December 31, 2018 and 2017 , consist of: Gross Amount Accumulated Amortization Net Amount As of December 31, 2018 Customer relationships $ 36.6 $ (7.4 ) $ 29.2 Technology 19.3 (4.6 ) 14.7 Other 1.0 (1.0 ) — Intangible assets $ 56.9 $ (13.0 ) $ 43.9 As of December 31, 2017 Customer relationships $ 36.6 $ (2.2 ) $ 34.4 Technology 19.3 (1.4 ) 17.9 Other 1.0 (0.4 ) 0.6 Intangible assets $ 56.9 $ (4.0 ) $ 52.9 Amortization expense related to intangible assets was $9.0 and $4.0 in 2018 and 2017 . Amortization expense is included in costs of products sold. The remaining average life of our intangible assets is 5.6 years for customer relationships and 4.6 years for technology. Estimated annual amortization expense for intangible assets over the next five years is $8.4 each year from 2019 through 2022 and $7.1 in 2023 . Other Non-current Assets Other non-current assets as of December 31, 2018 and 2017 , consist of: 2018 2017 Investments in affiliates $ 80.5 $ 77.5 Other 23.4 33.3 Other non-current assets $ 103.9 $ 110.8 Accrued Liabilities Accrued liabilities as of December 31, 2018 and 2017 , consist of: 2018 2017 Salaries, wages and benefits $ 127.8 $ 101.3 Interest 34.8 35.0 Other 126.3 134.2 Accrued liabilities $ 288.9 $ 270.5 Ashland Works Closure In January 2019, our Board of Directors approved and we announced that we intend to close our Ashland Works, including the previously idled blast furnace and steelmaking operations (“Ashland Works Hot End”) and a single hot dip galvanizing coating line that had remained operational, subject to negotiations with the labor union at that facility. Factors that influenced our decision to close Ashland Works included an uncertain global trade landscape influenced by shifting domestic and international political priorities, Ashland Works’ high cost of production, and continued intense competition from domestic and foreign steel competitors. These conditions directly impact our pricing, which in turn directly impacts our assessment of the demand forecasts for the markets we serve. Despite several successful trade actions, we continue to see a high level of carbon steel imports driven by global overcapacity, particularly in China. We also have seen significant capacity restarted or new capacity additions announced in the United States. In addition, we have recently concluded that we have sufficient coating capacity to meet our customers’ needs without using our coating operations at Ashland Works. We will continue to operate the Ashland Works coating line until the end of 2019 to allow us time to complete the transition of products to our other coating lines in the U.S. We expect to record a charge of approximately $80.0 during the first quarter of 2019, which includes approximately $20.0 for termination of certain take-or-pay supply agreements, approximately $30.0 for supplemental unemployment and other employee benefit costs, an estimated multiemployer plan withdrawal liability of $25.0 , and approximately $5.0 for other costs. The supplemental unemployment and other employee benefit costs are expected to be paid primarily in 2020 and 2021. With respect to the $80.0 charge, we expect to make cash payments of approximately $15.0 in 2019, $30.0 in 2020 and the remaining amount over several years thereafter. The actual multiemployer plan withdrawal liability will not be known until 2020 and is expected to be paid over a number of years. In addition to the $80.0 charge recorded in the first quarter of 2019, we expect to record expenses of approximately $14.0 over the full-year 2019, consisting of cash costs of approximately $10.0 related to closing the facility and $4.0 of accelerated depreciation related to the coating line fixed assets. These cash costs related to closing the facility will decline in future years and the accelerated depreciation expense will not be incurred beyond 2019. On-going costs for maintenance of the equipment, utilities and supplier obligations related to the idled Ashland Works Hot End were $20.0 , $21.2 , and $22.1 for the years ended December 31, 2018 , 2017 , and 2016 . In the fourth quarter of 2015, we temporarily idled the Ashland Works Hot End. We incurred charges of $28.1 in the fourth quarter of 2015, which included $22.2 for supplemental unemployment and other employee benefit costs and $5.9 for equipment idling, asset preservation and other costs. The supplemental unemployment and other employee benefit costs were recorded as accrued liabilities, and the activity for the years ended December 31, 2018 , 2017 , and 2016 was as follows: 2018 2017 2016 Balance at beginning of year $ 1.5 $ 6.2 $ 22.2 Payments (1.5 ) (5.3 ) (20.1 ) Additions to the reserve — 0.6 4.1 Balance at end of year $ — $ 1.5 $ 6.2 During 2017, we recognized a non-cash asset impairment charge of $75.6

Acquisition of Precision Partne

Acquisition of Precision Partners (Notes)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisition of Precision Partners	Acquisition of Precision Partners On August 4, 2017 , we acquired PPHC Holdings, LLC (“Precision Partners”), which provides advanced-engineered solutions, tool design and build, hot- and cold-stamped steel components and complex assemblies for the automotive market. Precision Partners is headquartered in Ontario, Canada and operates eight plants in Ontario, Alabama and Kentucky. We acquired Precision Partners to advance our core focus on the high-growth automotive lightweighting market and our prominent position in advanced high strength steels, further strengthen our close collaboration with automotive market customers, and leverage both companies’ research and innovation in metals forming. The consolidated financial statements reflect the effects of the acquisition and Precision Partner’s financial results beginning August 4, 2017 . We finalized the purchase price allocation as of March 31, 2018, with an insignificant adjustment to goodwill. For the year ended December 31, 2017 , we incurred acquisition costs of $6.2

Investments in Affiliates (Note

Investments in Affiliates (Notes)	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Investments in Affiliates	Investments in Affiliates We have investments in several businesses accounted for using the equity method of accounting. Investees and equity ownership percentages are presented below: Equity Ownership % Combined Metals of Chicago, LLC 40.0% Delaco Processing, LLC 49.0% Rockport Roll Shop LLC 50.0% Spartan Steel Coating, LLC 48.0% Cost of products sold includes $6.6 , $7.0 and $12.3 in 2018 , 2017 and 2016 for our share of income of equity investees. As of December 31, 2018 , our carrying cost of our investment in Spartan Steel exceeded our share of the underlying equity in net assets by $9.2 . This difference is being amortized and the amortization expense is included in cost of products sold. Summarized financial statement data for all investees is presented below: 2018 2017 2016 Revenue $ 329.8 $ 292.7 $ 286.4 Gross profit 91.0 88.9 96.3 Net income (loss) 19.4 20.7 31.8 2018 2017 Current assets $ 123.6 $ 115.2 Noncurrent assets 74.4 73.5 Current liabilities 16.9 16.2 Noncurrent liabilities 54.2 58.9 We regularly transact business with these equity investees. Transactions with all equity investees for the years indicated are presented below: 2018 2017 2016 Sales to equity investees $ 104.4 $ 80.6 $ 69.2 Purchases from equity investees 31.2 33.0 213.5 Outstanding receivables and payables with all equity investees as of the end of the year indicated are presented below: 2018 2017 Accounts receivable from equity investees $ 1.9 $ 0.7 Accounts payable to equity investees 6.4 4.1 Magnetation In 2016, we made a cash payment (“Termination Payment”) of $36.6 to the Chapter 11 estate of Magnetation LLC (“Magnetation”), our former joint venture, in order to terminate our iron ore pellet offtake agreement with Magnetation and cease purchasing iron ore pellets from Magnetation. In connection with the payment of the Termination Payment to the bankruptcy estate, we recognized a charge in 2016 for the Termination Payment and a charge of $32.9 for the present value of remaining obligations under contracts with other third parties to transport pellets to our facilities. In the fourth quarter of 2017, we reached an agreement for transportation services that provides a timeframe to begin using the rail cars that were idled after the termination of the pellet supply agreement. As a result, we recorded a credit of $19.3

Income Taxes (Notes)

Income Taxes (Notes)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We and our subsidiaries file a consolidated federal income tax return that includes all domestic companies owned 80% or more by us and the proportionate share of our interest in equity method investments. State tax returns are filed on a consolidated, combined or separate basis depending on the applicable laws relating to us and our domestic subsidiaries. Components of income (loss) before income taxes for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 United States $ 168.3 $ 91.6 $ (40.4 ) Foreign 11.5 9.7 6.7 Noncontrolling interests 58.1 61.4 66.0 Income before income taxes $ 237.9 $ 162.7 $ 32.3 Significant components of deferred tax assets and liabilities at December 31, 2018 and 2017 are presented below: 2018 2017 Deferred tax assets: Net operating and capital loss and tax credit carryforwards $ 516.7 $ 619.5 Postretirement benefits 81.8 92.5 Pension benefits 114.1 117.5 Inventories 38.5 47.9 Other assets 65.1 71.6 Valuation allowance (693.5 ) (735.7 ) Total deferred tax assets 122.7 213.3 Deferred tax liabilities: Depreciable assets (108.3 ) (121.9 ) Other liabilities (33.4 ) (118.3 ) Total deferred tax liabilities (141.7 ) (240.2 ) Net deferred tax liabilities $ (19.0 ) $ (26.9 ) We regularly evaluate the need for a valuation allowance for deferred tax assets by assessing whether it is more likely than not that we will realize future deferred tax assets. We assess the valuation allowance each reporting period and reflect any additions or adjustments in earnings in the same period. At December 31, 2018, we considered the existence of recent cumulative income from U.S. operations as a source of positive evidence. We have generated losses from U.S. operations for several of our recent periods through 2016 and accordingly have generated significant cumulative losses in those periods, which is a significant source of objective negative evidence. Despite the recent income reported in 2017 and 2018 from U.S. operations, the following forms of negative evidence concerning our ability to realize our domestic deferred tax assets were considered: • we have historical evidence that the steel industry we operate within has business cycles of longer than a few years and therefore attribute significant weight to our cumulative losses over longer business cycles in evaluating our ability to generate future taxable income; • the global steel industry has been experiencing global overcapacity and periods of increased foreign steel imports into the U.S., which have created volatile economic conditions and uncertainty relative to predictions of future income; • while we have changed our business model to de-emphasize sales of commodity products and believe that this model will generate improved financial results throughout an industry cycle, we have not experienced all parts of the cycle since we made these changes and therefore we do not know what results our business model will produce in all circumstances; • our U.S. operations have generated significant losses in prior years and the competitive landscape in the steel industry reflects shifting domestic and international political priorities, an uncertain global trade landscape, and continued intense competition from domestic and foreign steel competitors, all of which present significant uncertainty regarding our ability to routinely generate U.S. income in the near term; • there has been significant recent volatility in spot market selling prices for carbon steel; and • a substantial portion of our U.S. deferred tax assets consists of tax carryforwards with expiration dates that may prevent us from using them prior to expiration. As of December 31, 2018 and 2017 , we concluded that the negative evidence outweighed the positive evidence and we maintained a valuation allowance for our net deferred tax assets in the U.S. To determine the appropriate valuation allowance, we considered the timing of future reversal of our taxable temporary differences that supports realizing a portion of our federal and state deferred tax assets. This accounting treatment has no effect on our ability to use the loss carryforwards and tax credits to reduce future cash tax payments. Changes in the valuation allowance for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 Balance at beginning of year $ 735.7 $ 1,189.7 $ 1,232.3 Change in valuation allowance: Included in income tax expense (benefit) (52.8 ) (62.3 ) 11.0 Change in deferred assets in other comprehensive income 10.6 8.5 (53.6 ) Effect of tax rate changes — (400.2 ) — Balance at end of year $ 693.5 $ 735.7 $ 1,189.7 At December 31, 2018 , we had $2,174.0 in federal regular net operating loss carryforwards, which will expire between 2030 and 2037 . Our net operating loss carryovers generated through 2017 retain the original 20-year carryover periods and can be used to offset future taxable income without limitation. At December 31, 2018 , we had research and development (“R&D”) credit carryforwards of $1.2 that we may use to offset future income tax liabilities. The R&D credits expire between 2027 and 2028 . At December 31, 2018 , we had $89.2 in deferred tax assets for state net operating loss carryforwards and tax credit carryforwards, before considering valuation allowances, which will expire between 2018 and 2038 . Significant components of income tax expense (benefit) are presented below: 2018 2017 2016 Current: Federal $ (0.5 ) $ (4.5 ) $ (3.7 ) State (0.3 ) 0.3 0.2 Foreign 2.1 2.4 1.7 Deferred: Federal (5.3 ) 0.7 15.1 State — 0.1 1.4 Foreign (2.2 ) (0.4 ) — Benefits of operating loss carryforwards — — (16.1 ) Amount allocated to other comprehensive income — — (15.5 ) Change in valuation allowance on beginning-of-the-year deferred tax assets — (0.8 ) — Income tax expense (benefit) $ (6.2 ) $ (2.2 ) $ (16.9 ) The Tax Cuts and Jobs Act of 2017 (the “Tax Act”), signed into law on December 22, 2017, reduced the corporate income tax rate to 21% beginning in 2018, among other provisions. We recognized the effects of changes in tax rates and laws on deferred tax balances in 2017, the period in which the legislation was enacted. At December 31, 2017, we remeasured our deferred tax assets and liabilities based on the rate at which they are expected to reverse in the future, which is generally 21% at the U.S. federal level. As a result, our income tax expense for the fourth quarter of 2017 included a non-cash credit of $4.3 for the decrease in the value of our net deferred tax liabilities. The Tax Act also introduced a one-time transition tax on the cumulative undistributed earnings of our foreign subsidiaries as of December 31, 2017. As a result, our taxable income for 2017 included $24.3 as our gross transition tax obligation. We did not incur a cash tax liability for the transition tax due to the availability of existing net operating loss carryforwards. At December 31, 2018 we had $7.3 of accumulated undistributed earnings of our foreign subsidiaries that has not been subject to U.S. income tax as they are considered indefinitely reinvested. Substantially all of the earnings as of December 31, 2017 were subject to U.S. taxation as a result of the transition tax inclusion provided for by the Tax Act. The Tax Act also establishes a broad exemption from U.S. taxation for dividends paid from our foreign affiliates after 2017. Consequently, there will generally be no incremental U.S. taxable income generated if we repatriate these foreign earnings in the future. However, foreign withholding taxes on dividend distributions could apply, unless they are eliminated by a treaty between the United States and the country where our foreign affiliate is located. Since we consider these earnings to be permanently invested in our foreign subsidiaries, we did not record any withholding taxes that would be assessed if the earnings were repatriated by payment of a dividend. If we repatriated the earnings, we estimate that the withholding tax liability would not be material at December 31, 2018. Staff Accounting Bulletin No. 118 established a one-year period from the date of enactment in which to account for the impact of the Tax Act. During the quarter ended March 31, 2018, we reduced our valuation allowance and recorded an income tax benefit of $5.3 as a result of changes to the tax net operating carryover rules included in the Tax Act that allow us to use certain indefinite-lived deferred tax liabilities as a source of future income to realize deferred tax assets. As of December 31, 2018, we have accounted for the material aspects of the Tax Act. The reconciliation of income tax on income before income taxes computed at the U.S. federal statutory tax rates to actual income tax expense is presented below: 2018 2017 2016 Income tax expense at U.S. federal statutory rate $ 50.0 $ 57.2 $ 11.3 Income tax expense calculated on noncontrolling interests (12.2 ) (21.5 ) (23.1 ) State and foreign tax expense, net of federal tax (2.3 ) 6.3 0.2 Increase (decrease) in deferred tax asset valuation allowance (52.8 ) (51.8 ) 11.0 Amount allocated to other comprehensive income — — (15.5 ) Remeasurement of deferred taxes for U.S. tax legislation — (4.3 ) — Transition tax on foreign earnings — 7.9 — Non-deductible compensation 8.1 — — Other differences 3.0 4.0 (0.8 ) Income tax expense (benefit) $ (6.2 ) $ (2.2 ) $ (16.9 ) Our federal, state and local tax returns are subject to examination by various taxing authorities. Federal returns for periods beginning in 2015 are open for examination, while certain state and local returns are open for examination for periods beginning in 2007 . However, taxing authorities have the ability to adjust net operating loss carryforwards generated in years before these periods. We have not recognized certain tax benefits because of the uncertainty of realizing the entire value of the tax position taken on income tax returns until taxing authorities review them. We have established appropriate income tax accruals, and believe that the outcomes of future federal examinations, as well as ongoing and future state and local examinations, will not have a material adverse impact on our financial position, results of operations or cash flows. When statutes of limitations expire or taxing authorities resolve uncertain tax positions, we will adjust income tax expense for the unrecognized tax benefits. We have no tax positions for which it is reasonably possible that the total amounts of unrecognized tax benefits will significantly change within twelve months of December 31, 2018 . A reconciliation of the change in unrecognized tax benefits for 2018 , 2017 and 2016 is presented below: 2018 2017 2016 Balance at beginning of year $ 89.4 $ 124.2 $ 130.3 Decreases for prior year tax positions (2.2 ) (0.5 ) (4.5 ) Increases (decreases) for current year tax positions — 0.3 (1.6 ) Increases (decreases) related to tax rate changes (a) — (34.6 ) — Balance at end of year $ 87.2 $ 89.4 $ 124.2 (a) As a result of the Tax Act, the value of unrecognized tax benefits associated with NOL carryforwards and other temporary differences was reduced to reflect the lower tax rates that will apply if the uncertainties related to these deferred tax assets materialize in the future. Included in the balance of unrecognized tax benefits at December 31, 2018 and 2017 , are $72.8 and $75.0 of tax benefits that, if recognized, would affect the effective tax rate. Also included in the balance of unrecognized tax benefits at December 31, 2018 and 2017 , are $14.5 and $14.4

Long-term Debt and Other Financ

Long-term Debt and Other Financing (Notes)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long-term Debt and Other Financing	Long-term Debt and Other Financing Debt balances at December 31, 2018 and 2017 , are presented below: 2018 2017 Credit Facility $ 335.0 $ 450.0 7.50% Senior Secured Notes due July 2023 (effective rate of 8.3%) 380.0 380.0 5.00% Exchangeable Senior Notes due November 2019 (effective rate of 10.8%) 148.5 150.0 7.625% Senior Notes due October 2021 406.2 406.2 6.375% Senior Notes due October 2025 (effective rate of 7.1%) 274.8 280.0 7.00% Senior Notes due March 2027 391.6 400.0 Industrial Revenue Bonds due 2020 through 2028 99.3 99.3 Unamortized debt discount and issuance costs (41.7 ) (55.4 ) Total long-term debt $ 1,993.7 $ 2,110.1 During 2018 , we were in compliance with all the terms and conditions of our debt agreements. Maturities of long-term debt for the next five years, at December 31, 2018 , are presented below: Year Debt Maturities 2019 (a) $ 148.5 2020 7.3 2021 406.2 2022 335.0 2023 380.0 (a) Amounts maturing in 2019 are classified as long-term based on our ability and intent to refinance on a long-term basis. Credit Facility We have a $1,350.0 revolving credit facility (the “Credit Facility”) that expires in September 2022 and is guaranteed by AK Steel’s parent company, AK Holding, and by AK Tube LLC (“AK Tube”), AK Steel Properties, Inc. (“AK Properties”) and Mountain State Carbon LLC (“Mountain State Carbon”), three 100%-owned subsidiaries of AK Steel (referred to together as the “Subsidiary Guarantors”). The Credit Facility contains customary restrictions, including limitations on, among other things, distributions and dividends, acquisitions and investments, dispositions, indebtedness, liens and affiliate transactions. The Credit Facility requires that we maintain a minimum fixed charge coverage ratio of one to one if availability under the Credit Facility is less than $135.0 . The Credit Facility’s current availability significantly exceeds $135.0 . Availability is calculated as the lesser of the Credit Facility commitments or eligible collateral after advance rates, less outstanding revolver borrowings and letters of credit. We secure our Credit Facility obligations with our inventory and accounts receivable, and the Credit Facility’s availability fluctuates monthly based on the varying levels of eligible collateral. We do not expect any of these restrictions to affect or limit our ability to conduct business in the ordinary course. The Credit Facility includes a “first-in, last-out” or “FILO” tranche, which allows us to use a portion of our eligible collateral at higher advance rates. At December 31, 2018 , our aggregate borrowing base, after application of applicable advance rates, was $1,350.0 . As of December 31, 2018 , we had $335.0 in outstanding borrowings. Availability as of December 31, 2018 was further reduced by $73.2 for outstanding letters of credit, resulting in remaining availability of $941.8 . The weighted-average interest rate on the outstanding borrowings at December 31, 2018 was 4.10% . Senior Secured Notes AK Steel has outstanding 7.50% Senior Secured Notes due July 2023 (the “Secured Notes”). The Secured Notes are fully and unconditionally guaranteed by AK Holding and the Subsidiary Guarantors. The Secured Notes are secured by first priority liens on the plant, property and equipment (other than certain excluded property, and subject to permitted liens) of AK Steel and the Subsidiary Guarantors and any proceeds from them. The book value of the collateral as of December 31, 2018 was approximately $1.4 billion . The indenture governing the Secured Notes includes covenants with customary restrictions on (a) the incurrence of additional debt by certain subsidiaries, (b) the incurrence of certain liens, (c) the incurrence of sale/leaseback transactions, (d) the use of proceeds from the sale of collateral, and (e) our ability to merge or consolidate with other entities or to sell, lease or transfer all or substantially all of our assets to another entity. The Secured Notes also contain customary events of default. Before July 15, 2019, we may redeem the Secured Notes at a price equal to 100.000% of par plus a make-whole premium and all accrued and unpaid interest to the date of redemption. After July 15, 2019, we may redeem them at 103.750% until July 15, 2020, 101.875% until July 15, 2021, and 100.000% thereafter, together with all accrued and unpaid interest to the date of redemption. After we issued the Secured Notes in 2016, we repurchased then outstanding senior secured notes and recognized other expense of $12.4 for expenses related to the debt retirement in 2016. Exchangeable Notes AK Steel has outstanding 5.0% Exchangeable Senior Notes due November 2019 (the “Exchangeable Notes”). We may not redeem the Exchangeable Notes before their maturity date. The indenture governing the Exchangeable Notes (the “Exchangeable Notes Indenture”) provides holders with an exchange right at their option before August 15, 2019, if the closing price of our common stock is greater than or equal to $7.02 per share ( 130% of the exchange price of the Exchangeable Notes) for at least 20 trading days during the last 30 consecutive trading days of a calendar quarter. The triggering condition was not met as of January 1, 2019 nor January 1, 2018. The triggering condition is reassessed at the beginning of each quarter while any Exchangeable Notes remain outstanding. We would be required to pay cash to holders for the principal amount of the Exchangeable Notes and to pay cash or issue common stock (at our option) for the premium if the holders elect to exchange their Exchangeable Notes. If holders of Exchangeable Notes elect to exchange, we expect to fund any cash settlement from cash or borrowings under our Credit Facility or both. On or after August 15, 2019, holders may exchange their Exchangeable Notes at any time, and we would be obligated to (i) pay an amount in cash equal to the aggregate principal amount of the Exchangeable Notes to be exchanged and (ii) at our election, pay cash, deliver shares of AK Holding common stock or a combination for any remaining exchange obligation in excess of the aggregate principal amount of the Exchangeable Notes being exchanged. Holders may exchange their Exchangeable Notes into shares of AK Holding common stock at their option at an initial exchange rate of 185.1852 shares of AK Holding common stock per $1,000 principal amount of Exchangeable Notes. The initial exchange rate is equivalent to a conversion price of approximately $5.40 per share of common stock, which equates to 27.5 million shares to be used to determine the aggregate equity consideration to be delivered upon exchange, which could be adjusted for certain dilutive effects from potential future events. The Exchangeable Notes Indenture does not contain any financial or operating covenants or restrict us or our subsidiaries from paying dividends, incurring debt or issuing or repurchasing securities. If we undergo a fundamental change, as defined in Exchangeable Notes Indenture (which, for example, would include various transactions in which we would undergo a change of control), holders may require us to repurchase the Exchangeable Notes in whole or in part for cash at a price equal to par plus any accrued and unpaid interest. In addition, if we undergo a “make-whole fundamental change,” as defined in the Exchangeable Notes Indenture, before the maturity date, in addition to requiring us to repurchase the Exchangeable Notes in whole or in part for cash at a price equal to par plus any accrued and unpaid interest, the exchange rate will be increased in certain circumstances for holders who elect to exchange their notes in connection with the event. Based on the initial exchange rate, the Exchangeable Notes are exchangeable into a maximum of 37.1 million shares of AK Holding common stock. However, we would only deliver the maximum amount of shares if, following a “make-whole fundamental change” described above, we elect to deliver the shares to satisfy the higher exchange rate. Although the Exchangeable Notes were issued at par, for accounting purposes the proceeds received from the issuance of the notes are allocated between debt and equity to reflect the fair value of the exchange option embedded in the notes and the fair value of similar debt without the exchange option. Therefore, we recorded $38.7 of the gross proceeds of the Exchangeable Notes as an increase in additional paid-in capital with the offsetting amount recorded as a debt discount. We are amortizing the debt discount and issuance costs over the term of the Exchangeable Notes using the effective interest method. As of December 31, 2018 and 2017 , the net carrying amount of the Exchangeable Notes was $141.4 and $135.3 . During 2018, we repurchased an aggregate principal amount of $1.5 of the Exchangeable Notes in private, open market transactions. Senior Unsecured Notes AK Steel has outstanding 7.625% Senior Notes due October 2021 (the “2021 Notes”). We may redeem the 2021 Notes at 101.906% until October 1, 2019 and 100.0% thereafter, together with all accrued and unpaid interest to the date of redemption. AK Steel has outstanding 6.375% Senior Unsecured Notes due October 2025 (the “2025 Notes”). Before October 15, 2020, we may redeem the 2025 Notes at a price equal to par plus a make-whole premium and all accrued and unpaid interest to the date of redemption. After that date, we may redeem them at 103.188% until October 15, 2021, 101.594% thereafter until October 15, 2022, and 100.000% thereafter, together with all accrued and unpaid interest to the date of redemption. In 2017, we recognized other expense of $8.4 related to the issuance of the 2025 Notes. During 2018, we repurchased an aggregate principal amount of $5.2 of the 2025 Notes in private, open market transactions. We recognized a net gain on the repurchases totaling $0.7 for the year ended December 31, 2018, which is included in other (income) expense. AK Steel has outstanding 7.00% Senior Unsecured Notes due March 2027 (the “2027 Notes”). Before March 15, 2022, we may redeem the 2027 Notes at a price equal to par plus a make-whole premium and all accrued and unpaid interest to the date of redemption. After that date, we may redeem them at 103.500% until March 15, 2023, 102.333% thereafter until March 15, 2024, 101.167% thereafter until March 15, 2025, and 100.000% thereafter, together with all accrued and unpaid interest to the date of redemption. In 2017, we recognized other expense of $13.1 related to the issuance of the 2027 Notes. During 2018, we repurchased an aggregate principal amount of $8.4 of the 2027 Notes in private, open market transactions. We recognized a net gain on the repurchases totaling $1.3 for the year ended December 31, 2018, which is included in other (income) expense. The Exchangeable Notes, the 2021 Notes, the 2025 Notes, the 2027 Notes and the unsecured industrial revenue bonds (“IRBs”) discussed below (collectively, the “Senior Unsecured Notes”) are equal in right of payment. AK Holding and the Subsidiary Guarantors each, fully and unconditionally, jointly and severally, guarantees the payment of interest, principal and premium, if any, on the Senior Unsecured Notes other than the Exchangeable Notes, which are guaranteed only by AK Holding. The indentures governing the 2021 Notes, the 2025 Notes, the 2027 Notes and the unsecured IRBs include covenants with customary restrictions on (a) the incurrence of additional debt by certain subsidiaries, (b) the incurrence of certain liens, (c) the amount of sale/leaseback transactions, and (d) our ability to merge or consolidate with other entities or to sell, lease or transfer all or substantially all of our assets to another entity. The indentures governing the Senior Unsecured Notes also contain customary events of default. The Senior Unsecured Notes rank junior in priority to the Secured Notes to the extent of the value of the assets securing the Secured Notes. Industrial Revenue Bonds AK Steel has outstanding $73.3 aggregate principal amount of fixed-rate, tax-exempt IRBs (the “unsecured IRBs”) at December 31, 2018 . The weighted-average fixed interest rate of the unsecured IRBs is 6.8% . The unsecured IRBs are unsecured senior debt obligations of AK Steel that are equal in ranking with the other Senior Unsecured Notes. In addition, AK Steel has outstanding $26.0 aggregate principal amount of variable-rate taxable IRBs at December 31, 2018

Pension and Other Postretiremen

Pension and Other Postretirement Benefits (Notes)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits, Description [Abstract]
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits Summary We provide noncontributory pension and various healthcare and life insurance benefits to a significant portion of our employees and retirees. Benefits are provided through defined benefit and defined contribution plans that we sponsor, as well as multiemployer plans for certain union members. Our defined benefit pension plans are not fully funded. We will be required to make pension contributions of approximately $45.0 for 2019 . Based on current actuarial assumptions, we expect to make required pension contributions of approximately $50.0 for 2020 and $50.0 for 2021 . Factors that affect future funding projections include differences between expected and actual returns on plan assets, actuarial data and assumptions relating to plan participants, the discount rate used to measure the pension obligations and changes to regulatory funding requirements. We expect to make other postretirement benefit (“OPEB”) payments, after receipt of Medicare subsidy reimbursements, of approximately $37.5 in 2019 . Defined Benefit Plans Plan Obligations Amounts presented below are calculated based on benefit obligation and asset valuation measurement dates of December 31, 2018 and 2017 : Pension Benefits Other Benefits 2018 2017 2018 2017 Change in benefit obligations: Benefit obligations at beginning of year $ 2,808.0 $ 2,874.8 $ 448.5 $ 443.7 Service cost 3.2 2.8 4.5 4.7 Interest cost 94.5 108.2 15.6 17.3 Plan participants’ contributions — — 24.7 23.3 Actuarial loss (gain) (148.8 ) 91.0 (23.7 ) 27.1 Amendments — — (11.1 ) (4.7 ) Benefits paid (268.1 ) (269.0 ) (62.6 ) (65.5 ) Annuity settlement (278.8 ) — — — Medicare subsidy reimbursement received — — 2.3 2.6 Foreign currency exchange rate changes — 0.2 — — Benefit obligations at end of year $ 2,210.0 $ 2,808.0 $ 398.2 $ 448.5 Change in plan assets: Fair value of plan assets at beginning of year $ 2,322.2 $ 2,183.5 $ — $ — Actual gain (loss) on plan assets (87.0 ) 362.4 — — Employer contributions 51.3 45.3 35.6 39.6 Plan participants’ contributions — — 24.7 23.3 Benefits paid (268.1 ) (269.0 ) (62.6 ) (65.5 ) Annuity settlement (278.8 ) — — — Medicare subsidy reimbursement received — — 2.3 2.6 Fair value of plan assets at end of year $ 1,739.6 $ 2,322.2 $ — $ — Funded status $ (470.4 ) $ (485.8 ) $ (398.2 ) $ (448.5 ) Amounts recognized in the consolidated balance sheets: Current liabilities $ (1.2 ) $ (1.3 ) $ (37.5 ) $ (38.8 ) Noncurrent liabilities (469.2 ) (484.5 ) (360.7 ) (409.7 ) Total $ (470.4 ) $ (485.8 ) $ (398.2 ) $ (448.5 ) Amounts recognized in accumulated other comprehensive loss, before taxes: Actuarial loss (gain) $ 134.1 $ 77.6 $ (35.4 ) $ (13.0 ) Prior service cost (credit) 19.4 23.2 (82.4 ) (84.9 ) Total $ 153.5 $ 100.8 $ (117.8 ) $ (97.9 ) The accumulated benefit obligation for all defined benefit pension plans was $2,188.6 and $2,767.1 at December 31, 2018 and 2017 . All our defined benefit pension plans have an accumulated benefit obligation in excess of plan assets. The amounts included in current liabilities represent only the amounts of our unfunded pension and OPEB benefit plans that we expect to pay in the next year. During the fourth quarter of 2018, we transferred to a highly rated insurance company $278.8 of pension obligations for approximately 5,400 retirees or their beneficiaries. As part of this transaction, we transferred a similar amount of pension trust assets to purchase a non-participating annuity contract that requires the insurance company to pay the transferred pension obligations to the pension participants. As a result of the transfer of pension assets in October 2018, we recorded a settlement loss of $14.5 in the fourth quarter of 2018 to recognize a portion of the unrealized actuarial loss associated with the transferred obligations. The 2018 change in the actuarial loss (gain) for the pension plans in the table above primarily consisted of a loss of $235.8 for actual pension asset return less than expected, partially offset by a gain of $154.6 for the increase in discount rate used to value the benefit obligations. The 2018 change in the actuarial loss (gain) for the OPEB plan in the table above primarily consisted of a gain of $27.7 for the increase in discount rate used to value the benefit obligations. Assumptions used to value benefit obligations and determine pension and OPEB (income) expense are presented below: Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Assumptions used to determine benefit obligations at December 31: Discount rate 4.22 % 3.54 % 3.93 % 4.27 % 3.59 % 4.04 % Rate of compensation increase 4.00 % 4.00 % 4.00 % Interest crediting rate 3.80 % 3.80 % 3.80 % Subsequent year healthcare cost trend rate 6.50 % 6.65 % 7.00 % Ultimate healthcare cost trend rate 4.50 % 4.50 % 4.50 % Year ultimate healthcare cost trend rate begins 2025 2025 2025 Assumptions used to determine pension and OPEB (income) expense for the year ended December 31: Discount rate 3.69 % 3.93 % 3.95 % 3.59 % 4.04 % 4.22 % Expected return on plan assets 7.00 % 7.25 % 7.25 % Rate of compensation increase 4.00 % 4.00 % 4.00 % Interest crediting rate 3.80 % 3.80 % 4.30 % We determine the discount rate at each remeasurement by finding a hypothetical portfolio of individual high-quality corporate bonds available at the measurement date with coupon and principal payments that could satisfy the plans’ expected future benefit payments that we use to calculate the projected benefit obligation. The discount rate is the single rate that is equivalent to the average yield on that hypothetical portfolio of bonds. We changed our assumption for future expected returns on pension plan assets to 6.75% from 7.00% , effective January 1, 2019. Estimated future benefit payments to beneficiaries are presented below: Pension Plans Other Benefits 2019 $ 216.5 $ 37.5 2020 211.2 35.6 2021 198.9 33.8 2022 196.0 32.2 2023 180.6 30.6 2024 through 2028 835.3 133.4 Plan Assets Our investments in the master pension trust primarily include indexed and actively-managed funds. A fiduciary committee sets the target asset mix and monitors asset performance. We determine the master pension trust’s projected long-term rate of return based on the asset allocation, the trust’s investment policy statement and our long-term capital market return assumptions for the master trust. We have developed an investment policy that considers liquidity requirements, expected investment return, funded status and expected asset risk, as well as standard industry practices. The target asset allocation for the master pension trust at December 31, 2018 was 40% equity and 60% fixed income. Equity investments consist of individual securities, equity mutual funds and common/collective trusts with equity investment strategies, which are diversified across multiple industry sectors, company market capitalizations and geographical investment strategies. The equity mutual funds and common/collective trusts have no unfunded commitments or significant redemption restrictions. Fixed-income investments consist of individual securities and common/collective trusts, which invest primarily in investment-grade and high-yield corporate bonds and U.S. Treasury securities. The fixed-income investments are diversified by ratings, maturities, industries and other factors. Plan assets contain no significant concentrations of risk from individual securities or industry sectors. The master pension trust has no direct investments in our common stock or fixed-income securities. Master pension trust investments measured at fair value on a recurring basis at December 31, 2018 and 2017 are presented below, with certain assets presented by level within the fair value hierarchy. As a practical expedient, we estimate the value of common/collective trusts and equity mutual funds by using the net asset value (“NAV”) per share multiplied by the number of shares of the trust investment held as of the measurement date. If we have the ability to redeem our investment in the respective alternative investment at the NAV with no significant restrictions on the redemption at the consolidated balance sheet date, excluding equity mutual funds, we categorized the alternative investment as a reconciliation of pension investments reported in the fair value hierarchy to the master pension trust’s balance. See Note 16 for more information on the determination of fair value. Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs (Level 1) (Level 2) Total 2018 2017 2018 2017 2018 2017 Investments in fair value hierarchy Equity investments: U.S. securities $ 35.4 $ 46.6 $ — $ — $ 35.4 $ 46.6 Global securities — — 131.4 327.9 131.4 327.9 Fixed-income investments: High-yield U.S. securities — — 84.5 111.8 84.5 111.8 Other U.S. securities — — 700.8 524.6 700.8 524.6 Global securities — — 82.8 — 82.8 — Other investments — — 78.0 30.6 78.0 30.6 Total pension investments in fair value hierarchy $ 35.4 $ 46.6 $ 1,077.5 $ 994.9 $ 1,112.9 $ 1,041.5 Investments with fair values measured at net asset value Common/collective trusts: U.S. equity securities (a) 355.8 194.6 Global equity securities (a) 178.2 707.0 U.S. corporate fixed-income securities (b) — 379.1 Global fixed-income securities (b) 92.7 — Total pension assets at fair value $ 1,739.6 $ 2,322.2 (a) Investments may include common stocks, options and futures. (b) Investments may include investment-grade and high-yield corporate bonds, interest rate swaps, options and futures. Periodic Benefit Costs Components of pension and OPEB (income) expense for the years 2018 , 2017 and 2016 are presented below: Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Components of pension and OPEB (income) expense: Service cost $ 3.2 $ 2.8 $ 3.0 $ 4.5 $ 4.7 $ 4.9 Interest cost 94.5 108.2 120.4 15.6 17.3 19.9 Expected return on plan assets (148.8 ) (149.9 ) (167.1 ) — — — Amortization of prior service cost (credit) 3.8 4.7 5.6 (13.6 ) (58.5 ) (60.4 ) Recognized net actuarial loss (gain): Annual amortization 16.1 10.5 29.2 (1.3 ) (4.2 ) (4.3 ) Corridor charge (credit) — — 78.4 — — (35.3 ) Settlement loss 14.5 — 29.9 — — — Pension and OPEB (income) expense $ (16.7 ) $ (23.7 ) $ 99.4 $ 5.2 $ (40.7 ) $ (75.2 ) In 2016, we recognized settlement losses of $25.0 as a result of two transactions to purchase non-participating annuities from an insurance company. Also during 2016, we recognized a settlement loss as a result of lump sum benefit payments made to retired participants under an unfunded supplemental retirement plan. Defined Contribution Plans All employees are eligible to participate in various defined contribution plans. Certain of these plans have features with matching contributions or other company contributions based on our financial results. Total expense from these plans was $31.1 , $24.9 and $23.1 in 2018 , 2017 and 2016 . Multiemployer Pension Plans We contribute to multiemployer pension plans according to collective bargaining agreements that cover certain union-represented employees. The following risks of participating in these multiemployer plans differ from single employer pension plans: • Employer contributions to a multiemployer plan may be used to provide benefits to employees of other participating employers. • If a participating employer stops contributing to a multiemployer plan, the remaining participating employers may need to assume the unfunded obligations of the plan. • If the multiemployer plan becomes significantly underfunded or is unable to pay its benefits, we may be required to contribute additional amounts in excess of the rate required by the collective bargaining agreements. • If we choose to stop participating in a multiemployer plan, we may be required to pay that plan an amount based on the underfunded status of the plan, referred to as a withdrawal liability. We are a party to a collective bargaining agreement at Ashland Works that requires contributions to the Steelworkers Pension Trust multiemployer pension plan. We expect to incur an estimated withdrawal liability of $25.0 in the first quarter of 2019 as a result of the closure of that facility. The actual withdrawal liability will not be known until 2020. See Note 2 for further information. Our participation in these multiemployer plans for the years ended December 31, 2018 , 2017 and 2016 , is presented below. We do not provide more than five percent of the total contributions to any multiemployer plan. Forms 5500 are not yet available for plan years ending in 2018 . Pension Fund EIN/Pension Plan Number Pension Protection Act Zone Status (a) FIP/RP Status Pending/Implemented (b) Contributions Surcharge Imposed (c) Expiration Date of Collective Bargaining Agreement 2018 2017 2018 2017 2016 Steelworkers Pension Trust 23-6648508/499 Green Green No $ 4.2 $ 6.3 $ 6.8 No 3/1/2019 to 3/31/2021 (d) IAM National Pension Fund’s National Pension Plan 51-6031295/002 Green Green No 17.7 18.4 18.0 No 4/1/2019 to 3/15/2020 (e) $ 21.9 $ 24.7 $ 24.8 (a) The most recent Pension Protection Act zone status available in 2018 and 2017 is for each plan’s year-end at December 31, 2017 and 2016 . The plan’s actuary certifies the zone status. Generally, plans in the red zone are less than 65% funded, plans in the yellow zone are between 65% and 80% funded, and plans in the green zone are at least 80% funded. The Steelworkers Pension Trust and IAM National Pension Fund’s National Pension Plan elected funding relief under section 431(b)(8) of the Internal Revenue Code and section 304(b)(8) of the Employment Retirement Income Security Act of 1974 (ERISA). This election allows those plans’ investment losses for the plan year ended December 31, 2008, to be amortized over 29 years for funding purposes. (b) The “FIP/RP Status Pending/Implemented” column indicates plans for which a financial improvement plan (FIP) or a rehabilitation plan (RP) is either pending or has been implemented, as defined by ERISA. (c) The surcharge represents an additional required contribution due as a result of the critical funding status of the plan. (d) We are a party to three collective bargaining agreements at our Ashland Works, Mansfield Works and at the AK Tube Walbridge plant that require contributions to the Steelworkers Pension Trust. The labor contract for approximately 230 hourly employees at the Ashland Works is currently under a rolling 60-day extension. The labor contract for approximately 110 hourly employees at the AK Tube Walbridge plant expires January 22, 2021 . The labor contract for approximately 300 hourly employees at Mansfield Works expires on March 31, 2021 . (e) We are a party to three collective bargaining agreements at our Butler Works, Middletown Works and Zanesville Works that require contributions to the IAM National Pension Fund’s National Pension Plan. The labor contract for approximately 1,170 hourly employees at Butler Works expires on April 16, 2019 . The labor contract for approximately 100 hourly employees at Zanesville Works expires on May 31, 2019 . The labor contract for approximately 1,760 hourly employees at Middletown Works expires on March 15, 2020

Operating Leases

Operating Leases	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Operating Leases	Operating Leases Rental expense was $48.1 , $43.1 and $46.7 for 2018 , 2017 and 2016 . Obligations to make future minimum lease payments at December 31, 2018 , are presented below: 2019 $ 23.3 2020 20.8 2021 20.6 2022 18.7 2023 17.3 2024 and thereafter 83.6 Total minimum lease payments $ 184.3

Commitments

Commitments	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments	Commitments We purchase substantial portions of the principal raw materials required for our steel manufacturing operations under annual and multi-year agreements, some of which have minimum quantity requirements. We also use large volumes of natural gas, electricity and industrial gases in our steel manufacturing operations. We negotiate most of our purchases of chrome, coke, industrial gases, iron ore and a portion of our electricity under multi-year agreements. The iron ore agreements typically have a variable-price mechanism that adjusts the price of iron ore periodically, based on reference to an iron ore index and other market-based factors. We typically purchase coal under annual fixed-price agreements. We also purchase certain transportation services under multi-year contracts with minimum quantity requirements. Commitments for future capital investments at December 31, 2018 , totaled approximately $51.6 , all of which we expect to incur in 2019

Environmental and Legal Conting

Environmental and Legal Contingencies (Notes)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Environmental and Legal Contingencies	Environmental and Legal Contingencies Environmental Contingencies Domestic steel producers, including us, must follow stringent federal, state and local laws and regulations designed to protect human health and the environment. We have spent the following amounts over the past three years for environmental-related capital investments and environmental compliance: 2018 2017 2016 Environmental-related capital investments $ 7.1 $ 6.8 $ 4.9 Environmental compliance costs 126.3 129.5 123.9 We and our predecessors have been involved in steel manufacturing and related operations since 1900. Although we believe our operating practices have been consistent with prevailing industry standards, hazardous materials may have been released at operating sites or third-party sites in the past, including operating sites that we no longer own. If we reasonably can, we have estimated potential remediation expenditures for those sites where future remediation efforts are probable based on identified conditions, regulatory requirements or contractual obligations arising from the sale of a business or facility. For sites involving government-required investigations, we typically make an estimate of potential remediation expenditures only after the investigation is complete and when we better understand the nature and scope of the remediation. In general, the material factors in these estimates include the costs associated with investigations, delineations, risk assessments, remedial work, governmental response and oversight, site monitoring, and preparation of reports to the appropriate environmental agencies. We have recorded the following liabilities for environmental matters on our consolidated balance sheets: 2018 2017 Accrued liabilities $ 8.0 $ 8.5 Other non-current liabilities 31.2 35.4 We cannot predict the ultimate costs for each site with certainty because of the evolving nature of the investigation and remediation process. Rather, to estimate the probable costs, we must make certain assumptions. The most significant of these assumptions is for the nature and scope of the work that will be necessary to investigate and remediate a particular site and the cost of that work. Other significant assumptions include the cleanup technology that will be used, whether and to what extent any other parties will participate in paying the investigation and remediation costs, reimbursement of past response and future oversight costs by governmental agencies, and the reaction of the governing environmental agencies to the proposed work plans. Costs for future investigation and remediation are not discounted to their present value. To the extent that we have been able to reasonably estimate future liabilities, we do not believe that there is a reasonable possibility that we will incur a loss or losses that exceed the amounts we accrued for the environmental matters discussed below that would, either individually or in the aggregate, have a material adverse effect on our consolidated financial condition, results of operations or cash flows. However, since we recognize amounts in the consolidated financial statements in accordance with accounting principles generally accepted in the United States that exclude potential losses that are not probable or that may not be currently estimable, the ultimate costs of these environmental proceedings may be higher than the liabilities we currently have recorded in our consolidated financial statements. Except as we expressly note below, we do not currently anticipate any material effect on our consolidated financial position, results of operations or cash flows as a result of compliance with current environmental regulations. Moreover, because all domestic steel producers operate under the same federal environmental regulations, we do not believe that we are more disadvantaged than our domestic competitors by our need to comply with these regulations. Some foreign competitors may benefit from less stringent environmental requirements in the countries where they produce, resulting in lower compliance costs for them and providing those foreign competitors with a cost advantage on their products. According to the Resource Conservation and Recovery Act (“RCRA”), which governs the treatment, handling and disposal of hazardous waste, the EPA and authorized state environmental agencies may conduct inspections of RCRA-regulated facilities to identify areas where there have been releases of hazardous waste or hazardous constituents into the environment and may order the facilities to take corrective action to remediate such releases. Environmental regulators may inspect our major steelmaking facilities. While we cannot predict the future actions of these regulators, it is possible that they may identify conditions in future inspections of these facilities which they believe require corrective action. Under authority from the Comprehensive Environmental Response, Compensation and Liability Act (“CERCLA”), the EPA and state environmental authorities have conducted site investigations at certain of our facilities and other third-party facilities, portions of which previously may have been used for disposal of materials that are currently regulated. The results of these investigations are still pending, and we could be directed to spend funds for remedial activities at the former disposal areas. Because of the uncertain status of these investigations, however, we cannot reliably predict whether or when such spending might be required or their magnitude. As previously noted, on April 29, 2002, we entered a mutually agreed-upon administrative order on consent with the EPA pursuant to Section 122 of CERCLA to perform a Remedial Investigation/Feasibility Study (“RI/FS”) of the Hamilton Plant site located in New Miami, Ohio. The plant ceased operations in 1990 and all of its former structures have been demolished. We submitted the investigation portion of the RI/FS, and we completed a supplemental study in 2014. We currently have accrued $0.7 for the remaining cost of the RI/FS. Until the RI/FS is complete, we cannot reliably estimate the additional costs, if any, we may incur for potentially required remediation of the site or when we may incur them. As previously reported, on September 30, 1998, our predecessor, Armco Inc., received an order from the EPA under Section 3013 of RCRA requiring it to develop a plan for investigation of eight areas of our Mansfield Works that allegedly could be sources of contamination. A site investigation began in November 2000 and is continuing. We cannot reliably estimate how long it will take to complete this site investigation. We currently have accrued $1.1 for the projected cost of the study. Until the site investigation is complete, we cannot reliably estimate the additional costs, if any, we may incur for potentially required remediation of the site or when we may incur them. As previously noted, on September 26, 2012, the EPA issued an order under Section 3013 of RCRA requiring us to develop a plan for investigation of four areas at our Ashland Works coke plant. The Ashland Works coke plant ceased operations in 2011 and all of its former structures have been demolished and removed. In 1981, we acquired the plant from Honeywell International Corporation (as successor to Allied Corporation), who had managed the coking operations there for approximately 60 years. In connection with the sale of the coke plant, Honeywell agreed to indemnify us from certain claims and obligations that could arise from the investigation and we intend to pursue such indemnification from Honeywell, if necessary. We cannot reliably estimate how long it will take to complete the site investigation. On March 10, 2016, the EPA invited us to participate in settlement discussions regarding an enforcement action. Settlement discussions between the parties are ongoing, though whether the parties will reach agreement and any such agreement’s terms are uncertain. We currently have accrued $1.4 for the projected cost of the investigation and known remediation. Until the site investigation is complete, we cannot reliably estimate the costs, if any, we may incur for potential additional required remediation of the site or when we may incur them. As previously reported, on July 15, 2009, we and the Pennsylvania Department of Environmental Protection (“PADEP”) entered a Consent Order and Agreement (the “Consent Order”) to resolve an alleged unpermitted discharge of wastewater from the closed Hillside Landfill at our former Ambridge Works. Under the terms of the Consent Order, we paid a penalty and also agreed to implement various corrective actions, including an investigation of the area where landfill activities occurred, submission of a plan to collect and treat surface waters and seep discharges, and upon approval from PADEP, implementation of that plan. We have accrued $5.6 for the remedial work required under the approved plan and Consent Order. We submitted a National Pollution Discharge Elimination System (“NPDES”) permit application to move to the next work phase. We currently estimate that the remaining work will be completed in 2020, though it may be delayed. As previously reported, on June 29, 2000, the United States filed a complaint on behalf of the EPA against us in the U.S. District Court for the Southern District of Ohio, Case No. C-1-00530, alleging violations of the Clean Air Act, the Clean Water Act and RCRA at our Middletown Works. Subsequently, the State of Ohio, the Sierra Club and the National Resources Defense Council intervened. On May 15, 2006, the court entered a Consent Decree in Partial Resolution of Pending Claims (the “Consent Decree”). Under the Consent Decree, we agreed to undertake a comprehensive RCRA facility investigation at Middletown Works and, as appropriate, complete a corrective measures study. The Consent Decree also required us to implement certain RCRA corrective action interim measures. We have completed the remedial activity at Dicks Creek, but continue to work on the RCRA facility investigation and certain interim measures. We have accrued $13.1 for the cost of known work required under the Consent Decree for the RCRA facility investigation and remaining interim measures. As previously reported, on May 12, 2014, the Michigan Department of Environmental Quality (“MDEQ”) issued to our Dearborn Works an Air Permit to Install No. 182-05C (the “PTI”) to increase the emission limits for the blast furnace and other emission sources. The PTI was issued as a correction to a prior permit to install that did not include certain information during the prior permitting process. On July 10, 2014, the South Dearborn Environmental Improvement Association (“SDEIA”), Detroiters Working for Environmental Justice, Original United Citizens of Southwest Detroit and the Sierra Club filed a Claim of Appeal of the PTI in the State of Michigan, Wayne County Circuit, Case No. 14-008887-AA. Appellants and the MDEQ required the intervention of Severstal Dearborn, LLC (“Dearborn”) (now owned by us) in this action as an additional appellee. The appellants allege multiple deficiencies with the PTI and the permitting process. Until the appeal is resolved, we cannot determine what the ultimate permit limits will be. Until the permit limits are determined and final, we cannot reliably estimate the costs we incur, if any, or when we may incur them. As previously reported, on August 21, 2014, the SDEIA filed a Complaint under the Michigan Environmental Protection Act (“MEPA”) in the State of Michigan, Wayne County Circuit Case No. 14-010875-CE. The plaintiffs allege that the air emissions from our Dearborn Works are impacting the air, water and other natural resources, as well as the public trust in such resources. The plaintiffs are requesting, among other requested relief, that the court assess and determine the sufficiency of the PTI’s limitations. On October 15, 2014, the court ordered a stay of the proceedings until a final order is issued in Wayne County Circuit Court Case No. 14-008887-AA (discussed above). When the proceedings resume, we will vigorously contest these claims. Until the claims in this Complaint are resolved, we cannot reliably estimate the costs we may incur, if any, or when we may incur them. As previously reported, on April 27, 2000, MDEQ issued a RCRA Corrective Action Order No. 111-04-00-07E to Rouge Steel Company and Ford Motor Company for the property that includes our Dearborn Works. The Corrective Action Order has been amended five times. We are a party to the Corrective Action Order as the successor-in-interest to Dearborn, which was the successor-in-interest to Rouge Steel Company. The Corrective Action Order requires the site-wide investigation, and where appropriate, remediation of the facility. The site investigation and remediation are ongoing. We cannot reliably estimate how long it will take to complete this site investigation and remediation. To date, Ford Motor Company has incurred most of the costs of the investigation and remediation due to its prior ownership of the steelmaking operations at Dearborn Works. Until the site investigation is complete, we cannot reliably estimate the additional costs we may incur, if any, for any potentially required remediation of the site or when we may incur them. As previously reported, we received an order in October 2002 from the EPA under Section 3013 of RCRA requiring us to investigate several areas of Zanesville Works that allegedly could be sources of contamination. A site investigation began in 2003 and was approved by EPA in November 2012. On October 28, 2016, the EPA requested that we conduct a corrective measures study and implement these measures as necessary. We subsequently agreed to proceed with a voluntary corrective measures study and have accrued $0.1 for the study. Until the study is complete, we cannot reliably estimate the costs, if any, we may incur for potential required remediation of the site or when we may incur them. In addition to the foregoing matters, we are or may be involved in proceedings with various regulatory authorities that may require us to pay fines, comply with more rigorous standards or other requirements or incur capital and operating expenses for environmental compliance. We believe that the ultimate disposition of the proceedings will not have, individually or in the aggregate, a material adverse effect on our consolidated financial condition, results of operations or cash flows. Legal Contingencies As previously reported, since 1990 we have been named as a defendant in numerous lawsuits alleging personal injury as a result of exposure to asbestos. The great majority of these lawsuits have been filed on behalf of people who claim to have been exposed to asbestos while visiting the premises of one of our current or former facilities. The majority of asbestos cases pending in which we are a defendant do not include a specific dollar claim for damages. In the cases that do include specific dollar claims for damages, the complaint typically includes a monetary claim for compensatory damages and a separate monetary claim in an equal amount for punitive damages, and does not attempt to allocate the total monetary claim among the various defendants. The number of asbestos cases pending at December 31, 2018 , is presented below: Asbestos Cases Pending at December 31, 2018 Cases with specific dollar claims for damages: Claims up to $0.2 160 Claims above $0.2 to $5.0 4 Claims above $5.0 to $20.0 3 Total claims with specific dollar claims for damages (a) 167 Cases without a specific dollar claim for damages 176 Total asbestos cases pending 343 (a) Involve a total of 2,242 plaintiffs and 19,356 defendants In each case, the amount described is per plaintiff against all of the defendants, collectively. Thus, it usually is not possible at the outset of a case to determine the specific dollar amount of a claim against us. In fact, it usually is not even possible at the outset to determine which of the plaintiffs actually will pursue a claim against us. Typically, that can only be determined through written interrogatories or other discovery after a case has been filed. Therefore, in a case involving multiple plaintiffs and multiple defendants, we initially only account for the lawsuit as one claim. After we have determined through discovery whether a particular plaintiff will pursue a claim, we make an appropriate adjustment to statistically account for that specific claim. It has been our experience that only a small percentage of asbestos plaintiffs ultimately identify us as a target defendant from whom they actually seek damages and most of these claims ultimately are either dismissed or settled for a small fraction of the damages initially claimed. Asbestos-related claims information in 2018 , 2017 and 2016 , is presented below: 2018 2017 2016 New Claims Filed 68 58 40 Pending Claims Disposed Of 61 61 84 Total Amount Paid in Settlements $ 1.4 $ 1.2 $ 0.9 Since the onset of asbestos claims against us in 1990, five asbestos claims against us have proceeded to trial in four separate cases. All five concluded with a verdict in our favor. We continue to vigorously defend the asbestos claims. Based upon present knowledge, and the factors above, we believe it is unlikely that the resolution in the aggregate of the asbestos claims against us will have a materially adverse effect on our consolidated results of operations, cash flows or financial condition. However, predictions about the outcome of pending litigation, particularly claims alleging asbestos exposure, are subject to substantial uncertainties. These uncertainties include (1) the significantly variable rate at which new claims may be filed, (2) the effect of bankruptcies of other companies currently or historically defending asbestos claims, (3) the litigation process from jurisdiction to jurisdiction and from case to case, (4) the type and severity of the disease each claimant alleged to suffer, and (5) the potential for enactment of legislation affecting asbestos litigation. As previously reported, in September and October 2008 and again in July 2010, several companies filed purported class actions in the United States District Court for the Northern District of Illinois against nine steel manufacturers, including us. The case numbers for these actions are 08CV5214, 08CV5371, 08CV5468, 08CV5633, 08CV5700, 08CV5942, 08CV6197 and 10CV04236. On December 28, 2010, another action, case number 32,321, was filed in state court in the Circuit Court for Cocke County, Tennessee. The defendants removed the Tennessee case to federal court and in March 2012 it was transferred to the Northern District of Illinois. The plaintiffs in the various pending actions are companies that purport to have purchased steel products, directly or indirectly, from one or more of the defendants and they claim to file the actions on behalf of all persons and entities who purchased steel products for delivery or pickup in the United States from any of the named defendants at any time from at least as early as January 2005. The complaints allege that the defendant steel producers have conspired in violation of antitrust laws to restrict output and to fix, raise, stabilize and maintain artificially high prices for steel products in the United States. In March 2014, we reached an agreement with the direct purchaser plaintiffs to tentatively settle the claims asserted against us, subject to certain court approvals below. According to that settlement, we agreed to pay $5.8 to the plaintiff class of direct purchasers in exchange for the members of that class to completely release all claims. We continue to believe that the claims made against us lack any merit, but we elected to enter the settlement to avoid the ongoing expense of defending ourselves in this protracted and expensive antitrust litigation. We provided notice of the proposed settlement to members of the settlement class. After several class members received the notice, they elected to opt out of the class settlement. Following a fairness hearing, on October 21, 2014 the Court entered an order and judgment approving the settlement and dismissing all of the direct plaintiffs’ claims against us with prejudice as to the settlement class. On March 3, 2017, the Court granted the defendants’ motion to dismiss the indirect plaintiffs’ amended complaint on the grounds that the plaintiffs lacked antitrust standing. On April 4, 2017, the indirect plaintiffs filed a motion for reconsideration and the defendants filed an opposition to that motion. On July 13, 2017, the Court denied the indirect plaintiffs’ motion for reconsideration. On September 15, 2017 the indirect plaintiffs filed a notice of appeal with the Seventh Circuit Court of Appeals. On September 6, 2018, the Seventh Circuit affirmed the judgment of the District Court. The time period for the indirect plaintiffs to petition for a writ of certiorari with the United States Supreme Court has expired and the matter is now closed. As previously reported, on January 20, 2010, ArcelorMittal France and ArcelorMittal Atlantique et Lorraine (collectively “ArcelorMittal”) filed an action in the United States District Court for the District of Delaware, Case No. 10-050-SLR against us, Dearborn, and Wheeling-Nisshin Inc., whom Dearborn indemnified in this action. By virtue of our responsibility as a successor-in-interest to Dearborn and an indemnitor of Wheeling-Nisshin Inc., we now have complete responsibility for the defense of this action. The three named defendants are collectively referred to hereafter as “we” or “us”, though the precise claims against each separate defendant may vary. The complaint alleges that we are infringing the claims of U.S. Patent No. 6,296,805 (the “Patent”) in making pre-coated cold-rolled boron steel sheet and seeks injunctive relief and unspecified compensatory damages. We filed an answer denying ArcelorMittal’s claims and raised various affirmative defenses. We also filed counterclaims against ArcelorMittal for a declaratory judgment that we are not infringing the Patent and that the Patent is invalid. Subsequently, the trial court separated the issues of liability and damages. The case proceeded with a trial to a jury on the issue of liability during the week of January 15, 2011. The jury returned a verdict that we did not infringe the Patent and that the Patent was invalid. Judgment then was entered in our favor. ArcelorMittal filed an appeal with the United States Court of Appeals for the Federal Circuit. On November 30, 2012, the court of appeals issued a decision reversing certain findings related to claim construction and the validity of the Patent and remanded the case to the trial court for further proceedings. On January 30, 2013, ArcelorMittal filed a motion for rehearing with the court of appeals. On March 20, 2013, the court of appeals denied ArcelorMittal’s motion for rehearing. The case then was remanded to the trial court for further proceedings. On April 16, 2013, according to a petition previously filed by ArcelorMittal and ArcelorMittal USA LLC, the U.S. Patent and Trademark Office (“PTO”) reissued the Patent as U.S. Reissue Patent RE44,153 (the “Reissued Patent”). Also on April 16, 2013, ArcelorMittal filed a second action against us in the United States District Court for the District of Delaware, Case Nos. 1:13-cv-00685 and 1:13-cv-00686 (collectively the “Second Action”). The complaint filed in the Second Action alleges that we are infringing the claims of the Reissued Patent and seeks injunctive relief and unspecified compensatory damages. On April 23, 2013, we filed a motion to dismiss key elements of the complaint filed in the Second Action. In addition, the parties briefed related non-infringement and claims construction issues in the original action. On October 25, 2013, the district court granted summary judgment in our favor, confirming that our product does not infringe the original Patent or the Reissued Patent. The court further ruled that ArcelorMittal’s Reissued Patent was invalid due to ArcelorMittal’s deliberate violation of a statutory prohibition on broadening a patent through reissue more than two years after the original Patent was granted and that the original Patent had been surrendered when the Reissued Patent was issued and thus is no longer in effect. Final Judgment was entered on October 31, 2013. On November 6, 2013, ArcelorMittal filed a motion to clarify or, in the alternative, to alter or amend the October 31, 2013 judgment. We opposed the motion. On December 5, 2013, the court issued a memorandum and order denying the motion and entered final judgment in our favor, and against ArcelorMittal, specifically ruling that all claims of ArcelorMittal’s Reissued Patent are invalid as violative of 35 U.S.C. §251(d). On December 30, 2013, ArcelorMittal filed notices of appeal to the Federal Circuit Court of Appeals. On May 12, 2015, the Federal Circuit issued its decision affirming in part and reversing in part the trial court’s decision and remanding the case for further proceedings. The Federal Circuit ruled that 23 of the 25 claims of the Reissued Patent were improperly broadened and therefore invalid. However, the Federal Court found that the district court erred in invalidating the remaining two claims and remanded the case for further proceedings before the district court. Following the remand, ArcelorMittal filed a motion in the trial court for leave to amend the Second Action to assert additional patent infringement claims based on another, related patent that the PTO issued on June 10, 2014, No. RE44,940 (Second Reissue Patent). It also filed a motion to dismiss the original action on the grounds that it is now moot in light of the Court of Appeals’ last ruling. We opposed both of those motions. In addition, we filed separate motions for summary judgment in the original action on the grounds of non-infringement and invalidity. A hearing on all motions was held on October 27, 2015. On December 4, 2015, the district court issued an order granting our motion for summary judgment that neither of the remaining claims of the Reissued Patent are infringed and both are invalid as obvious. The court therefore entered final judgment in favor of the defendants in the original case. In the court’s order, the judge also granted ArcelorMittal’s motion to file a first amended complaint and ArcelorMittal did file an amended complaint in Case No. 1:13-cv-00685 (“685 Action”) alleging we are infringing the claims of the Second Reissue Patent, which we deny. On December 21, 2015, ArcelorMittal filed a notice of appeal from the district court’s December 4, 2015 final judgment. On May 16, 2017, the Federal Circuit Court of Appeals affirmed the district court’s judgment of invalidity and non-infringement of the reissued Patent. On June 14, 2017, ArcelorMittal filed a petition to the Federal Circuit for rehearing en banc of the May 16, 2017 decision. On August 14, 2017, the Federal Court of Appeals denied ArcelorMittal’s petition for rehearing en banc. On January 20, 2016, we filed a motion to dismiss the amended complaint in the 685 Action, or in the alternative, a motion to stay pending a resolution of the appeal in the original case. On April 19, 2016, the district court issued an order denying our motion and ordering limited discovery. Following discovery, on August 17, 2016, we filed a motion for summary judgment on the basis that the claims in the 685 Action are precluded by the judgment in the original case. On January 19, 2017, the district court issued an opinion granting summary judgment in our favor in the 685 Action on the grounds of non-infringement and also entered a final judgment on that basis. On February 14, 2017, ArcelorMittal filed a notice of appeal of the district court's order in the Federal Circuit Court of Appeals. On November 5, 2018, the Federal Court of Appeals issued a decision vacating the judgment of non-infringement entered by the district court. The decision remands the case back to the district court for further proceedings. We intend to continue to contest this matter vigorously. We have not made a determination that a loss is probable and we do not have adequate information to reliably or accurately estimate a potential loss if ArcelorMittal prevails on remand. Because we have been unable to determine that the potential loss in this case is probable or estimable, we have not recorded an accrual for this matter. If our assumptions used to evaluate whether a loss in this matter is either probable or estimable prove to be incorrect or change, we may be required to record a liability for an adverse outcome. Other Contingencies

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock Our common stockholders may receive dividends when and as declared by the Board of Directors out of funds legally available for distribution. The holders have one vote per share in respect of all matters and are not entitled to preemptive rights. In May 2016, AK Holding issued 59.8 million shares of common stock at $4.40 per share for net proceeds of $249.5 after underwriting discounts and other fees. In November 2016, AK Holding issued an additional 74.8 million shares of common stock at $4.90 per share for net proceeds of $351.0 after underwriting discounts and other fees. We used the net proceeds from the sales of common stock to reduce our debt by repaying outstanding borrowings under our Credit Facility and for general corporate purposes. Preferred Stock There are 25,000,000 shares of preferred stock authorized; no shares are issued or outstanding. Dividends The instruments governing our outstanding senior debt allow dividend payments. However, our Credit Facility restricts dividend payments under certain conditions. Dividends are permitted if no default or event of default exists under the terms of the Credit Facility and (i) availability under the Credit Facility exceeds 20% of the lesser of the Credit Facility commitment or eligible collateral after advance rates or (ii) availability exceeds 15% of the lesser of the Credit Facility commitment or eligible collateral after advance rates and we meet a fixed charge coverage ratio of one to one as of the most recently ended fiscal quarter. At December 31, 2018 , availability under the Credit Facility significantly exceeds these amounts. If we cannot meet either of these thresholds, annual dividends would be limited to the greater of $18.0 or 0.5% of consolidated total assets, with additional dividends permitted equal to the greater of $25.0 or 0.7% of consolidated total assets in aggregate over the life of the Credit Facility. Share Repurchase Program In October 2008, the Board of Directors authorized us to repurchase, from time to time, up to $150.0 of our outstanding common stock. We have not made any common stock repurchases under this program in the last three years. As of December 31, 2018 , we had remaining $125.6

Share-based Compensation (Notes

Share-based Compensation (Notes)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation	Share-based Compensation AK Holding’s Stock Incentive Plan (the “SIP”) permits us to grant nonqualified stock option, restricted stock, performance share and restricted stock unit (“RSUs”) awards to our Directors, officers and other employees. Stockholders have approved an aggregate maximum of 28 million shares issuable under the SIP through December 31, 2019, of which approximately 6 million shares were available for future grant as of December 31, 2018 . Share-based compensation expense for the years ended December 31, 2018 , 2017 and 2016 , is presented below: Share-based Compensation Expense 2018 2017 2016 Stock options $ 2.5 $ 2.1 $ 1.0 Restricted stock 3.1 2.9 1.6 Restricted stock units issued to Directors 1.2 1.2 1.3 Performance shares 2.0 1.5 1.5 Equity-based long-term performance plan 0.4 — — Pre-tax share-based compensation expense $ 9.2 $ 7.7 $ 5.4 Stock Options Stock options have a maximum term of ten years and holders may not exercise them earlier than six months after the grant date or another term the award agreement may specify. Stock options granted to officers and other employees vest and become exercisable in three equal installments on the first, second and third anniversaries of the grant date. The exercise price of each option must equal or exceed the market price of our common stock on the grant date. We have not and, pursuant to the terms of our Stock Incentive Plan may not, reprice stock options to lower the exercise price. We use the Black-Scholes option valuation model to value the nonqualified stock options. We use historical data of stock option exercise behaviors to estimate the expected life that granted options will be outstanding. The risk-free interest rate is based on the Daily Treasury Yield Curve published by the U.S. Treasury on the grant date. The expected volatility is determined by using a blend of historical and implied volatility. We do not expect to pay dividends over the term of the options based on our current dividend policy. We also estimate that option holders will forfeit 5% of the options. The following weighted-average assumptions are used in the Black-Scholes option pricing model to estimate the fair value of granted options as of the grant date: 2018 2017 2016 Expected volatility 58.8% – 61.6% 61.5% – 64.0% 90.3% – 91.5% Weighted-average volatility 59.5% 62.5% 90.7% Expected term (in years) 3.4 – 6.6 3.3 – 6.5 3.3 – 6.7 Risk-free interest rate 2.3% – 2.6% 1.6% – 2.2% 1.2% – 1.8% Weighted-average grant-date fair value per share of granted options $3.51 $5.33 $1.29 Option activity for the year ended December 31, 2018 , is presented below: Stock Options Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate Intrinsic Value Outstanding at December 31, 2017 2,994,206 $ 7.69 Granted 842,000 6.56 Exercised (201,700 ) 3.82 Forfeited and expired (230,644 ) 18.56 Outstanding at December 31, 2018 3,403,862 6.90 6.1 $ 0.3 Exercisable at December 31, 2018 2,046,546 7.07 4.7 0.2 Unvested at December 31, 2018 1,357,316 6.66 8.5 0.1 Unvested at December 31, 2018 expected to vest 1,289,450 6.66 8.5 0.1 The total intrinsic value of stock option awards that holders exercised during the years ended December 31, 2018 , 2017 , and 2016 was $0.3 , $0.2 and $1.4 . Each exercised option’s intrinsic value is the quoted average of the reported high and low sales price on the exercise date. As of December 31, 2018 , total unrecognized compensation costs for non-vested stock options were $1.5 , which we expect to recognize over a weighted-average period of 1.7 years. Restricted Stock Restricted stock awards granted to officers and other employees ordinarily vest ratably on the first, second and third anniversaries of the grant. Non-vested restricted stock awards activity for the year ended December 31, 2018 , is presented below: Restricted Stock Awards Restricted Shares Weighted- Average Grant Date Fair Value Outstanding at December 31, 2017 518,184 $ 5.38 Granted 521,100 6.56 Vested/restrictions lapsed (513,848 ) 5.48 Canceled (18,733 ) 6.16 Outstanding at December 31, 2018 506,703 6.45 The weighted-average grant date fair value of restricted stock awards granted during the years ended December 31, 2018 , 2017 and 2016 , was $6.56 , $9.78 and $1.80 per share. The total intrinsic value of restricted stock awards that vested (i.e., restrictions lapsed) during the years ended December 31, 2018 , 2017 and 2016 , was $3.2 , $4.1 and $1.4 . As of December 31, 2018 , total unrecognized compensation costs for non-vested restricted stock awards granted under the SIP were $1.6 , which we expect to recognize over a weighted-average period of 1.4 years . Restricted Stock Units Restricted stock units (“RSUs”) represent equity-based compensation granted to Directors. RSU grants vest immediately, but we do not settle them (i.e., issue the underlying shares of stock) until one year after the grant date, unless a Director elects to defer the settlement to six months after his or her Board service is terminated. They may elect to take settlement in a single distribution or in annual installments up to fifteen years . Performance Shares Performance shares are granted to executive officers and other employees. They earn the awards by meeting performance measures over a three -year period. Though a target number of performance shares are awarded on the grant date, for 2018 grants the total number of performance shares that will actually be issued to the participant, if any, at the expiration of the performance period will be based on our total share return compared to the VanEck Vectors Steel ETF. For 2017 and 2016 grants, the total number of performance shares that will be issued to the participant, if any, at the expiration of the performance periods for each of those grants will be based on two equally-rated metrics: (i) our share performance compared to a prescribed compounded annual growth rate and (ii) our total share return compared to the VanEck Vectors Steel ETF for the 2017 grants and the Standard & Poor’s MidCap 400 index for 2016 grants. The following weighted-average assumptions are used in a Monte Carlo simulation model to estimate the fair value of performance shares granted: 2018 2017 2016 Company expected volatility 67.3 % 68.0 % 60.8 % VanEck Vectors Steel ETF expected volatility 52.2 % 48.9 % NA S&P’s MidCap 400 index expected volatility NA NA 27.6 % Risk-free interest rate 2.2 % 1.5 % 1.1 % Weighted-average grant-date fair value per performance share granted $ 8.05 $ 10.78 $ 1.74 Non-vested performance share awards activity for the year ended December 31, 2018 , is presented below: Performance Share Awards Performance Shares Weighted- Average Grant Date Fair Value Outstanding at December 31, 2017 718,668 $ 5.04 Granted 366,500 8.05 Earned (277,971 ) 1.74 Expired or forfeited (192,397 ) 5.55 Outstanding at December 31, 2018 614,800 9.19 The total intrinsic value of performance share awards that were earned during the year ended December 31, 2018 , was $0.7 . As of December 31, 2018 , total unrecognized compensation costs for non-vested performance share awards granted under the SIP were $2.6 , which we expect to recognize over a weighted-average period of 1.7 years . Equity-based Long-term Performance Plan During 2018, in order to further align our management with stockholder interest in maximizing long-term value, the Board of Directors changed the structure of long-term incentive compensation for executive officers, such that awards will be 30%

Comprehensive Income (Loss) (No

Comprehensive Income (Loss) (Notes)	12 Months Ended
	Dec. 31, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Comprehensive Income (Loss)	Comprehensive Income (Loss) Other comprehensive income (loss), net of tax, information is presented below: 2018 2017 2016 Foreign currency translation Balance at beginning of period $ 1.1 $ (3.6 ) $ (2.1 ) Other comprehensive income (loss)—foreign currency translation gain (loss) (1.7 ) 4.7 (1.5 ) Balance at end of period $ (0.6 ) $ 1.1 $ (3.6 ) Cash flow hedges Balance at beginning of period $ 22.3 $ 39.9 $ (44.8 ) Cumulative effect of adopting new hedging standard 0.8 — — Other comprehensive income (loss): Gains (losses) arising in period (5.6 ) (11.5 ) 56.1 Income tax expense (benefit) — — 6.2 Gains (losses) arising in period, net of tax (5.6 ) (11.5 ) 49.9 Reclassification of losses (gains) to net income (loss): Recorded in cost of products sold (10.3 ) (6.1 ) 39.1 Income tax (expense) benefit (b) — — 4.3 Net amount of reclassification of losses (gains) to net income (loss), net of tax (10.3 ) (6.1 ) 34.8 Total other comprehensive income (loss), net of tax (15.9 ) (17.6 ) 84.7 Balance at end of period $ 7.2 $ 22.3 $ 39.9 Pension and OPEB plans Balance at beginning of period $ (73.6 ) $ (125.0 ) $ (166.4 ) Other comprehensive income (loss): Prior service credit (cost) arising in period 11.1 4.7 (8.3 ) Gains (losses) arising in period (63.6 ) 94.2 11.6 Subtotal (52.5 ) 98.9 3.3 Income tax expense (benefit) — — 0.4 Gains (losses) arising in period, net of tax (52.5 ) 98.9 2.9 Reclassification to net income (loss): Prior service costs (credits) (a) (9.8 ) (53.8 ) (54.8 ) Actuarial (gains) losses (a) 29.3 6.3 97.9 Subtotal 19.5 (47.5 ) 43.1 Income tax (expense) benefit (b) — — 4.6 Amount of reclassification to net income (loss), net of tax 19.5 (47.5 ) 38.5 Total other comprehensive income (loss), net of tax (33.0 ) 51.4 41.4 Balance at end of period $ (106.6 ) $ (73.6 ) $ (125.0 ) (a) Included in pension and OPEB (income) expense (b)

Earnings Per Share (Notes)

Earnings Per Share (Notes)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings per Share Reconciliation of the numerators and denominators for basic and diluted EPS computations is presented below: 2018 2017 2016 Net income (loss) attributable to AK Steel Holding Corporation $ 186.0 $ 103.5 $ (16.8 ) Less: distributed earnings to common stockholders and holders of certain stock compensation awards — — — Undistributed earnings (loss) $ 186.0 $ 103.5 $ (16.8 ) Common stockholders earnings—basic and diluted: Distributed earnings to common stockholders $ — $ — $ — Undistributed earnings (loss) to common stockholders 185.7 103.5 (16.7 ) Common stockholders earnings (loss)—basic and diluted $ 185.7 $ 103.5 $ (16.7 ) Common shares outstanding (weighted-average shares in millions): Common shares outstanding for basic earnings per share 314.8 314.3 230.0 Effect of Exchangeable Notes — 4.5 — Effect of dilutive stock-based compensation 0.8 0.9 — Common shares outstanding for diluted earnings per share 315.6 319.7 230.0 Basic earnings per share: Distributed earnings $ — $ — $ — Undistributed earnings (loss) 0.59 0.33 (0.07 ) Basic earnings (loss) per share $ 0.59 $ 0.33 $ (0.07 ) Diluted earnings per share: Distributed earnings $ — $ — $ — Undistributed earnings (loss) 0.59 0.32 (0.07 ) Diluted earnings (loss) per share $ 0.59 $ 0.32 $ (0.07 ) Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect 2.4 1.4 3.0

Variable Interest Entities (Not

Variable Interest Entities (Notes)	12 Months Ended
	Dec. 31, 2018
Variable Interest Entity, Primary Beneficiary, Does Not Hold Majority Voting Interest, Disclosures [Abstract]
Variable Interest Entities Disclosure [Text Block]	Variable Interest Entities SunCoke Middletown We purchase all the coke and electrical power generated from SunCoke Middletown’s plant under long-term supply agreements. SunCoke Middletown is a variable interest entity because we have committed to purchase all the expected production from the facility through at least 2031 and we are the primary beneficiary. Therefore, we consolidate SunCoke Middletown’s financial results with our financial results, even though we have no ownership interest in SunCoke Middletown. SunCoke Middletown had income before income taxes of $58.4 , $61.7 and $66.0 for the years ended December 31, 2018 , 2017 and 2016 that was included in our consolidated income before income taxes. Vicksmetal/Armco Associates We own a 50%

Fair Value Measurements (Notes)

Fair Value Measurements (Notes)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We measure certain assets and liabilities at fair value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (i.e., the “exit price”) in an orderly transaction between market participants at the measurement date. In determining fair value, we use various valuation approaches. The hierarchy of those valuation approaches is in three levels based on the reliability of inputs. Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Below is a summary of the hierarchy levels: • Level 1 inputs are quoted prices in active markets for identical assets or liabilities that we have the ability to access at the measurement date. • Level 2 inputs are inputs, other than quoted prices, that are directly or indirectly observable for the asset or liability. Level 2 inputs include model-generated values that rely on inputs either directly observed or readily-derived from available market data sources, such as Bloomberg or other news and data vendors. They include quoted prices for similar assets or liabilities in active markets, inputs other than quoted prices that are observable for the asset or liability (e.g., interest rates and yield curves observable at commonly quoted intervals or current market) and contractual prices for the underlying financial instrument, as well as other relevant economic factors. As a practical expedient, we estimate the value of money market mutual funds by using a $1.00 per share multiplied by the number of shares in the fund as of the measurement date. We generate fair values for our commodity derivative contracts and foreign currency forward contracts from observable futures prices for the respective commodity or currency, from sources such as the New York Mercantile Exchange (NYMEX) or the London Metal Exchange (LME). In cases where the derivative is an option contract (including caps, floors and collars), we adjust our valuations to reflect the counterparty’s valuation assumptions. After validating that the counterparty’s assumptions for implied volatilities reflect independent source’s assumptions, we discount these model-generated future values with discount factors that reflect the counterparty’s credit quality. We apply different discount rates to different contracts since the maturities and counterparties differ. As of December 31, 2018 , a spread over benchmark rates of less than 1.5% was used for derivatives valued as assets and less than 2.4% for derivatives valued as liabilities. We have estimated the fair value of long-term debt based upon quoted market prices for the same or similar issues or on the current interest rates available to us for debt on similar terms and with similar maturities. • Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs are used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date. This level of categorization is not applicable to our valuations on a normal recurring basis. Assets and liabilities measured at fair value on a recurring basis are presented below: 2018 2017 Level 1 Level 2 Total Level 1 Level 2 Total Assets measured at fair value Cash and cash equivalents $ 48.6 $ — $ 48.6 $ 38.0 $ — $ 38.0 Other current assets: Foreign exchange contracts — 0.1 0.1 — 0.2 0.2 Commodity hedge contracts — 13.0 13.0 — 35.2 35.2 Other non-current assets: Foreign exchange contracts — 0.4 0.4 — 1.7 1.7 Commodity hedge contracts — 2.9 2.9 — 10.6 10.6 Assets measured at fair value $ 48.6 $ 16.4 $ 65.0 $ 38.0 $ 47.7 $ 85.7 Liabilities measured at fair value Accrued liabilities: Foreign exchange contracts $ — $ (1.2 ) $ (1.2 ) $ — $ (0.3 ) $ (0.3 ) Commodity hedge contracts — (5.9 ) (5.9 ) — (4.9 ) (4.9 ) Other non-current liabilities: Foreign exchange contracts — (1.5 ) (1.5 ) — — — Commodity hedge contracts — (1.6 ) (1.6 ) — (0.5 ) (0.5 ) Liabilities measured at fair value $ — $ (10.2 ) $ (10.2 ) $ — $ (5.7 ) $ (5.7 ) Liabilities measured at other than fair value Long-term debt, including current portions: Fair value $ — $ (1,852.4 ) $ (1,852.4 ) $ — $ (2,273.4 ) $ (2,273.4 ) Carrying amount — (1,993.7 ) (1,993.7 ) — (2,110.1 ) (2,110.1 ) See Note 7 for information on the fair value of pension plan assets. The carrying amounts of our other financial instruments do not differ materially from their estimated fair values at December 31, 2018 and 2017

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities (Notes)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities Exchange rate fluctuations affect a portion of revenues and operating costs that are denominated in foreign currencies, and we use forward currency and currency option contracts to reduce our exposure to certain of these currency price fluctuations. Contracts to sell euros have not been designated as cash flow hedges for accounting purposes, and gains or losses are reported in earnings immediately in other (income) expense. Contracts to purchase Canadian dollars are designated as cash flow hedges for accounting purposes, and we record the gains and losses for the derivatives and premiums paid for option contracts in accumulated other comprehensive income (loss) until we reclassify them into cost of products sold when we recognize the associated underlying operating costs. We are exposed to fluctuations in market prices of raw materials and energy sources. We may use cash-settled commodity price swaps and options to hedge the market risk associated with the purchase of certain of our raw materials and energy requirements. For input commodities, these derivatives are typically used for a portion of our electricity, iron ore, natural gas, nickel and zinc requirements. Our hedging strategy is to reduce the effect on earnings from the price volatility of these various commodity exposures, including timing differences between when we incur raw material commodity costs and when we receive sales surcharges from our customers based on those raw materials. Independent of any hedging activities, price changes in any of these commodity markets could negatively affect operating costs. All commodity derivatives are recognized as an asset or liability at fair value. We record the gains and losses and premiums paid for option contracts for commodity derivatives designated as cash flow hedges of forecasted purchases of raw materials and energy sources in accumulated other comprehensive income (loss) and reclassify them into cost of products sold when we recognize earnings for the associated underlying transaction. We record all gains or losses from commodity derivatives for which hedge accounting treatment has not been elected to earnings immediately in cost of products sold. We routinely use iron ore derivatives to reduce the volatility of the cost of our iron ore purchases. These derivatives do not qualify for hedge accounting treatment. We have no collateral deposited with counterparties under collateral funding arrangements as of December 31, 2018 . Outstanding derivative contracts and the period over which we are hedging our exposure to the volatility in future cash flows are presented below: Hedge Contracts Settlement Dates 2018 2017 Commodity contracts: Nickel (in lbs) — 500,000 Natural gas (in MMBTUs) January 2019 to December 2020 39,868,000 41,338,000 Zinc (in lbs) January 2019 to December 2020 52,150,000 50,350,000 Iron ore (in metric tons) January 2019 to December 2020 2,125,000 2,340,000 Electricity (in MWHs) January 2019 to September 2020 1,461,000 1,553,000 Foreign exchange contracts: Euros January 2019 to June 2019 € 4,000,000 € 26,000,000 Canadian dollars January 2019 to December 2021 C$ 118,560,000 C$ 148,080,000 The fair value of derivative instruments as of December 31, 2018 and 2017 , is presented below: Asset (liability) 2018 2017 Derivatives designated as hedging instruments: Other current assets: Commodity contracts $ 3.4 $ 9.0 Foreign exchange contracts — 0.2 Other non-current assets: Commodity contracts 1.0 2.3 Foreign exchange contracts 0.4 1.7 Accrued liabilities: Commodity contracts (4.7 ) (4.6 ) Foreign exchange contracts (1.2 ) (0.2 ) Other non-current liabilities: Commodity contracts (1.2 ) (0.5 ) Foreign exchange contracts (1.5 ) — Derivatives not designated as hedging instruments: Other current assets: Commodity contracts 9.6 26.2 Foreign exchange contracts 0.1 — Other non-current assets—commodity contracts 1.9 8.3 Accrued liabilities: Commodity contracts (1.2 ) (0.3 ) Foreign exchange contracts — (0.1 ) Other non-current liabilities—commodity contracts (0.4 ) — Gains (losses) on derivative instruments for the years ended December 31, 2018 , 2017 and 2016 , are presented below: Gain (loss) 2018 2017 2016 Derivatives designated as cash flow hedges— Commodity contracts: Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness $ (0.2 ) $ (11.5 ) $ 56.1 Reclassified from accumulated other comprehensive income into cost of products sold 11.2 6.1 (39.1 ) Foreign exchange contract: Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness (5.4 ) — — Reclassified from accumulated other comprehensive income into cost of products sold (0.9 ) — — Derivatives not designated as hedging instruments: Commodity contracts—recognized in cost of products sold (2.4 ) 31.6 38.6 Foreign exchange contracts—recognized in other (income) expense 0.1 (1.6 ) (0.9 ) Gains (losses) before tax expected to be reclassified into cost of products sold within the next twelve months for our existing commodity contracts that qualify for hedge accounting are presented below: Hedge Gains (losses) Natural gas $ 5.1 Electricity 2.7 Zinc (4.8 ) Canadian dollars (1.5 )

Supplementary Cash Flow Informa

Supplementary Cash Flow Information (Notes)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Supplementary Cash Flow Information	Supplementary Cash Flow Information Net cash paid (received) during the period for interest, net of capitalized interest, and income taxes are presented below: 2018 2017 2016 Net cash paid (received) during the period for: Interest, net of capitalized interest $ 136.3 $ 130.5 $ 137.1 Income taxes (5.5 ) 0.1 (2.6 ) Included in net cash flows from operations was cash provided by SunCoke Middletown of $76.6 , $77.1 and $83.3 for the years ended December 31, 2018 , 2017 and 2016 . Consolidated cash and cash equivalents at December 31, 2018 , and 2017 , include SunCoke Middletown’s cash and cash equivalents of $1.1 and $0.1 . SunCoke Middletown’s cash and cash equivalents have no compensating balance arrangements or legal restrictions, but are not available for our use. We had capital investments during the years ended December 31, 2018 , 2017 and 2016 , that had not been paid as of the end of the respective period. These amounts are included in accounts payable and accrued liabilities and have been excluded from the consolidated statements of cash flows until paid. We included our leased Research and Innovation Center in property, plant and equipment and as a capital lease obligation in the consolidated balance sheets during its construction, which was completed in early 2017 and represented a non-cash transaction for us. In October 2017, we acquired the Research and Innovation Center capital lease with cash, effectively settling the obligation. We also granted restricted stock to certain employees and restricted stock units to directors under the SIP. Non-cash investing and financing activities for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 Capital investments $ 33.4 $ 37.3 $ 33.2 Research and Innovation Center capital lease — 1.1 25.2 Issuance of restricted stock and restricted stock units 4.5 4.6 2.3

Quarterly Information (Unaudite

Quarterly Information (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Information (Unaudited)	Quarterly Information (Unaudited) Earnings per share for each quarter and the year are calculated individually and may not sum to the total for the year. 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Year Net sales $ 1,658.9 $ 1,746.6 $ 1,735.6 $ 1,677.1 $ 6,818.2 Operating profit (loss) 63.6 99.5 114.8 86.5 364.4 Net income (loss) attributable to AK Holding 28.7 56.6 67.2 33.5 186.0 Basic and diluted earnings (loss) per share $ 0.09 $ 0.18 $ 0.21 $ 0.11 $ 0.59 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Year Net sales $ 1,533.4 $ 1,557.2 $ 1,494.3 $ 1,495.6 $ 6,080.5 Operating profit (loss) 129.7 116.5 66.3 (52.3 ) 260.2 Net income (loss) attributable to AK Holding 84.4 77.2 22.3 (80.4 ) 103.5 Basic earnings (loss) per share $ 0.27 $ 0.25 $ 0.07 $ (0.26 ) $ 0.33 Diluted earnings (loss) per share 0.26 0.24 0.07 (0.26 ) 0.32 Included in net income attributable to AK Holding in the fourth quarter and full year of 2018 was a pension settlement charge of $14.5 . Included in net income attributable to AK Holding in the fourth quarter and full year of 2017 were a credit of $19.3 to reduce a transportation liability and a non-cash charge of $75.6

Supplementary Guarantor Informa

Supplementary Guarantor Information (Notes)	12 Months Ended
	Dec. 31, 2018
Supplemental Guarantor Information [Abstract]
Supplemental Guarantor Information	Supplementary Guarantor Information AK Steel’s Secured Notes, 2021 Notes, 2025 Notes and 2027 Notes (collectively, the “Senior Notes”) and the Exchangeable Notes are governed by indentures entered into by AK Holding and its 100%-owned subsidiary, AK Steel. Under the terms of the indentures, AK Holding and the Subsidiary Guarantors each fully and unconditionally, jointly and severally, guarantee the payment of interest, principal and premium, if any, on each of the notes included in the Senior Notes. Under the terms of the indenture for the Exchangeable Notes, AK Holding fully and unconditionally, jointly and severally, guarantees the payment of interest, principal and premium, if any, on the notes. AK Holding is the sole guarantor of the Exchangeable Notes. We present all investments in subsidiaries in the supplementary guarantor information using the equity method of accounting. Therefore, the net income (loss) of the subsidiaries accounted for using the equity method is in their parents’ investment accounts. The principal elimination entries eliminate investments in subsidiaries and inter-company balances and transactions. The following supplementary condensed consolidating financial statements present information about AK Holding, AK Steel, the Subsidiary Guarantors and the other non-guarantor subsidiaries. Condensed Statements of Comprehensive Income (Loss) Year Ended December 31, 2018 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net sales $ — $ 6,244.7 $ 320.8 $ 752.8 $ (500.1 ) $ 6,818.2 Cost of products sold (exclusive of items shown separately below) — 5,519.8 221.4 620.9 (451.1 ) 5,911.0 Selling and administrative expenses 3.5 320.0 14.5 34.2 (49.6 ) 322.6 Depreciation — 171.5 8.0 40.7 — 220.2 Total operating costs 3.5 6,011.3 243.9 695.8 (500.7 ) 6,453.8 Operating profit (loss) (3.5 ) 233.4 76.9 57.0 0.6 364.4 Interest expense — 145.9 — 5.7 — 151.6 Pension and OPEB (income) expense — (19.2 ) (19.2 ) Other (income) expense — 8.7 (16.4 ) (2.9 ) 4.7 (5.9 ) Income (loss) before income taxes (3.5 ) 98.0 93.3 54.2 (4.1 ) 237.9 Income tax expense (benefit) — (26.5 ) 23.3 (2.0 ) (1.0 ) (6.2 ) Equity in net income (loss) of subsidiaries 189.5 65.0 — 0.7 (255.2 ) — Net income (loss) 186.0 189.5 70.0 56.9 (258.3 ) 244.1 Less: Net income attributable to noncontrolling interests — — — 58.1 — 58.1 Net income (loss) attributable to AK Steel Holding Corporation 186.0 189.5 70.0 (1.2 ) (258.3 ) 186.0 Other comprehensive income (loss) (50.6 ) (50.6 ) — (1.7 ) 52.3 (50.6 ) Comprehensive income (loss) attributable to AK Steel Holding Corporation $ 135.4 $ 138.9 $ 70.0 $ (2.9 ) $ (206.0 ) $ 135.4 Condensed Statements of Comprehensive Income (Loss) Year Ended December 31, 2017 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net sales $ — $ 5,755.1 $ 285.9 $ 496.3 $ (456.8 ) $ 6,080.5 Cost of products sold (exclusive of items shown separately below) — 5,082.0 197.7 387.2 (413.8 ) 5,253.1 Selling and administrative expenses 3.7 285.5 13.5 26.9 (44.7 ) 284.9 Depreciation — 189.3 7.5 29.2 — 226.0 Charge (credit) for termination of pellet agreement and related transportation costs — (19.3 ) — — — (19.3 ) Asset impairment charge — 75.6 — — — 75.6 Total operating costs 3.7 5,613.1 218.7 443.3 (458.5 ) 5,820.3 Operating profit (loss) (3.7 ) 142.0 67.2 53.0 1.7 260.2 Interest expense — 150.3 — 2.0 — 152.3 Pension and OPEB (income) expense — (71.9 ) — — — (71.9 ) Other (income) expense — 30.1 (11.4 ) (5.4 ) 3.8 17.1 Income (loss) before income taxes (3.7 ) 33.5 78.6 56.4 (2.1 ) 162.7 Income tax expense (benefit) — (29.4 ) 29.9 (1.8 ) (0.9 ) (2.2 ) Equity in net income (loss) of subsidiaries 107.2 44.3 — — (151.5 ) — Net income (loss) 103.5 107.2 48.7 58.2 (152.7 ) 164.9 Less: Net income attributable to noncontrolling interests — — — 61.4 — 61.4 Net income (loss) attributable to AK Steel Holding Corporation 103.5 107.2 48.7 (3.2 ) (152.7 ) 103.5 Other comprehensive income (loss) 38.5 38.5 — 4.7 (43.2 ) 38.5 Comprehensive income (loss) attributable to AK Steel Holding Corporation $ 142.0 $ 145.7 $ 48.7 $ 1.5 $ (195.9 ) $ 142.0 Condensed Statements of Comprehensive Income (Loss) Year Ended December 31, 2016 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net sales $ — $ 5,681.0 $ 250.9 $ 411.5 $ (460.9 ) $ 5,882.5 Cost of products sold (exclusive of items shown separately below) — 5,044.8 171.7 299.4 (416.2 ) 5,099.7 Selling and administrative expenses 4.4 282.7 12.7 22.6 (43.3 ) 279.1 Depreciation — 187.8 7.0 21.8 — 216.6 Charge (credit) for termination of pellet agreement and related transportation costs — 69.5 — — — 69.5 Total operating costs 4.4 5,584.8 191.4 343.8 (459.5 ) 5,664.9 Operating profit (loss) (4.4 ) 96.2 59.5 67.7 (1.4 ) 217.6 Interest expense — 162.3 — 1.6 — 163.9 Pension and OPEB (income) expense — 16.5 — — — 16.5 Other (income) expense — 16.4 (8.1 ) (8.6 ) 5.2 4.9 Income (loss) before income taxes (4.4 ) (99.0 ) 67.6 74.7 (6.6 ) 32.3 Income tax expense (benefit) — (43.7 ) 25.7 3.6 (2.5 ) (16.9 ) Equity in net income (loss) of subsidiaries (12.4 ) 42.9 — (0.7 ) (29.8 ) — Net income (loss) (16.8 ) (12.4 ) 41.9 70.4 (33.9 ) 49.2 Less: Net income attributable to noncontrolling interests — — — 66.0 — 66.0 Net income (loss) attributable to AK Steel Holding Corporation (16.8 ) (12.4 ) 41.9 4.4 (33.9 ) (16.8 ) Other comprehensive income (loss) 124.6 124.6 — (1.5 ) (123.1 ) 124.6 Comprehensive income (loss) attributable to AK Steel Holding Corporation $ 107.8 $ 112.2 $ 41.9 $ 2.9 $ (157.0 ) $ 107.8 Condensed Balance Sheets December 31, 2018 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company ASSETS Current assets: Cash and cash equivalents $ — $ 22.1 $ 8.2 $ 18.3 $ — $ 48.6 Accounts receivable, net — 515.4 34.0 95.3 (8.9 ) 635.8 Inventory — 1,299.6 53.9 75.6 (9.2 ) 1,419.9 Other current assets — 85.5 0.1 11.4 — 97.0 Total current assets — 1,922.6 96.2 200.6 (18.1 ) 2,201.3 Property, plant and equipment — 6,111.1 189.7 668.4 — 6,969.2 Accumulated depreciation — (4,785.5 ) (102.8 ) (169.3 ) — (5,057.6 ) Property, plant and equipment, net — 1,325.6 86.9 499.1 — 1,911.6 Other non-current assets: Investment in subsidiaries (3,017.4 ) 1,931.1 — 68.2 1,018.1 — Inter-company accounts 3,117.3 — 1,630.7 — (4,748.0 ) — Goodwill and intangible assets — — 32.9 266.0 — 298.9 Other non-current assets — 54.3 — 49.6 — 103.9 TOTAL ASSETS $ 99.9 $ 5,233.6 $ 1,846.7 $ 1,083.5 $ (3,748.0 ) $ 4,515.7 LIABILITIES AND EQUITY (DEFICIT) Current liabilities: Accounts payable $ — $ 722.5 $ 26.2 $ 55.5 $ (3.2 ) $ 801.0 Accrued liabilities — 251.5 8.7 28.7 — 288.9 Current portion of pension and other postretirement benefit obligations — 38.4 — 0.3 — 38.7 Total current liabilities — 1,012.4 34.9 84.5 (3.2 ) 1,128.6 Non-current liabilities: Long-term debt — 1,993.7 — — — 1,993.7 Pension and other postretirement benefit obligations — 827.0 — 2.9 — 829.9 Inter-company accounts — 4,312.3 — 511.2 (4,823.5 ) — Other non-current liabilities — 105.6 0.2 28.2 — 134.0 TOTAL LIABILITIES — 8,251.0 35.1 626.8 (4,826.7 ) 4,086.2 Equity (deficit): Total stockholders’ equity (deficit) 99.9 (3,017.4 ) 1,811.6 127.1 1,078.7 99.9 Noncontrolling interests — — — 329.6 — 329.6 TOTAL EQUITY (DEFICIT) 99.9 (3,017.4 ) 1,811.6 456.7 1,078.7 429.5 TOTAL LIABILITIES AND EQUITY (DEFICIT) $ 99.9 $ 5,233.6 $ 1,846.7 $ 1,083.5 $ (3,748.0 ) $ 4,515.7 Condensed Balance Sheets December 31, 2017 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company ASSETS Current assets: Cash and cash equivalents $ — $ 14.5 $ 7.2 $ 16.3 $ — $ 38.0 Accounts receivable, net — 432.4 33.2 65.4 (13.2 ) 517.8 Inventory — 1,231.5 55.1 108.3 (9.9 ) 1,385.0 Other current assets — 124.7 0.2 5.4 — 130.3 Total current assets — 1,803.1 95.7 195.4 (23.1 ) 2,071.1 Property, plant and equipment — 6,004.0 181.5 646.3 — 6,831.8 Accumulated depreciation — (4,620.8 ) (94.8 ) (130.0 ) — (4,845.6 ) Property, plant and equipment, net — 1,383.2 86.7 516.3 — 1,986.2 Other non-current assets: Investment in subsidiaries (3,127.4 ) 1,844.9 — 67.5 1,215.0 — Inter-company accounts 3,082.8 — 1,523.1 — (4,605.9 ) — Goodwill and intangible assets — — 32.8 273.9 — 306.7 Other non-current assets — 66.3 0.2 44.3 — 110.8 TOTAL ASSETS $ (44.6 ) $ 5,097.5 $ 1,738.5 $ 1,097.4 $ (3,414.0 ) $ 4,474.8 LIABILITIES AND EQUITY (DEFICIT) Current liabilities: Accounts payable $ — $ 623.3 $ 17.9 $ 50.9 $ (1.7 ) $ 690.4 Accrued liabilities — 228.2 7.8 34.5 — 270.5 Current portion of pension and other postretirement benefit obligations — 39.7 — 0.4 — 40.1 Total current liabilities — 891.2 25.7 85.8 (1.7 ) 1,001.0 Non-current liabilities: Long-term debt — 2,110.1 — — — 2,110.1 Pension and other postretirement benefit obligations — 890.8 — 3.4 — 894.2 Inter-company accounts — 4,199.6 — 489.1 (4,688.7 ) — Other non-current liabilities — 133.2 1.0 34.7 — 168.9 TOTAL LIABILITIES — 8,224.9 26.7 613.0 (4,690.4 ) 4,174.2 Equity (deficit): Total stockholders’ equity (deficit) (44.6 ) (3,127.4 ) 1,711.8 139.2 1,276.4 (44.6 ) Noncontrolling interests — — — 345.2 — 345.2 TOTAL EQUITY (DEFICIT) (44.6 ) (3,127.4 ) 1,711.8 484.4 1,276.4 300.6 TOTAL LIABILITIES AND EQUITY (DEFICIT) $ (44.6 ) $ 5,097.5 $ 1,738.5 $ 1,097.4 $ (3,414.0 ) $ 4,474.8 Condensed Statements of Cash Flows Year Ended December 31, 2018 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net cash flows from operating activities $ (2.3 ) $ 209.7 $ 83.1 $ 83.8 $ (9.6 ) $ 364.7 Cash flows from investing activities: Capital investments — (122.9 ) (8.1 ) (21.0 ) — (152.0 ) Other investing items, net — 0.8 — (0.7 ) — 0.1 Net cash flows from investing activities — (122.1 ) (8.1 ) (21.7 ) — (151.9 ) Cash flows from financing activities: Net borrowings (repayments) under credit facility — (115.0 ) — — — (115.0 ) Redemption of long-term debt — (12.6 ) — — — (12.6 ) Inter-company activity 2.5 48.3 (74.0 ) 13.6 9.6 — SunCoke Middletown distributions to noncontrolling interest owners — — — (73.7 ) — (73.7 ) Other financing items, net (0.2 ) (0.7 ) — — — (0.9 ) Net cash flows from financing activities 2.3 (80.0 ) (74.0 ) (60.1 ) 9.6 (202.2 ) Net increase (decrease) in cash and cash equivalents — 7.6 1.0 2.0 — 10.6 Cash and equivalents, beginning of year — 14.5 7.2 16.3 — 38.0 Cash and equivalents, end of year $ — $ 22.1 $ 8.2 $ 18.3 $ — $ 48.6 Condensed Statements of Cash Flows Year Ended December 31, 2017 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net cash flows from operating activities $ (2.5 ) $ 67.3 $ 73.3 $ 61.7 $ (1.0 ) $ 198.8 Cash flows from investing activities: Capital investments — (131.8 ) (5.6 ) (15.1 ) — (152.5 ) Investment in acquired business, net of cash acquired — (360.4 ) — — — (360.4 ) Other investing items, net — 4.0 — 0.2 — 4.2 Net cash flows from investing activities — (488.2 ) (5.6 ) (14.9 ) — (508.7 ) Cash flows from financing activities: Net borrowings (repayments) under credit facility — 450.0 — — — 450.0 Proceeds from issuance of long-term debt — 680.0 — — — 680.0 Redemption of long-term debt — (848.4 ) — — — (848.4 ) Debt issuance costs — (25.3 ) — — — (25.3 ) Inter-company activity 5.0 31.2 (64.9 ) 27.7 1.0 — SunCoke Middletown distributions to noncontrolling interest owners — — — (79.1 ) — (79.1 ) Other financing items, net (2.5 ) — — — — (2.5 ) Net cash flows from financing activities 2.5 287.5 (64.9 ) (51.4 ) 1.0 174.7 Net increase (decrease) in cash and cash equivalents — (133.4 ) 2.8 (4.6 ) — (135.2 ) Cash and equivalents, beginning of year — 147.9 4.4 20.9 — 173.2 Cash and equivalents, end of year $ — $ 14.5 $ 7.2 $ 16.3 $ — $ 38.0 Condensed Statements of Cash Flows Year Ended December 31, 2016 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net cash flows from operating activities $ (3.1 ) $ 186.5 $ 44.3 $ 92.2 $ (15.3 ) $ 304.6 Cash flows from investing activities: Capital investments — (116.0 ) (8.8 ) (2.8 ) — (127.6 ) Other investing items, net — 3.0 — (0.7 ) — 2.3 Net cash flows from investing activities — (113.0 ) (8.8 ) (3.5 ) — (125.3 ) Cash flows from financing activities: Net borrowings (repayments) under credit facility — (550.0 ) — — — (550.0 ) Proceeds from issuance of long-term debt — 380.0 — — — 380.0 Redemption of long-term debt — (392.8 ) — — — (392.8 ) Proceeds from issuance of common stock 600.4 — — — — 600.4 Debt issuance costs — (20.4 ) — — — (20.4 ) Inter-company activity (602.4 ) 630.5 (36.8 ) (6.6 ) 15.3 — SunCoke Middletown distributions to noncontrolling interest owners — — — (85.1 ) — (85.1 ) Other financing items, net 5.1 0.1 — — — 5.2 Net cash flows from financing activities 3.1 47.4 (36.8 ) (91.7 ) 15.3 (62.7 ) Net increase (decrease) in cash and cash equivalents — 120.9 (1.3 ) (3.0 ) — 116.6 Cash and equivalents, beginning of year — 27.0 5.7 23.9 — 56.6 Cash and equivalents, end of year $ — $ 147.9 $ 4.4 $ 20.9 $ — $ 173.2

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation—These financial statements consolidate the operations and accounts of AK Steel Holding Corporation (“AK Holding”), its wholly owned subsidiary AK Steel Corporation (“AK Steel”), all subsidiaries in which AK Holding has a controlling interest, and two variable interest entities for which AK Steel is the primary beneficiary. Unless the context indicates otherwise, references to “we,” “us” and “our” refer to AK Holding and its subsidiaries. We also operate Mexican and European trading companies that buy and sell steel and steel products and other materials. We manage operations on a consolidated, integrated basis so that we can use the most appropriate equipment and facilities for the production of a product, regardless of product line. Therefore, we conclude that we operate in a single business segment. All intercompany transactions and balances have been eliminated.
Use of Estimates	Use of Estimates—The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires the use of estimates and assumptions that affect the amounts reported. We base these estimates on historical experience and information available to us about current events and actions we may take in the future. Estimates and assumptions affect significant items that include the carrying value of long-lived assets, including investments and goodwill; valuation allowances for receivables, inventories and deferred income tax assets; legal and environmental liabilities; workers compensation and asbestos liabilities; share-based compensation; and assets and obligations of employee benefit plans. There can be no assurance that actual results will not differ from these estimates.
Revenue Recognition	Revenue Recognition— We generate our revenue through product sales, and shipping terms generally indicate when we have fulfilled our performance obligations and passed control of products to our customer. Our revenue transactions consist of a single performance obligation to transfer promised goods. We have contracts with a substantial portion of our customers. These contracts usually define the mechanism for determining the sales price, but the contracts do not impose a specific quantity on either party. Quantities to be delivered to the customer are determined at a point near the date of delivery through purchase orders or other written instructions we receive from the customer. Spot market sales are made through purchase orders or other written instructions. We recognize revenue when we have fulfilled a performance obligation, which is typically when we have shipped products at the customer’s instructions. For sales with shipping terms that transfer title and control at the destination point, we recognize revenue when the customer receives the goods and our performance obligation is complete. For sales with shipping terms that transfer title and control at the shipping point with us bearing responsibility for freight costs to the destination, we determine that we have fulfilled a single performance obligation and recognize revenue when we ship the goods. For our tooling solutions, we record progress payments that we receive from a customer as accrued liabilities until we recognize the revenue when the customer provides written acceptance that our performance obligation has been fulfilled.
Cost of Products Sold	Cost of Products Sold—Cost of products sold consists primarily of raw materials, energy costs, supplies consumed in the manufacturing process, manufacturing labor, contract labor and direct overhead expense necessary to manufacture the finished steel product, as well as distribution and warehousing costs. Our share of the income (loss) of investments in associated companies accounted for under the equity method is included in costs of products sold since these operations are integrated with our overall steelmaking operations.
Share-Based Compensation	Share-Based Compensation—Compensation costs for stock awards granted under our Stock Incentive Plan are recognized over their vesting period using the straight-line method. We estimate stock award forfeitures expected to occur to determine the compensation cost we recognize each period.
Legal Fees	Legal Fees—Legal fees associated with litigation and similar proceedings that are not expected to provide a benefit in future periods are expensed as incurred. Legal fees associated with activities that are expected to provide a benefit in future periods, such as costs associated with the issuance of debt, are capitalized as incurred.
Income Taxes	Income Taxes—Interest and penalties from uncertain tax positions are included in income tax expense.
Earnings per Share	Earnings per Share—Earnings per share is calculated using the “two-class” method. Under the “two-class” method, undistributed earnings are allocated to both common shares and participating securities. We divide the sum of distributed earnings to common stockholders and undistributed earnings allocated to common stockholders by the weighted-average number of common shares outstanding during the period. The restricted stock granted by AK Holding is entitled to non-forfeitable dividends before vesting and meets the criteria of a participating security.
Cash Equivalents	Cash Equivalents—Cash equivalents include short-term, highly liquid investments that are readily convertible to known amounts of cash and have an original maturity of three months or less.
Inventory	Inventory— Inventories are valued at the lower of cost or net realizable value. We measure the cost of inventories using the average cost method. See Note 2
Property, Plant and Equipment	Property, Plant and Equipment— Plant and equipment are depreciated under the straight-line method over their estimated lives. Estimated lives are as follows: land improvements over 20 years , leaseholds over the life of the related operating lease term, buildings over 40 years and machinery and equipment over two to 20 years . The estimated weighted-average life of our machinery and equipment is 13 years at the end of 2018
Property, Plant and Equipment, Planned Major Maintenance Activities	We expense costs for major maintenance activities at our operating facilities when the activities occur.
Property, Plant and Equipment, Impairment or Disposal of Long-Lived Assets	We review the carrying value of long-lived assets to be held and used and long-lived assets to be disposed of when events and circumstances warrant such a review. If the carrying value of a long-lived asset exceeds its fair value, an impairment has occurred and a loss is recognized based on the amount by which the carrying value exceeds the fair value, less cost to dispose, for assets to be sold or abandoned. We determine fair value by using quoted market prices, estimates based on prices of similar assets or anticipated cash flows discounted at a rate commensurate with risk.
Equity Method Investments	Investments— Investments in associated companies are accounted for under the equity method. We review investments for impairment when circumstances indicate that a loss in value below its carrying amount is other than temporary.
Goodwill	Goodwill and Intangible Assets—Goodwill relates to our tubular and Precision Partners’ businesses. Intangible assets are recorded at cost, and those with finite lives are amortized over their estimated useful lives. We review goodwill for potential impairment at least annually on October 1 each year and whenever events or circumstances make it more likely than not that impairment may have occurred. Considering operating results and the estimated fair value of the businesses, the most recent annual goodwill impairment tests indicated that the fair value of each of our business reporting units was in excess of its carrying value. No goodwill impairment was recorded as a result of the annual impairment tests in the past three years.
Debt Issuance Costs	Debt Issuance Costs—Debt issuance costs for the revolving credit facility are included in other non-current assets and all other debt issuance costs reduce the carrying amount of long-term debt.
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits—We recognize, as of a measurement date, any unrecognized actuarial net gains or losses that exceed 10% of the larger of the projected benefit obligations or the plan assets, defined as the “corridor.” Amounts inside the corridor are amortized over the plan participants’ life expectancy. We determine the expected return on assets using the fair value of plan assets.
Concentrations of Credit Risk	Concentrations of Credit Risk— We are primarily a producer of carbon, stainless and electrical steels and steel products, which are sold to a number of markets, including automotive, infrastructure and manufacturing, and distributors and converters. We had two customers that accounted for 11% and 10% of net sales in 2018 , one customer that accounted for 12% of net sales in 2017 , and two customers that accounted for 12% and 11% of net sales in 2016
Concentrations of Credit Risk, Trade Accounts Receivable	Approximately 52% and 55% of accounts receivable outstanding at December 31, 2018 and 2017 , are due from businesses associated with the U.S. automotive industry, including 13% of receivables due from one automotive customer as of December 31, 2018 , and 18% due from one automotive customer as of December 31, 2017
Labor Agreements	Labor Agreements— At December 31, 2018 , we employed approximately 9,500 people, of which approximately 5,700 are represented by labor unions under various agreements that expire between 2019 and 2021 . In March 2018, members of the International Association of Machinists and Aerospace Workers, Local 1943 , ratified a labor agreement covering approximately 1,760 production employees at Middletown Works. The new agreement expires March 15, 2020 . With our January 28, 2019, announcement of plans to permanently close the Ashland Works facility by the end of 2019, over the coming months we expect to engage in negotiations with the United Steelworkers, Local 1865 , regarding the plant closure in accordance with applicable law and the terms and conditions of the labor agreement. The labor agreement, with an original expiration date of September 1, 2018 , is by mutual agreement being extended on a rolling 60-day basis, subject to further notification of termination by either party. Other agreements that expire within the next twelve months include an agreement with the United Steelworkers, Local 1190 , which governs approximately 230 production employees at Mountain State Carbon LLC, is scheduled to expire on March 1, 2019 . An agreement with the United Auto Workers, Local 3303 , which governs approximately 1,170 production employees at Butler Works, was originally scheduled to expire on April 1, 2019 . By mutual agreement, the labor agreement has been extended and is now scheduled to expire on April 16, 2019 . An agreement with the United Auto Workers, Local 4104 , which governs approximately 100 production employees at Zanesville Works, is scheduled to expire on May 31, 2019 . An agreement with the United Auto Workers, Local 3462 , which governs approximately 300 production employees at Coshocton Works, is scheduled to expire on September 30, 2019
Financial Instruments, Derivatives	Financial Instruments— We are a party to derivative instruments that are designated and qualify as hedges for accounting purposes. We may also use derivative instruments to which we do not apply hedge accounting treatment. Our objective in using these instruments is to limit operating cash flow exposure to fluctuations in the fair value of selected commodities and currencies. Fluctuations in the price of certain commodities we use in production processes may affect our income and cash flows. We have implemented raw material and energy surcharges for some contract customers. For certain commodities where such exposure exists, we may use cash-settled commodity price swaps, collars and purchase options, with a duration of up to two years , to hedge the price of a portion of our natural gas, iron ore, electricity, zinc and nickel requirements. We may designate some of these instruments as cash flow hedges and changes in their fair value and settlements are recorded in accumulated other comprehensive income. We subsequently reclassify gains and losses from accumulated other comprehensive income to cost of products sold in the same period we recognize the earnings associated with the underlying transaction. The change in fair value for other instruments is immediately recorded in cost of products sold with the offset recorded as assets or liabilities. Exchange rate fluctuations affect a portion of revenues and operating costs that are denominated in foreign currencies, and we use currency forwards and options to reduce our exposure to these currency price fluctuations. These derivative contracts are entered into with durations up to three years . Contracts that sell euros have not been designated as hedges for accounting purposes and gains or losses are reported in earnings immediately in other income (expense). Contracts that purchase Canadian dollars are designated as hedges for accounting purposes, which requires us to record the gains and losses for the derivatives in accumulated other comprehensive income and reclassify them into cost of products sold in the same period we recognize costs for the associated underlying operations.
Asbestos and Environmental Reserves	Asbestos and Environmental Accruals—For a number of years, we have been remediating sites where hazardous materials may have been released, including sites no longer owned by us. In addition, a number of lawsuits alleging asbestos exposure have been filed and continue to be filed against us. We have established accruals for estimated probable costs from asbestos claim settlements and environmental investigation, monitoring and remediation. If the accruals are not adequate to meet future claims, operating results and cash flows may be negatively affected. Our accruals do not consider the potential for insurance recoveries, for which we have partial insurance coverage for some future asbestos claims. In addition, some existing insurance policies covering asbestos and environmental contingencies may serve to partially reduce future covered expenditures.
New Accounting Pronouncements	Adoption of New Accounting Principles— On January 1, 2018, we adopted the following new accounting principles, both of which have been applied retrospectively to all periods presented. On January 1, 2018, we adopted Accounting Standards Update No. 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . Under this standard, the service cost component of periodic pension and other postretirement benefit expense is included in cost of products sold and selling and administrative expenses, consistent with our treatment of other employee compensation costs. The remainder of periodic pension and other postretirement benefit (income) expense of $(19.2) , $(71.9) and $16.5 for the years ended December 31, 2018, 2017 and 2016, is recorded separately in the consolidated statements of operations below operating profit. We have retrospectively applied the change in accounting principle to all periods presented. The adoption of this standard update had no other effect on our consolidated financial statements. On January 1, 2018, we changed our accounting method for valuing inventories to the average cost method for inventories previously valued using the last-in, first-out (LIFO) method. The effects of this change in accounting principle from LIFO to average cost have been retrospectively applied to all periods presented. See Note 2 for additional information. Other New Accounting Pronouncements Adopted— We adopted Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) , as of January 1, 2018, through the modified retrospective method applied to those contracts that were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018, are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with our historic accounting under ASC Topic 605. There was no adjustment required to adopt Topic 606 since our revenue recognition under Topic 606 is substantially the same as under Topic 605. In August 2017, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities , to better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. Among other amendments, the update allows entities to designate the variability in cash flows attributable to changes in a contractually specified component stated in the contract as the hedged risk in a cash flow hedge of a forecasted purchase or sale of a nonfinancial asset. We adopted the standard update effective as of January 1, 2018, and have applied the new hedge guidance for certain hedges entered since adoption. The effect of adoption of the new guidance was not significant. In February 2018, FASB issued Accounting Standards Update 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted in December 2017. We early adopted this standard update as of December 31, 2018. We elected to not reclassify the income tax effects of the Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. Recent Accounting Pronouncements Not Yet Adopted— FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) , during the first quarter of 2016. Topic 842 requires entities to recognize lease assets and lease liabilities for substantially all leases, with the exception of short-term leases, and disclose key information about leasing arrangements for certain leases. We intend to recognize and measure leases beginning at the adoption date using a modified retrospective approach. Under the modified retrospective approach, we will not adjust our comparative period financial information or make the new lease disclosures for periods before the effective date. Topic 842 is effective for us beginning January 1, 2019. The new guidance provides a number of optional practical expedients in transition and we have determined to use certain of these practical expedients. We have designed new processes and controls, cataloged and entered our leases into a recently implemented software solution and evaluated our population of leased assets to assess the effect of the new guidance on our consolidated financial statements. We currently expect that the adoption of the standard will result in a material increase to the assets and liabilities on our consolidated balance sheets, but will not have a material effect on our results of operations or cash flows. We expect adoption of the standard will result in the recognition of additional lease assets and lease liabilities between $250.0 and $350.0 as of January 1, 2019. The range reflects our current best estimates as we are still evaluating whether to separate lease and non-lease components for certain asset types, particularly for leases embedded within service contracts. In June 2016, FASB issued Accounting Standards Update 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , to replace the incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. In connection with recognizing credit losses on receivables and other financial instruments, we will be required to use a forward-looking expected loss model rather than the incurred loss model. The new standard will be effective for us beginning January 1, 2020, with early adoption permitted beginning January 1, 2019. Adoption of this standard is through a cumulative-effect adjustment to retained earnings as of the effective date. We are currently evaluating the effect of this standard on our consolidated financial position and results of operations.
Reclassifications	Reclassifications—We reclassified certain prior-year amounts to conform to the current-year presentation.

Supplementary Financial State_2

Supplementary Financial Statement Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplementary Financial Statement Information [Abstract]
Disaggregation of Revenue	Net sales by market are presented below: 2018 2017 2016 Automotive $ 4,284.7 $ 3,951.5 $ 3,906.8 Infrastructure and Manufacturing 1,049.1 948.0 936.7 Distributors and Converters 1,484.4 1,181.0 1,039.0 Total $ 6,818.2 $ 6,080.5 $ 5,882.5 Net sales by product line are presented below: 2018 2017 2016 Carbon steel $ 4,409.1 $ 4,034.5 $ 4,014.5 Stainless and electrical steel 1,793.8 1,687.6 1,654.1 Tubular products, components and other 615.3 358.4 213.9 Total $ 6,818.2 $ 6,080.5 $ 5,882.5
Allowance for doubtful accounts	Changes in the allowance for doubtful accounts for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 Balance at beginning of year $ 6.8 $ 7.8 $ 6.0 Increase (decrease) in allowance 0.3 (1.0 ) 2.4 Receivables written off (0.5 ) — (0.6 ) Balance at end of year $ 6.6 $ 6.8 $ 7.8
Inventory	Inventories as of December 31, 2018 and 2017 , consist of: 2018 2017 Finished and semi-finished $ 1,054.4 $ 996.8 Raw materials 365.5 388.2 Inventory $ 1,419.9 $ 1,385.0
Schedule of Changes in Accounting Principles	The effects of the change in accounting principle from LIFO to average cost have been retrospectively applied to all periods presented. As a result of the retrospective application of the change in accounting principle, certain financial statement line items in our consolidated balance sheet as of December 31, 2017 and our consolidated statements of operations, comprehensive income and cash flows for years ended December 31, 2017 and 2016 were adjusted as follows: As Originally Reported Effect of Change As Adjusted Consolidated statement of operations for the year ended December 31, 2017: Cost of products sold (a) $ 5,365.2 $ (112.1 ) $ 5,253.1 Income tax expense (benefit) (17.0 ) 14.8 (2.2 ) Net income 67.6 97.3 164.9 Net income attributable to AK Steel Holding Corporation 6.2 97.3 103.5 Net income per share attributable to AK Steel Holding Corporation common stockholders: Basic $ 0.02 $ 0.31 $ 0.33 Diluted 0.02 0.30 0.32 Consolidated statement of comprehensive income for the year ended December 31, 2017: Cash flow hedges—Reclassification of losses (gains) to net income $ (12.5 ) $ 6.4 $ (6.1 ) Comprehensive income 91.1 112.3 203.4 Comprehensive income attributable to AK Steel Holding Corporation 29.7 112.3 142.0 Consolidated balance sheet as of December 31, 2017: Inventory $ 1,147.8 $ 237.2 $ 1,385.0 Other non-current assets 169.3 (58.5 ) 110.8 Other non-current liabilities 161.6 7.3 168.9 Accumulated deficit (3,058.6 ) 181.6 (2,877.0 ) Accumulated other comprehensive loss (40.0 ) (10.2 ) (50.2 ) Consolidated statement of cash flows for the year ended December 31, 2017: Net income $ 67.6 $ 97.3 $ 164.9 Deferred income taxes (15.2 ) 6.2 (9.0 ) Changes in working capital 1.8 (118.5 ) (116.7 ) Other operating items, net 5.1 15.0 20.1 Consolidated statement of operations for the year ended December 31, 2016: Cost of products sold (a) $ 5,070.6 $ 29.1 $ 5,099.7 Income tax expense (benefit) 3.2 (20.1 ) (16.9 ) Net income 58.2 (9.0 ) 49.2 Net income attributable to AK Steel Holding Corporation (7.8 ) (9.0 ) (16.8 ) Net income per share attributable to AK Steel Holding Corporation common stockholders: Basic $ (0.03 ) $ (0.04 ) $ (0.07 ) Diluted (0.03 ) (0.04 ) (0.07 ) Consolidated statement of comprehensive income for the year ended December 31, 2016: Cash flow hedges—Reclassification of losses (gains) to net income $ 27.2 $ 11.9 $ 39.1 Comprehensive income 181.9 (8.1 ) 173.8 As Originally Reported Effect of Change As Adjusted Comprehensive income attributable to AK Steel Holding Corporation 115.9 (8.1 ) 107.8 Consolidated statement of cash flows for the year ended December 31, 2016: Net income $ 58.2 $ (9.0 ) $ 49.2 Deferred income taxes 5.0 (9.1 ) (4.1 ) Changes in working capital 112.4 17.2 129.6 Other operating items, net 2.1 0.9 3.0 (a) Cost of products sold as originally reported reflects the change in presentation of pension and OPEB (income) expense further described in Note 1 . The following table shows the effects of the change in accounting principle from LIFO to average cost as of December 31, 2018 and for the year ended December 31, 2018 : As Computed under LIFO As Reported under Average Cost Effect of Change Consolidated statement of operations for the year ended December 31, 2018: Cost of products sold $ 5,966.7 $ 5,911.0 $ (55.7 ) Income tax expense (benefit) (19.4 ) (6.2 ) 13.2 Net income 201.6 244.1 42.5 Net income attributable to AK Steel Holding Corporation 143.5 186.0 42.5 Net income per share attributable to AK Steel Holding Corporation common stockholders: Basic $ 0.46 $ 0.59 $ 0.13 Diluted 0.45 0.59 0.14 Consolidated statement of comprehensive income for the year ended December 31, 2018: Comprehensive income $ 151.0 $ 193.5 $ 42.5 Comprehensive income attributable to AK Steel Holding Corporation 92.9 135.4 42.5 Consolidated balance sheet as of December 31, 2018: Inventory $ 1,128.7 $ 1,419.9 $ 291.2 Other non-current assets 180.9 103.9 (77.0 ) Other non-current liabilities 132.0 134.0 2.0 Accumulated deficit (2,915.9 ) (2,691.8 ) 224.1 Consolidated statement of cash flows for the year ended December 31, 2018: Net income $ 201.6 $ 244.1 $ 42.5 Deferred income taxes (21.2 ) (8.0 ) 13.2 Changes in working capital 66.7 12.7 (54.0 ) Other operating items, net 4.1 2.4 (1.7 )
Property, plant and equipment	Property, plant and equipment as of December 31, 2018 and 2017 , consist of: 2018 2017 Land, land improvements and leaseholds $ 272.1 $ 275.3 Buildings 509.7 509.0 Machinery and equipment 6,061.6 5,958.2 Construction in progress 125.8 89.3 Total 6,969.2 6,831.8 Less accumulated depreciation (5,057.6 ) (4,845.6 ) Property, plant and equipment, net $ 1,911.6 $ 1,986.2
Goodwill	Changes in goodwill for the years ended December 31, 2018 , 2017 and 2016 are presented below: 2018 2017 2016 Balance at beginning of year $ 253.8 $ 32.8 $ 32.8 Acquisition 1.2 221.0 — Balance at end of year $ 255.0 $ 253.8 $ 32.8
Intangible assets	Intangible assets at December 31, 2018 and 2017 , consist of: Gross Amount Accumulated Amortization Net Amount As of December 31, 2018 Customer relationships $ 36.6 $ (7.4 ) $ 29.2 Technology 19.3 (4.6 ) 14.7 Other 1.0 (1.0 ) — Intangible assets $ 56.9 $ (13.0 ) $ 43.9 As of December 31, 2017 Customer relationships $ 36.6 $ (2.2 ) $ 34.4 Technology 19.3 (1.4 ) 17.9 Other 1.0 (0.4 ) 0.6 Intangible assets $ 56.9 $ (4.0 ) $ 52.9
Other non-current assets	Other non-current assets as of December 31, 2018 and 2017 , consist of: 2018 2017 Investments in affiliates $ 80.5 $ 77.5 Other 23.4 33.3 Other non-current assets $ 103.9 $ 110.8
Accrued liabilities	Accrued liabilities as of December 31, 2018 and 2017 , consist of: 2018 2017 Salaries, wages and benefits $ 127.8 $ 101.3 Interest 34.8 35.0 Other 126.3 134.2 Accrued liabilities $ 288.9 $ 270.5
Facility idling	The supplemental unemployment and other employee benefit costs were recorded as accrued liabilities, and the activity for the years ended December 31, 2018 , 2017 , and 2016 was as follows: 2018 2017 2016 Balance at beginning of year $ 1.5 $ 6.2 $ 22.2 Payments (1.5 ) (5.3 ) (20.1 ) Additions to the reserve — 0.6 4.1 Balance at end of year $ — $ 1.5 $ 6.2

Investments in Affiliates (Tabl

Investments in Affiliates (Tables)	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments [Table Text Block]	Investees and equity ownership percentages are presented below: Equity Ownership % Combined Metals of Chicago, LLC 40.0% Delaco Processing, LLC 49.0% Rockport Roll Shop LLC 50.0% Spartan Steel Coating, LLC 48.0% 2018 2017 2016 Revenue $ 329.8 $ 292.7 $ 286.4 Gross profit 91.0 88.9 96.3 Net income (loss) 19.4 20.7 31.8 2018 2017 Current assets $ 123.6 $ 115.2 Noncurrent assets 74.4 73.5 Current liabilities 16.9 16.2 Noncurrent liabilities 54.2 58.9
Schedule of Related Party Transactions [Table Text Block]	Transactions with all equity investees for the years indicated are presented below: 2018 2017 2016 Sales to equity investees $ 104.4 $ 80.6 $ 69.2 Purchases from equity investees 31.2 33.0 213.5 Outstanding receivables and payables with all equity investees as of the end of the year indicated are presented below: 2018 2017 Accounts receivable from equity investees $ 1.9 $ 0.7 Accounts payable to equity investees 6.4 4.1

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Components of income (loss) before income taxes for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 United States $ 168.3 $ 91.6 $ (40.4 ) Foreign 11.5 9.7 6.7 Noncontrolling interests 58.1 61.4 66.0 Income before income taxes $ 237.9 $ 162.7 $ 32.3
Schedule of Deferred Tax Assets and Liabilities	Significant components of deferred tax assets and liabilities at December 31, 2018 and 2017 are presented below: 2018 2017 Deferred tax assets: Net operating and capital loss and tax credit carryforwards $ 516.7 $ 619.5 Postretirement benefits 81.8 92.5 Pension benefits 114.1 117.5 Inventories 38.5 47.9 Other assets 65.1 71.6 Valuation allowance (693.5 ) (735.7 ) Total deferred tax assets 122.7 213.3 Deferred tax liabilities: Depreciable assets (108.3 ) (121.9 ) Other liabilities (33.4 ) (118.3 ) Total deferred tax liabilities (141.7 ) (240.2 ) Net deferred tax liabilities $ (19.0 ) $ (26.9 )
Summary of Valuation Allowance	Changes in the valuation allowance for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 Balance at beginning of year $ 735.7 $ 1,189.7 $ 1,232.3 Change in valuation allowance: Included in income tax expense (benefit) (52.8 ) (62.3 ) 11.0 Change in deferred assets in other comprehensive income 10.6 8.5 (53.6 ) Effect of tax rate changes — (400.2 ) — Balance at end of year $ 693.5 $ 735.7 $ 1,189.7
Schedule of Components of Income Tax Expense (Benefit)	Significant components of income tax expense (benefit) are presented below: 2018 2017 2016 Current: Federal $ (0.5 ) $ (4.5 ) $ (3.7 ) State (0.3 ) 0.3 0.2 Foreign 2.1 2.4 1.7 Deferred: Federal (5.3 ) 0.7 15.1 State — 0.1 1.4 Foreign (2.2 ) (0.4 ) — Benefits of operating loss carryforwards — — (16.1 ) Amount allocated to other comprehensive income — — (15.5 ) Change in valuation allowance on beginning-of-the-year deferred tax assets — (0.8 ) — Income tax expense (benefit) $ (6.2 ) $ (2.2 ) $ (16.9 )
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation of income tax on income before income taxes computed at the U.S. federal statutory tax rates to actual income tax expense is presented below: 2018 2017 2016 Income tax expense at U.S. federal statutory rate $ 50.0 $ 57.2 $ 11.3 Income tax expense calculated on noncontrolling interests (12.2 ) (21.5 ) (23.1 ) State and foreign tax expense, net of federal tax (2.3 ) 6.3 0.2 Increase (decrease) in deferred tax asset valuation allowance (52.8 ) (51.8 ) 11.0 Amount allocated to other comprehensive income — — (15.5 ) Remeasurement of deferred taxes for U.S. tax legislation — (4.3 ) — Transition tax on foreign earnings — 7.9 — Non-deductible compensation 8.1 — — Other differences 3.0 4.0 (0.8 ) Income tax expense (benefit) $ (6.2 ) $ (2.2 ) $ (16.9 )
Schedule of Unrecognized Tax Benefits Roll Forward	A reconciliation of the change in unrecognized tax benefits for 2018 , 2017 and 2016 is presented below: 2018 2017 2016 Balance at beginning of year $ 89.4 $ 124.2 $ 130.3 Decreases for prior year tax positions (2.2 ) (0.5 ) (4.5 ) Increases (decreases) for current year tax positions — 0.3 (1.6 ) Increases (decreases) related to tax rate changes (a) — (34.6 ) — Balance at end of year $ 87.2 $ 89.4 $ 124.2 (a)

Long-term Debt and Other Fina_2

Long-term Debt and Other Financing (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	Debt balances at December 31, 2018 and 2017 , are presented below: 2018 2017 Credit Facility $ 335.0 $ 450.0 7.50% Senior Secured Notes due July 2023 (effective rate of 8.3%) 380.0 380.0 5.00% Exchangeable Senior Notes due November 2019 (effective rate of 10.8%) 148.5 150.0 7.625% Senior Notes due October 2021 406.2 406.2 6.375% Senior Notes due October 2025 (effective rate of 7.1%) 274.8 280.0 7.00% Senior Notes due March 2027 391.6 400.0 Industrial Revenue Bonds due 2020 through 2028 99.3 99.3 Unamortized debt discount and issuance costs (41.7 ) (55.4 ) Total long-term debt $ 1,993.7 $ 2,110.1
Schedule of Maturities of Long-term Debt	Maturities of long-term debt for the next five years, at December 31, 2018 , are presented below: Year Debt Maturities 2019 (a) $ 148.5 2020 7.3 2021 406.2 2022 335.0 2023 380.0 (a) Amounts maturing in 2019

Pension and Other Postretirem_2

Pension and Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits, Description [Abstract]
Schedule of Defined Benefit Plans Disclosures	Amounts presented below are calculated based on benefit obligation and asset valuation measurement dates of December 31, 2018 and 2017 : Pension Benefits Other Benefits 2018 2017 2018 2017 Change in benefit obligations: Benefit obligations at beginning of year $ 2,808.0 $ 2,874.8 $ 448.5 $ 443.7 Service cost 3.2 2.8 4.5 4.7 Interest cost 94.5 108.2 15.6 17.3 Plan participants’ contributions — — 24.7 23.3 Actuarial loss (gain) (148.8 ) 91.0 (23.7 ) 27.1 Amendments — — (11.1 ) (4.7 ) Benefits paid (268.1 ) (269.0 ) (62.6 ) (65.5 ) Annuity settlement (278.8 ) — — — Medicare subsidy reimbursement received — — 2.3 2.6 Foreign currency exchange rate changes — 0.2 — — Benefit obligations at end of year $ 2,210.0 $ 2,808.0 $ 398.2 $ 448.5 Change in plan assets: Fair value of plan assets at beginning of year $ 2,322.2 $ 2,183.5 $ — $ — Actual gain (loss) on plan assets (87.0 ) 362.4 — — Employer contributions 51.3 45.3 35.6 39.6 Plan participants’ contributions — — 24.7 23.3 Benefits paid (268.1 ) (269.0 ) (62.6 ) (65.5 ) Annuity settlement (278.8 ) — — — Medicare subsidy reimbursement received — — 2.3 2.6 Fair value of plan assets at end of year $ 1,739.6 $ 2,322.2 $ — $ — Funded status $ (470.4 ) $ (485.8 ) $ (398.2 ) $ (448.5 ) Amounts recognized in the consolidated balance sheets: Current liabilities $ (1.2 ) $ (1.3 ) $ (37.5 ) $ (38.8 ) Noncurrent liabilities (469.2 ) (484.5 ) (360.7 ) (409.7 ) Total $ (470.4 ) $ (485.8 ) $ (398.2 ) $ (448.5 ) Amounts recognized in accumulated other comprehensive loss, before taxes: Actuarial loss (gain) $ 134.1 $ 77.6 $ (35.4 ) $ (13.0 ) Prior service cost (credit) 19.4 23.2 (82.4 ) (84.9 ) Total $ 153.5 $ 100.8 $ (117.8 ) $ (97.9 )
Schedule of Assumptions Used	Assumptions used to value benefit obligations and determine pension and OPEB (income) expense are presented below: Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Assumptions used to determine benefit obligations at December 31: Discount rate 4.22 % 3.54 % 3.93 % 4.27 % 3.59 % 4.04 % Rate of compensation increase 4.00 % 4.00 % 4.00 % Interest crediting rate 3.80 % 3.80 % 3.80 % Subsequent year healthcare cost trend rate 6.50 % 6.65 % 7.00 % Ultimate healthcare cost trend rate 4.50 % 4.50 % 4.50 % Year ultimate healthcare cost trend rate begins 2025 2025 2025 Assumptions used to determine pension and OPEB (income) expense for the year ended December 31: Discount rate 3.69 % 3.93 % 3.95 % 3.59 % 4.04 % 4.22 % Expected return on plan assets 7.00 % 7.25 % 7.25 % Rate of compensation increase 4.00 % 4.00 % 4.00 % Interest crediting rate 3.80 % 3.80 % 4.30 %
Schedule of Expected Benefit Payments	Estimated future benefit payments to beneficiaries are presented below: Pension Plans Other Benefits 2019 $ 216.5 $ 37.5 2020 211.2 35.6 2021 198.9 33.8 2022 196.0 32.2 2023 180.6 30.6 2024 through 2028 835.3 133.4
Schedule of Plan Assets	Master pension trust investments measured at fair value on a recurring basis at December 31, 2018 and 2017 are presented below, with certain assets presented by level within the fair value hierarchy. As a practical expedient, we estimate the value of common/collective trusts and equity mutual funds by using the net asset value (“NAV”) per share multiplied by the number of shares of the trust investment held as of the measurement date. If we have the ability to redeem our investment in the respective alternative investment at the NAV with no significant restrictions on the redemption at the consolidated balance sheet date, excluding equity mutual funds, we categorized the alternative investment as a reconciliation of pension investments reported in the fair value hierarchy to the master pension trust’s balance. See Note 16 for more information on the determination of fair value. Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs (Level 1) (Level 2) Total 2018 2017 2018 2017 2018 2017 Investments in fair value hierarchy Equity investments: U.S. securities $ 35.4 $ 46.6 $ — $ — $ 35.4 $ 46.6 Global securities — — 131.4 327.9 131.4 327.9 Fixed-income investments: High-yield U.S. securities — — 84.5 111.8 84.5 111.8 Other U.S. securities — — 700.8 524.6 700.8 524.6 Global securities — — 82.8 — 82.8 — Other investments — — 78.0 30.6 78.0 30.6 Total pension investments in fair value hierarchy $ 35.4 $ 46.6 $ 1,077.5 $ 994.9 $ 1,112.9 $ 1,041.5 Investments with fair values measured at net asset value Common/collective trusts: U.S. equity securities (a) 355.8 194.6 Global equity securities (a) 178.2 707.0 U.S. corporate fixed-income securities (b) — 379.1 Global fixed-income securities (b) 92.7 — Total pension assets at fair value $ 1,739.6 $ 2,322.2 (a) Investments may include common stocks, options and futures. (b)
Schedule of Net Benefit Costs	Components of pension and OPEB (income) expense for the years 2018 , 2017 and 2016 are presented below: Pension Benefits Other Benefits 2018 2017 2016 2018 2017 2016 Components of pension and OPEB (income) expense: Service cost $ 3.2 $ 2.8 $ 3.0 $ 4.5 $ 4.7 $ 4.9 Interest cost 94.5 108.2 120.4 15.6 17.3 19.9 Expected return on plan assets (148.8 ) (149.9 ) (167.1 ) — — — Amortization of prior service cost (credit) 3.8 4.7 5.6 (13.6 ) (58.5 ) (60.4 ) Recognized net actuarial loss (gain): Annual amortization 16.1 10.5 29.2 (1.3 ) (4.2 ) (4.3 ) Corridor charge (credit) — — 78.4 — — (35.3 ) Settlement loss 14.5 — 29.9 — — — Pension and OPEB (income) expense $ (16.7 ) $ (23.7 ) $ 99.4 $ 5.2 $ (40.7 ) $ (75.2 )
Schedule of Multiemployer Plans	Our participation in these multiemployer plans for the years ended December 31, 2018 , 2017 and 2016 , is presented below. We do not provide more than five percent of the total contributions to any multiemployer plan. Forms 5500 are not yet available for plan years ending in 2018 . Pension Fund EIN/Pension Plan Number Pension Protection Act Zone Status (a) FIP/RP Status Pending/Implemented (b) Contributions Surcharge Imposed (c) Expiration Date of Collective Bargaining Agreement 2018 2017 2018 2017 2016 Steelworkers Pension Trust 23-6648508/499 Green Green No $ 4.2 $ 6.3 $ 6.8 No 3/1/2019 to 3/31/2021 (d) IAM National Pension Fund’s National Pension Plan 51-6031295/002 Green Green No 17.7 18.4 18.0 No 4/1/2019 to 3/15/2020 (e) $ 21.9 $ 24.7 $ 24.8 (a) The most recent Pension Protection Act zone status available in 2018 and 2017 is for each plan’s year-end at December 31, 2017 and 2016 . The plan’s actuary certifies the zone status. Generally, plans in the red zone are less than 65% funded, plans in the yellow zone are between 65% and 80% funded, and plans in the green zone are at least 80% funded. The Steelworkers Pension Trust and IAM National Pension Fund’s National Pension Plan elected funding relief under section 431(b)(8) of the Internal Revenue Code and section 304(b)(8) of the Employment Retirement Income Security Act of 1974 (ERISA). This election allows those plans’ investment losses for the plan year ended December 31, 2008, to be amortized over 29 years for funding purposes. (b) The “FIP/RP Status Pending/Implemented” column indicates plans for which a financial improvement plan (FIP) or a rehabilitation plan (RP) is either pending or has been implemented, as defined by ERISA. (c) The surcharge represents an additional required contribution due as a result of the critical funding status of the plan. (d) We are a party to three collective bargaining agreements at our Ashland Works, Mansfield Works and at the AK Tube Walbridge plant that require contributions to the Steelworkers Pension Trust. The labor contract for approximately 230 hourly employees at the Ashland Works is currently under a rolling 60-day extension. The labor contract for approximately 110 hourly employees at the AK Tube Walbridge plant expires January 22, 2021 . The labor contract for approximately 300 hourly employees at Mansfield Works expires on March 31, 2021 . (e) We are a party to three collective bargaining agreements at our Butler Works, Middletown Works and Zanesville Works that require contributions to the IAM National Pension Fund’s National Pension Plan. The labor contract for approximately 1,170 hourly employees at Butler Works expires on April 16, 2019 . The labor contract for approximately 100 hourly employees at Zanesville Works expires on May 31, 2019 . The labor contract for approximately 1,760 hourly employees at Middletown Works expires on March 15, 2020

Operating Leases (Tables)

Operating Leases (Tables)	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Future minimum lease payments	Obligations to make future minimum lease payments at December 31, 2018 , are presented below: 2019 $ 23.3 2020 20.8 2021 20.6 2022 18.7 2023 17.3 2024 and thereafter 83.6 Total minimum lease payments $ 184.3

Environmental and Legal Conti_2

Environmental and Legal Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of environmental-related capital investments and compliance costs	We have spent the following amounts over the past three years for environmental-related capital investments and environmental compliance: 2018 2017 2016 Environmental-related capital investments $ 7.1 $ 6.8 $ 4.9 Environmental compliance costs 126.3 129.5 123.9
Schedule of accrual of liabilities related to environmental loss contingencies	We have recorded the following liabilities for environmental matters on our consolidated balance sheets: 2018 2017 Accrued liabilities $ 8.0 $ 8.5 Other non-current liabilities 31.2 35.4
Schedule of information on pending asbestos cases	The number of asbestos cases pending at December 31, 2018 , is presented below: Asbestos Cases Pending at December 31, 2018 Cases with specific dollar claims for damages: Claims up to $0.2 160 Claims above $0.2 to $5.0 4 Claims above $5.0 to $20.0 3 Total claims with specific dollar claims for damages (a) 167 Cases without a specific dollar claim for damages 176 Total asbestos cases pending 343 (a) Involve a total of 2,242 plaintiffs and 19,356 defendants
Schedule of number of new asbestos claims filed, number of pending asbestos claims disposed, and amount paid in settlements	Asbestos-related claims information in 2018 , 2017 and 2016 , is presented below: 2018 2017 2016 New Claims Filed 68 58 40 Pending Claims Disposed Of 61 61 84 Total Amount Paid in Settlements $ 1.4 $ 1.2 $ 0.9

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of information about share-based compensation expense	Share-based compensation expense for the years ended December 31, 2018 , 2017 and 2016 , is presented below: Share-based Compensation Expense 2018 2017 2016 Stock options $ 2.5 $ 2.1 $ 1.0 Restricted stock 3.1 2.9 1.6 Restricted stock units issued to Directors 1.2 1.2 1.3 Performance shares 2.0 1.5 1.5 Equity-based long-term performance plan 0.4 — — Pre-tax share-based compensation expense $ 9.2 $ 7.7 $ 5.4
Schedule of weighted-average assumptions used in Black-Scholes option calculation	The following weighted-average assumptions are used in the Black-Scholes option pricing model to estimate the fair value of granted options as of the grant date: 2018 2017 2016 Expected volatility 58.8% – 61.6% 61.5% – 64.0% 90.3% – 91.5% Weighted-average volatility 59.5% 62.5% 90.7% Expected term (in years) 3.4 – 6.6 3.3 – 6.5 3.3 – 6.7 Risk-free interest rate 2.3% – 2.6% 1.6% – 2.2% 1.2% – 1.8% Weighted-average grant-date fair value per share of granted options $3.51 $5.33 $1.29
Schedule of stock options activity	Option activity for the year ended December 31, 2018 , is presented below: Stock Options Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate Intrinsic Value Outstanding at December 31, 2017 2,994,206 $ 7.69 Granted 842,000 6.56 Exercised (201,700 ) 3.82 Forfeited and expired (230,644 ) 18.56 Outstanding at December 31, 2018 3,403,862 6.90 6.1 $ 0.3 Exercisable at December 31, 2018 2,046,546 7.07 4.7 0.2 Unvested at December 31, 2018 1,357,316 6.66 8.5 0.1 Unvested at December 31, 2018 expected to vest 1,289,450 6.66 8.5 0.1
Schedule of nonvested restricted stock units activity	Non-vested restricted stock awards activity for the year ended December 31, 2018 , is presented below: Restricted Stock Awards Restricted Shares Weighted- Average Grant Date Fair Value Outstanding at December 31, 2017 518,184 $ 5.38 Granted 521,100 6.56 Vested/restrictions lapsed (513,848 ) 5.48 Canceled (18,733 ) 6.16 Outstanding at December 31, 2018 506,703 6.45
Schedule of weighted-average assumptions used in Monte Carlo simulation	The following weighted-average assumptions are used in a Monte Carlo simulation model to estimate the fair value of performance shares granted: 2018 2017 2016 Company expected volatility 67.3 % 68.0 % 60.8 % VanEck Vectors Steel ETF expected volatility 52.2 % 48.9 % NA S&P’s MidCap 400 index expected volatility NA NA 27.6 % Risk-free interest rate 2.2 % 1.5 % 1.1 % Weighted-average grant-date fair value per performance share granted $ 8.05 $ 10.78 $ 1.74
Schedule of nonvested performance-based units activity	Non-vested performance share awards activity for the year ended December 31, 2018 , is presented below: Performance Share Awards Performance Shares Weighted- Average Grant Date Fair Value Outstanding at December 31, 2017 718,668 $ 5.04 Granted 366,500 8.05 Earned (277,971 ) 1.74 Expired or forfeited (192,397 ) 5.55 Outstanding at December 31, 2018 614,800 9.19

Comprehensive Income (Loss) (Ta

Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Accumulated Other Comprehensive Income (Loss), Net of Tax	Other comprehensive income (loss), net of tax, information is presented below: 2018 2017 2016 Foreign currency translation Balance at beginning of period $ 1.1 $ (3.6 ) $ (2.1 ) Other comprehensive income (loss)—foreign currency translation gain (loss) (1.7 ) 4.7 (1.5 ) Balance at end of period $ (0.6 ) $ 1.1 $ (3.6 ) Cash flow hedges Balance at beginning of period $ 22.3 $ 39.9 $ (44.8 ) Cumulative effect of adopting new hedging standard 0.8 — — Other comprehensive income (loss): Gains (losses) arising in period (5.6 ) (11.5 ) 56.1 Income tax expense (benefit) — — 6.2 Gains (losses) arising in period, net of tax (5.6 ) (11.5 ) 49.9 Reclassification of losses (gains) to net income (loss): Recorded in cost of products sold (10.3 ) (6.1 ) 39.1 Income tax (expense) benefit (b) — — 4.3 Net amount of reclassification of losses (gains) to net income (loss), net of tax (10.3 ) (6.1 ) 34.8 Total other comprehensive income (loss), net of tax (15.9 ) (17.6 ) 84.7 Balance at end of period $ 7.2 $ 22.3 $ 39.9 Pension and OPEB plans Balance at beginning of period $ (73.6 ) $ (125.0 ) $ (166.4 ) Other comprehensive income (loss): Prior service credit (cost) arising in period 11.1 4.7 (8.3 ) Gains (losses) arising in period (63.6 ) 94.2 11.6 Subtotal (52.5 ) 98.9 3.3 Income tax expense (benefit) — — 0.4 Gains (losses) arising in period, net of tax (52.5 ) 98.9 2.9 Reclassification to net income (loss): Prior service costs (credits) (a) (9.8 ) (53.8 ) (54.8 ) Actuarial (gains) losses (a) 29.3 6.3 97.9 Subtotal 19.5 (47.5 ) 43.1 Income tax (expense) benefit (b) — — 4.6 Amount of reclassification to net income (loss), net of tax 19.5 (47.5 ) 38.5 Total other comprehensive income (loss), net of tax (33.0 ) 51.4 41.4 Balance at end of period $ (106.6 ) $ (73.6 ) $ (125.0 ) (a) Included in pension and OPEB (income) expense (b)

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings per share	Reconciliation of the numerators and denominators for basic and diluted EPS computations is presented below: 2018 2017 2016 Net income (loss) attributable to AK Steel Holding Corporation $ 186.0 $ 103.5 $ (16.8 ) Less: distributed earnings to common stockholders and holders of certain stock compensation awards — — — Undistributed earnings (loss) $ 186.0 $ 103.5 $ (16.8 ) Common stockholders earnings—basic and diluted: Distributed earnings to common stockholders $ — $ — $ — Undistributed earnings (loss) to common stockholders 185.7 103.5 (16.7 ) Common stockholders earnings (loss)—basic and diluted $ 185.7 $ 103.5 $ (16.7 ) Common shares outstanding (weighted-average shares in millions): Common shares outstanding for basic earnings per share 314.8 314.3 230.0 Effect of Exchangeable Notes — 4.5 — Effect of dilutive stock-based compensation 0.8 0.9 — Common shares outstanding for diluted earnings per share 315.6 319.7 230.0 Basic earnings per share: Distributed earnings $ — $ — $ — Undistributed earnings (loss) 0.59 0.33 (0.07 ) Basic earnings (loss) per share $ 0.59 $ 0.33 $ (0.07 ) Diluted earnings per share: Distributed earnings $ — $ — $ — Undistributed earnings (loss) 0.59 0.32 (0.07 ) Diluted earnings (loss) per share $ 0.59 $ 0.32 $ (0.07 ) Potentially issuable common shares (in millions) excluded from earnings per share calculation due to anti-dilutive effect 2.4 1.4 3.0

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value assets and liabilities measured on a recurring basis	Assets and liabilities measured at fair value on a recurring basis are presented below: 2018 2017 Level 1 Level 2 Total Level 1 Level 2 Total Assets measured at fair value Cash and cash equivalents $ 48.6 $ — $ 48.6 $ 38.0 $ — $ 38.0 Other current assets: Foreign exchange contracts — 0.1 0.1 — 0.2 0.2 Commodity hedge contracts — 13.0 13.0 — 35.2 35.2 Other non-current assets: Foreign exchange contracts — 0.4 0.4 — 1.7 1.7 Commodity hedge contracts — 2.9 2.9 — 10.6 10.6 Assets measured at fair value $ 48.6 $ 16.4 $ 65.0 $ 38.0 $ 47.7 $ 85.7 Liabilities measured at fair value Accrued liabilities: Foreign exchange contracts $ — $ (1.2 ) $ (1.2 ) $ — $ (0.3 ) $ (0.3 ) Commodity hedge contracts — (5.9 ) (5.9 ) — (4.9 ) (4.9 ) Other non-current liabilities: Foreign exchange contracts — (1.5 ) (1.5 ) — — — Commodity hedge contracts — (1.6 ) (1.6 ) — (0.5 ) (0.5 ) Liabilities measured at fair value $ — $ (10.2 ) $ (10.2 ) $ — $ (5.7 ) $ (5.7 ) Liabilities measured at other than fair value Long-term debt, including current portions: Fair value $ — $ (1,852.4 ) $ (1,852.4 ) $ — $ (2,273.4 ) $ (2,273.4 ) Carrying amount — (1,993.7 ) (1,993.7 ) — (2,110.1 ) (2,110.1 )

Derivative Instruments and He_2

Derivative Instruments and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Outstanding commodity price swaps and options and forward foreign exchange contracts	Outstanding derivative contracts and the period over which we are hedging our exposure to the volatility in future cash flows are presented below: Hedge Contracts Settlement Dates 2018 2017 Commodity contracts: Nickel (in lbs) — 500,000 Natural gas (in MMBTUs) January 2019 to December 2020 39,868,000 41,338,000 Zinc (in lbs) January 2019 to December 2020 52,150,000 50,350,000 Iron ore (in metric tons) January 2019 to December 2020 2,125,000 2,340,000 Electricity (in MWHs) January 2019 to September 2020 1,461,000 1,553,000 Foreign exchange contracts: Euros January 2019 to June 2019 € 4,000,000 € 26,000,000 Canadian dollars January 2019 to December 2021 C$ 118,560,000 C$ 148,080,000
Fair value of derivative instruments in the condensed consolidated balance sheets	The fair value of derivative instruments as of December 31, 2018 and 2017 , is presented below: Asset (liability) 2018 2017 Derivatives designated as hedging instruments: Other current assets: Commodity contracts $ 3.4 $ 9.0 Foreign exchange contracts — 0.2 Other non-current assets: Commodity contracts 1.0 2.3 Foreign exchange contracts 0.4 1.7 Accrued liabilities: Commodity contracts (4.7 ) (4.6 ) Foreign exchange contracts (1.2 ) (0.2 ) Other non-current liabilities: Commodity contracts (1.2 ) (0.5 ) Foreign exchange contracts (1.5 ) — Derivatives not designated as hedging instruments: Other current assets: Commodity contracts 9.6 26.2 Foreign exchange contracts 0.1 — Other non-current assets—commodity contracts 1.9 8.3 Accrued liabilities: Commodity contracts (1.2 ) (0.3 ) Foreign exchange contracts — (0.1 ) Other non-current liabilities—commodity contracts (0.4 ) —
Gains (losses) on derivative instruments included in the condensed consolidated statements of operations	Gains (losses) on derivative instruments for the years ended December 31, 2018 , 2017 and 2016 , are presented below: Gain (loss) 2018 2017 2016 Derivatives designated as cash flow hedges— Commodity contracts: Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness $ (0.2 ) $ (11.5 ) $ 56.1 Reclassified from accumulated other comprehensive income into cost of products sold 11.2 6.1 (39.1 ) Foreign exchange contract: Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness (5.4 ) — — Reclassified from accumulated other comprehensive income into cost of products sold (0.9 ) — — Derivatives not designated as hedging instruments: Commodity contracts—recognized in cost of products sold (2.4 ) 31.6 38.6 Foreign exchange contracts—recognized in other (income) expense 0.1 (1.6 ) (0.9 )
Amount of gains (losses) expected to be reclassified into earnings within the next twelve months	Gains (losses) before tax expected to be reclassified into cost of products sold within the next twelve months for our existing commodity contracts that qualify for hedge accounting are presented below: Hedge Gains (losses) Natural gas $ 5.1 Electricity 2.7 Zinc (4.8 ) Canadian dollars (1.5 )

Supplementary Cash Flow Infor_2

Supplementary Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Schedule of cash flow, supplemental disclosures	Net cash paid (received) during the period for interest, net of capitalized interest, and income taxes are presented below: 2018 2017 2016 Net cash paid (received) during the period for: Interest, net of capitalized interest $ 136.3 $ 130.5 $ 137.1 Income taxes (5.5 ) 0.1 (2.6 )
Schedule of non-cash investing and financing activities	Non-cash investing and financing activities for the years ended December 31, 2018 , 2017 and 2016 , are presented below: 2018 2017 2016 Capital investments $ 33.4 $ 37.3 $ 33.2 Research and Innovation Center capital lease — 1.1 25.2 Issuance of restricted stock and restricted stock units 4.5 4.6 2.3

Quarterly Information (Unaudi_2

Quarterly Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Earnings per share for each quarter and the year are calculated individually and may not sum to the total for the year. 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Year Net sales $ 1,658.9 $ 1,746.6 $ 1,735.6 $ 1,677.1 $ 6,818.2 Operating profit (loss) 63.6 99.5 114.8 86.5 364.4 Net income (loss) attributable to AK Holding 28.7 56.6 67.2 33.5 186.0 Basic and diluted earnings (loss) per share $ 0.09 $ 0.18 $ 0.21 $ 0.11 $ 0.59 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Year Net sales $ 1,533.4 $ 1,557.2 $ 1,494.3 $ 1,495.6 $ 6,080.5 Operating profit (loss) 129.7 116.5 66.3 (52.3 ) 260.2 Net income (loss) attributable to AK Holding 84.4 77.2 22.3 (80.4 ) 103.5 Basic earnings (loss) per share $ 0.27 $ 0.25 $ 0.07 $ (0.26 ) $ 0.33 Diluted earnings (loss) per share 0.26 0.24 0.07 (0.26 ) 0.32

Supplementary Guarantor Infor_2

Supplementary Guarantor Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Guarantor Information [Abstract]
Condensed Statements of Comprehensive Income (Loss)	Condensed Statements of Comprehensive Income (Loss) Year Ended December 31, 2018 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net sales $ — $ 6,244.7 $ 320.8 $ 752.8 $ (500.1 ) $ 6,818.2 Cost of products sold (exclusive of items shown separately below) — 5,519.8 221.4 620.9 (451.1 ) 5,911.0 Selling and administrative expenses 3.5 320.0 14.5 34.2 (49.6 ) 322.6 Depreciation — 171.5 8.0 40.7 — 220.2 Total operating costs 3.5 6,011.3 243.9 695.8 (500.7 ) 6,453.8 Operating profit (loss) (3.5 ) 233.4 76.9 57.0 0.6 364.4 Interest expense — 145.9 — 5.7 — 151.6 Pension and OPEB (income) expense — (19.2 ) (19.2 ) Other (income) expense — 8.7 (16.4 ) (2.9 ) 4.7 (5.9 ) Income (loss) before income taxes (3.5 ) 98.0 93.3 54.2 (4.1 ) 237.9 Income tax expense (benefit) — (26.5 ) 23.3 (2.0 ) (1.0 ) (6.2 ) Equity in net income (loss) of subsidiaries 189.5 65.0 — 0.7 (255.2 ) — Net income (loss) 186.0 189.5 70.0 56.9 (258.3 ) 244.1 Less: Net income attributable to noncontrolling interests — — — 58.1 — 58.1 Net income (loss) attributable to AK Steel Holding Corporation 186.0 189.5 70.0 (1.2 ) (258.3 ) 186.0 Other comprehensive income (loss) (50.6 ) (50.6 ) — (1.7 ) 52.3 (50.6 ) Comprehensive income (loss) attributable to AK Steel Holding Corporation $ 135.4 $ 138.9 $ 70.0 $ (2.9 ) $ (206.0 ) $ 135.4 Condensed Statements of Comprehensive Income (Loss) Year Ended December 31, 2017 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net sales $ — $ 5,755.1 $ 285.9 $ 496.3 $ (456.8 ) $ 6,080.5 Cost of products sold (exclusive of items shown separately below) — 5,082.0 197.7 387.2 (413.8 ) 5,253.1 Selling and administrative expenses 3.7 285.5 13.5 26.9 (44.7 ) 284.9 Depreciation — 189.3 7.5 29.2 — 226.0 Charge (credit) for termination of pellet agreement and related transportation costs — (19.3 ) — — — (19.3 ) Asset impairment charge — 75.6 — — — 75.6 Total operating costs 3.7 5,613.1 218.7 443.3 (458.5 ) 5,820.3 Operating profit (loss) (3.7 ) 142.0 67.2 53.0 1.7 260.2 Interest expense — 150.3 — 2.0 — 152.3 Pension and OPEB (income) expense — (71.9 ) — — — (71.9 ) Other (income) expense — 30.1 (11.4 ) (5.4 ) 3.8 17.1 Income (loss) before income taxes (3.7 ) 33.5 78.6 56.4 (2.1 ) 162.7 Income tax expense (benefit) — (29.4 ) 29.9 (1.8 ) (0.9 ) (2.2 ) Equity in net income (loss) of subsidiaries 107.2 44.3 — — (151.5 ) — Net income (loss) 103.5 107.2 48.7 58.2 (152.7 ) 164.9 Less: Net income attributable to noncontrolling interests — — — 61.4 — 61.4 Net income (loss) attributable to AK Steel Holding Corporation 103.5 107.2 48.7 (3.2 ) (152.7 ) 103.5 Other comprehensive income (loss) 38.5 38.5 — 4.7 (43.2 ) 38.5 Comprehensive income (loss) attributable to AK Steel Holding Corporation $ 142.0 $ 145.7 $ 48.7 $ 1.5 $ (195.9 ) $ 142.0 Condensed Statements of Comprehensive Income (Loss) Year Ended December 31, 2016 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net sales $ — $ 5,681.0 $ 250.9 $ 411.5 $ (460.9 ) $ 5,882.5 Cost of products sold (exclusive of items shown separately below) — 5,044.8 171.7 299.4 (416.2 ) 5,099.7 Selling and administrative expenses 4.4 282.7 12.7 22.6 (43.3 ) 279.1 Depreciation — 187.8 7.0 21.8 — 216.6 Charge (credit) for termination of pellet agreement and related transportation costs — 69.5 — — — 69.5 Total operating costs 4.4 5,584.8 191.4 343.8 (459.5 ) 5,664.9 Operating profit (loss) (4.4 ) 96.2 59.5 67.7 (1.4 ) 217.6 Interest expense — 162.3 — 1.6 — 163.9 Pension and OPEB (income) expense — 16.5 — — — 16.5 Other (income) expense — 16.4 (8.1 ) (8.6 ) 5.2 4.9 Income (loss) before income taxes (4.4 ) (99.0 ) 67.6 74.7 (6.6 ) 32.3 Income tax expense (benefit) — (43.7 ) 25.7 3.6 (2.5 ) (16.9 ) Equity in net income (loss) of subsidiaries (12.4 ) 42.9 — (0.7 ) (29.8 ) — Net income (loss) (16.8 ) (12.4 ) 41.9 70.4 (33.9 ) 49.2 Less: Net income attributable to noncontrolling interests — — — 66.0 — 66.0 Net income (loss) attributable to AK Steel Holding Corporation (16.8 ) (12.4 ) 41.9 4.4 (33.9 ) (16.8 ) Other comprehensive income (loss) 124.6 124.6 — (1.5 ) (123.1 ) 124.6 Comprehensive income (loss) attributable to AK Steel Holding Corporation $ 107.8 $ 112.2 $ 41.9 $ 2.9 $ (157.0 ) $ 107.8
Condensed Balance Sheets	Condensed Balance Sheets December 31, 2018 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company ASSETS Current assets: Cash and cash equivalents $ — $ 22.1 $ 8.2 $ 18.3 $ — $ 48.6 Accounts receivable, net — 515.4 34.0 95.3 (8.9 ) 635.8 Inventory — 1,299.6 53.9 75.6 (9.2 ) 1,419.9 Other current assets — 85.5 0.1 11.4 — 97.0 Total current assets — 1,922.6 96.2 200.6 (18.1 ) 2,201.3 Property, plant and equipment — 6,111.1 189.7 668.4 — 6,969.2 Accumulated depreciation — (4,785.5 ) (102.8 ) (169.3 ) — (5,057.6 ) Property, plant and equipment, net — 1,325.6 86.9 499.1 — 1,911.6 Other non-current assets: Investment in subsidiaries (3,017.4 ) 1,931.1 — 68.2 1,018.1 — Inter-company accounts 3,117.3 — 1,630.7 — (4,748.0 ) — Goodwill and intangible assets — — 32.9 266.0 — 298.9 Other non-current assets — 54.3 — 49.6 — 103.9 TOTAL ASSETS $ 99.9 $ 5,233.6 $ 1,846.7 $ 1,083.5 $ (3,748.0 ) $ 4,515.7 LIABILITIES AND EQUITY (DEFICIT) Current liabilities: Accounts payable $ — $ 722.5 $ 26.2 $ 55.5 $ (3.2 ) $ 801.0 Accrued liabilities — 251.5 8.7 28.7 — 288.9 Current portion of pension and other postretirement benefit obligations — 38.4 — 0.3 — 38.7 Total current liabilities — 1,012.4 34.9 84.5 (3.2 ) 1,128.6 Non-current liabilities: Long-term debt — 1,993.7 — — — 1,993.7 Pension and other postretirement benefit obligations — 827.0 — 2.9 — 829.9 Inter-company accounts — 4,312.3 — 511.2 (4,823.5 ) — Other non-current liabilities — 105.6 0.2 28.2 — 134.0 TOTAL LIABILITIES — 8,251.0 35.1 626.8 (4,826.7 ) 4,086.2 Equity (deficit): Total stockholders’ equity (deficit) 99.9 (3,017.4 ) 1,811.6 127.1 1,078.7 99.9 Noncontrolling interests — — — 329.6 — 329.6 TOTAL EQUITY (DEFICIT) 99.9 (3,017.4 ) 1,811.6 456.7 1,078.7 429.5 TOTAL LIABILITIES AND EQUITY (DEFICIT) $ 99.9 $ 5,233.6 $ 1,846.7 $ 1,083.5 $ (3,748.0 ) $ 4,515.7 Condensed Balance Sheets December 31, 2017 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company ASSETS Current assets: Cash and cash equivalents $ — $ 14.5 $ 7.2 $ 16.3 $ — $ 38.0 Accounts receivable, net — 432.4 33.2 65.4 (13.2 ) 517.8 Inventory — 1,231.5 55.1 108.3 (9.9 ) 1,385.0 Other current assets — 124.7 0.2 5.4 — 130.3 Total current assets — 1,803.1 95.7 195.4 (23.1 ) 2,071.1 Property, plant and equipment — 6,004.0 181.5 646.3 — 6,831.8 Accumulated depreciation — (4,620.8 ) (94.8 ) (130.0 ) — (4,845.6 ) Property, plant and equipment, net — 1,383.2 86.7 516.3 — 1,986.2 Other non-current assets: Investment in subsidiaries (3,127.4 ) 1,844.9 — 67.5 1,215.0 — Inter-company accounts 3,082.8 — 1,523.1 — (4,605.9 ) — Goodwill and intangible assets — — 32.8 273.9 — 306.7 Other non-current assets — 66.3 0.2 44.3 — 110.8 TOTAL ASSETS $ (44.6 ) $ 5,097.5 $ 1,738.5 $ 1,097.4 $ (3,414.0 ) $ 4,474.8 LIABILITIES AND EQUITY (DEFICIT) Current liabilities: Accounts payable $ — $ 623.3 $ 17.9 $ 50.9 $ (1.7 ) $ 690.4 Accrued liabilities — 228.2 7.8 34.5 — 270.5 Current portion of pension and other postretirement benefit obligations — 39.7 — 0.4 — 40.1 Total current liabilities — 891.2 25.7 85.8 (1.7 ) 1,001.0 Non-current liabilities: Long-term debt — 2,110.1 — — — 2,110.1 Pension and other postretirement benefit obligations — 890.8 — 3.4 — 894.2 Inter-company accounts — 4,199.6 — 489.1 (4,688.7 ) — Other non-current liabilities — 133.2 1.0 34.7 — 168.9 TOTAL LIABILITIES — 8,224.9 26.7 613.0 (4,690.4 ) 4,174.2 Equity (deficit): Total stockholders’ equity (deficit) (44.6 ) (3,127.4 ) 1,711.8 139.2 1,276.4 (44.6 ) Noncontrolling interests — — — 345.2 — 345.2 TOTAL EQUITY (DEFICIT) (44.6 ) (3,127.4 ) 1,711.8 484.4 1,276.4 300.6 TOTAL LIABILITIES AND EQUITY (DEFICIT) $ (44.6 ) $ 5,097.5 $ 1,738.5 $ 1,097.4 $ (3,414.0 ) $ 4,474.8
Condensed Statements of Cash Flows	Condensed Statements of Cash Flows Year Ended December 31, 2018 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net cash flows from operating activities $ (2.3 ) $ 209.7 $ 83.1 $ 83.8 $ (9.6 ) $ 364.7 Cash flows from investing activities: Capital investments — (122.9 ) (8.1 ) (21.0 ) — (152.0 ) Other investing items, net — 0.8 — (0.7 ) — 0.1 Net cash flows from investing activities — (122.1 ) (8.1 ) (21.7 ) — (151.9 ) Cash flows from financing activities: Net borrowings (repayments) under credit facility — (115.0 ) — — — (115.0 ) Redemption of long-term debt — (12.6 ) — — — (12.6 ) Inter-company activity 2.5 48.3 (74.0 ) 13.6 9.6 — SunCoke Middletown distributions to noncontrolling interest owners — — — (73.7 ) — (73.7 ) Other financing items, net (0.2 ) (0.7 ) — — — (0.9 ) Net cash flows from financing activities 2.3 (80.0 ) (74.0 ) (60.1 ) 9.6 (202.2 ) Net increase (decrease) in cash and cash equivalents — 7.6 1.0 2.0 — 10.6 Cash and equivalents, beginning of year — 14.5 7.2 16.3 — 38.0 Cash and equivalents, end of year $ — $ 22.1 $ 8.2 $ 18.3 $ — $ 48.6 Condensed Statements of Cash Flows Year Ended December 31, 2017 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net cash flows from operating activities $ (2.5 ) $ 67.3 $ 73.3 $ 61.7 $ (1.0 ) $ 198.8 Cash flows from investing activities: Capital investments — (131.8 ) (5.6 ) (15.1 ) — (152.5 ) Investment in acquired business, net of cash acquired — (360.4 ) — — — (360.4 ) Other investing items, net — 4.0 — 0.2 — 4.2 Net cash flows from investing activities — (488.2 ) (5.6 ) (14.9 ) — (508.7 ) Cash flows from financing activities: Net borrowings (repayments) under credit facility — 450.0 — — — 450.0 Proceeds from issuance of long-term debt — 680.0 — — — 680.0 Redemption of long-term debt — (848.4 ) — — — (848.4 ) Debt issuance costs — (25.3 ) — — — (25.3 ) Inter-company activity 5.0 31.2 (64.9 ) 27.7 1.0 — SunCoke Middletown distributions to noncontrolling interest owners — — — (79.1 ) — (79.1 ) Other financing items, net (2.5 ) — — — — (2.5 ) Net cash flows from financing activities 2.5 287.5 (64.9 ) (51.4 ) 1.0 174.7 Net increase (decrease) in cash and cash equivalents — (133.4 ) 2.8 (4.6 ) — (135.2 ) Cash and equivalents, beginning of year — 147.9 4.4 20.9 — 173.2 Cash and equivalents, end of year $ — $ 14.5 $ 7.2 $ 16.3 $ — $ 38.0 Condensed Statements of Cash Flows Year Ended December 31, 2016 AK Holding AK Steel Guarantor Subsidiaries of the Senior Notes Other Non-Guarantor Subsidiaries Eliminations Consolidated Company Net cash flows from operating activities $ (3.1 ) $ 186.5 $ 44.3 $ 92.2 $ (15.3 ) $ 304.6 Cash flows from investing activities: Capital investments — (116.0 ) (8.8 ) (2.8 ) — (127.6 ) Other investing items, net — 3.0 — (0.7 ) — 2.3 Net cash flows from investing activities — (113.0 ) (8.8 ) (3.5 ) — (125.3 ) Cash flows from financing activities: Net borrowings (repayments) under credit facility — (550.0 ) — — — (550.0 ) Proceeds from issuance of long-term debt — 380.0 — — — 380.0 Redemption of long-term debt — (392.8 ) — — — (392.8 ) Proceeds from issuance of common stock 600.4 — — — — 600.4 Debt issuance costs — (20.4 ) — — — (20.4 ) Inter-company activity (602.4 ) 630.5 (36.8 ) (6.6 ) 15.3 — SunCoke Middletown distributions to noncontrolling interest owners — — — (85.1 ) — (85.1 ) Other financing items, net 5.1 0.1 — — — 5.2 Net cash flows from financing activities 3.1 47.4 (36.8 ) (91.7 ) 15.3 (62.7 ) Net increase (decrease) in cash and cash equivalents — 120.9 (1.3 ) (3.0 ) — 116.6 Cash and equivalents, beginning of year — 27.0 5.7 23.9 — 56.6 Cash and equivalents, end of year $ — $ 147.9 $ 4.4 $ 20.9 $ — $ 173.2

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Property Plant and Equipment Useful Lives (Details)	12 Months Ended
	Dec. 31, 2018
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Minimum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Maximum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Weighted Average [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	13 years

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details2)	12 Months Ended
	Dec. 31, 2018USD ($)employees	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2019USD ($)
Concentration Of Risk [Line Items]
Number of Employees	9,500
Pension and OPEB (income) expense | $	$ (19,200,000)	$ (71,900,000)	$ 16,500,000
Goodwill, Impairment Loss | $	$ 0	$ 0	$ 0
Workforce Subject to Collective Bargaining Arrangements [Member]
Concentration Of Risk [Line Items]
Number of Employees	5,700
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Mountain State Carbon [Member]
Concentration Of Risk [Line Items]
Number of Employees	230
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Coshocton Works [Member]
Concentration Of Risk [Line Items]
Number of Employees	300
Customer Concentration Risk [Member] | Sales Revenue, Goods, Net [Member]
Concentration Of Risk [Line Items]
Number Of Major Customers	2	1	2
Customer Concentration Risk [Member] | Major Customer A [Member] | Sales Revenue, Goods, Net [Member]
Concentration Of Risk [Line Items]
Percentage of total (in hundredths)	11.00%	12.00%	12.00%
Customer Concentration Risk [Member] | Major Customer B [Member] | Sales Revenue, Goods, Net [Member]
Concentration Of Risk [Line Items]
Percentage of total (in hundredths)	10.00%		11.00%
Credit Concentration Risk [Member] | Accounts Receivable [Member]
Concentration Of Risk [Line Items]
Number Of Major Customers	1	1
Credit Concentration Risk [Member] | Automotive Market [Member] | Accounts Receivable [Member]
Concentration Of Risk [Line Items]
Percentage of total (in hundredths)	52.00%	55.00%
Credit Concentration Risk [Member] | Major Customer A [Member] | Accounts Receivable [Member]
Concentration Of Risk [Line Items]
Percentage of total (in hundredths)	13.00%	18.00%
Maximum [Member] | Commodity [Member]
Concentration Of Risk [Line Items]
Derivative contracts duration (in months)	2 years
Maximum [Member] | Forward Contracts [Member]
Concentration Of Risk [Line Items]
Derivative contracts duration (in months)	3 years
IAM National Pension Fund's National Pension Plan [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] | Middletown Works [Member]
Concentration Of Risk [Line Items]
Number of Employees	1,760
IAM National Pension Fund's National Pension Plan [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Butler Works [Member]
Concentration Of Risk [Line Items]
Number of Employees	1,170
IAM National Pension Fund's National Pension Plan [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Zanesville Works [Member]
Concentration Of Risk [Line Items]
Number of Employees	100
Machinery and equipment [Member] | Maximum [Member]
Concentration Of Risk [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Machinery and equipment [Member] | Minimum [Member]
Concentration Of Risk [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Accounting Standards Update 2016-02 [Member] | Scenario, Forecast [Member] | Maximum [Member]
Concentration Of Risk [Line Items]
Operating Lease, Right-of-use Asset | $				$ 350,000,000
Operating Lease, Liability | $				350,000,000
Accounting Standards Update 2016-02 [Member] | Scenario, Forecast [Member] | Minimum [Member]
Concentration Of Risk [Line Items]
Operating Lease, Right-of-use Asset | $				250,000,000
Operating Lease, Liability | $				$ 250,000,000

Supplementary Financial State_3

Supplementary Financial Statement Information - Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Net sales	$ 1,677.1	$ 1,735.6	$ 1,746.6	$ 1,658.9	$ 1,495.6	$ 1,494.3	$ 1,557.2	$ 1,533.4	$ 6,818.2	$ 6,080.5	$ 5,882.5
Non-US [Member]
Disaggregation of Revenue [Line Items]
Net sales									634.8	627.1	655.6
Carbon [Member]
Disaggregation of Revenue [Line Items]
Net sales									4,409.1	4,034.5	4,014.5
Stainless And Electrical [Member]
Disaggregation of Revenue [Line Items]
Net sales									1,793.8	1,687.6	1,654.1
Other Product Lines [Member]
Disaggregation of Revenue [Line Items]
Net sales									615.3	358.4	213.9
Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Net sales									4,284.7	3,951.5	3,906.8
Infrastructure and Manufacturing Market [Member]
Disaggregation of Revenue [Line Items]
Net sales									1,049.1	948	936.7
Distributors and Converters Market [Member]
Disaggregation of Revenue [Line Items]
Net sales									$ 1,484.4	$ 1,181	$ 1,039

Supplementary Financial State_4

Supplementary Financial Statement Information - Research & Development (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplementary Financial Statement Information [Abstract]
Research and development costs	$ 29.4	$ 28.1	$ 28.3

Supplementary Financial State_5

Supplementary Financial Statement Information - Allowance for Doubtful Accounts (Details2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance For Doubtful Accounts
Balance at beginning of year	$ 6.8	$ 7.8	$ 6
Increase (decrease) in allowance	0.3	(1)	2.4
Receivables written off	(0.5)	0	(0.6)
Balance at end of year	$ 6.6	$ 6.8	$ 7.8

Supplementary Financial State_6

Supplementary Financial Statement Information - Inventory (Details3) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished and semi-finished	$ 1,054.4	$ 996.8
Raw materials	365.5	388.2
Inventory	$ 1,419.9	$ 1,385

Supplementary Financial State_7

Supplementary Financial Statement Information - LIFO Recast (Details4) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of products sold										$ 5,911	$ 5,253.1	$ 5,099.7
Income tax expense (benefit)										(6.2)	(2.2)	(16.9)
Net income										244.1	164.9	49.2
Net income attributable to AK Steel Holding Corporation		$ 33.5	$ 67.2	$ 56.6	$ 28.7	$ (80.4)	$ 22.3	$ 77.2	$ 84.4	$ 186	$ 103.5	$ (16.8)
Earnings Per Share, Basic						$ (0.26)	$ 0.07	$ 0.25	$ 0.27	$ 0.59	$ 0.33	$ (0.07)
Earnings Per Share, Diluted						$ (0.26)	$ 0.07	$ 0.24	$ 0.26	$ 0.59	$ 0.32	$ (0.07)
Reclassification of losses (gains) to net income										$ (10.3)	$ (6.1)	$ 39.1
Comprehensive income										193.5	203.4	173.8
Comprehensive income attributable to AK Steel Holding Corporation										135.4	142	107.8
Inventory		1,419.9				$ 1,385				1,419.9	1,385
Other non-current assets		103.9				110.8				103.9	110.8
Other non-current liabilities		134				168.9				134	168.9
Accumulated deficit		(2,691.8)				(2,877)				(2,691.8)	(2,877)
Accumulated other comprehensive loss		(100)				(50.2)				(100)	(50.2)
Deferred income taxes										(8)	(9)	(4.1)
Changes in working capital										12.7	(116.7)	129.6
Other operating items, net										2.4	20.1	3
AdjustmentAsIfUnderLifo [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of products sold										(55.7)
Income tax expense (benefit)										13.2
Net income										42.5
Net income attributable to AK Steel Holding Corporation										$ 42.5
Earnings Per Share, Basic										$ 0.13
Earnings Per Share, Diluted										$ 0.14
Comprehensive income										$ 42.5
Comprehensive income attributable to AK Steel Holding Corporation										42.5
Inventory		291.2								291.2
Other non-current assets		(77)								(77)
Other non-current liabilities		2								2
Accumulated deficit		224.1								224.1
Deferred income taxes										13.2
Changes in working capital										(54)
Other operating items, net										(1.7)
ChangeFromLifoToAverageCostMethod [Member] | AsIfUnderLifo [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of products sold										5,966.7
Income tax expense (benefit)										(19.4)
Net income										201.6
Net income attributable to AK Steel Holding Corporation										$ 143.5
Earnings Per Share, Basic										$ 0.46
Earnings Per Share, Diluted										$ 0.45
Comprehensive income										$ 151
Comprehensive income attributable to AK Steel Holding Corporation										92.9
Inventory		1,128.7								1,128.7
Other non-current assets		180.9								180.9
Other non-current liabilities		132								132
Accumulated deficit		$ (2,915.9)								(2,915.9)
Deferred income taxes										(21.2)
Changes in working capital										66.7
Other operating items, net										$ 4.1
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of products sold	[1]										5,365.2	5,070.6
Income tax expense (benefit)											(17)	3.2
Net income											67.6	58.2
Net income attributable to AK Steel Holding Corporation											$ 6.2	$ (7.8)
Earnings Per Share, Basic											$ 0.02	$ (0.03)
Earnings Per Share, Diluted											$ 0.02	$ (0.03)
Reclassification of losses (gains) to net income											$ (12.5)	$ 27.2
Comprehensive income											91.1	181.9
Comprehensive income attributable to AK Steel Holding Corporation											29.7	115.9
Inventory						1,147.8					1,147.8
Other non-current assets						169.3					169.3
Other non-current liabilities						161.6					161.6
Accumulated deficit						(3,058.6)					(3,058.6)
Accumulated other comprehensive loss						(40)					(40)
Deferred income taxes											(15.2)	5
Changes in working capital											1.8	112.4
Other operating items, net											5.1	2.1
Restatement Adjustment [Member] | ChangeFromLifoToAverageCostMethod [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of products sold											(112.1)	29.1
Income tax expense (benefit)											14.8	(20.1)
Net income											97.3	(9)
Net income attributable to AK Steel Holding Corporation											$ 97.3	$ (9)
Earnings Per Share, Basic											$ 0.31	$ (0.04)
Earnings Per Share, Diluted											$ 0.30	$ (0.04)
Reclassification of losses (gains) to net income											$ 6.4	$ 11.9
Comprehensive income											112.3	(8.1)
Comprehensive income attributable to AK Steel Holding Corporation											112.3	(8.1)
Inventory						237.2					237.2
Other non-current assets						(58.5)					(58.5)
Other non-current liabilities						7.3					7.3
Accumulated deficit						181.6					181.6
Accumulated other comprehensive loss						$ (10.2)					(10.2)
Deferred income taxes											6.2	(9.1)
Changes in working capital											(118.5)	17.2
Other operating items, net											$ 15	$ 0.9
[1]	(a) Cost of products sold as originally reported reflects the change in presentation of pension and OPEB (income) expense further described in Note 1

Supplementary Financial State_8

Supplementary Financial Statement Information - Property, Plant and Equipment (Details5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 6,969.2	$ 6,831.8
Less accumulated depreciation	(5,057.6)	(4,845.6)
Property, plant and equipment, net	1,911.6	1,986.2
Capitalized interest on capital projects	1.6	1.9	$ 3.1
Asset retirement obligations	8.5	7.8
Land, land improvements and leaseholds [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	272.1	275.3
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	509.7	509
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	6,061.6	5,958.2
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 125.8	$ 89.3

Supplementary Financial State_9

Supplementary Financial Statement Information - Goodwill (Details 6) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at beginning of year	$ 253.8	$ 32.8	$ 32.8
Acquisition	1.2	221	0
Balance at end of year	$ 255	$ 253.8	$ 32.8

Supplementary Financial Stat_10

Supplementary Financial Statement Information - Intangibles (Details6a) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 56.9	$ 56.9
Finite-Lived Intangible Assets, Accumulated Amortization	(13)	(4)
Finite-Lived Intangible Assets, Net	43.9	52.9
Amortization of Intangible Assets	9	4
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	8.4
Finite-Lived Intangible Assets, Amortization Expense, Year Two	8.4
Finite-Lived Intangible Assets, Amortization Expense, Year Three	8.4
Finite-Lived Intangible Assets, Amortization Expense, Year Four	8.4
Finite-Lived Intangible Assets, Amortization Expense, Year Five	7.1
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	36.6	36.6
Finite-Lived Intangible Assets, Accumulated Amortization	(7.4)	(2.2)
Finite-Lived Intangible Assets, Net	$ 29.2	34.4
Finite-Lived Intangible Assets, Remaining Amortization Period	5 years 7 months 6 days
Technology-Based Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 19.3	19.3
Finite-Lived Intangible Assets, Accumulated Amortization	(4.6)	(1.4)
Finite-Lived Intangible Assets, Net	$ 14.7	17.9
Finite-Lived Intangible Assets, Remaining Amortization Period	4 years 7 months 6 days
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 1	1
Finite-Lived Intangible Assets, Accumulated Amortization	(1)	(0.4)
Finite-Lived Intangible Assets, Net	$ 0	$ 0.6

Supplementary Financial Stat_11

Supplementary Financial Statement Information - Other Non-current Assets (Details7) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Assets, Noncurrent [Abstract]
Investments in affiliates	$ 80.5	$ 77.5
Other Assets, Miscellaneous, Noncurrent	23.4	33.3
Other non-current assets	$ 103.9	$ 110.8

Supplementary Financial Stat_12

Supplementary Financial Statement Information - Accrued Liabilities (Details8) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Supplementary Financial Statement Information [Abstract]
Salaries, wages and benefits	$ 127.8	$ 101.3
Interest	34.8	35
Other accrued liabilities	126.3	134.2
Accrued liabilities	$ 288.9	$ 270.5

Supplementary Financial Stat_13

Supplementary Financial Statement Information - Facility Idling (Details9) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2019	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Asset impairment charge						$ 0	$ 75.6	$ 0
Ashland Works Hot End [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Idling			$ 28.1
Costs For Temporarily Idled Operations						20	21.2	22.1
Asset impairment charge		$ 75.6					75.6
Restructuring Reserve [Roll Forward]
Balance at beginning of year	$ 0				$ 0	1.5	6.2	22.2
Payments for restructuring						(1.5)	(5.3)	(20.1)
Additions to the reserve						0	0.6	4.1
Balance at end of year		$ 1.5	22.2			$ 0	$ 1.5	$ 6.2
Ashland Works Hot End [Member] | Supplemental Unemployment Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Idling			22.2
Ashland Works Hot End [Member] | Equipment Idling And Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Idling			$ 5.9
Scenario, Forecast [Member] | Ashland Works Hot End [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Closure	80
Cash Payments Related To Facility Closure				$ 30	15
Cash Charge For Facility Closure					14
Scenario, Forecast [Member] | Ashland Works Hot End [Member] | Take-Or-Pay Supply Agreements [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Closure	20
Scenario, Forecast [Member] | Ashland Works Hot End [Member] | Supplemental Unemployment Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Closure	30
Scenario, Forecast [Member] | Ashland Works Hot End [Member] | Multiemployer Plan Withdrawal [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Closure	25
Scenario, Forecast [Member] | Ashland Works Hot End [Member] | Equipment Idling And Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Charge For Facility Closure	$ 5
Scenario, Forecast [Member] | Ashland Works Hot End [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Cash Charge For Facility Closure					10
Scenario, Forecast [Member] | Ashland Works Hot End [Member] | Accelerated Depreciation Due To Facility Closure [Member]
Restructuring Cost and Reserve [Line Items]
Cash Charge For Facility Closure					$ 4

Acquisition of Precision Part_2

Acquisition of Precision Partners (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Precision Partners Holding Company [Member]
Business Acquisition [Line Items]
Entity Number Of Plants	8
Precision Partners Holding Company [Member] | Selling, General and Administrative Expenses [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs	$ 6.2

Investments in Affiliates (Deta

Investments in Affiliates (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Gain on termination of pellet agreement and related transportation costs		$ 0	$ 19.3	$ (69.5)
Combined Metals of Chicago, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		40.00%
Delaco Processing, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		49.00%
Rockport Roll Shop LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		50.00%
Spartan Steel Coating, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage (in hundredths)		48.00%
Difference between carrying amount and underlying equity		$ 9.2
Cost of Products Sold [Member]
Schedule of Equity Method Investments [Line Items]
Share of income (loss) from equity method investments		$ 6.6	$ 7	12.3
Global Settlement Agreement [Member] | Magnetation LLC [Member]
Schedule of Equity Method Investments [Line Items]
Payments for Legal Settlements				36.6
Iron Ore Pellets Agreements [Member]
Schedule of Equity Method Investments [Line Items]
Gain on termination of pellet agreement and related transportation costs	$ 19.3
Iron Ore Pellets Agreements [Member] | Magnetation LLC [Member]
Schedule of Equity Method Investments [Line Items]
Loss on Contracts				$ 32.9
Gain on termination of pellet agreement and related transportation costs	$ 19.3

Investments in Affiliates Equit

Investments in Affiliates Equity Investee Summarized Financial Information (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investment, Summarized Financial Information [Abstract]
Revenue	$ 329.8	$ 292.7	$ 286.4
Gross profit	91	88.9	96.3
Net income (loss)	19.4	20.7	$ 31.8
Current assets	123.6	115.2
Noncurrent assets	74.4	73.5
Current liabilities	16.9	16.2
Noncurrent liabilities	$ 54.2	$ 58.9

Investments in Affiliates Relat

Investments in Affiliates Related Party Transactions (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transactions [Abstract]
Sales to equity investees	$ 104.4	$ 80.6	$ 69.2
Purchases from equity investees	31.2	33	$ 213.5
Accounts receivable from equity investees	1.9	0.7
Accounts payable to equity investees	$ 6.4	$ 4.1

Income Taxes - Detail of Income

Income Taxes - Detail of Income (Loss) before Taxes by Geography (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest [Abstract]
United States	$ 168.3	$ 91.6	$ (40.4)
Foreign	11.5	9.7	6.7
Noncontrolling interests	58.1	61.4	66
Income before income taxes	$ 237.9	$ 162.7	$ 32.3

Income Taxes - Detail of Deferr

Income Taxes - Detail of Deferred Tax Assets and Liabilities (Details 2) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating and capital loss and tax credit carryforwards	$ 516.7	$ 619.5
Postretirement benefits	81.8	92.5
Pension benefits	114.1	117.5
Inventories	38.5	47.9
Other assets	65.1	71.6
Valuation allowance	(693.5)	(735.7)	$ (1,189.7)	$ (1,232.3)
Total deferred tax assets	122.7	213.3
Deferred tax liabilities:
Depreciable assets	(108.3)	(121.9)
Other liabilities	(33.4)	(118.3)
Total deferred tax liabilities	(141.7)	(240.2)
Net deferred tax liabilities	$ (19)	$ (26.9)

Income Taxes - Valuation Allowa

Income Taxes - Valuation Allowance (Details 3) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 735.7	$ 735.7	$ 1,189.7	$ 1,232.3
Change in valuation allowance	$ (5.3)
Balance at end of year		693.5	735.7	1,189.7
Included in income tax expense (benefit) [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance		(52.8)	(62.3)	11
Change in deferred assets in other comprehensive income [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance		10.6	8.5	(53.6)
Effect of tax rate changes [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Change in valuation allowance		$ 0	$ (400.2)	$ 0

Income Taxes - Loss Carryforwar

Income Taxes - Loss Carryforwards (Details 4) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Domestic Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	$ 2,174
Domestic Tax Authority [Member] | Research [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	1.2
State and Local Jurisdiction [Member] | Operating Loss and Tax Credit Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Deferred tax assets from operating loss and tax credit carryforwards	$ 89.2
Earliest Tax Year [Member] | Domestic Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Open Tax Year	2,015
Earliest Tax Year [Member] | Domestic Tax Authority [Member] | Research [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2027
Earliest Tax Year [Member] | Domestic Tax Authority [Member] | Operating Loss Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2030
Earliest Tax Year [Member] | State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Open Tax Year	2,007
Earliest Tax Year [Member] | State and Local Jurisdiction [Member] | Operating Loss and Tax Credit Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Operating Loss and Tax Credit Carryforwards, Expiration Date	Dec. 31, 2018
Latest Tax Year [Member] | Domestic Tax Authority [Member] | Research [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2028
Latest Tax Year [Member] | Domestic Tax Authority [Member] | Operating Loss Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Latest Tax Year [Member] | State and Local Jurisdiction [Member] | Operating Loss and Tax Credit Carryforwards [Member]
Tax Credit Carryforward [Line Items]
Operating Loss and Tax Credit Carryforwards, Expiration Date	Dec. 31, 2038

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Details 5) - USD ($) $ in Millions	Jan. 01, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Remeasurement of deferred taxes for U.S. tax legislation			$ 0	$ (4.3)	$ 0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Transition tax on foreign earnings				24.3
Undistributed Earnings of Foreign Subsidiaries			7.3
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		$ (5.3)
Current:
Federal			(0.5)	(4.5)	(3.7)
State			(0.3)	0.3	0.2
Foreign			2.1	2.4	1.7
Deferred:
Federal			(5.3)	0.7	15.1
State			0	0.1	1.4
Deferred Foreign Income Tax Expense (Benefit)			(2.2)	(0.4)	0
Benefit Of Operating Loss Carryforwards			0	0	(16.1)
Amount allocated to other comprehensive income			0	0	(15.5)
Change in valuation allowance on beginning-of-the-year deferred tax assets			0	(0.8)	0
Income tax expense (benefit)			$ (6.2)	$ (2.2)	$ (16.9)

Income Taxes - Effective Tax Ra

Income Taxes - Effective Tax Rate Reconciliation (Details 6) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense at U.S. federal statutory rate	$ 50	$ 57.2	$ 11.3
Income tax expense calculated on noncontrolling interests	(12.2)	(21.5)	(23.1)
State and foreign tax expense, net of federal tax	(2.3)	6.3	0.2
Increase (decrease) in deferred tax asset valuation allowance	(52.8)	(51.8)	11
Amount allocated to other comprehensive income	0	0	(15.5)
Remeasurement of deferred taxes for U.S. tax legislation	0	(4.3)	0
Transition tax on foreign earnings	0	7.9	0
Non-deductible compensation	8.1	0	0
Other differences	3	4	(0.8)
Income tax expense (benefit)	$ (6.2)	$ (2.2)	$ (16.9)

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details 7) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 89.4	$ 124.2	$ 130.3
Decreases for prior year tax positions	(2.2)	(0.5)	(4.5)
Increases (decreases) for current year tax positions	0	0.3	(1.6)
Increases (decreases) related to tax rate changes (a)	0	(34.6)	0
Balance at end of year	87.2	89.4	$ 124.2
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	72.8	75
Unrecognized tax benefits that would result in adjustments to other tax accounts	$ 14.5	$ 14.4
Earliest Tax Year [Member] | Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2,015
Earliest Tax Year [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2,007

Long-term Debt and Other Fina_3

Long-term Debt and Other Financing Debt Instrument Table (Details) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2012USD ($)	Dec. 31, 2018USD ($)shares$ / shares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Unamortized discount/premium and debt issuance costs		$ (41.7)	$ (55.4)
Total long-term debt		1,993.7	2,110.1
Gains (losses) on retirement of debt		2	(21.3)	$ (9.2)
Senior Secured Notes Due July 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 380	$ 380
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)		7.50%	7.50%
Debt Instrument, Maturity Date		Jul. 15, 2023
Assets Pledged as Collateral, Carrying Amount		$ 1,400
Debt Instrument, Convertible, Effective Interest Rate		8.30%	8.30%
Senior Secured Notes Due July 2023 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption, Description		Before July 15, 2019, we may redeem the Secured Notes at a price equal to 100.000% of par plus a make-whole premium and all accrued and unpaid interest to the date of redemption.
Debt Instrument, Redemption Price Percentage		100.00%
Debt Instrument, Redemption Period, End Date		Jul. 14, 2019
Senior Secured Notes Due July 2023 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		103.75%
Debt Instrument, Redemption Period, Start Date		Jul. 15, 2019
Debt Instrument, Redemption Period, End Date		Jul. 14, 2020
Senior Secured Notes Due July 2023 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		101.875%
Debt Instrument, Redemption Period, Start Date		Jul. 15, 2020
Debt Instrument, Redemption Period, End Date		Jul. 14, 2021
Senior Secured Notes Due July 2023 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		100.00%
Debt Instrument, Redemption Period, Start Date		Jul. 15, 2021
Debt Instrument, Redemption Period, End Date		Jul. 15, 2023
Senior Secured Notes Due December 2018 [Member] | Other Income (Expense) [Member]
Debt Instrument [Line Items]
Gains (losses) on retirement of debt				$ (12.4)
Exchangeable Senior Notes Due November 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 148.5	$ 150
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)		5.00%	5.00%
Debt Instrument, Maturity Date		Nov. 15, 2019
Debt Instrument, Convertible, Effective Interest Rate		10.80%	10.80%
Debt Instrument, Repurchased Face Amount		$ 1.5
Debt Instrument, Convertible, Stock Price Trigger | $ / shares		$ 7.02
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger		130.00%
Debt Instrument, Convertible, Threshold Trading Days		20
Debt Instrument, Convertible, Threshold Consecutive Trading Days		30
Debt Instrument, Convertible, Conversion Ratio (in shares per $1,000 principal amount)		185.1852
Debt Instrument, Convertible, Conversion Price (in dollars per share) | $ / shares		$ 5.40
Debt Instrument, Convertible, Number Of Equity Instruments (in shares) | shares		27,500,000
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	$ 38.7
Carrying Value of Long-term Debt		$ 141.4	$ 135.3
Exchangeable Senior Notes Due November 2019 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Number Of Equity Instruments (in shares) | shares		37,100,000
Senior Notes Due October 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 406.2	$ 406.2
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)		7.625%	7.625%
Debt Instrument, Maturity Date		Oct. 1, 2021
Senior Notes Due October 2021 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Period, End Date		Sep. 30, 2019
Senior Notes Due October 2021 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		101.906%
Debt Instrument, Redemption Period, Start Date		Oct. 1, 2019
Debt Instrument, Redemption Period, End Date		Sep. 30, 2021
Senior Notes Due October 2021 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		100.00%
Senior Notes Due October 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 274.8	$ 280
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)		6.375%	6.375%
Debt Instrument, Maturity Date		Oct. 15, 2025
Debt Instrument, Convertible, Effective Interest Rate		7.10%	7.10%
Debt Instrument, Repurchased Face Amount		$ 5.2
Gains (losses) on retirement of debt			$ (8.4)
Senior Notes Due October 2025 [Member] | Other Income (Expense) [Member]
Debt Instrument [Line Items]
Gains (losses) on retirement of debt		$ 0.7
Senior Notes Due October 2025 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Period, End Date		Oct. 14, 2020
Senior Notes Due October 2025 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		103.188%
Debt Instrument, Redemption Period, Start Date		Oct. 15, 2020
Debt Instrument, Redemption Period, End Date		Oct. 14, 2021
Senior Notes Due October 2025 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		101.594%
Debt Instrument, Redemption Period, Start Date		Oct. 15, 2021
Debt Instrument, Redemption Period, End Date		Oct. 14, 2022
Senior Notes Due October 2025 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		100.00%
Debt Instrument, Redemption Period, Start Date		Oct. 15, 2022
Debt Instrument, Redemption Period, End Date		Oct. 14, 2025
Senior Notes Due March 2027 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 391.6	$ 400
Debt Instrument, Interest Rate, Stated Percentage (in hundredths)		7.00%	7.00%
Debt Instrument, Maturity Date		Mar. 15, 2027
Debt Instrument, Repurchased Face Amount		$ 8.4
Gains (losses) on retirement of debt			$ (13.1)
Senior Notes Due March 2027 [Member] | Other Income (Expense) [Member]
Debt Instrument [Line Items]
Gains (losses) on retirement of debt		$ 1.3
Senior Notes Due March 2027 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Period, End Date		Mar. 14, 2022
Senior Notes Due March 2027 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		103.50%
Debt Instrument, Redemption Period, Start Date		Mar. 15, 2022
Debt Instrument, Redemption Period, End Date		Mar. 14, 2023
Senior Notes Due March 2027 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		102.333%
Debt Instrument, Redemption Period, Start Date		Mar. 15, 2023
Debt Instrument, Redemption Period, End Date		Mar. 14, 2024
Senior Notes Due March 2027 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		101.167%
Debt Instrument, Redemption Period, Start Date		Mar. 15, 2024
Debt Instrument, Redemption Period, End Date		Mar. 14, 2025
Senior Notes Due March 2027 [Member] | Debt Instrument, Redemption, Period Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price Percentage		100.00%
Debt Instrument, Redemption Period, Start Date		Mar. 15, 2025
Debt Instrument, Redemption Period, End Date		Mar. 14, 2027
Unsecured Industrial Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 73.3
Long-term Debt, Weighted Average Interest Rate, at Point in Time		6.80%
Secured Industrial Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 26
Industrial Revenue Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 99.3	99.3
Debt Instrument, Maturity Date Range, Start		Nov. 15, 2020
Debt Instrument, Maturity Date Range, End		Jun. 1, 2028
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit Facility		$ 335	$ 450

Long-term Debt and Other Fina_4

Long-term Debt and Other Financing Debt Maturities (Details 2) $ in Millions	Dec. 31, 2018USD ($)
Maturities of Long-term Debt [Abstract]
2019 debt maturities	$ 148.5	[1]
2020 debt maturities	7.3
2021 debt maturities	406.2
2022 debt maturities	335
2023 debt maturities	$ 380
[1]	(a) Amounts maturing in 2019

Credit Facility and Other Finan

Credit Facility and Other Financing Information (Details 3) - Revolving Credit Facility [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,350,000,000
Line of credit facility, expiration date	Sep. 30, 2022
Debt Instrument, Covenant Description	The Credit Facility contains common restrictions, including limitations on, among other things, distributions and dividends, acquisitions and investments, indebtedness, liens and affiliate transactions. The Credit Facility requires that we maintain a minimum fixed charge coverage ratio of one to one if availability under the Credit Facility is less than $150.0. The Credit Facility?s current availability significantly exceeds $150.0. Availability is calculated as the lesser of the total commitments under the Credit Facility or eligible collateral after advance rates, less outstanding revolver borrowings and letters of credit. We secure our Credit Facility obligations with our inventory and accounts receivable, and the Credit Facility?s availability fluctuates monthly based on the varying levels of eligible collateral.
Minimum amount of borrowing capacity before a fixed charge coverage ratio applies	$ 135,000,000
Line of credit, current borrowing capacity based on eligible collateral	1,350,000,000
Current borrowings on credit facility	335,000,000	$ 450,000,000
Letters of credit, outstanding	73,200,000
Line of credit facility, remaining borrowing capacity	$ 941,800,000
Line of credit facility, Weighted Average Interest Rate (in hundredths)	4.10%

Pension and Other Postretirem_3

Pension and Other Postretirement Benefits (Details) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018USD ($)employees	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Amounts recognized in the consolidated balance sheets:
Current liabilities	$ (38.7)		$ (38.7)	$ (40.1)
Noncurrent liabilities	(829.9)		(829.9)	(894.2)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Future pension contributions in next fiscal year	45		45
Defined Benefit Plans, Estimated Future Employer Contributions, Year Two	50		50
Defined Benefit Plans, Estimated Future Employer Contributions, Year Three	50		50
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	216.5		216.5
Change in benefit obligations:
Benefit obligations at beginning of year			2,808	2,874.8
Service cost			3.2	2.8	$ 3
Interest cost			94.5	108.2	120.4
Plan participants’ contributions			0	0
Actuarial loss (gain)			(148.8)	91
Amendments			0	0
Benefits paid			(268.1)	(269)
Annuity settlement	(278.8)		(278.8)	0
Medicare subsidy reimbursement received			0	0
Foreign currency exchange rate changes			0	0.2
Benefit obligations at end of year	2,210	$ 2,874.8	2,210	2,808	2,874.8
Change in plan assets:
Fair value of plan assets at beginning of year			2,322.2	2,183.5
Actual gain (loss) on plan assets			(87)	362.4
Employer contributions			51.3	45.3
Plan participants’ contributions			0	0
Benefits paid			(268.1)	(269)
Annuity settlement			(278.8)	0
Medicare subsidy reimbursement received			0	0
Fair value of plan assets at end of year	1,739.6	2,183.5	1,739.6	2,322.2	2,183.5
Funded status	(470.4)		(470.4)	(485.8)
Amounts recognized in the consolidated balance sheets:
Current liabilities	(1.2)		(1.2)	(1.3)
Noncurrent liabilities	(469.2)		(469.2)	(484.5)
Net amount recognized	(470.4)		(470.4)	(485.8)
Amounts recognized in accumulated other comprehensive loss, before taxes:
Actuarial loss (gain)	134.1		134.1	77.6
Prior service cost (credit)	19.4		19.4	23.2
Net amount recognized	153.5		153.5	100.8
Aggregate accumulated benefit obligation	$ 2,188.6		2,188.6	2,767.1
Number Of Retirees Beneficiaries Affected By Settlement | employees	5,400
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ (14.5)	(25)	(14.5)	0	(29.9)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	37.5		37.5
Change in benefit obligations:
Benefit obligations at beginning of year			448.5	443.7
Service cost			4.5	4.7	4.9
Interest cost			15.6	17.3	19.9
Plan participants’ contributions			24.7	23.3
Actuarial loss (gain)			(23.7)	27.1
Amendments			(11.1)	(4.7)
Benefits paid			(62.6)	(65.5)
Annuity settlement			0	0
Medicare subsidy reimbursement received			2.3	2.6
Foreign currency exchange rate changes			0	0
Benefit obligations at end of year	398.2	443.7	398.2	448.5	443.7
Change in plan assets:
Fair value of plan assets at beginning of year			0	0
Actual gain (loss) on plan assets			0	0
Employer contributions			35.6	39.6
Plan participants’ contributions			24.7	23.3
Benefits paid			(62.6)	(65.5)
Annuity settlement			0	0
Medicare subsidy reimbursement received			2.3	2.6
Fair value of plan assets at end of year	0	$ 0	0	0	0
Funded status	(398.2)		(398.2)	(448.5)
Amounts recognized in the consolidated balance sheets:
Current liabilities	(37.5)		(37.5)	(38.8)
Noncurrent liabilities	(360.7)		(360.7)	(409.7)
Net amount recognized	(398.2)		(398.2)	(448.5)
Amounts recognized in accumulated other comprehensive loss, before taxes:
Actuarial loss (gain)	(35.4)		(35.4)	(13)
Prior service cost (credit)	(82.4)		(82.4)	(84.9)
Net amount recognized	$ (117.8)		(117.8)	(97.9)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement			0	$ 0	$ 0
Change In Assumptions For Pension Plans Return Rate [Member] | Pension Plans, Defined Benefit [Member]
Change in benefit obligations:
Actuarial loss (gain)			235.8
Change In Assumptions For Pension Plans Discount Rate [Member] | Pension Plans, Defined Benefit [Member]
Change in benefit obligations:
Actuarial loss (gain)			(154.6)
Change in Assumptions for Defined Benefit Plans [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Change in benefit obligations:
Actuarial loss (gain)			$ (27.7)

Pension and Other Postretirem_4

Pension and Other Postretirement Benefits - Assumptions (Details 2)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Interest crediting rate		3.80%	3.80%	4.30%
Pension Plans, Defined Benefit [Member]
Assumptions used to determine benefit obligations at December 31:
Discount rate		4.22%	3.54%	3.93%
Rate of compensation increase		4.00%	4.00%	4.00%
Interest crediting rate		3.80%	3.80%	3.80%
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Discount rate		3.69%	3.93%	3.95%
Expected return on plan assets		7.00%	7.25%	7.25%
Rate of compensation increase		4.00%	4.00%	4.00%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Assumptions used to determine benefit obligations at December 31:
Discount rate		4.27%	3.59%	4.04%
Subsequent year healthcare cost trend rate		6.50%	6.65%	7.00%
Ultimate healthcare cost trend rate		4.50%	4.50%	4.50%
Year ultimate healthcare cost trend rate begins		2,025	2,025	2,025
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Discount rate		3.59%	4.04%	4.22%
Scenario, Forecast [Member] | Pension Plans, Defined Benefit [Member]
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Expected return on plan assets	6.75%

Pension and Other Postretirem_5

Pension and Other Postretirement Benefits - Expected Benefit Payments (Details 3) $ in Millions	Dec. 31, 2018USD ($)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Future Benefit Payments in 2019	$ 216.5
Expected Future Benefit Payments in 2020	211.2
Expected Future Benefit Payments in 2021	198.9
Expected Future Benefit Payments in 2022	196
Expected Future Benefit Payments in 2023	180.6
Expected Future Benefit Payments in 2024 through 2028	835.3
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Future Benefit Payments in 2019	37.5
Expected Future Benefit Payments in 2020	35.6
Expected Future Benefit Payments in 2021	33.8
Expected Future Benefit Payments in 2022	32.2
Expected Future Benefit Payments in 2023	30.6
Expected Future Benefit Payments in 2024 through 2028	$ 133.4

Pension and Other Postretirem_6

Pension and Other Postretirement Benefits - Plan Assets (Details 4) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		$ 1,739.6	$ 2,322.2	$ 2,183.5
Fixed Income Securities [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocations percentage		60.00%
Equity Securities [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocations percentage		40.00%
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		$ 1,739.6	2,322.2
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		35.4	46.6
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		35.4	46.6
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment Companies [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		1,077.5	994.9
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		131.4	327.9
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		84.5	111.8
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		700.8	524.6
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		82.8	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment Companies [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		78	30.6
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		1,112.9	1,041.5
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		35.4	46.6
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		131.4	327.9
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		84.5	111.8
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		700.8	524.6
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		82.8	0
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment Companies [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		78	30.6
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[1]	355.8	194.6
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Measurements, Recurring [Member] | Global Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[1]	178.2	707
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Corporate Fixed-Income Securities Common/Collective Trusts [Member] [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[2]	0	379.1
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Measurements, Recurring [Member] | Global Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[2]	$ 92.7	$ 0
[1]	Investments may include common stocks, options and futures.
[2]	Investments may include investment-grade and high-yield corporate bonds, interest rate swaps, options and futures.

Pension and Other Postretirem_7

Pension and Other Postretirement Benefits - Benefit Costs (Details 5) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Recognized net actuarial loss (gain):
Pension and OPEB (income) expense			$ (11.6)	$ (64.4)	$ 24.3
Expense for defined contribution plans			31.1	24.9	23.1
Pension Plans, Defined Benefit [Member]
Components of pension and OPEB (income) expense:
Service cost			3.2	2.8	3
Interest cost			94.5	108.2	120.4
Expected return on plan assets			(148.8)	(149.9)	(167.1)
Amortization of prior service cost (credit)			3.8	4.7	5.6
Recognized net actuarial loss (gain):
Annual amortization			16.1	10.5	29.2
Pension/OPEB corridor charge/credit			0	0	78.4
Settlement (gain) loss	$ 14.5	$ 25	14.5	0	29.9
Pension and OPEB (income) expense			(16.7)	(23.7)	99.4
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of pension and OPEB (income) expense:
Service cost			4.5	4.7	4.9
Interest cost			15.6	17.3	19.9
Expected return on plan assets			0	0	0
Amortization of prior service cost (credit)			(13.6)	(58.5)	(60.4)
Recognized net actuarial loss (gain):
Annual amortization			(1.3)	(4.2)	(4.3)
Pension/OPEB corridor charge/credit			0	0	(35.3)
Settlement (gain) loss			0	0	0
Pension and OPEB (income) expense			$ 5.2	$ (40.7)	$ (75.2)

Pension and Other Postretirem_8

Pension and Other Postretirement Benefits - Multiemployer Plans (Details 6) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)employees	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Multiemployer Plans [Line Items]
Contributions to multiemployer plans		$ 21.9	$ 24.7	$ 24.8
Number of Employees | employees		9,500
Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Contributions to multiemployer plans		$ 4.2	6.3	6.8
IAM National Pension Fund's National Pension Plan [Member]
Multiemployer Plans [Line Items]
Contributions to multiemployer plans		$ 17.7	$ 18.4	$ 18
Mansfield Works [Member] | Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Number of Employees | employees		300
Walbridge Tube [Member] | Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Number of Employees | employees		110
Ashland Works [Member] | Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Number of Employees | employees		230
Scenario, Forecast [Member] | Ashland Works Hot End [Member]
Multiemployer Plans [Line Items]
Withdrawal Liability	$ 80
Multiemployer Plan Withdrawal [Member] | Scenario, Forecast [Member] | Ashland Works Hot End [Member]
Multiemployer Plans [Line Items]
Withdrawal Liability	$ 25

Operating Leases (Details)

Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Leases [Abstract]
Rental Expense	$ 48.1	$ 43.1	$ 46.7
Minimum Lease Payments 2019	23.3
Minimum Lease Payments 2020	20.8
Minimum Lease Payments 2021	20.6
Minimum Lease Payments 2022	18.7
Minimum Lease Payments 2023	17.3
Minimum Lease Payments 2024 and thereafter	83.6
Total minimum lease payments	$ 184.3

Commitments (Details)

Commitments (Details) $ in Millions	Dec. 31, 2018USD ($)
Capital Investment Commitments [Member]
Long-term Purchase Commitment [Line Items]
Commitments for future capital investments	$ 51.6

Environmental and Legal Conti_3

Environmental and Legal Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Environmental-related capital investments	$ 7.1	$ 6.8	$ 4.9
Environmental compliance costs	$ 126.3	$ 129.5	$ 123.9

Environmental and Legal Conti_4

Environmental and Legal Contingencies (Details 2) - USD ($) $ in Millions	1 Months Ended
	Mar. 31, 2014	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Member]
Accrued liabilities		$ 8	$ 8.5
Other Noncurrent Liabilities [Member]
Other non-current liabilities		$ 31.2	$ 35.4
Antitrust Case [Member]
Payments for Legal Settlements	$ 5.8

Environmental and Legal Conti_5

Environmental and Legal Contingencies (Details 3) $ in Millions	Dec. 31, 2018USD ($)
Hamilton Plant [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	$ 0.7
Mansfield Works [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	1.1
Ashland coke plant [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	1.4
Ambridge Works [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	5.6
Middletown Works RCRA Site [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	13.1
Zanesville Works RCRA [Member]
Site Contingency [Line Items]
Site contingency accrual, undiscounted amount	$ 0.1

Environmental and Legal Conti_6

Environmental and Legal Contingencies (Details 4)	12 Months Ended
	Dec. 31, 2018USD ($)defendantsplaintiffsclaims-lawsuits
Asbestos Claims With Specific Dollar Claim For Damages [Member]
Information on pending asbestos cases [Line Items]
Total asbestos cases pending | claims-lawsuits	167	[1]
Claims with specific dollar claims for damages [Abstract]
Asbestos Lawsuits Pending With Dollars Number Of Plaintiffs | plaintiffs	2,242
Asbestos Lawsuits Pending With Dollars Number Of Defendants | defendants	19,356
Asbestos Claims With Specific Dollar Claim For Damages [Member] | Asbestos claims up to $0.2 [Member]
Information on pending asbestos cases [Line Items]
Total asbestos cases pending | claims-lawsuits	160
Claims with specific dollar claims for damages [Abstract]
Asbestos Lawsuits Pending With Dollars Lower Range | $	$ 0
Asbestos Lawsuits Pending With Dollars Upper Range | $	$ 200,000
Asbestos Claims With Specific Dollar Claim For Damages [Member] | Asbestos claims above $0.2 to $5.0 [Member]
Information on pending asbestos cases [Line Items]
Total asbestos cases pending | claims-lawsuits	4
Claims with specific dollar claims for damages [Abstract]
Asbestos Lawsuits Pending With Dollars Lower Range | $	$ 200,000
Asbestos Lawsuits Pending With Dollars Upper Range | $	$ 5,000,000
Asbestos Claims With Specific Dollar Claim For Damages [Member] | Asbestos claims above $5.0 to $20.0 [Member]
Information on pending asbestos cases [Line Items]
Total asbestos cases pending | claims-lawsuits	3
Claims with specific dollar claims for damages [Abstract]
Asbestos Lawsuits Pending With Dollars Lower Range | $	$ 5,000,000
Asbestos Lawsuits Pending With Dollars Upper Range | $	$ 20,000,000
Asbestos Claims Without Specific Dollar Claim For Damages [Member]
Information on pending asbestos cases [Line Items]
Total asbestos cases pending | claims-lawsuits	176
Asbestos Issue [Member]
Information on pending asbestos cases [Line Items]
Total asbestos cases pending | claims-lawsuits	343
[1]	Involve a total of 2,242 plaintiffs and 19,356

Environmental and Legal Conti_7

Environmental and Legal Contingencies (Details 5) - Asbestos Issue [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)claims-lawsuits	Dec. 31, 2017USD ($)claims-lawsuits	Dec. 31, 2016USD ($)claims-lawsuits
Loss Contingency, Claims Quantities [Abstract]
New Claims Filed	68	58	40
Pending Claims Disposed Of	61	61	84
Liability for Asbestos and Environmental Claims, Net, Claims Paid | $	$ 1.4	$ 1.2	$ 0.9

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Nov. 30, 2016	May 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 01, 2016	May 04, 2016	Oct. 31, 2008
Summary of Stockholders' Equity Disclosure [Line Items]
Stock Issued During Period, Shares, New Issues	74,800,000	59,800,000
Shares Issued, Price Per Share						$ 4.90	$ 4.40
Proceeds from issuance of common stock	$ 351	$ 249.5	$ 0	$ 0	$ 600.4
Preferred stock authorized (in shares)			25,000,000
Preferred stock issued (in shares)			0
Preferred stock outstanding (in shares)			0
Stock Repurchase Program, Authorized Amount								$ 150
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 125.6
Minimum [Member] | Revolving Credit Facility [Member]
Summary of Stockholders' Equity Disclosure [Line Items]
Amount Of Threshold Under Credit Facility, Dividend Restriction, Unlimited			20.00%
Amount Of Threshold Under Credit Facility, Dividend Restriction, Unlimited with Financial Covenant Compliance			15.00%
Maximum [Member] | Revolving Credit Facility [Member]
Summary of Stockholders' Equity Disclosure [Line Items]
Annual Dividend Restriction Monetary Limit			$ 18
Annual Dividend Restriction Rate Limit			0.50%
Aggregate Dividend Restriction Monetary Limit			$ 25
Aggregate Dividend Restriction Rate Limit			0.70%

Share-based Compensation (Detai

Share-based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuable shares under Stock Incentive Plan	28,000,000
Shares available for future grant under Stock Incentive Plan	6,000,000
Share-based Compensation Expense [Abstract]
Share-based Compensation Expense	$ 9.2	$ 7.7	$ 5.4
Stock Options [Member]
Share-based Compensation Expense [Abstract]
Share-based Compensation Expense	$ 2.5	$ 2.1	$ 1
Share based compensation estimated to be forfeited (in hundredths)	5.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility, minimum (in hundredths)	58.80%	61.50%	90.30%
Expected volatility, maximum (in hundredths)	61.60%	64.00%	91.50%
Weighted-average volatility (in hundredths)	59.50%	62.50%	90.70%
Risk-free interest rate, minimum (in hundredths)	2.30%	1.60%	1.20%
Risk-free interest rate, maximum (in hundredths)	2.60%	2.20%	1.80%
Weighted-average grant-date fair value per share of options granted	$ 3.51	$ 5.33	$ 1.29
Summary of changes in shares outstanding under all long-term incentive plans [Rollforward]
Number of options outstanding, beginning balance (in shares)	2,994,206
Number of options granted (in shares)	842,000
Number of options exercised (in shares)	(201,700)
Number of options canceled (in shares)	(230,644)
Number of options outstanding, ending balance (in shares)	3,403,862	2,994,206
Number of exercisable options (in shares)	2,046,546
Number of unvested options (in shares)	1,357,316
Number of unvested options that are expected to vest (in shares)	1,289,450
Weighted average exercise price per option, outstanding, beginning of period (dollars per share)	$ 7.69
Weighted average exercise price per option granted (dollars per share)	6.56
Weighted average exercise price per option exercised (dollars per share)	3.82
Weighted average exercise price per option canceled (dollars per share)	18.56
Weighted average exercise price per option, outstanding, end of period (dollars per share)	6.90	$ 7.69
Weighted average exercise price per exercisable option (dollars per share)	7.07
Weighted average exercise price per unvested options (dollars per share)	6.66
Weighted average exercise price per unvested options that expected to vest (dollars per share)	$ 6.66
Remaining average contractual life of options outstanding (in years)	6 years 1 month 6 days
Remaining average contractual life of options exercisable (in years)	4 years 8 months 12 days
Remaining average contractual life of unvested options (in years)	8 years 6 months
Remaining average contractual life of unvested options that are expected to vest (in years)	8 years 6 months
Aggregate intrinsic value of options outstanding, outstanding	$ 0.3
Aggregate intrinsic value of options outstanding, exercisable	0.2
Aggregate intrinsic value of options outstanding, unvested	0.1
Aggregate intrinsic value of options outstanding, unvested and expected to vest	0.1
Intrinsic value of stock options exercised	0.3	$ 0.2	$ 1.4
Amount of unrecognized compensation costs	$ 1.5
Weighted average period of recognition (in years)	1 year 8 months 12 days
Restricted Stock [Member]
Share-based Compensation Expense [Abstract]
Share-based Compensation Expense	$ 3.1	$ 2.9	$ 1.6
Summary of changes in shares outstanding under all long-term incentive plans [Rollforward]
Amount of unrecognized compensation costs	$ 1.6
Weighted average period of recognition (in years)	1 year 4 months 24 days
Summary of nonvested shares [Roll Forward]
Nonvested, beginning of period (in shares)	518,184
Granted (in shares)	521,100
Vested/restrictions lapsed/earned (in shares)	(513,848)
Canceled (in shares)	(18,733)
Nonvested, end of period (in shares)	506,703	518,184
Weighted average grant date fair value, nonvested, beginning of period (dollars per share)	$ 5.38
Weighted average grant date fair value, granted (dollars per share)	6.56	$ 9.78	$ 1.80
Weighted average grant date fair value, vested/restrictions lapsed/earned (dollars per share)	5.48
Weighted average grant date fair value, canceled (dollars per share)	6.16
Weighted average grant date fair value, nonvested, end of period (dollars per share)	$ 6.45	$ 5.38
Intrinsic value of shares vested/restrictions lapsed during the period	$ 3.2	$ 4.1	$ 1.4
Restricted Stock Units Issued to Directors [Member]
Share-based Compensation Expense [Abstract]
Share-based Compensation Expense	$ 1.2	1.2	1.3
Summary of nonvested shares [Roll Forward]
Share Based Compensation Arrangement By Share Based Payment Award, Award Period Until Settlement	1 year
Deferred Compensation Arrangement With Individual, Period To Defer Settlement Following Termination Of Service	6 months
Deferred Compensation Arrangement with Individual, Maximum Period to Receive Installments	15 years
Performance Share Awards [Member]
Share-based Compensation Expense [Abstract]
Share-based Compensation Expense	$ 2	$ 1.5	$ 1.5
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Weighted-average volatility (in hundredths)	67.30%	68.00%	60.80%
Weighted-average volatility VanEck Vectors Steel ETF (in hundredths)	52.20%	48.90%
Weighted-average volatility S&P MidCap 400 Index (in hundredths)			27.60%
Risk-free interest rate (in hundredths)	2.20%	1.50%	1.10%
Summary of changes in shares outstanding under all long-term incentive plans [Rollforward]
Amount of unrecognized compensation costs	$ 2.6
Weighted average period of recognition (in years)	1 year 8 months 12 days
Summary of nonvested shares [Roll Forward]
Nonvested, beginning of period (in shares)	718,668
Granted (in shares)	366,500
Vested/restrictions lapsed/earned (in shares)	(277,971)
Canceled (in shares)	(192,397)
Nonvested, end of period (in shares)	614,800	718,668
Weighted average grant date fair value, nonvested, beginning of period (dollars per share)	$ 5.04
Weighted average grant date fair value, granted (dollars per share)	8.05	$ 10.78	$ 1.74
Weighted average grant date fair value, vested/restrictions lapsed/earned (dollars per share)	1.74
Weighted average grant date fair value, canceled (dollars per share)	5.55
Weighted average grant date fair value, nonvested, end of period (dollars per share)	$ 9.19	$ 5.04
Intrinsic value of shares vested/restrictions lapsed during the period	$ 0.7
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period	3 years
Long-term Performance Plan [Member]
Share-based Compensation Expense [Abstract]
Share-based Compensation Expense	$ 0.4	$ 0	$ 0
Summary of nonvested shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period	3 years
Equity-Based Long-Term Performance Plan Stock Portion Percentage Of Total Award	30.00%
Minimum [Member] | Stock Options [Member]
Share-based Compensation Expense [Abstract]
Minimum vesting period for stock option awards (in number of months)	6 months
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected term	3 years 5 months	3 years 4 months	3 years 3 months
Maximum [Member] | Stock Options [Member]
Share-based Compensation Expense [Abstract]
Maximum term of stock option awards (in number of years)	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected term	6 years 7 months	6 years 6 months	6 years 8 months

Comprehensive Income (Loss) (De

Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Foreign currency translation
Balance at beginning of period		$ 1.1	$ (3.6)	$ (2.1)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax [Abstract]
Foreign currency translation gain (loss)		(1.7)	4.7	(1.5)
Balance at end of period		(0.6)	1.1	(3.6)
Cash flow hedges
Balance at beginning of period		7.2	22.3	39.9	$ (44.8)
Cumulative effect of adopting new hedging standard			0.8	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract]
Gains (losses) arising in period		(5.6)	(11.5)	56.1
Income tax expense (benefit)		0	0	6.2
Gains (losses) arising in period, net of tax		(5.6)	(11.5)	49.9
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, before Tax [Abstract]
Reclassification of losses (gains) to net income		(10.3)	(6.1)	39.1
Income tax (expense) benefit (b)	[1]	0	0	4.3
Net amount of reclassification of losses (gains) to net income (loss), net of tax		(10.3)	(6.1)	34.8
Total other comprehensive income (loss), net of tax		(15.9)	(17.6)	84.7
Balance at end of period		7.2	22.3	39.9	$ (44.8)
Pension and OPEB Plans
Balance at beginning of period		(73.6)	(125)	(166.4)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Prior service credit (cost) arising in period		11.1	4.7	(8.3)
Gains (losses) arising in period		(63.6)	94.2	11.6
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment and Tax		(52.5)	98.9	3.3
Income tax expense (benefit)		0	0	0.4
Gains (losses) arising in period, net of tax		(52.5)	98.9	2.9
Other Comprehensive Income (Loss), Reclassification Adjustment, Pension and Other Postretirement Benefit Plans, Included in Net Income, before Tax [Abstract]
Reclassification of prior service cost (credits) included in net income		(9.8)	(53.8)	(54.8)
Reclassification of actuarial (gains) losses included in net income (loss)		29.3	6.3	97.9
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		19.5	(47.5)	43.1
Income tax (expense) benefit	[1]	0	0	4.6
Amount of reclassification to net income (loss), net of tax		19.5	(47.5)	38.5
Total other comprehensive income (loss), net of tax		(33)	51.4	41.4
Balance at end of period		(106.6)	(73.6)	(125)
Pension and OPEB Expense (Income) [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment, Pension and Other Postretirement Benefit Plans, Included in Net Income, before Tax [Abstract]
Reclassification of prior service cost (credits) included in net income	[2]	(9.8)	(53.8)	(54.8)
Reclassification of actuarial (gains) losses included in net income (loss)	[2]	$ 29.3	$ 6.3	$ 97.9
[1]	Included in income tax expense (benefit)
[2]	Included in pension and OPEB (income) expense

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income attributable to AK Steel Holding Corporation	$ 33.5	$ 67.2	$ 56.6	$ 28.7	$ (80.4)	$ 22.3	$ 77.2	$ 84.4	$ 186	$ 103.5	$ (16.8)
Less: distributed earnings to common stockholders and holders of certain stock compensation awards									0	0	0
Undistributed earnings (loss)									186	103.5	(16.8)
Common stockholders earnings - basic [Abstract]
Distributed earnings to common stockholders									0	0	0
Undistributed earnings (loss) to common stockholders - basic									185.7	103.5	(16.7)
Common stockholders earnings (loss) - basic									185.7	103.5	(16.7)
Common stockholders earnings - diluted [Abstract]
Distributed earnings to common stockholders									0	0	0
Undistributed earnings to common stockholders - diluted									185.7	103.5	(16.7)
Common stockholders earnings - diluted									$ 185.7	$ 103.5	$ (16.7)
Common shares outstanding (weighted-average shares in millions) [Abstract]
Common shares outstanding for basic earnings per share (in shares)									314.8	314.3	230
Effect of exchangeable debt									0	4.5	0
Effect of dilutive stock-based compensation (in shares)									0.8	0.9	0
Common shares outstanding for diluted earnings per share (in shares)									315.6	319.7	230
Basic earnings per share [Abstract]
Distributed earnings - basic (in dollars per share)									$ 0	$ 0	$ 0
Undistributed earnings (loss) - basic (in dollars per share)									0.59	0.33	(0.07)
Basic earnings (loss) per share (in dollars per share)					$ (0.26)	$ 0.07	$ 0.25	$ 0.27	0.59	0.33	(0.07)
Diluted earnings per share [Abstract]
Distributed earnings - diluted (in dollars per share)									0	0	0
Undistributed earnings (loss) - diluted (in dollars per share)									0.59	0.32	(0.07)
Diluted earnings (loss) per share (in dollars per share)					$ (0.26)	$ 0.07	$ 0.24	$ 0.26	$ 0.59	$ 0.32	$ (0.07)
Potentially issuable common shares excluded from earnings per share calculation due to anti-dilutive effect (in millions of shares)									2.4	1.4	3

Variable Interest Entities (Det

Variable Interest Entities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Income before income taxes	$ 237.9	$ 162.7	$ 32.3
SunCoke Middletown [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage	0.00%
Income before income taxes	$ 58.4	$ 61.7	$ 66
Vicksmetal Armco Associates [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable interest entity, ownership percentage	50.00%

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Estimate of Fair Value Measurement [Member] | Long-term Debt [Member]
Liabilities measured at fair value
Long-term debt, including current maturities	$ (1,852.4)	$ (2,273.4)
Estimate of Fair Value Measurement [Member] | Long-term Debt [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities measured at fair value
Long-term debt, including current maturities	0	0
Estimate of Fair Value Measurement [Member] | Long-term Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities measured at fair value
Long-term debt, including current maturities	(1,852.4)	(2,273.4)
Reported Value Measurement [Member] | Long-term Debt [Member]
Liabilities measured at fair value
Long-term debt, including current maturities	(1,993.7)	(2,110.1)
Reported Value Measurement [Member] | Long-term Debt [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities measured at fair value
Long-term debt, including current maturities	0	0
Reported Value Measurement [Member] | Long-term Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities measured at fair value
Long-term debt, including current maturities	(1,993.7)	(2,110.1)
Fair Value, Measurements, Recurring [Member]
Assets measured at fair value
Assets measured at fair value	65	85.7
Liabilities measured at fair value
Liabilities measured at fair value	(10.2)	(5.7)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Assets measured at fair value	48.6	38
Liabilities measured at fair value
Liabilities measured at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Assets measured at fair value	16.4	47.7
Liabilities measured at fair value
Liabilities measured at fair value	(10.2)	(5.7)
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member]
Assets measured at fair value
Cash and cash equivalents	48.6	38
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Cash and cash equivalents	48.6	38
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Cash and cash equivalents	0	0
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member]
Assets measured at fair value
Derivative assets, current	0.1	0.2
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Derivative assets, current	0	0
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Derivative assets, current	0.1	0.2
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member]
Assets measured at fair value
Derivative Asset, Noncurrent	0.4	1.7
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Derivative Asset, Noncurrent	0	0
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Derivative Asset, Noncurrent	0.4	1.7
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member]
Liabilities measured at fair value
Commodity hedge contracts-current	(1.2)	(0.3)
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities measured at fair value
Commodity hedge contracts-current	0	0
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities measured at fair value
Commodity hedge contracts-current	(1.2)	(0.3)
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Liabilities [Member]
Liabilities measured at fair value
Commodity hedge contracts-noncurrent	(1.5)	0
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities measured at fair value
Commodity hedge contracts-noncurrent	0	0
Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities measured at fair value
Commodity hedge contracts-noncurrent	(1.5)	0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member]
Assets measured at fair value
Derivative assets, current	13	35.2
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Derivative assets, current	0	0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Derivative assets, current	13	35.2
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member]
Assets measured at fair value
Derivative Asset, Noncurrent	2.9	10.6
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Derivative Asset, Noncurrent	0	0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Derivative Asset, Noncurrent	2.9	10.6
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member]
Liabilities measured at fair value
Commodity hedge contracts-current	(5.9)	(4.9)
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities measured at fair value
Commodity hedge contracts-current	0	0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities measured at fair value
Commodity hedge contracts-current	(5.9)	(4.9)
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Liabilities [Member]
Liabilities measured at fair value
Commodity hedge contracts-noncurrent	(1.6)	(0.5)
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities measured at fair value
Commodity hedge contracts-noncurrent	0	0
Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities measured at fair value
Commodity hedge contracts-noncurrent	$ (1.6)	$ (0.5)
Measurement Input, Counterparty Credit Risk [Member] | Liability [Member] | Maximum [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Benchmark interest rates for contracts (in hundredths)		0.024
Measurement Input, Counterparty Credit Risk [Member] | Assets [Member] | Maximum [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Benchmark interest rates for contracts (in hundredths)		0.015

Derivative Instruments and He_3

Derivative Instruments and Hedging Activities (Details)	12 Months Ended
	Dec. 31, 2018CAD ($)MMBTUMWtlb	Dec. 31, 2018EUR (€)MMBTUMWtlb	Dec. 31, 2017CAD ($)MMBTUMWtlb	Dec. 31, 2017EUR (€)MMBTUMWtlb
Commodity Contract [Member] | Nickel [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives	0	0	500,000	500,000
Commodity Contract [Member] | Natural Gas [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | MMBTU	39,868,000	39,868,000	41,338,000	41,338,000
Investment Contract Settlement Date Range Start	Jan. 1, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2020
Commodity Contract [Member] | Zinc [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives	52,150,000	52,150,000	50,350,000	50,350,000
Investment Contract Settlement Date Range Start	Jan. 1, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2020
Commodity Contract [Member] | Iron Ore [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | t	2,125,000	2,125,000	2,340,000	2,340,000
Investment Contract Settlement Date Range Start	Jan. 1, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2020
Commodity Contract [Member] | Electricity [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | MW	1,461,000	1,461,000	1,553,000	1,553,000
Investment Contract Settlement Date Range Start	Jan. 1, 2019
Investment Contract Settlement Date Range End	Sep. 30, 2020
Foreign Exchange Contract [Member] | Euro Member Countries, Euro
Derivative [Line Items]
Derivative, Notional Amount | €		€ 4,000,000		€ 26,000,000
Investment Contract Settlement Date Range Start	Jan. 1, 2019
Investment Contract Settlement Date Range End	Jun. 1, 2019
Foreign Exchange Contract [Member] | Canada, Dollars
Derivative [Line Items]
Derivative, Notional Amount | $	$ 118,560,000		$ 148,080,000
Investment Contract Settlement Date Range Start	Jan. 1, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2021

Derivative Instruments and He_4

Derivative Instruments and Hedging Activities (Details 2) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 0
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0	$ 0.2
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Noncurrent	0.4	1.7
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	(1.2)	(0.2)
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent	(1.5)	0
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	3.4	9
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Noncurrent	1	2.3
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	(4.7)	(4.6)
Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent	(1.2)	(0.5)
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0.1	0
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	0	(0.1)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	9.6	26.2
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Noncurrent	1.9	8.3
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, current	(1.2)	(0.3)
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, noncurrent	$ (0.4)	$ 0

Derivative Instruments and He_5

Derivative Instruments and Hedging Activities (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness	$ (5.6)	$ (11.5)	$ 56.1
Reclassification of losses (gains) from accumulated other comprehensive income to net income (loss)	10.3	6.1	(39.1)
Foreign Exchange Contract [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized gains (losses) in consolidated statement of operations	0.1	(1.6)	(0.9)
Commodity Contract [Member] | Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) before tax expected to be reclassified into earnings within the next twelve months	5.1
Commodity Contract [Member] | Electricity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) before tax expected to be reclassified into earnings within the next twelve months	2.7
Commodity Contract [Member] | Zinc [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) before tax expected to be reclassified into earnings within the next twelve months	(4.8)
Commodity Contract [Member] | Cost of Products Sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized gains (losses) in consolidated statement of operations	(2.4)	31.6	38.6
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness	(5.4)	0	0
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member] | Cost of Products Sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification of losses (gains) from accumulated other comprehensive income to net income (loss)	(0.9)	0	0
Cash Flow Hedging [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recognized in accumulated other comprehensive income that were included in the assessment of effectiveness	(0.2)	(11.5)	56.1
Cash Flow Hedging [Member] | Commodity Contract [Member] | Cost of Products Sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification of losses (gains) from accumulated other comprehensive income to net income (loss)	11.2	$ 6.1	$ (39.1)
Canada, Dollars | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) before tax expected to be reclassified into earnings within the next twelve months	$ (1.5)

Supplementary Cash Flow Infor_3

Supplementary Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Cash Flow [Line Items]
Net cash flows from operating activities	$ 364.7	$ 198.8	$ 304.6
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations	48.6	38	173.2	$ 56.6
Supplementary cash flow, noncash investing and financing activities [Abstract]
Capital investments	33.4	37.3	33.2
Interest, net of capitalized interest	136.3	130.5	137.1
Income taxes	(5.5)	0.1	(2.6)
Restricted stock and RSUs [Member]
Supplementary cash flow, noncash investing and financing activities [Abstract]
Issuance of restricted stock and restricted stock units	4.5	4.6	2.3
Research And Innovation Center Middletown OH [Member]
Supplementary cash flow, noncash investing and financing activities [Abstract]
Research and innovations center capital lease	0	1.1	25.2
SunCoke Middletown [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Supplementary Cash Flow [Line Items]
Net cash flows from operating activities	76.6	77.1	$ 83.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations	$ 1.1	$ 0.1

Quarterly Information (Unaudi_3

Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Gain on termination of pellet agreement and related transportation costs									$ 0	$ 19.3	$ (69.5)
Asset impairment charge									0	75.6	0
Net sales	$ 1,677.1	$ 1,735.6	$ 1,746.6	$ 1,658.9	$ 1,495.6	$ 1,494.3	$ 1,557.2	$ 1,533.4	6,818.2	6,080.5	5,882.5
Operating profit (loss)	86.5	114.8	99.5	63.6	(52.3)	66.3	116.5	129.7	364.4	260.2	217.6
Net income (loss) attributable to AK Holding	$ 33.5	$ 67.2	$ 56.6	$ 28.7	$ (80.4)	$ 22.3	$ 77.2	$ 84.4	$ 186	$ 103.5	$ (16.8)
Earnings Per Share, Basic					$ (0.26)	$ 0.07	$ 0.25	$ 0.27	$ 0.59	$ 0.33	$ (0.07)
Earnings Per Share, Diluted					$ (0.26)	$ 0.07	$ 0.24	$ 0.26	0.59	$ 0.32	$ (0.07)
Basic and diluted earnings (loss) per share (in dollars per share)	$ 0.11	$ 0.21	$ 0.18	$ 0.09					$ 0.59
Pension Plans, Defined Benefit [Member]
Business Acquisition [Line Items]
Pension settlement charges	$ 14.5
Ashland Works Hot End [Member]
Business Acquisition [Line Items]
Asset impairment charge					$ 75.6					$ 75.6

Supplementary Guarantor Infor_3

Supplementary Guarantor Information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended								12 Months Ended
	Nov. 30, 2016	May 31, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statements of Operations [Abstract]
Net sales			$ 1,677.1	$ 1,735.6	$ 1,746.6	$ 1,658.9	$ 1,495.6	$ 1,494.3	$ 1,557.2	$ 1,533.4	$ 6,818.2	$ 6,080.5	$ 5,882.5
Cost of products sold (exclusive of items shown separately below)											5,911	5,253.1	5,099.7
Selling and administrative expenses											322.6	284.9	279.1
Depreciation											220.2	226	216.6
Charge (credit) for termination of pellet agreement and related transportation costs											0	(19.3)	69.5
Asset impairment charge											0	75.6	0
Total operating costs											6,453.8	5,820.3	5,664.9
Operating profit (loss)			86.5	114.8	99.5	63.6	(52.3)	66.3	116.5	129.7	364.4	260.2	217.6
Interest expense											151.6	152.3	163.9
Pension and OPEB (income) expense											(19.2)	(71.9)	16.5
Other (income) expense											(5.9)	17.1	4.9
Income (loss) before income taxes											237.9	162.7	32.3
Income tax expense (benefit)											(6.2)	(2.2)	(16.9)
Equity in net income (loss) of subsidiaries											0	0	0
Net income											244.1	164.9	49.2
Less: Net income attributable to noncontrolling interests											58.1	61.4	66
Net income attributable to AK Steel Holding Corporation			33.5	$ 67.2	$ 56.6	28.7	(80.4)	$ 22.3	$ 77.2	84.4	186	103.5	(16.8)
Other comprehensive income (loss)											(50.6)	38.5	124.6
Comprehensive income attributable to AK Steel Holding Corporation											135.4	142	107.8
Current assets:
Cash and cash equivalents			48.6			38	38			173.2	48.6	38	173.2	$ 48.6	$ 38	$ 173.2
Accounts receivable, net														635.8	517.8
Inventory														1,419.9	1,385
Other current assets														97	130.3
Total current assets														2,201.3	2,071.1
Property, plant and equipment														6,969.2	6,831.8
Accumulated depreciation														(5,057.6)	(4,845.6)
Property, plant and equipment, net														1,911.6	1,986.2
Other non-current assets:
Investment in subsidiaries														0	0
Inter-company accounts														0	0
Goodwill and intangible assets														298.9	306.7
Other non-current assets														103.9	110.8
TOTAL ASSETS														4,515.7	4,474.8
Current liabilities:
Accounts payable														801	690.4
Accrued liabilities														288.9	270.5
Current portion of pension and other postretirement benefit obligations														38.7	40.1
Total current liabilities														1,128.6	1,001
Non-current liabilities:
Long-term debt														1,993.7	2,110.1
Pension and other postretirement benefit obligations														829.9	894.2
Inter-company accounts														0	0
Other non-current liabilities														134	168.9
TOTAL LIABILITIES														4,086.2	4,174.2
Equity (deficit):
Total stockholders’ equity (deficit)														99.9	(44.6)
Noncontrolling interests														329.6	345.2
TOTAL EQUITY (DEFICIT)														429.5	300.6	149.8
TOTAL LIABILITIES AND EQUITY (DEFICIT)														4,515.7	4,474.8
Condensed Cash Flows [Abstract]
Net cash flows from operating activities											364.7	198.8	304.6
Cash flows from investing activities:
Capital investments											(152)	(152.5)	(127.6)
Investment in acquired business, net of cash acquired											0	(360.4)	0
Other investing items, net											0.1	4.2	2.3
Net cash flows from investing activities											(151.9)	(508.7)	(125.3)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net borrowings (repayments) under credit facility											(115)	450	(550)
Proceeds from issuance of long-term debt											0	680	380
Redemption of long-term debt											(12.6)	(848.4)	(392.8)
Proceeds from issuance of common stock	$ 351	$ 249.5									0	0	600.4
Debt issuance costs											0	(25.3)	(20.4)
Inter-company activity											0	0	0
SunCoke Middletown distributions to noncontrolling interest owners											(73.7)	(79.1)	(85.1)
Other financing items, net											(0.9)	(2.5)	5.2
Net cash flows from financing activities											(202.2)	174.7	(62.7)
Net increase (decrease) in cash and cash equivalents											10.6	(135.2)	116.6
Cash and cash equivalents, beginning of year						38				173.2	38	173.2	56.6
Cash and cash equivalents, end of year			48.6				38				48.6	38	173.2
Parent Company [Member]
Condensed Statements of Operations [Abstract]
Net sales											0	0	0
Cost of products sold (exclusive of items shown separately below)											0	0	0
Selling and administrative expenses											3.5	3.7	4.4
Depreciation											0	0	0
Charge (credit) for termination of pellet agreement and related transportation costs												0	0
Asset impairment charge												0
Total operating costs											3.5	3.7	4.4
Operating profit (loss)											(3.5)	(3.7)	(4.4)
Interest expense											0	0	0
Pension and OPEB (income) expense											0	0	0
Other (income) expense											0	0	0
Income (loss) before income taxes											(3.5)	(3.7)	(4.4)
Income tax expense (benefit)											0	0	0
Equity in net income (loss) of subsidiaries											189.5	107.2	(12.4)
Net income											186	103.5	(16.8)
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to AK Steel Holding Corporation											186	103.5	(16.8)
Other comprehensive income (loss)											(50.6)	38.5	124.6
Comprehensive income attributable to AK Steel Holding Corporation											135.4	142	107.8
Current assets:
Cash and cash equivalents			0			0	0			0	0	0	0	0	0	0
Accounts receivable, net														0	0
Inventory														0	0
Other current assets														0	0
Total current assets														0	0
Property, plant and equipment														0	0
Accumulated depreciation														0	0
Property, plant and equipment, net														0	0
Other non-current assets:
Investment in subsidiaries														(3,017.4)	(3,127.4)
Inter-company accounts														3,117.3	3,082.8
Goodwill and intangible assets														0	0
Other non-current assets														0	0
TOTAL ASSETS														99.9	(44.6)
Current liabilities:
Accounts payable														0	0
Accrued liabilities														0	0
Current portion of pension and other postretirement benefit obligations														0	0
Total current liabilities														0	0
Non-current liabilities:
Long-term debt														0	0
Pension and other postretirement benefit obligations														0	0
Inter-company accounts														0	0
Other non-current liabilities														0	0
TOTAL LIABILITIES														0	0
Equity (deficit):
Total stockholders’ equity (deficit)														99.9	(44.6)
Noncontrolling interests														0	0
TOTAL EQUITY (DEFICIT)														99.9	(44.6)
TOTAL LIABILITIES AND EQUITY (DEFICIT)														99.9	(44.6)
Condensed Cash Flows [Abstract]
Net cash flows from operating activities											(2.3)	(2.5)	(3.1)
Cash flows from investing activities:
Capital investments											0	0	0
Investment in acquired business, net of cash acquired												0
Other investing items, net											0	0	0
Net cash flows from investing activities											0	0	0
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net borrowings (repayments) under credit facility											0	0	0
Proceeds from issuance of long-term debt												0	0
Redemption of long-term debt											0	0	0
Proceeds from issuance of common stock													600.4
Debt issuance costs												0	0
Inter-company activity											2.5	5	(602.4)
SunCoke Middletown distributions to noncontrolling interest owners											0	0	0
Other financing items, net											(0.2)	(2.5)	5.1
Net cash flows from financing activities											2.3	2.5	3.1
Net increase (decrease) in cash and cash equivalents											0	0	0
Cash and cash equivalents, beginning of year						0				0	0	0	0
Cash and cash equivalents, end of year			0				0				0	0	0
AK Steel [Member]
Condensed Statements of Operations [Abstract]
Net sales											6,244.7	5,755.1	5,681
Cost of products sold (exclusive of items shown separately below)											5,519.8	5,082	5,044.8
Selling and administrative expenses											320	285.5	282.7
Depreciation											171.5	189.3	187.8
Charge (credit) for termination of pellet agreement and related transportation costs												(19.3)	69.5
Asset impairment charge												75.6
Total operating costs											6,011.3	5,613.1	5,584.8
Operating profit (loss)											233.4	142	96.2
Interest expense											145.9	150.3	162.3
Pension and OPEB (income) expense											(19.2)	(71.9)	16.5
Other (income) expense											8.7	30.1	16.4
Income (loss) before income taxes											98	33.5	(99)
Income tax expense (benefit)											(26.5)	(29.4)	(43.7)
Equity in net income (loss) of subsidiaries											65	44.3	42.9
Net income											189.5	107.2	(12.4)
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to AK Steel Holding Corporation											189.5	107.2	(12.4)
Other comprehensive income (loss)											(50.6)	38.5	124.6
Comprehensive income attributable to AK Steel Holding Corporation											138.9	145.7	112.2
Current assets:
Cash and cash equivalents			22.1			14.5	14.5			147.9	22.1	14.5	27	22.1	14.5	147.9
Accounts receivable, net														515.4	432.4
Inventory														1,299.6	1,231.5
Other current assets														85.5	124.7
Total current assets														1,922.6	1,803.1
Property, plant and equipment														6,111.1	6,004
Accumulated depreciation														(4,785.5)	(4,620.8)
Property, plant and equipment, net														1,325.6	1,383.2
Other non-current assets:
Investment in subsidiaries														1,931.1	1,844.9
Inter-company accounts														0	0
Goodwill and intangible assets														0	0
Other non-current assets														54.3	66.3
TOTAL ASSETS														5,233.6	5,097.5
Current liabilities:
Accounts payable														722.5	623.3
Accrued liabilities														251.5	228.2
Current portion of pension and other postretirement benefit obligations														38.4	39.7
Total current liabilities														1,012.4	891.2
Non-current liabilities:
Long-term debt														1,993.7	2,110.1
Pension and other postretirement benefit obligations														827	890.8
Inter-company accounts														4,312.3	4,199.6
Other non-current liabilities														105.6	133.2
TOTAL LIABILITIES														8,251	8,224.9
Equity (deficit):
Total stockholders’ equity (deficit)														(3,017.4)	(3,127.4)
Noncontrolling interests														0	0
TOTAL EQUITY (DEFICIT)														(3,017.4)	(3,127.4)
TOTAL LIABILITIES AND EQUITY (DEFICIT)														5,233.6	5,097.5
Condensed Cash Flows [Abstract]
Net cash flows from operating activities											209.7	67.3	186.5
Cash flows from investing activities:
Capital investments											(122.9)	(131.8)	(116)
Investment in acquired business, net of cash acquired												(360.4)
Other investing items, net											0.8	4	3
Net cash flows from investing activities											(122.1)	(488.2)	(113)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net borrowings (repayments) under credit facility											(115)	450	(550)
Proceeds from issuance of long-term debt												680	380
Redemption of long-term debt											(12.6)	(848.4)	(392.8)
Proceeds from issuance of common stock													0
Debt issuance costs												(25.3)	(20.4)
Inter-company activity											48.3	31.2	630.5
SunCoke Middletown distributions to noncontrolling interest owners											0	0	0
Other financing items, net											(0.7)	0	0.1
Net cash flows from financing activities											(80)	287.5	47.4
Net increase (decrease) in cash and cash equivalents											7.6	(133.4)	120.9
Cash and cash equivalents, beginning of year						14.5				147.9	14.5	147.9	27
Cash and cash equivalents, end of year			22.1				14.5				22.1	14.5	147.9
Guarantor Subsidiaries of the Senior Notes [Member]
Condensed Statements of Operations [Abstract]
Net sales											320.8	285.9	250.9
Cost of products sold (exclusive of items shown separately below)											221.4	197.7	171.7
Selling and administrative expenses											14.5	13.5	12.7
Depreciation											8	7.5	7
Charge (credit) for termination of pellet agreement and related transportation costs												0	0
Asset impairment charge												0
Total operating costs											243.9	218.7	191.4
Operating profit (loss)											76.9	67.2	59.5
Interest expense											0	0	0
Pension and OPEB (income) expense												0	0
Other (income) expense											(16.4)	(11.4)	(8.1)
Income (loss) before income taxes											93.3	78.6	67.6
Income tax expense (benefit)											23.3	29.9	25.7
Equity in net income (loss) of subsidiaries											0	0	0
Net income											70	48.7	41.9
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to AK Steel Holding Corporation											70	48.7	41.9
Other comprehensive income (loss)											0	0	0
Comprehensive income attributable to AK Steel Holding Corporation											70	48.7	41.9
Current assets:
Cash and cash equivalents			8.2			7.2	7.2			4.4	8.2	7.2	5.7	8.2	7.2	4.4
Accounts receivable, net														34	33.2
Inventory														53.9	55.1
Other current assets														0.1	0.2
Total current assets														96.2	95.7
Property, plant and equipment														189.7	181.5
Accumulated depreciation														(102.8)	(94.8)
Property, plant and equipment, net														86.9	86.7
Other non-current assets:
Investment in subsidiaries														0	0
Inter-company accounts														1,630.7	1,523.1
Goodwill and intangible assets														32.9	32.8
Other non-current assets														0	0.2
TOTAL ASSETS														1,846.7	1,738.5
Current liabilities:
Accounts payable														26.2	17.9
Accrued liabilities														8.7	7.8
Current portion of pension and other postretirement benefit obligations														0	0
Total current liabilities														34.9	25.7
Non-current liabilities:
Long-term debt														0	0
Pension and other postretirement benefit obligations														0	0
Inter-company accounts														0	0
Other non-current liabilities														0.2	1
TOTAL LIABILITIES														35.1	26.7
Equity (deficit):
Total stockholders’ equity (deficit)														1,811.6	1,711.8
Noncontrolling interests														0	0
TOTAL EQUITY (DEFICIT)														1,811.6	1,711.8
TOTAL LIABILITIES AND EQUITY (DEFICIT)														1,846.7	1,738.5
Condensed Cash Flows [Abstract]
Net cash flows from operating activities											83.1	73.3	44.3
Cash flows from investing activities:
Capital investments											(8.1)	(5.6)	(8.8)
Investment in acquired business, net of cash acquired												0
Other investing items, net											0	0	0
Net cash flows from investing activities											(8.1)	(5.6)	(8.8)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net borrowings (repayments) under credit facility											0	0	0
Proceeds from issuance of long-term debt												0	0
Redemption of long-term debt											0	0	0
Proceeds from issuance of common stock													0
Debt issuance costs												0	0
Inter-company activity											(74)	(64.9)	(36.8)
SunCoke Middletown distributions to noncontrolling interest owners											0	0	0
Other financing items, net											0	0	0
Net cash flows from financing activities											(74)	(64.9)	(36.8)
Net increase (decrease) in cash and cash equivalents											1	2.8	(1.3)
Cash and cash equivalents, beginning of year						7.2				4.4	7.2	4.4	5.7
Cash and cash equivalents, end of year			8.2				7.2				8.2	7.2	4.4
Other Non-Guarantor Subsidiaries [Member]
Condensed Statements of Operations [Abstract]
Net sales											752.8	496.3	411.5
Cost of products sold (exclusive of items shown separately below)											620.9	387.2	299.4
Selling and administrative expenses											34.2	26.9	22.6
Depreciation											40.7	29.2	21.8
Charge (credit) for termination of pellet agreement and related transportation costs												0	0
Asset impairment charge												0
Total operating costs											695.8	443.3	343.8
Operating profit (loss)											57	53	67.7
Interest expense											5.7	2	1.6
Pension and OPEB (income) expense												0	0
Other (income) expense											(2.9)	(5.4)	(8.6)
Income (loss) before income taxes											54.2	56.4	74.7
Income tax expense (benefit)											(2)	(1.8)	3.6
Equity in net income (loss) of subsidiaries											0.7	0	(0.7)
Net income											56.9	58.2	70.4
Less: Net income attributable to noncontrolling interests											58.1	61.4	66
Net income attributable to AK Steel Holding Corporation											(1.2)	(3.2)	4.4
Other comprehensive income (loss)											(1.7)	4.7	(1.5)
Comprehensive income attributable to AK Steel Holding Corporation											(2.9)	1.5	2.9
Current assets:
Cash and cash equivalents			18.3			16.3	16.3			20.9	18.3	20.9	20.9	18.3	16.3	20.9
Accounts receivable, net														95.3	65.4
Inventory														75.6	108.3
Other current assets														11.4	5.4
Total current assets														200.6	195.4
Property, plant and equipment														668.4	646.3
Accumulated depreciation														(169.3)	(130)
Property, plant and equipment, net														499.1	516.3
Other non-current assets:
Investment in subsidiaries														68.2	67.5
Inter-company accounts														0	0
Goodwill and intangible assets														266	273.9
Other non-current assets														49.6	44.3
TOTAL ASSETS														1,083.5	1,097.4
Current liabilities:
Accounts payable														55.5	50.9
Accrued liabilities														28.7	34.5
Current portion of pension and other postretirement benefit obligations														0.3	0.4
Total current liabilities														84.5	85.8
Non-current liabilities:
Long-term debt														0	0
Pension and other postretirement benefit obligations														2.9	3.4
Inter-company accounts														511.2	489.1
Other non-current liabilities														28.2	34.7
TOTAL LIABILITIES														626.8	613
Equity (deficit):
Total stockholders’ equity (deficit)														127.1	139.2
Noncontrolling interests														329.6	345.2
TOTAL EQUITY (DEFICIT)														456.7	484.4
TOTAL LIABILITIES AND EQUITY (DEFICIT)														1,083.5	1,097.4
Condensed Cash Flows [Abstract]
Net cash flows from operating activities											83.8	61.7	92.2
Cash flows from investing activities:
Capital investments											(21)	(15.1)	(2.8)
Investment in acquired business, net of cash acquired												0
Other investing items, net											(0.7)	0.2	(0.7)
Net cash flows from investing activities											(21.7)	(14.9)	(3.5)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net borrowings (repayments) under credit facility											0	0	0
Proceeds from issuance of long-term debt												0	0
Redemption of long-term debt											0	0	0
Proceeds from issuance of common stock													0
Debt issuance costs												0	0
Inter-company activity											13.6	27.7	(6.6)
SunCoke Middletown distributions to noncontrolling interest owners											(73.7)	(79.1)	(85.1)
Other financing items, net											0	0	0
Net cash flows from financing activities											(60.1)	(51.4)	(91.7)
Net increase (decrease) in cash and cash equivalents											2	(4.6)	(3)
Cash and cash equivalents, beginning of year						16.3				20.9	16.3	20.9	23.9
Cash and cash equivalents, end of year			18.3				16.3				18.3	16.3	20.9
Eliminations [Member]
Condensed Statements of Operations [Abstract]
Net sales											(500.1)	(456.8)	(460.9)
Cost of products sold (exclusive of items shown separately below)											(451.1)	(413.8)	(416.2)
Selling and administrative expenses											(49.6)	(44.7)	(43.3)
Depreciation											0	0	0
Charge (credit) for termination of pellet agreement and related transportation costs												0	0
Asset impairment charge												0
Total operating costs											(500.7)	(458.5)	(459.5)
Operating profit (loss)											0.6	1.7	(1.4)
Interest expense											0	0	0
Pension and OPEB (income) expense												0	0
Other (income) expense											4.7	3.8	5.2
Income (loss) before income taxes											(4.1)	(2.1)	(6.6)
Income tax expense (benefit)											(1)	(0.9)	(2.5)
Equity in net income (loss) of subsidiaries											(255.2)	(151.5)	(29.8)
Net income											(258.3)	(152.7)	(33.9)
Less: Net income attributable to noncontrolling interests											0	0	0
Net income attributable to AK Steel Holding Corporation											(258.3)	(152.7)	(33.9)
Other comprehensive income (loss)											52.3	(43.2)	(123.1)
Comprehensive income attributable to AK Steel Holding Corporation											(206)	(195.9)	(157)
Current assets:
Cash and cash equivalents			0			0	0			0	0	0	0	0	0	$ 0
Accounts receivable, net														(8.9)	(13.2)
Inventory														(9.2)	(9.9)
Other current assets														0	0
Total current assets														(18.1)	(23.1)
Property, plant and equipment														0	0
Accumulated depreciation														0	0
Property, plant and equipment, net														0	0
Other non-current assets:
Investment in subsidiaries														1,018.1	1,215
Inter-company accounts														(4,748)	(4,605.9)
Goodwill and intangible assets														0	0
Other non-current assets														0	0
TOTAL ASSETS														(3,748)	(3,414)
Current liabilities:
Accounts payable														(3.2)	(1.7)
Accrued liabilities														0	0
Current portion of pension and other postretirement benefit obligations														0	0
Total current liabilities														(3.2)	(1.7)
Non-current liabilities:
Long-term debt														0	0
Pension and other postretirement benefit obligations														0	0
Inter-company accounts														(4,823.5)	(4,688.7)
Other non-current liabilities														0	0
TOTAL LIABILITIES														(4,826.7)	(4,690.4)
Equity (deficit):
Total stockholders’ equity (deficit)														1,078.7	1,276.4
Noncontrolling interests														0	0
TOTAL EQUITY (DEFICIT)														1,078.7	1,276.4
TOTAL LIABILITIES AND EQUITY (DEFICIT)														$ (3,748)	$ (3,414)
Condensed Cash Flows [Abstract]
Net cash flows from operating activities											(9.6)	(1)	(15.3)
Cash flows from investing activities:
Capital investments											0	0	0
Investment in acquired business, net of cash acquired												0
Other investing items, net											0	0	0
Net cash flows from investing activities											0	0	0
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net borrowings (repayments) under credit facility											0	0	0
Proceeds from issuance of long-term debt												0	0
Redemption of long-term debt											0	0	0
Proceeds from issuance of common stock													0
Debt issuance costs												0	0
Inter-company activity											9.6	1	15.3
SunCoke Middletown distributions to noncontrolling interest owners											0	0	0
Other financing items, net											0	0	0
Net cash flows from financing activities											9.6	1	15.3
Net increase (decrease) in cash and cash equivalents											0	0	0
Cash and cash equivalents, beginning of year						$ 0				$ 0	0	0	0
Cash and cash equivalents, end of year			$ 0				$ 0				$ 0	$ 0	$ 0