American Axle & Manufacturing (AXL) 10-K 12 Feb 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 09, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-14303
Entity Registrant Name	AMERICAN AXLE & MANUFACTURING HOLDINGS, INC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	38-3161171
Entity Address, Address Line One	One Dauch Drive
Entity Address, City or Town	Detroit
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	48211-1198
City Area Code	313
Local Phone Number	758-2000
Title of 12(b) Security	Common Stock, Par Value $0.01 Per Share
Trading Symbol	AXL
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 850.4
Entity Common Stock, Shares Outstanding		113,295,610
Documents Incorporated by Reference	Portions of the registrant's Annual Report to Stockholders for the year ended December 31, 2020 and Proxy Statement for use in connection with its Annual Meeting of Stockholders to be held on May 6, 2021, to be filed with the Securities and Exchange Commission pursuant to Regulation 14A not later than 120 days after December 31, 2020, are incorporated by reference in Part I (Items 1, 1A, 1B, 2, 3 and 4), Part II (Items 5, 6, 7, 7A, 8, 9, 9A and 9B), Part III (Items 10, 11, 12, 13 and 14) and Part IV (Item 15) of this Report.
Entity Central Index Key	0001062231
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net sales	$ 4,710.8	$ 6,530.9	$ 7,270.4
Cost of goods sold	4,128.1	5,628.3	6,130
Gross profit	582.7	902.6	1,140.4
Selling, general and administrative expenses	313.9	364.7	385.7
Amortization of intangible assets	86.6	95.4	99.4
Impairment charges	510	665	485.5
Restructuring and acquisition-related costs	67.2	57.8	78.9
Loss (gain) on sale of business	1	21.3	(15.5)
Operating income (loss)	(396)	(301.6)	106.4
Interest expense	(212.3)	(217.3)	(216.3)
Interest income	11.6	5.8	2
Other income (expense)
Debt refinancing and redemption costs	(7.9)	(8.4)	(19.4)
Gain on bargain purchase of business	0	10.8	0
Gain on settlement of capital lease	0	0	15.6
Pension settlement charges	(0.5)	(9.8)	0
Other expense, net	(5.2)	(12.5)	(2.2)
Loss before income taxes	(610.3)	(533)	(113.9)
Income tax benefit	(49.2)	(48.9)	(57.1)
Net loss	(561.1)	(484.1)	(56.8)
Net income attributable to noncontrolling interests	(0.2)	(0.4)	(0.7)
Net loss attributable to AAM	$ (561.3)	$ (484.5)	$ (57.5)
Basic loss per share	$ (4.96)	$ (4.31)	$ (0.51)
Diluted loss per share	$ (4.96)	$ (4.31)	$ (0.51)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net loss	$ (561.1)	$ (484.1)	$ (56.8)
Other comprehensive income (loss)
Defined benefit plans, net of $12.7 million, $3.0 million and $(9.8) million of tax in 2020, 2019 and 2018, respectively	(51.1)	(18.3)	38.1
Foreign currency translation adjustments	(0.2)	(4.6)	(62.5)
Changes in cash flow hedges, net of tax of $1.3 million, $6.1 million and $0.5 million in 2020, 2019 and 2018, respectively	(4.4)	(14.6)	5.5
Other comprehensive loss	(55.7)	(37.5)	(18.9)
Comprehensive loss	(616.8)	(521.6)	(75.7)
Net income attributable to noncontrolling interests	(0.2)	(0.4)	(0.7)
Foreign currency translation adjustments attributable to noncontrolling interests	0.3	0	0
Comprehensive loss attributable to AAM	$ (616.7)	$ (522)	$ (76.4)

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Comprehensive Income (Loss), Tax, Parenthetical Disclosures [Abstract]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	$ 12.7	$ 3	$ (9.8)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	$ 1.3	$ 6.1	$ 0.5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 557	$ 532
Accounts receivable, net	793.2	815.4
Inventories, net	323.2	373.6
Prepaid expenses and other	203.6	136.8
Total current assets	1,877	1,857.8
Property, plant and equipment, net	2,163.8	2,358.4
Deferred income taxes	107.8	64.1
Goodwill	185.7	699.1
Other intangible assets, net	780.7	864.5
GM postretirement cost sharing asset	237	223.3
Operating lease right-of-use assets	116.6	118.5
Other assets and deferred charges	447.7	458.9
Total assets	5,916.3	6,644.6
Current liabilities
Current portion of long-term debt	13.7	28.7
Accounts payable	578.9	623.5
Accrued compensation and benefits	170.9	154.4
Deferred revenue	23.4	18.9
Current portion of operating lease liabilities	22.6	21.8
Accrued expenses and other	169.8	179.1
Total current liabilities	979.3	1,026.4
Long-term debt, net	3,441.3	3,612.3
Deferred revenue	91	83.7
Deferred income taxes	13.2	19.6
Long-term portion of operating lease liabilities	94.4	96.7
Postretirement benefits and other long-term liabilities	923.9	825.5
Total liabilities	5,543.1	5,664.2
Stockholders' equity
Preferred stock, par value $0.01 per share; 10.0 million shares authorized; no shares outstanding in 2020 or 2019	0	0
Series common stock, par value $0.01 per share; 40.0 million shares authorized; no shares outstanding in 2020 or 2019	0	0
Common stock, par value $0.01 per share; 150.0 million shares authorized; 121.3 million and 120.2 million shares issued as of December 31, 2020 and December 31, 2019, respectively	1.2	1.2
Paid-in capital	1,333.3	1,313.9
Retained earnings (Accumulated deficit)	(319.8)	248.6
Treasury stock at cost, 8.0 million shares in 2020 and 7.6 million shares in 2019	(212)	(209.3)
Accumulated other comprehensive loss
Defined benefit plans, net of tax	(311)	(259.9)
Foreign currency translation adjustments	(101.1)	(101.2)
Unrecognized loss on cash flow hedges, net of tax	(20.1)	(15.7)
Total AAM stockholders' equity	370.5	977.6
Noncontrolling interests in subsidiaries	2.7	2.8
Total stockholders' equity	373.2	980.4
Total liabilities and stockholders' equity	$ 5,916.3	$ 6,644.6

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Millions	Dec. 31, 2020	Dec. 31, 2019
Common stock, shares, outstanding	113.3	112.6
Preferred Stock [Member]
Preferred stock, par or stated value per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	10	10
Preferred stock, shares outstanding	0	0
Series Common Stock [Member]
Common stock, par or stated value per share	$ 0.01	$ 0.01
Common stock, shares authorized	40	40
Common stock, shares, outstanding	0	0
Common Stock [Member]
Common stock, par or stated value per share	$ 0.01	$ 0.01
Common stock, shares authorized	150	150
Common stock, shares issued	121.3	120.2
Treasury stock, shares	8	7.6

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (561.1)	$ (484.1)	$ (56.8)
Adjustments to reconcile net loss to net cash provided by operating activities
Depreciation and amortization	521.9	536.9	528.8
Impairment charges	510	667.9	515.5
Deferred income taxes	(34.1)	(94.6)	(35)
Stock-based compensation	19.4	22.4	27.9
Pensions and other postretirement benefits, net of contributions	(15.7)	(8.8)	(9.9)
Loss (gain) on sale or acquisition of business, net	1	10.5	(15.5)
Loss (gain) on disposal of property, plant and equipment, net	20.6	4.1	(3.2)
Debt refinancing and redemption costs	7.9	8.4	4
Changes in operating assets and liabilities, net of amounts acquired or disposed
Accounts receivable	28.9	63.9	56.1
Inventories	53.7	56.1	(83.1)
Accounts payable and accrued expenses	(37.1)	(97.7)	7.5
Deferred revenue	5.5	(17.9)	10.7
Other assets and liabilities	(66.2)	(107.5)	(175.5)
Net cash provided by operating activities	454.7	559.6	771.5
Investing activities
Purchases of property, plant and equipment	(215.6)	(433.3)	(524.7)
Proceeds from sale of property, plant and equipment	1.7	5	4.9
Purchase buyouts of leased equipment	(0.1)	(0.9)	(0.5)
Final settlement on sale of business	(4.4)	0	0
Proceeds from sale of business, net	0	141.2	47.1
Acquisition of business, net of cash acquired	0	(9.4)	(1.3)
Investment in affiliates	0	(9.2)	(3.7)
Net cash used in investing activities	(218.4)	(306.6)	(478.2)
Financing activities
Proceeds from Revolving Credit Facility	350	0	0
Payments of Revolving Credit Facility	(350)	0	0
Proceeds from issuance of long-term debt	408	356.3	509.6
Payments of long-term debt, finance lease obligations and other	(610.5)	(545.5)	(681.2)
Debt issuance costs	(11)	(3.3)	(6.9)
Purchase of treasury stock	(2.7)	(7.5)	(3.7)
Purchase of noncontrolling interest	0	0	(2.3)
Other financing activities	1.7	0	0
Net cash used in financing activities	(214.5)	(200)	(184.5)
Effect of exchange rate changes on cash	3.2	0.1	(6.7)
Net increase in cash, cash equivalents and restricted cash	25	53.1	102.1
Cash, cash equivalents and restricted cash at beginning of year	532	478.9	376.8
Cash, cash equivalents and restricted cash at end of year	557	532	478.9
Supplemental cash flow information
Interest paid	192.4	205.4	199.7
Income taxes paid, net	2.1	57.1	46
Twelve year deferred payment obligation at 6% [Member]
Supplemental cash flow information
Non-cash investing activities: Debt security received for sale of U.S. Casting	$ 0	$ 60	$ 0

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Treasury Stock	AOCI Attributable to Parent	Noncontrolling Interest in Subsidiaries
Common stock, shares, outstanding at Dec. 31, 2017	111.3
Total AAM stockholders' equity at Dec. 31, 2017		$ 1.2	$ 1,264.6	$ 761	$ (198.1)	$ (292.7)	$ 4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Loss Attributable to AAM	$ (57.5)			(57.5)
Net income attributable to noncontrolling interests	(0.7)						0.7
Changes in cash flow hedges						5.5
Foreign currency translation adjustments						(62.5)
Foreign currency translation adjustments attributable to noncontrolling interests	$ 0
Defined benefit plans, net						38.1
Purchase of noncontrolling interest							(2.3)
Stock issued during period, shares, share-based compensation, net of forfeitures	0.7
Stock issued during period, value, share-based compensation, net of forfeitures			0.1
Stock-based compensation			27.9
Treasury stock, shares, acquired	(0.3)
Purchase of treasury stock	$ 3.7				(3.7)
Common stock, shares, outstanding at Dec. 31, 2018	111.7
Total AAM stockholders' equity at Dec. 31, 2018		1.2	1,292.6	703.5	(201.8)	(311.6)	2.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Loss Attributable to AAM	$ (484.5)			(484.5)
Net income attributable to noncontrolling interests	(0.4)						0.4
Changes in cash flow hedges						(14.6)
Foreign currency translation adjustments						(4.6)
Foreign currency translation adjustments attributable to noncontrolling interests	$ 0
Defined benefit plans, net						(18.3)
Stock issued during period, shares, share-based compensation, net of forfeitures	1.3
Stock-based compensation			21.3
New accounting pronouncement, effect of adoption | ASU 2016-02 [Member]				1.9
New accounting pronouncement, effect of adoption | ASU 2018-02 [Member]	$ 27.7			27.7		(27.7)
Treasury stock, shares, acquired	(0.4)
Purchase of treasury stock	$ 7.5				(7.5)
Common stock, shares, outstanding at Dec. 31, 2019	112.6
Total AAM stockholders' equity at Dec. 31, 2019	$ 977.6	1.2	1,313.9	248.6	(209.3)	(376.8)	2.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Loss Attributable to AAM	(561.3)			(561.3)
Net income attributable to noncontrolling interests	(0.2)						0.2
Changes in cash flow hedges						(4.4)
Foreign currency translation adjustments						0.1
Foreign currency translation adjustments attributable to noncontrolling interests	$ (0.3)						(0.3)
Defined benefit plans, net						(51.1)
Stock issued during period, shares, share-based compensation, net of forfeitures	1.1
Stock-based compensation			19.4
New accounting pronouncement, effect of adoption | ASU 2016-13 [Member]				(7.1)
Treasury stock, shares, acquired	(0.4)
Purchase of treasury stock	$ 2.7				(2.7)
Common stock, shares, outstanding at Dec. 31, 2020	113.3
Total AAM stockholders' equity at Dec. 31, 2020	$ 370.5	$ 1.2	$ 1,333.3	$ (319.8)	$ (212)	$ (432.2)	$ 2.7

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block]	1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES ORGANIZATION We are a global Tier 1 supplier to the automotive industry. We design, engineer and manufacture driveline and metal forming products that are making the next generation of vehicles smarter, lighter, safer and more efficient. We employ approximately 20,000 associates, operating at nearly 80 facilities in 17 countries, to support our customers on global and regional platforms with a continued focus on delivering operational excellence, quality and technology leadership. PRINCIPLES OF CONSOLIDATION We include the accounts of American Axle & Manufacturing Holdings, Inc. (Holdings) and its subsidiaries in our consolidated financial statements. We eliminate the effects of all intercompany transactions, balances and profits in our consolidation. CASH AND CASH EQUIVALENTS Cash and cash equivalents include all cash balances, savings accounts, sweep accounts, and highly liquid investments in money market funds and certificates of deposit with maturities of 90 days or less at the time of purchase. REVENUE RECOGNITION We are obligated under our contracts with customers to manufacture and supply products for use in our customers’ operations. We satisfy these performance obligations at the point in time that the customer obtains control of the products, which is the point in time that the customer is able to direct the use of, and obtain substantially all of the remaining benefits from, the products. This typically occurs upon shipment to the customer in accordance with purchase orders and delivery releases issued by our customers. See Note 13 - Revenue from Contracts with Customers for more detail on our revenue. ACCOUNTS RECEIVABLE The majority of our accounts receivable are due from original equipment manufacturers (OEMs) in the automotive industry and are considered past due when payment is not received within the terms stated within the contract. Trade accounts receivable for our customers are generally due within approximately 50 days from the date our customers receive our product. Amounts due from customers are stated net of allowances for credit losses. We determine our allowances by considering our expected credit losses, in addition to factors such as our previous loss history, customers' ability to pay their obligations to us, and the condition of the general economy and industry as a whole. The allowance for credit losses was $4.5 million and $8.0 million as of December 31, 2020 and 2019, respectively. We write-off accounts receivable when they become uncollectible. We have agreements in place with factoring companies to sell customer receivables on a nonrecourse basis from certain of our locations in Europe. The factoring companies collect payment for the sold receivables and AAM has no continuing involvement with such receivables. We also participate in an early payment program offered by our largest customer, which allows us to sell certain of our North American receivables from this customer to a third party at our discretion. AAM has no continuing involvement with the sold receivables. CUSTOMER TOOLING AND PRE-PRODUCTION COSTS RELATED TO LONG-TERM SUPPLY AGREEMENTS Engineering, research and development (R&D), and other pre-production design and development costs for products sold on long-term supply arrangements are expensed as incurred unless we have a contractual guarantee for reimbursement from the customer. Reimbursements received for pre-production costs relating to awarded programs are deferred and recognized into revenue over the life of the associated program. Reimbursements received for pre-production costs relating to future programs that have not been awarded, or amounts received for programs that become discontinued prior to production, are recorded as a reduction of expense. Costs for tooling used to make products sold on long-term supply arrangements for which we have either title to the assets or the noncancelable right to use the assets during the term of the supply arrangement are capitalized in property, plant and equipment. Reimbursable costs for tooling assets for which our customer has title and we do not have a noncancelable right to use during the term of the supply arrangement, are recorded in accounts receivable in our consolidated balance sheets. The reimbursement for the customer-owned tooling is recorded as a reduction of accounts receivable upon collection. Capitalized items and customer receipts in excess of tooling costs specifically related to a supply arrangement are amortized over the shorter of the term of the arrangement or over the estimated useful lives of the related assets. INVENTORIES We state our inventories at the lower of cost or net realizable value. The cost of our inventories is determined using the first-in-first-out (FIFO) method. When we determine that our gross inventories exceed usage requirements, or if inventories become obsolete or otherwise not saleable, we record a provision for such loss as a component of our inventory accounts. Inventories consist of the following: December 31, 2020 2019 (in millions) Raw materials and work-in-progress $ 276.2 $ 310.4 Finished goods 70.4 83.7 Gross inventories 346.6 394.1 Inventory valuation reserves (23.4) (20.5) Inventories, net $ 323.2 $ 373.6 MAINTENANCE, REPAIR AND OPERATIONS (MRO) MATERIALS We include all spare parts and other durable materials for machinery and equipment that are consumed in the manufacturing process in MRO, which is included in Other assets and deferred charges in our Consolidated Balance Sheets. MRO assets are capitalized at actual cost and amortized on a straight-line basis over a useful life of six years, beginning from their purchase date. Repair costs for MRO assets are expensed in the period incurred. Amortization expense related to MRO was $62.4 million, $67.7 million and $62.4 million for 2020, 2019 and 2018, respectively. PROPERTY, PLANT AND EQUIPMENT (PP&E) We state property, plant and equipment, including amortizable tooling, at historical cost, as adjusted for impairments. Construction in progress includes costs incurred for the construction of buildings and building improvements, and machinery and equipment in process. Repair and maintenance costs that do not extend the useful life or otherwise improve the utility of the asset beyond its existing useful state are expensed in the period incurred. We record depreciation and tooling amortization using the straight-line method over the estimated useful lives of the depreciable assets. Depreciation and tooling amortization amounted to $372.9 million, $373.8 million and $367.0 million in 2020, 2019 and 2018, respectively. Property, plant and equipment consists of the following: Estimated December 31, Useful Lives 2020 2019 (years) (in millions) Land Indefinite $ 49.2 $ 45.1 Land improvements 10-15 26.3 24.4 Buildings and building improvements 15-40 554.3 512.7 Machinery and equipment 3-12 3,703.7 3,645.6 Construction in progress 122.1 219.5 4,455.6 4,447.3 Accumulated depreciation and amortization (2,291.8) (2,088.9) Property, plant and equipment, net $ 2,163.8 $ 2,358.4 As of December 31, 2020, 2019 and 2018, we had unpaid purchases of plant and equipment in our accounts payable of $20.4 million, $46.0 million and $84.1 million, respectively. IMPAIRMENT OF LONG-LIVED ASSETS When impairment indicators exist, we evaluate the carrying value of long-lived assets for potential impairment. We consider projected future undiscounted cash flows, trends and other circumstances in making such estimates and evaluations. If impairment is deemed to exist, the carrying amount of the asset is adjusted based on its fair value. Recoverability of assets “held for use” is determined by comparing the forecasted undiscounted cash flows of the operations to which the assets relate to their carrying amount. When the carrying value of an asset group exceeds its fair value and is therefore nonrecoverable, those assets are written down to fair value. Fair value is determined based on market prices, when available, or a discounted cash flow analysis is performed using management estimates. GOODWILL We record goodwill when the purchase price of acquired businesses exceeds the value of their identifiable net tangible and intangible assets acquired. We test our goodwill annually as of October 1, or more frequently if necessary, for impairment in accordance with the accounting guidance for goodwill and other indefinite-lived intangibles. See Note 3 - Goodwill and Other Intangible Assets, for more detail on our goodwill. OTHER INTANGIBLE ASSETS Intangible assets are valued using primarily the relief from royalty method or the multi-period excess earnings method, both of which utilize significant unobservable inputs. These inputs are defined in the fair value hierarchy as Level 3 inputs, which require management to make estimates and assumptions regarding certain financial measures using forecasted or projected information. See Note 3 - Goodwill and Other Intangible Assets, for more detail on our intangible assets. LEASING We record a right of use asset and lease liability when an agreement grants us the right to substantially all of the economic benefits associated with an identified asset, and we are able to direct the use of that asset throughout the term of the agreement, if such term exceeds 12 months. Options to extend or terminate the agreements have been included in the relevant lease term to the extent that they are reasonably certain to be exercised. For agreements that contain both lease and non-lease components, we account for these agreements as a single lease component for all classes of underlying assets. See Note 14 - Leasing for more detail on our leases. DEBT ISSUANCE COSTS The costs related to the issuance or modification of long-term debt are deferred and amortized into interest expense over the expected life of the borrowings. As of December 31, 2020 and December 31, 2019, our unamortized debt issuance costs were $57.8 million and $63.3 million, respectively. Debt issuance costs associated with our senior unsecured notes, as well as our Term Loan A Facility due 2024 and Term Loan B Facility (as defined in Note 4 - Long-Term Debt), are recorded as a reduction to the related debt liability. Debt issuance costs of $12.2 million and $12.1 million related to our Revolving Credit Facility (also as defined in Note 4 - Long-Term Debt), are classified as Other assets and deferred charges on our Consolidated Balance Sheets as of December 31, 2020 and December 31, 2019, respectively. Unamortized debt issuance costs that exist upon the extinguishment of debt are expensed and classified as Debt refinancing and redemption costs on our Consolidated Statements of Operations. DERIVATIVES We recognize all derivatives on the balance sheet at fair value and we are not subject to master netting agreements. If a derivative qualifies under the accounting guidance as a hedge, depending on the nature of the hedge, changes in the fair value of the derivative are either offset against the change in fair value of the hedged asset, liability or firm commitment through earnings or recognized in other comprehensive income until the hedged item is recognized in earnings. Changes in the fair value of derivatives that do not qualify as hedges, are immediately recognized in earnings. See Note 5 - Derivatives and Risk Management, for more detail on our derivatives. CURRENCY TRANSLATION AND REMEASUREMENT We translate the assets and liabilities of our foreign subsidiaries to United States (U.S.) dollars at end-of-period exchange rates. We translate the income statement elements of our foreign subsidiaries to U.S. dollars at average-period exchange rates. We report the effect of translation for our foreign subsidiaries that use the local currency as their functional currency as a separate component of stockholders' equity. Gains and losses resulting from the remeasurement of assets and liabilities in a currency other than the functional currency of a subsidiary are reported in current period income. We also report any gains and losses arising from transactions denominated in a currency other than the functional currency of a subsidiary in current period income. These foreign currency gains and losses resulted in net losses of $0.5 million, $6.5 million and $0.2 million for the years 2020, 2019 and 2018, respectively, in Other expense, net. PENSION AND OTHER POSTRETIREMENT DEFINED BENEFIT PLANS Net pension and postretirement benefit expenses and the related liabilities are determined on an actuarial basis. These plan expenses and obligations are dependent on management's assumptions developed in consultation with our actuaries. We review these actuarial assumptions at least annually and make modifications when appropriate. See Note 7 - Employee Benefit Plans, for more detail on our pension and other postretirement defined benefit plans. STOCK-BASED COMPENSATION AND OTHER INCENTIVE COMPENSATION We award stock-based compensation in the form of restricted stock units (RSUs) and performance shares. For non-performance based awards, the grant date fair value is measured as the stock price at the date of grant. For certain performance based awards, fair value is estimated using valuation techniques that require management to use estimates and assumptions. Certain awards require that management's estimates and assumptions be evaluated at each reporting date to determine if compensation expense related to the award should be adjusted, both on a catch-up and go-forward basis. Compensation expense is recognized over the period during which the requisite service is provided, referred to as the vesting period. We also award incentive compensation in the form of performance units (PU). We grant PU payable in cash to officers and certain other associates which vest in full over a three-year performance period and are based primarily on AAM's three-year cumulative free cash flow. See Note 8 - Stock-Based Compensation and Other Incentive Compensation, for more detail on our accounting for stock-based compensation and other incentive compensation. RESEARCH AND DEVELOPMENT COSTS We expense R&D, as incurred, in selling, general and administrative expenses on our Consolidated Statements of Operations. R&D spending was $117.4 million, $144.7 million and $146.2 million in 2020, 2019 and 2018, respectively. DEFERRED INCOME TAX ASSETS AND LIABILITIES AND VALUATION ALLOWANCES Our deferred income tax assets and liabilities reflect the impact of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the basis of such assets and liabilities for income tax purposes. In accordance with the accounting guidance for income taxes, we review the likelihood that we will realize the benefit of deferred tax assets and estimate whether recoverability of our deferred tax assets is “more likely than not,” based on forecasts of taxable income in the related tax jurisdictions. In determining the requirement for a valuation allowance, the historical results, projected future operating results based upon approved business plans, eligible carry forward periods, and tax planning opportunities are considered, along with other relevant positive and negative evidence. If, based upon available evidence, it is more likely than not the deferred tax assets will not be realized, a valuation allowance is recorded. We record uncertain tax positions on the basis of a two-step process whereby: (1) we determine whether it is "more likely than not" that the tax positions will be sustained based on the technical merits of the position: and (2) for those positions that meet the "more likely than not" recognition threshold, we recognize the largest amount of tax benefit that is greater than 50% likely to be realized upon ultimate settlement with the related tax authority. We record interest and penalties on uncertain tax positions in income tax expense (benefit). See Note 9 - Income Taxes, for more detail on our accounting for income taxes. EARNINGS (LOSS) PER SHARE (EPS) We present EPS using the two-class method. This method allocates undistributed earnings between common shares and non-vested share based payment awards that entitle the holder to non-forfeitable dividend rights. Our participating securities include non-vested restricted stock units. See Note 10 - Earnings (Loss) Per Share (EPS), for more detail on our accounting for EPS. PRODUCT WARRANTY We record estimated warranty obligation liabilities at the dates our products are sold, using sales volumes and internal and external warranty data where there is no payment history and historical information about the average cost of warranty claims for customers with prior claims. We estimate our costs based on the contractual arrangements with our customers, existing customer warranty terms and internal and external warranty data, which includes a determination of our warranty claims and actions taken to improve product quality and minimize warranty claims. See Note 11 - Commitments and Contingencies, for detail on our accounting for product warranties. USE OF ESTIMATES In order to prepare consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP), we are required to make estimates and assumptions that affect the reported amounts and disclosures in our consolidated financial statements. Actual results could differ from those estimates. EFFECT OF NEW ACCOUNTING STANDARDS Standards Recently Adopted Accounting Standards Update 2018-15 On August 15, 2018, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) 2018-15 - Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract (Topic 350-40). ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a cloud computing or hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This guidance became effective at the beginning of our 2020 fiscal year and we adopted this guidance prospectively on January 1, 2020. The adoption of this standard did not have a material impact on our consolidated financial statements. Accounting Standards Update 2016-13 On June 16, 2016, the FASB issued 2016-13 - Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . ASU 2016-13 replaces the incurred loss model under previous guidance, and requires entities to consider expected credit losses, in addition to past events and current conditions when measuring credit losses. This guidance applies to certain of our financial instruments and is primarily applicable to our trade accounts receivable. We adopted this guidance on January 1, 2020, using a modified-retrospective transition method and the adoption of this standard did not have a material impact on our condensed consolidated financial statements. See the Statement of Stockholders' Equity for the implementation impact of ASU 2016-13. Standards Not Yet Adopted Accounting Standard Update 2020-04 On March 12, 2020, the FASB issued ASU 2020-04 - Reference Rate Reform (Topic 848) . This guidance provides optional expedients and exceptions that are intended to ease the burden of updating contracts to contain a new reference rate due to the discontinuation of the London Inter-Bank Offered Rate (LIBOR). This guidance is available immediately and may be implemented in any period prior to the guidance expiration on December 31, 2022. We are currently assessing which of our various contracts could require an update for a new reference rate and will determine the timing for our implementation of this guidance at the completion of that analysis. We expect to utilize certain of the optional expedients and exceptions available under ASU 2020-04 and we do not expect the adoption of this guidance to have a material impact on our financial statements. Accounting Standards Update 2019-12 On December 18, 2019, the FASB issued ASU 2019-12 - Income Taxes (Topic 740) . This guidance is intended to simplify the accounting and disclosure requirements for income taxes by removing various exceptions, and requires that the effect of an enacted change in tax laws or rates be included in the annual effective tax rate computation in the interim period of the enactment. This guidance becomes effective at the beginning of our 2021 fiscal year. We expect to adopt this guidance on January 1, 2021 and we do not expect that this standard will have a material impact on our consolidated financial statements. Other Regulatory Standards Adopted Securities and Exchange Commission (SEC) Rule In the first quarter of 2020, the SEC adopted "Financial Disclosures about Guarantors and Issuers of Guaranteed Securities and Affiliates Whose Securities Collateralize a Registrant's Securities," a rule that amends the financial disclosure requirements for guarantors and issuers of registered guaranteed securities. This rule eliminates the previous requirement to present guarantor financial statement information in the notes to the financial statements and allows for the disclosure of summarized financial information for the most recent year and interim period, as well as expanded non-financial disclosures, in Management's Discussion and Analysis (MD&A). The effective date for this rule is January 4, 2021, however, the SEC permitted voluntary compliance prior to this date and we elected to adopt the new disclosure requirements in the first quarter of 2020. As such, we no longer present guarantor financial statement information in the notes to the consolidated financial statements, but instead present the required information within MD&A. Coronavirus Aid, Relief, and Economic Security Act The Coronavirus Aid, Relief, and Economic Security Act (the CARES Act) was enacted on March 27, 2020 in the United States. The key provisions of the CARES Act, as applicable to AAM, included the following: • The ability to use net operating losses (NOLs) to offset income without the 80% taxable income limitation enacted as part of the Tax Cuts and Jobs Act (TCJA) of 2017, and to carry back NOLs to offset prior year income for five years. These are temporary provisions that apply to NOLs incurred in 2018, 2019 or 2020 tax years. We recognized a tax benefit of $14.4 million for the year ended December 31, 2020 related to our ability to carry back prior year losses, as well as projected current year losses, under the CARES Act to years with the previous 35% tax rate. We also received an income tax refund of approximately $31.0 million during 2020 as a result of the provisions of the CARES Act. • The ability to claim a current deduction for interest expense up to 50% of Adjusted Taxable Income (ATI) for tax years 2019 and 2020. This limitation was previously 30% of ATI pursuant to the TCJA, and will revert to 30% after 2020. • The ability to defer the payment of the employer portion of social security taxes incurred between March 27, 2020 and December 31, 2020, with 50% of the deferred amount to be paid by December 31, 2021 and the remaining 50% to be paid by December 31, 2022. For the year ended December 31, 2020, we deferred $15.2 million of social security taxes that will be paid in 2021 and 2022. • The ability to claim an Employee Retention Credit (ERC), which is a refundable payroll tax credit, for 50% of qualified wages or benefits, subject to certain limitations, that are paid to an employee when they are not providing services due to Novel Coronavirus (COVID-19). The ERC applies to qualified wages paid or incurred during the period March 13, 2020 through December 31, 2020 and is available to eligible employers whose operations were fully or partially suspended due to COVID-19, or whose gross receipts declined by more than 50% when compared to the applicable period in the prior year.

Restructuring and Acquisition-R

Restructuring and Acquisition-Related Costs	12 Months Ended
	Dec. 31, 2020
Restructuring and Related Activities [Abstract]
Business Acquisition, Integration, Restructuring and Other Related Costs [Text Block]	2. RESTRUCTURING AND ACQUISITION-RELATED COSTS In 2016, AAM initiated actions under a global restructuring program (the 2016 Program) focused on creating a more streamlined organization in addition to reducing our cost structure and preparing for acquisition and integration activities. From inception of the 2016 Program, we incurred severance charges totaling $2.8 million and implementation costs totaling $29.6 million. The 2016 Program has concluded and we do not expect to incur any additional charges under this program. In addition to costs incurred under the 2016 program, we initiated actions in 2018 to exit operations at manufacturing facilities in our Driveline, Metal Forming and former Powertrain segments. In 2019, we initiated a global restructuring program (the 2019 Program). The primary objectives of the 2019 Program were to further the integration of Metaldyne Performance Group, Inc. (MPG), align AAM's product and process technologies, and to achieve efficiencies within our corporate and business unit support teams to reduce cost in our business. In the first quarter of 2020, we initiated a new global restructuring program (the 2020 Program) that supersedes the 2019 Program. The primary objectives of the 2020 Program are to achieve efficiencies within our corporate and business unit support teams to reduce cost in our business, and to structurally adjust our operations to a new level of market demand based on the impact of COVID-19. We expect to incur costs under the 2020 Program into 2022. A summary of our restructuring activity for the years 2020, 2019 and 2018 is shown below: Severance Charges Implementation Costs Asset Impairment Charges Total (in millions) Accrual at January 1, 2018 $ 0.3 $ — $ — $ 0.3 Charges 2.5 11.7 30.0 44.2 Cash utilization (0.4) (10.1) — (10.5) Non-cash utilization — — (30.0) (30.0) Accrual at December 31, 2018 2.4 1.6 — 4.0 Charges 19.4 20.4 — 39.8 Cash utilization (17.0) (14.6) — (31.6) Non-cash utilization — — — — Accrual at December 31, 2019 4.8 7.4 — 12.2 Charges 22.3 36.1 — 58.4 Cash utilization (25.4) (33.7) — (59.1) Non-cash utilization — — — — Accrual at December 31, 2020 $ 1.7 $ 9.8 $ — $ 11.5 As part of our total restructuring actions during 2020, we incurred severance charges of approximately $22.3 million, as well as implementation costs, consisting primarily of plant exit costs and professional fees, of approximately $36.1 million. Approximately $47.8 million of the restructuring costs incurred in 2020 were under the 2020 Program. Approximately $19.3 million and $16.0 million of our total restructuring costs in 2020 related to our Driveline and Metal Forming segments, respectively, while the remainder were corporate costs. In 2019, we incurred severance charges of approximately $19.4 million, as well as implementation costs, consisting primarily of plant exit costs, of approximately $20.4 million. Approximately $6.4 million, $21.5 million and $0.7 million of our total restructuring costs in 2019 related to our Driveline, Metal Forming and former Casting segments, respectively, while the remainder were corporate costs. In 2018, we incurred severance charges of approximately $2.5 million, as well as implementation costs, consisting primarily of plant exit costs and professional fees, of approximately $11.7 million and long-lived asset impairment charges of $30.0 million. Approximately $3.4 million, $37.6 million and $0.1 million of our total restructuring costs in 2018 related to our Driveline, Metal Forming and former Casting segments, respectively, while the remainder were corporate costs. We expect to incur approximately $50 million to $65 million of total restructuring charges in 2021, substantially all of which are under the 2020 Program. In 2019, we completed our acquisition of certain operations of Mitec Automotive AG, and in 2017, we completed our acquisitions of MPG and USM Mexico. The following table represents a summary of charges incurred in 2020, 2019 and 2018 associated with acquisition and integration costs: Acquisition-Related Costs Severance Charges Integration Expenses Total 2020 Charges $ — $ — $ 8.8 $ 8.8 2019 Charges 1.8 — 16.2 18.0 2018 Charges 1.2 0.5 33.0 34.7 Acquisition-related costs primarily consist of advisory, legal, accounting, valuation and certain other professional or consulting fees incurred. Integration expenses primarily reflect costs incurred for information technology infrastructure and enterprise resource planning systems, and consulting fees incurred in conjunction with the acquisitions. Total restructuring charges and acquisition-related charges of $67.2 million, $57.8 million and $78.9 million are shown on a separate line item titled "Restructuring and Acquisition-Related Costs" in our Consolidated Statements of Operations for 2020, 2019 and 2018, respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets [Abstract]
Goodwill and Intangible Assets Disclosure [Text Block]	3. GOODWILL AND OTHER INTANGIBLE ASSETS Goodwill The following table provides a reconciliation of changes in goodwill for the year ended December 31, 2020 and the year ended December 31, 2019: Driveline Metal Forming Powertrain Consolidated (in millions) Balance as of January 1, 2019 $ 212.1 $ 552.4 $ 377.3 $ 1,141.8 Reorganization 187.2 190.1 (377.3) — Impairment charge — (440.0) — (440.0) Foreign currency translation (1.0) (1.7) — (2.7) Balance as of December 31, 2019 $ 398.3 $ 300.8 $ — $ 699.1 Impairment charge (210.8) (299.2) — (510.0) Foreign currency translation (1.8) (1.6) — (3.4) Balance as of December 31, 2020 $ 185.7 $ — $ — $ 185.7 We conduct our annual goodwill impairment test in the fourth quarter of each year, as well as whenever adverse events or changes in circumstances indicate a possible impairment. In performing this test, we utilize a third-party valuation specialist to assist management in determining the fair value of our reporting units. Fair value of each reporting unit is estimated based on a combination of discounted cash flows and the use of pricing multiples derived from an analysis of comparable public companies multiplied against historical and/or anticipated financial metrics of each reporting unit. These calculations contain uncertainties as they require management to make assumptions including, but not limited to, market comparables, future cash flows of the reporting units, and appropriate discount and long-term growth rates. This fair value determination is categorized as Level 3 within the fair value hierarchy. We completed our annual goodwill impairment test for our Driveline reporting unit in the fourth quarter of 2020 and no impairment was identified. In the first quarter of 2020, the reduction in global automotive production volumes caused by the impact of COVID-19 represented an indicator to test our goodwill for impairment. This reduction in production volumes began in March of 2020 and resulted in lower forecasted sales volumes in the periods included in our long-range plan as revised in the first quarter of 2020. As a result of this goodwill impairment test in the first quarter of 2020, we determined that the carrying values of both our Driveline and Metal Forming reporting units were greater than their respective fair values. As such, we recorded a goodwill impairment charge of $210.8 million associated with our Driveline reporting unit and a goodwill impairment charge of $299.2 million associated with our Metal Forming reporting unit in the first quarter of 2020. The Metal Forming impairment charge represented a full impairment of the goodwill associated with that reporting unit. These impairment charges were primarily the result of a decline in the projected cash flows of these reporting units under our revised long-range plan completed in the first quarter of 2020. The revision to our long-range plan was driven by lower forecasted sales volumes in the internal and external data sources used to form our projections primarily due to the reduction in global automotive production volumes caused by the impact of COVID-19. The impairment charges were also the result of changes in certain market-related inputs to the analysis to reflect macro-economic changes caused by the impact of COVID-19, including increased discount rates and lower pricing multiples for comparable public companies. At December 31, 2020, accumulated goodwill impairment losses were $1,435.5 million. The reduction in production volumes and changes to macro-economic factors caused by the impact of COVID-19 also represented an indicator to test our long-lived assets, including other intangible assets and property, plant and equipment, for impairment. We completed this test in the first quarter of 2020 and there was no impairment of these assets. As a result of our annual goodwill impairment test in the fourth quarter of 2019, we determined that the carrying value of our Metal Forming reporting unit was greater than its fair value. As such, we recorded a goodwill impairment charge of $440.0 million in 2019 associated with this reporting unit. This impairment was primarily the result of a decline in the projected cash flows of this reporting unit under our long-range plan completed in the fourth quarter of 2019, as compared to the long-range plan completed in the fourth quarter of 2018. This was driven, in part, by lower forecasted sales volumes in the internal and external data sources used to form our projections. In the first quarter of 2019, we initiated a global restructuring program (the 2019 Program) to further streamline our business by consolidating our four existing segments into three segments. Prior to this reorganization, our former Powertrain segment was also a reporting unit for purposes of measuring and reporting goodwill. The goodwill that was previously attributable to the former Powertrain reporting unit was reallocated to the Driveline and Metal Forming reporting units based on the relative fair value of the respective portions that became attributable to those reporting units. The initiation of the 2019 Program and the reorganization of our business represented a triggering event in the first quarter of 2019 to test goodwill for impairment prior to reallocating the former Powertrain goodwill to Driveline and Metal Forming. No impairment was identified as a result of completing this goodwill impairment test. As a result of our test in the fourth quarter of 2018, we determined that the carrying values of our former Casting and Powertrain reporting units were greater than their respective fair values. As such, we recorded goodwill impairment charges of $405.5 million associated with our Casting reporting unit and $80.0 million associated with our former Powertrain reporting unit in 2018. These impairments were primarily the result of a general contraction of pricing multiples associated with capital intensive businesses such as the business conducted by our former Casting and Powertrain reporting units, as well as a decline in the projected cash flows of these reporting units under our long-range plan completed in the fourth quarter of 2018, as compared to the long-range plan completed in the fourth quarter of 2017. The decline in projected cash flows for our former Powertrain reporting unit was primarily the result of decreased contribution margin on lower production volumes for certain passenger car programs that we support. The decline in projected cash flows for our former Casting reporting unit was primarily the result of a projected increase in labor costs in an effort to address workforce shortages at certain locations, as well as an increase in other maintenance and capital requirements. Other Intangible Assets The following table provides a reconciliation of the gross carrying amount and associated accumulated amortization for AAM's other intangible assets, which are all subject to amortization, as of December 31, 2020 and December 31, 2019: December 31, December 31, 2020 2019 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (in millions) Capitalized computer software $ 47.6 $ (33.9) $ 13.7 $ 45.8 $ (27.6) $ 18.2 Customer platforms 856.2 (237.9) 618.3 856.2 (174.4) 681.8 Customer relationships 53.0 (12.8) 40.2 53.0 (9.4) 43.6 Technology and other 156.7 (48.2) 108.5 156.0 (35.1) 120.9 Total $ 1,113.5 $ (332.8) $ 780.7 $ 1,111.0 $ (246.5) $ 864.5 Amortization expense for our intangible assets was $86.6 million for the year ended December 31, 2020, $95.4 million for the year ended December 31, 2019, and $99.4 million for the year ended December 31, 2018. The change in amortization expense in 2020, as compared to 2019, was primarily attributable to the sale of the U.S. operations of our Casting business in the fourth quarter of 2019. Amortization expense for the years 2021 through 2025 is expected to be in the range of approximately $80 million to $85 million per year.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long-term Debt [Text Block]	4. LONG-TERM DEBT Long-term debt, net consists of the following: December 31, 2020 2019 (in millions) Revolving credit facility $ — $ — Term Loan A Facility 323.0 340.0 Term Loan B Facility 1,088.8 1,188.8 6.875% Notes due 2028 400.0 — 6.625% Notes due 2022 — 450.0 6.50% Notes due 2027 500.0 500.0 6.25% Notes due 2026 400.0 400.0 6.25% Notes due 2025 700.0 700.0 Foreign credit facilities and other 88.8 113.4 Total debt 3,500.6 3,692.2 Less: Current portion of long-term debt 13.7 28.7 Long-term debt 3,486.9 3,663.5 Less: Debt issuance costs 45.6 51.2 Long-term debt, net $ 3,441.3 $ 3,612.3 SENIOR SECURED CREDIT FACILITIES In 2017, Holdings and American Axle & Manufacturing, Inc. (AAM Inc.) entered into a credit agreement (the Credit Agreement). In connection with the Credit Agreement, Holdings, AAM, Inc. and certain of their restricted subsidiaries entered into a Collateral Agreement and Guarantee Agreement with the financial institutions party thereto. The Credit Agreement included a $100.0 million term loan A facility (the Term Loan A Facility), a $1.55 billion term loan B facility (the Term Loan B Facility) and a $932 million multi-currency revolving credit facility (the Revolving Credit Facility, and together with the Term Loan A Facility and the Term Loan B Facility, the Senior Secured Credit Facilities). In July 2019, Holdings, AAM, Inc., and certain subsidiaries of Holdings entered into the First Amendment to the Credit Agreement (as amended by the First Amendment, the Amended Credit Agreement). The First Amendment, among other things, established $340 million in incremental term loan A commitments under the Amended Credit Agreement with a maturity date of July 29, 2024 (Term Loan A Facility due 2024), reduced the availability under the Revolving Credit Facility from $932 million to $925 million and extended the maturity date of the Revolving Credit Facility from April 6, 2022 to July 29, 2024, and modified the applicable margin with respect to interest rates under the Term Loan A Facility due 2024 and interest rates and commitment fees under the Revolving Credit Facility. The applicable margin and the maturity date for the Term Loan B Facility remain unchanged. The proceeds of $340 million were used to repay all of the outstanding loans under the existing Term Loan A Facility and a portion of the outstanding Term Loan B Facility, resulting in no additional indebtedness. This also satisfied all payment requirements under the Term Loan B Facility until maturity in 2024. We expensed $5.1 million for the write-off of the unamortized debt issuance costs related to the existing Term Loan A Facility and a portion of the unamortized debt issuance costs related to our Term Loan B Facility that we had been amortizing over the expected life of the borrowings. In December 2019, we used a portion of the cash proceeds from the sale of the U.S. operations of our Casting segment (the Casting Sale) to make a payment on our Term Loan B Facility, which included a principal payment of $59.8 million and $0.4 million in accrued interest. We also expensed approximately $1.0 million for the write-off of the unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing. In April 2020, Holdings, AAM, Inc., and certain subsidiaries of Holdings entered into the Second Amendment to the Credit Agreement (Second Amendment). For the period from April 1, 2020 through March 31, 2022 (the Amendment Period), the Second Amendment, among other things, replaced the total net leverage ratio covenant with a new senior secured net leverage ratio covenant, reduced the minimum levels of the cash interest expense coverage ratio covenant, and modified certain covenants restricting the ability of Holdings, AAM and certain subsidiaries of Holdings to create, incur, assume or permit to exist certain additional indebtedness and liens and to make certain restricted payments, voluntary payments and distributions. The Second Amendment also increased the maximum levels of the total net leverage ratio covenant after the Amendment Period, modified the applicable margin with respect to interest rates under the Term Loan A Facility due 2024 and interest rates and commitment fees under the Revolving Credit Facility, and increased the minimum adjusted London Interbank Offered Rate for Eurodollar-based loans under the Term Loan A Facility due 2024 and Revolving Credit Facility. The applicable margin for the Term Loan B Facility remains unchanged. We paid debt issuance costs of $4.6 million in the year ended December 31, 2020 related to the Second Amendment. In December 2020, we made a voluntary prepayment of $100 million on our Term Loan B Facility and paid approximately $15 million on our Term Loan A Facility due 2024, which included approximately $12.8 million for the prepayment of all required payments under the Term Loan A Facility due 2024 for 2021. As a result, we expensed approximately $1.2 million for the write-off of the unamortized debt issuance costs that we had been amortizing over the life of these borrowings. At December 31, 2020, $891.2 million was available under the Revolving Credit Facility. This availability reflects a reduction of $33.8 million for standby letters of credit issued against the facility. The proceeds of the Revolving Credit Facility are used for general corporate purposes. The Senior Secured Credit Facilities provide back-up liquidity for our foreign credit facilities. We intend to use the availability of long-term financing under the Senior Secured Credit Facilities to refinance any current maturities related to such debt agreements that are not otherwise refinanced on a long-term basis in their local markets, except where otherwise reclassified to Current portion of long-term debt on our Consolidated Balance Sheet. 6.875% NOTES DUE 2028 In the second quarter of 2020, we issued $400 million in aggregate principal amount of 6.875% senior notes due 2028 (the 6.875% Notes). Proceeds from the 6.875% Notes were used primarily to fund the redemption of the remaining $350 million of 6.625% senior notes due 2022 described below and for general corporate purposes. We paid debt issuance costs of $6.4 million in the year ended December 31, 2020 related to the 6.875% Notes. REDEMPTION OF 6.625% NOTES DUE 2022 In the first quarter of 2020, we voluntarily redeemed a portion of our 6.625% Notes due 2022. This resulted in a principal payment of $100.0 million and $2.0 million in accrued interest. We also expensed approximately $0.4 million for the write-off of the unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing, and approximately $1.1 million for an early redemption premium. In the third quarter of 2020, we voluntarily redeemed the remaining portion of our 6.625% Notes due 2022. This resulted in a principal payment of $350 million and $5.7 million in accrued interest. We also expensed approximately $1.3 million for the write-off of the unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing, and approximately $3.9 million for the payment of an early redemption premium. In the second quarter of 2018, we voluntarily redeemed a portion of our 6.625% Notes due 2022. This resulted in a principal payment of $100.0 million, and a payment of $0.8 million in accrued interest. During 2018, we expensed $0.8 million for the write-off of a portion of the remaining unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing and $3.3 million for an early redemption premium. REDEMPTION OF 7.75% NOTES DUE 2019 In the second quarter of 2019, we voluntarily redeemed the remaining balance outstanding under our 7.75% Notes due 2019. This resulted in a principal payment of $100.0 million and $0.3 million in accrued interest. We also expensed approximately $0.1 million for the write-off of the unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing, and approximately $2.2 million for an early redemption premium. In the fourth quarter of 2018, we voluntarily redeemed a portion of our 7.75% Notes due 2019. This resulted in a principal payment of $100.0 million and $3.9 million in accrued interest. We also expensed approximately $0.3 million for the write-off of a portion of the unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing, and approximately $4.5 million for an early redemption premium. 6.25% NOTES DUE 2026 In the first quarter of 2018, we issued $400.0 million in aggregate principal amount of 6.25% senior notes due 2026 (the 6.25% Notes due 2026). Proceeds from the 6.25% Notes due 2026 were used primarily to fund the tender offer for the 6.25% senior notes due 2021 (the 6.25% Notes due 2021) described below. We paid debt issuance costs of $6.6 million during 2018 related to the 6.25% Notes due 2026. TENDER OFFER OF 6.25% NOTES DUE 2021 Also during the first quarter of 2018, we made a tender offer for our 6.25% Notes due 2021. Under this tender offer, we retired the $400.0 million of the 6.25% Notes due 2021 and expensed $2.5 million for the write-off of the remaining unamortized debt issuance costs that we had been amortizing over the expected life of the borrowing and $8.0 million in tender premiums. FOREIGN CREDIT FACILITIES We utilize local currency credit facilities to finance the operations of certain foreign subsidiaries. These credit facilities, some of which are guaranteed by Holdings and/or AAM, Inc., expire at various dates through May 2023. At December 31, 2020, $88.8 million was outstanding under our foreign credit facilities and an additional $72.8 million was available. At December 31, 2019, $106.0 million was outstanding under these facilities and an additional $89.1 million was available. DEBT MATURITIES Aggregate maturities of long-term debt are as follows (in millions) : 2021 $ 32.2 2022 34.2 2023 73.4 2024 1,360.8 2025 700.0 Thereafter 1,300.0 Total $ 3,500.6 INTEREST EXPENSE AND INTEREST INCOME Interest expense was $212.3 million in 2020, $217.3 million in 2019 and $216.3 million in 2018. We capitalized interest of $7.9 million in 2020, $15.5 million in 2019 and $28.4 million in 2018. The weighted-average interest rate of our long-term debt outstanding at December 31, 2020 and December 31, 2019 was 5.8%, as compared to 5.9% at December 31, 2018. Interest income was $11.6 million in 2020, $5.8 million in 2019 and $2.0 million in 2018. Interest income primarily includes interest earned on cash and cash equivalents, realized and unrealized gains and losses on our short-term investments during the period, and the impact of the interest rate differential on our fixed-to-fixed cross-currency swap.

Derivatives and Risk Management

Derivatives and Risk Management	12 Months Ended
	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	5. DERIVATIVES AND RISK MANAGEMENT DERIVATIVE FINANCIAL INSTRUMENTS In the normal course of business, we are exposed to market risk associated with changes in foreign currency exchange rates and interest rates. To manage a portion of these inherent risks, we may purchase certain types of derivative financial instruments based on management's judgment of the trade-off between risk, opportunity and cost. We do not hold or issue derivative financial instruments for trading or speculative purposes. The impact of hedge ineffectiveness was not significant in any of the periods presented. CURRENCY DERIVATIVE CONTRACTS From time to time, we use foreign currency forward contracts to reduce the effects of fluctuations in exchange rates relating to certain foreign currencies. We had currency forward contracts outstanding with a notional amount of $178.2 million and $180.1 million at December 31, 2020 and 2019, respectively, that hedge our exposure to changes in foreign currency exchange rates for certain payroll expenses into the third quarter of 2023 and the purchase of certain direct and indirect inventory and other working capital items into the fourth quarter of 2021. FIXED-TO-FIXED CROSS-CURRENCY SWAP In 2019, we entered into a fixed-to-fixed cross-currency swap to reduce the variability of functional currency equivalent cash flows associated with changes in exchange rates on certain Euro-based intercompany loans. In the first quarter of 2020, we discontinued this fixed-to-fixed cross-currency swap, which was in an asset position of $9.8 million on the date that it was discontinued. Also in the first quarter of 2020, we entered into a new fixed-to-fixed cross-currency swap to reduce the variability of functional currency equivalent cash flows associated with changes in exchange rates on certain Euro-based intercompany loans. As of December 31, 2020 and December 31, 2019 the notional amount of the fixed-to-fixed cross-currency swap was $244.2 million and $224.2 million, respectively, and hedges our exposure to changes in exchange rates on the intercompany loans into the second quarter of 2024. VARIABLE-TO-FIXED INTEREST RATE SWAP In 2017, we entered into a variable-to-fixed interest rate swap to reduce the variability of cash flows associated with interest payments on our variable rate debt. In 2018, we discontinued this variable-to-fixed interest rate swap, which was in an asset position of $5.6 million on the date that it was discontinued. Also in 2018, we entered into a new variable-to-fixed interest rate swap to reduce the variability of cash flows associated with interest payments on our variable rate debt. In 2019, we discontinued this variable-to-fixed interest rate swap, which was a liability of $9.7 million on the date that it was discontinued. Also in 2019, we entered into a new variable-to-fixed interest rate swap to reduce the variability of cash flows associated with interest payments on our variable rate debt. As of December 31, 2020, we have the following notional amounts hedged in relation to our variable-to-fixed interest rate swap: $900.0 million through May 2021, $750.0 million through May 2022, $600.0 million through May 2023 and $500.0 million through May 2024. The following table summarizes the reclassification of pre-tax derivative gains (losses) into net income (loss) from accumulated other comprehensive income (loss) for those derivative instruments designated as cash flow hedges under Accounting Standards Codification 815 - Derivatives and Hedging (ASC 815): Location of Gain (Loss) Reclassified into Net Income (Loss) Gain (Loss) Reclassified During the Twelve Months Ended December 31, Total of Financial Statement Line Item Gain (Loss) Expected to be Reclassified During the Next 12 Months 2020 2019 2018 2020 (in millions) Currency forward contracts Cost of Goods Sold $ (2.9) $ 2.4 $ (2.8) $ 4,128.1 $ 5.7 Fixed-to-fixed cross-currency swap Other Expense, net (18.7) 1.3 — (5.2) 1.7 Variable-to-fixed interest rate swap Interest Expense (14.2) (2.0) 3.2 (212.3) (15.3) See Note 12 - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) for amounts recognized in Accumulated other comprehensive income (loss) during the years ended December 31, 2020, December 31, 2019 and December 31, 2018. The following table summarizes the amount and location of gains (losses) recognized in the Consolidated Statements of Operations for those derivative instruments not designated as hedging instruments under ASC 815: Location of Gain (Loss) Recognized in Net Income (Loss) Gain (Loss) Recognized During the Twelve Months Ended December 31, Total of Financial Statement Line Item 2020 2019 2018 2020 (in millions) Currency forward contracts Cost of Goods Sold $ (6.7) $ 3.9 $ 1.6 $ 4,128.1 Currency forward contracts Other Expense, Net 0.6 — 1.4 (5.2) CONCENTRATIONS OF CREDIT RISK In the normal course of business, we provide credit to customers. We periodically evaluate the creditworthiness of our customers and we maintain reserves for potential credit losses. Sales to General Motors Company (GM) were approximately 39% of our consolidated net sales in 2020, 37% in 2019, and 41% in 2018. Accounts and other receivables due from GM were $297.5 million at year-end 2020 and $328.5 million at year-end 2019. Sales to FCA US LLC (FCA, now part of Stellantis N.V. effective January 2021), were approximately 19% of our consolidated net sales in 2020, 17% in 2019 and 13% in 2018. Accounts and other receivables due from FCA were $157.0 million at year-end 2020 and $154.8 million at year-end 2019. Sales to Ford Motor Company (Ford) were approximately 12% of our consolidated net sales in 2020, 9% in of 2019 and 8% in 2018. Accounts and other receivables due from Ford were $116.5 million at year-end 2020 and $111.7 million at year end 2019. No other single customer accounted for more than 10% of our consolidated net sales in any year presented. In addition, our total GM postretirement cost sharing asset was $250.0 million as of December 31, 2020 and $236.0 million as of December 31, 2019. See Note 7 - Employee Benefit Plans for more detail on this cost sharing asset. We diversify the concentration of invested cash and cash equivalents among different financial institutions and we monitor the selection of counterparties to other financial instruments to avoid unnecessary concentrations of credit risk.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	6. FAIR VALUE The fair value accounting guidance defines fair value as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The definition is based on an exit price rather than an entry price, regardless of whether the entity plans to hold or sell the asset. This guidance also establishes a fair value hierarchy to prioritize inputs used in measuring fair value as follows: • Level 1: Observable inputs such as quoted prices in active markets; • Level 2: Inputs, other than quoted prices in active markets, that are observable either directly or indirectly; and • Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. FINANCIAL INSTRUMENTS The estimated fair values of our financial assets and liabilities that are recognized at fair value on a recurring basis, using available market information and other observable data are as follows: December 31, 2020 December 31, 2019 Carrying Amount Fair Value Carrying Amount Fair Value Input (in millions) Balance Sheet Classification Cash equivalents $ 206.7 $ 206.7 $ 271.3 $ 271.3 Level 1 Prepaid expenses and other Cash flow hedges - currency forward contracts 5.8 5.8 5.0 5.0 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 4.9 4.9 0.9 0.9 Level 2 Nondesignated - currency forward contracts 0.2 0.2 1.9 1.9 Level 2 Other assets and deferred charges Cash flow hedges - currency forward contracts 3.3 3.3 3.4 3.4 Level 2 Cash flow hedges - fixed-to-fixed cross-currency swap — — 1.1 1.1 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 8.6 8.6 2.2 2.2 Level 2 Accrued expenses and other Cash flow hedges - currency forward contracts 0.1 0.1 — — Level 2 Cash flow hedges - variable-to-fixed interest rate swap 17.8 17.8 7.9 7.9 Level 2 Postretirement benefits and other long-term liabilities Cash flow hedges - currency forward contracts 0.1 0.1 — — Level 2 Cash flow hedges - fixed-to-fixed cross-currency swap 20.6 20.6 — — Level 2 Cash flow hedges - variable-to-fixed interest rate swap 32.1 32.1 18.4 18.4 Level 2 The carrying values of our cash, accounts receivable, accounts payable and accrued liabilities approximate their fair values due to the short-term maturities of these instruments. The carrying values of our borrowings under the foreign credit facilities approximate their fair values due to the frequent resetting of the interest rates. We estimated the fair value of our outstanding debt using available market information and other observable data to be as follows: December 31, 2020 December 31, 2019 Carrying Amount Fair Value Carrying Amount Fair Value Input (in millions) Revolving Credit Facility $ — $ — $ — $ — Level 2 Term Loan A Facility 323.0 318.6 340.0 337.9 Level 2 Term Loan B Facility 1,088.8 1,071.1 1,188.8 1,174.0 Level 2 6.875% Notes due 2028 400.0 426.0 — — Level 2 6.625% Notes due 2022 — — 450.0 455.4 Level 2 6.50% Notes due 2027 500.0 523.8 500.0 516.3 Level 2 6.25% Notes due 2026 400.0 411.0 400.0 409.0 Level 2 6.25% Notes due 2025 700.0 724.3 700.0 716.6 Level 2

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Compensation and Employee Benefit Plans [Text Block]	7. EMPLOYEE BENEFIT PLANS PENSION AND OTHER POSTRETIREMENT DEFINED BENEFIT PLANS We sponsor various qualified and non-qualified defined benefit pension plans for our eligible associates. We also maintain hourly and salaried benefit plans that provide postretirement medical, dental, vision and life insurance benefits (OPEB) to our eligible retirees and their dependents in the U.S. Actuarial valuations of our benefit plans were made as of December 31, 2020 and 2019. The primary weighted-average assumptions used in the year-end valuation of our principal plans appear in the following table. The U.S. discount rates are based on an actuarial review of a hypothetical portfolio of long-term, high quality corporate bonds matched against the expected payment stream for each of our plans. The United Kingdom (U.K.) discount rates are based on hypothetical yield curves developed from corporate bond yield information within each regional market. The assumptions for expected return on plan assets are based on future capital market expectations for the asset classes represented within our portfolios and a review of long-term historical returns. The rates of increase in compensation and health care costs are based on current market conditions, inflationary expectations and historical information. Pension Benefits OPEB 2020 2019 2018 2020 2019 2018 U.S. U.K. U.S. U.K. U.S. U.K. Discount rate 2.50 % 1.55 % 3.40 % 2.05 % 4.30 % 2.95 % 2.55 % 3.35 % 4.35 % Expected return on plan assets 7.25 % 4.00 % 7.25 % 4.00 % 7.50 % 5.10 % N/A N/A N/A Rate of compensation increase N/A 3.15 % N/A 3.15 % 4.00 % 3.40 % 4.00 % 4.00 % 4.00 % The accumulated benefit obligation for all defined benefit pension plans was $796.6 million and $737.8 million at December 31, 2020 and December 31, 2019, respectively. As of December 31, 2020, the accumulated benefit obligation for our underfunded defined benefit pension plans was $618.8 million, the projected benefit obligation was $618.8 million and the fair value of assets for these plans was $469.6 million. Certain eligible retirees under our OPEB plans have past service with both AAM and GM. AAM and GM share proportionally in the cost of OPEB for these retirees based on the length of service an employee had with AAM and GM. We have included in our OPEB obligation the amounts expected to be received pursuant to this agreement of $250.0 million and $236.0 million at December 31, 2020 and December 31, 2019, respectively. We have also recorded a corresponding asset for these amounts on our Consolidated Balance Sheets, $13.0 million that is classified as a current asset and $237.0 million that is classified as a noncurrent asset as of December 31, 2020. The following table summarizes the changes in projected benefit obligations and plan assets and reconciles the funded status of the benefit plans, which is the net benefit plan liability: Pension Benefits OPEB December 31, December 31, 2020 2019 2020 2019 (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 740.2 $ 734.5 $ 549.1 $ 537.3 Service cost 2.0 1.5 0.4 0.3 Interest cost 21.4 28.0 10.2 12.8 Actuarial loss 63.5 71.5 25.3 11.9 Change in GM portion of OPEB obligation — — 14.0 3.1 Participant contributions 0.2 0.2 — — Curtailments — (1.9) — — Settlements (3.3) (28.8) — — Benefit payments (34.4) (44.1) (12.5) (15.5) Sale of business — (26.2) — (0.8) Currency fluctuations 8.7 5.5 — — Other 0.6 — — — Net change 58.7 5.7 37.4 11.8 Benefit obligation at end of year $ 798.9 $ 740.2 $ 586.5 $ 549.1 Change in plan assets Fair value of plan assets at beginning of year $ 636.6 $ 625.8 $ — $ — Actual return on plan assets 55.7 87.5 — — Employer contributions 8.5 10.0 12.5 15.5 Participant contributions 0.2 0.2 — — Benefit payments (34.4) (44.1) (12.5) (15.5) Settlements (3.3) (28.8) — — Sale of business — (20.7) — — Currency fluctuations 6.6 6.7 — — Net change 33.3 10.8 — — Fair value of plan assets at end of year $ 669.9 $ 636.6 $ — $ — Amounts recognized in our Consolidated Balance Sheets are as follows: Pension Benefits OPEB December 31, December 31, 2020 2019 2020 2019 (in millions) Noncurrent assets $ 20.2 $ 21.2 $ — $ — Current liabilities (8.0) (6.6) (29.8) (29.1) Noncurrent liabilities (141.2) (118.2) (556.7) (520.0) Net liability $ (129.0) $ (103.6) $ (586.5) $ (549.1) Pre-tax amounts recorded in accumulated other comprehensive income (loss) (AOCI), not yet recognized in net periodic benefit cost (credit) as of December 31, 2020 and 2019, consists of: Pension Benefits OPEB December 31, December 31, 2020 2019 2020 2019 (in millions) Net actuarial gain (loss) $ (278.0) $ (239.2) $ (4.9) $ 19.3 Net prior service credit (cost) (1.8) (1.2) 3.1 4.7 Total amounts recorded $ (279.8) $ (240.4) $ (1.8) $ 24.0 The increase in net actuarial loss for pension benefits and decrease in net actuarial gain for OPEB as of December 31, 2020, as compared to December 31, 2019, is primarily attributable to a reduction in the discount rates used in the valuation at December 31, 2020 as compared to prior year. The components of net periodic benefit cost (credit) are as follows: Pension Benefits OPEB 2020 2019 2018 2020 2019 2018 (in millions) Service cost $ 2.0 $ 1.5 $ 2.6 $ 0.4 $ 0.3 $ 0.4 Interest cost 21.4 28.0 27.3 10.2 12.8 12.4 Expected asset return (38.4) (41.1) (45.8) — — — Amortized actuarial loss 8.6 6.4 7.8 1.0 0.1 0.8 Amortized prior service cost (credit) 0.1 — 0.1 (1.5) (1.5) (2.7) Curtailment loss (gain) — — 3.2 — — (0.6) Settlement charge 0.5 10.4 0.4 — — — Net periodic benefit cost (credit) $ (5.8) $ 5.2 $ (4.4) $ 10.1 $ 11.7 $ 10.3 Our postretirement cost sharing asset from GM is measured on the same basis as the portion of the obligation to which it relates. The actuarial gains and losses related to the GM portion of the OPEB obligation are recognized immediately in the Consolidated Statements of Operations as an offset against the gains and losses related to the change in the corresponding GM postretirement cost sharing asset. These items are presented net in the change in benefit obligation and net periodic benefit cost components disclosed above. Remaining actuarial gains and losses are deferred and amortized over the expected future service periods of the active participants or the remaining life expectancy of the inactive participants. For measurement purposes, a weighted average annual increase in the per-capita cost of covered health care benefits of 6.25% was assumed for 2021. The rate was assumed to decrease gradually to 5.00% by 2026 and to remain at that level thereafter. The expected future pension and other postretirement benefits to be paid, net of GM cost sharing, for each of the next five years and in the aggregate for the succeeding five years thereafter are as follows: $59.7 million in 2021; $55.2 million in 2022; $55.1 million in 2023; $56.4 million in 2024; $57.2 million in 2025 and $287.4 million for 2026 through 2030. These amounts were estimated using the same assumptions that were used to measure our 2020 year-end pension and OPEB obligations and include an estimate of future employee service. Contributions We contributed $4.2 million to our pension trusts in 2020. Due to the availability of our pre-funded pension balances (previous contributions in excess of prior required pension contributions), we expect our regulatory pension funding requirements in 2021 to be less than $1.0 million. We expect our cash payments, net of GM cost sharing, for OPEB to be approximately $17.0 million in 2021. Terminated vested lump sum payment offer In 2019, we offered a voluntary one-time lump sum payment option to certain eligible terminated vested participants in our U.S. pension plans that, if accepted, settled our pension obligations to them (AAM Pension Payout Offer). The lump sum settlements, which were paid from plan assets, reduced our liabilities and administrative costs going forward. The AAM Pension Payout Offer was offered to approximately 2,000 of our U.S. pension plan participants, of which 616 participants accepted the offer. We made a one-time lump sum payment from our pension trust of $28.4 million in 2019. As a result of this settlement, we remeasured the assets and liabilities of our U.S. pension plans, which reduced our projected benefit obligation by $32.5 million and resulted in a non-cash settlement charge of $9.8 million in the fourth quarter of 2019 related to the accelerated recognition of certain deferred losses. Pension plan assets The weighted-average asset allocations of our pension plan assets at December 31, 2020 and 2019 appear in the following table. The asset allocation for our plans is developed in consideration of the demographics of the plan participants and expected payment stream of the benefit obligation. U.S. U.K. Target Target 2020 2019 Allocation 2020 2019 Allocation Equity securities 34.7 % 35.2 % 25% - 40% 21.8 % 22.7 % 15% - 30% Fixed income securities 57.3 52.9 50% - 70% 65.9 66.8 60% - 80% Alternative assets 7.3 10.4 5% - 15% 8.9 9.4 5% - 15% Cash 0.7 1.5 0% - 5% 3.4 1.1 0% - 5% Total 100.0 % 100.0 % 100.0 % 100.0 % The primary objective of our pension plan assets is to provide a source of retirement income for participants and beneficiaries. Our primary financial objectives for the pension plan assets have been established in conjunction with a comprehensive review of our current and projected financial requirements. These objectives include having the ability to pay all future benefits and expenses when due, maintaining flexibility and minimizing volatility. These objectives are based on a long-term investment horizon. Defined Benefit Pension Plan Assets Investments in our defined benefit plans are stated at fair value. Level 1 assets are valued using quoted market prices that represent the asset value of the shares held by the trusts. The level 2 assets are investments in pooled funds, which are valued using a model to reflect the valuation of their underlying assets that are publicly traded with observable values. The fair values of our pension plan assets are as follows: December 31, 2020 Asset Categories Level 1 Level 2 Level 3 Total (in millions) Cash and Cash Equivalents $ 7.4 $ 2.9 $ — $ 10.3 Equity U.S. Large Cap 88.1 2.7 — 90.8 U.S. Small/Mid Cap 20.5 — — 20.5 World Equity 87.0 7.8 — 94.8 Fixed Income Securities Government & Agencies 84.1 45.9 — 130.0 Corporate Bonds - Investment Grade 219.0 2.7 — 221.7 Corporate Bonds - Non-investment Grade 22.4 0.7 — 23.1 Emerging Market Debt 21.1 1.1 — 22.2 Other 3.6 0.3 — 3.9 Other Property Funds (a) — — — 44.2 Liquid Alternatives Fund (a) — — — 1.8 Structured Credit Fund (a) — — — 6.6 Total Plan Assets $ 553.2 $ 64.1 $ — $ 669.9 December 31, 2019 Asset Categories Level 1 Level 2 Level 3 Total (in millions) Cash and Cash Equivalents $ 7.3 $ 2.0 $ — $ 9.3 Equity U.S. Large Cap 82.4 3.0 — 85.4 U.S. Small/Mid Cap 22.7 — — 22.7 World Equity 88.1 4.7 — 92.8 Fixed Income Securities Government & Agencies 74.3 45.0 — 119.3 Corporate Bonds - Investment Grade 185.8 0.6 — 186.4 Corporate Bonds - Non-investment Grade 21.7 1.1 — 22.8 Emerging Market Debt 20.4 0.7 — 21.1 Other 6.9 4.8 — 11.7 Other Property Funds (a) — — — 57.3 Liquid Alternatives Fund (a) — — — 1.6 Structured Credit Fund (a) — — — 6.2 Total Plan Assets $ 509.6 $ 61.9 $ — $ 636.6 (a) In accordance with ASC 820 - Fair Value Measurement certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the Consolidated Balance Sheets. DEFINED CONTRIBUTION PLANS Most of our salaried and hourly U.S. associates, including certain UAW represented associates at our U.S. locations, are eligible to participate in voluntary savings plans. Our maximum match is 50% of eligible associates' contribution up to 10% of their eligible salary. Matching contributions amounted to $7.9 million in 2020, $11.5 million in 2019 and $12.4 million in 2018. Certain U.S. associates are eligible annually to receive an additional AAM Retirement Contribution (ARC) benefit between 3% to 5% of eligible salary, depending on years of service. We made ARC contributions of $8.0 million, $10.3 million and $7.3 million in 2020, 2019 and 2018, respectively.

Stock Based Compensation and Ot

Stock Based Compensation and Other Incentive Compensation	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-based Payment and Other Incentive Payment Arrangements [Text Block]	8. STOCK-BASED COMPENSATION AND OTHER INCENTIVE COMPENSATION STOCK-BASED COMPENSATION At December 31, 2020, we had stock-based awards outstanding under stock compensation plans approved by our stockholders. Under these plans, shares have been authorized for issuance to our directors, officers and certain other associates in the form of unvested restricted stock units, performance shares or other awards that are based on the value of our common stock. Shares available for future grants at December 31, 2020 were 2.1 million. The current stock plan will expire in May 2028. RESTRICTED STOCK UNITS We have awarded restricted stock units (RSUs). Compensation expense associated with RSUs settled in stock is recorded to paid-in-capital ratably over the three-year vesting period. The following table summarizes activity relating to our RSUs: Weighted-Average Number of Grant Date Fair Shares/Units Value per Share/Unit (in millions, except per share data) Outstanding at January 1, 2018 2.5 $ 18.35 Granted 1.7 14.57 Vested (0.4) 24.16 Canceled (0.3) 15.84 Outstanding at December 31, 2018 3.5 $ 16.00 Granted 1.0 15.78 Vested (0.7) 15.53 Canceled (0.7) 16.05 Outstanding at December 31, 2019 3.1 $ 16.03 Granted 3.2 5.08 Vested (0.8) 18.22 Canceled (0.6) 10.33 Outstanding at December 31, 2020 4.9 $ 9.20 As of December 31, 2020, unrecognized compensation cost related to unvested RSUs totaled $15.5 million. The weighted average period over which this cost is expected to be recognized is approximately 2 years. In 2020 and 2019, the total fair market value of RSUs vested was $5.0 million and $10.9 million, respectively. PERFORMANCE SHARES As of December 31, 2020, we have performance shares (PS) outstanding under our 2018 Omnibus Incentive Plan. We grant performance shares payable in stock to officers which vest in full over a three-year performance period. In 2020, these grants were based on AAM's three-year cumulative free cash flow, adjusted based on a total shareholder return (TSR) measure. In 2019, these grants were based on a TSR measure, and in 2018, these grants were based equally on a TSR measure and AAM's three-year cumulative free cash flow. The TSR metric compares our TSR over the three-year performance period relative to the TSR of our pre-defined competitor peer group. Based on these free cash flow and relative TSR performance metrics, the number of performance shares that will vest will be between 0% and 200% of the grant date amount. Share price appreciation and dividends paid are measured over the performance period to determine TSR. As these awards are settled in stock, the compensation expense is recorded ratably over the vesting period to paid-in-capital. The following table summarizes activity relating to our performance shares: Weighted Average Number of Grant Date Fair Shares Value per Share EBITDA Awards (in millions, except per share data) Outstanding at January 1, 2018 0.6 $ 33.91 Granted — — Vested (0.1) 37.67 Canceled — — Outstanding at December 31, 2018 0.5 $ 34.49 Granted — — Vested (0.4) 31.21 Canceled — — Outstanding at December 31, 2019 0.1 $ 39.09 Granted — — Vested (0.1) 39.09 Canceled — — Outstanding at December 31, 2020 — $ — TSR Awards Outstanding at January 1, 2018 0.6 $ 20.93 Granted 0.3 13.91 Vested (0.1) 31.21 Canceled — — Outstanding at December 31, 2018 0.8 $ 16.25 Granted 0.3 24.36 Vested (0.2) 17.54 Canceled (0.1) 20.49 Outstanding at December 31, 2019 0.8 $ 20.13 Granted — — Vested (0.2) 24.63 Canceled — — Outstanding at December 31, 2020 0.6 $ 18.86 Free Cash Flow Awards Outstanding at January 1, 2018 — $ — Granted 0.3 14.28 Vested — — Canceled — — Outstanding at December 31, 2018 0.3 $ 14.28 Granted — — Vested — — Canceled — — Outstanding at December 31, 2019 0.3 $ 14.28 Granted 0.9 5.18 Vested — — Canceled — — Outstanding at December 31, 2020 1.2 $ 7.50 We estimate the fair value of our EBITDA performance shares on the date of grant using our estimated three-year adjusted EBITDA margin, based on AAM's budget and long-range plan assumptions at that time, and adjust quarterly as necessary. We estimate the fair value of our TSR performance shares on the date of grant using the Monte Carlo simulation approach. The Monte Carlo simulation approach utilizes inputs on volatility assumptions, risk free rates, the price of the Company’s and our competitor peer group's common stock and their correlation as of each valuation date. Volatility assumptions are based on historical and implied volatility measurements. We estimate the fair value of our free cash flow performance shares on the date of grant using our estimated three-year cumulative free cash flow, based on AAM's budget and long-range plan assumptions at the time, and adjust quarterly as necessary. Based on the current fair value, the estimated unrecognized compensation cost related to unvested PS totaled $5.3 million, as of December 31, 2020. The weighted-average period over which this cost is expected to be recognized is approximately two years. OTHER INCENTIVE COMPENSATION

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	9. INCOME TAXES The components of income (loss) before income taxes are as follows: 2020 2019 2018 (in millions) U.S. loss $ (721.6) $ (889.0) $ (549.4) Non - U.S. income 111.3 356.0 435.5 Total loss before income taxes $ (610.3) $ (533.0) $ (113.9) The following is a summary of the components of our provision for income taxes: 2020 2019 2018 (in millions) Current Federal $ 2.0 $ (11.9) $ (81.5) State and local 0.5 0.1 3.2 Foreign 20.2 49.3 46.5 Total current $ 22.7 $ 37.5 $ (31.8) Deferred Federal $ (60.0) $ (73.5) $ (5.1) State and local (0.7) (1.5) (6.7) Foreign (11.2) (11.4) (13.5) Total deferred (71.9) (86.4) (25.3) Total income tax benefit $ (49.2) $ (48.9) $ (57.1) The following is a reconciliation of income taxes calculated at the U.S. federal statutory income tax rate of 21% in 2020, 2019 and 2018 to our provision for income taxes: 2020 2019 2018 (in millions) Federal statutory $ (128.2) $ (111.9) $ (23.9) Foreign income taxes (21.5) (40.2) (39.7) Change in enacted tax rate 2.1 0.2 (8.3) Transition tax — (7.5) 5.8 State and local (5.0) (20.0) (12.8) Tax credits (9.7) (9.6) (20.1) Valuation allowance 19.8 12.6 12.9 Goodwill impairment 107.1 92.4 21.6 Withholding taxes 5.6 4.0 6.6 U.S. tax on unremitted foreign earnings — (2.8) 4.1 Tax benefit on loss carryback (14.4) — — Global intangible low-taxed income 2.3 31.1 8.0 Uncertain tax positions (8.8) 5.9 (9.8) Other 1.5 (3.1) (1.5) Effective income tax benefit $ (49.2) $ (48.9) $ (57.1) In 2020, our effective income tax rate varied from the U.S. federal statutory rate primarily as a result of the goodwill impairment charge, which resulted in no income tax benefit, as well as favorable foreign tax rates, the impact of tax credits, and the finalization of an advance pricing agreement in a foreign jurisdiction, which resulted in a tax benefit of approximately $6.8 million. We also recognized a tax benefit of approximately $14.4 million related to our ability to carry back prior year losses, as well as projected current year losses, under the CARES Act to years with the previous 35% tax rate. These income tax benefits were partially offset by our inability to realize an income tax benefit for losses incurred in certain foreign and state jurisdictions, as well as a partial valuation allowance of approximately $5.3 million on certain U.S. federal income tax attributes. In 2019, our income tax benefit varied from the tax benefit computed at the U.S. federal statutory rate primarily as a result of the goodwill impairment charge, which resulted in no income tax benefit, as well as the incremental tax expense associated with the global intangible low-taxed income inclusion under the Tax Cuts and Jobs Act of 2017 (the 2017 Act), and our inability to realize an income tax benefit for losses incurred in certain foreign and state jurisdictions. These items were partially offset by the impact of favorable foreign tax rates and income tax credits. In addition, as part of the 2017 Act, a one-time transition tax (Transition Tax) was imposed on certain foreign earnings for which U.S. income tax was previously deferred. The Department of Treasury and Internal Revenue Service issued final regulations on February 5, 2019 regarding the Transition Tax, which changed the manner in which we are required to compute the Transition Tax when it is recognized over a two-year period. The application of the final regulations resulted in a $9.3 million income tax benefit, which has been recorded in 2019, the period in which the final regulations were issued. In 2018, our income tax benefit varied from the tax benefit computed at the U.S. federal statutory rate primarily due to the impact of favorable foreign tax rates, and the impact of income tax credits, partially offset by our inability to realize an income tax benefit for losses incurred in certain foreign and state jurisdictions. In addition, during 2018, we finalized an advance pricing agreement in a foreign jurisdiction and settled various other matters, which resulted in an income tax benefit and a reduction of our liability for unrecognized tax benefits and related interest and penalties of approximately $20 million. We also recorded an income tax benefit of approximately $85 million in 2018 as a result of the goodwill impairment charge, partially offset by a discrete tax expense related to the sale of the aftermarket business associated with our former Powertrain segment. The 2017 Act subjects a U.S. shareholder to tax on global intangible low-taxed income (GILTI) earned by certain foreign subsidiaries. Under GAAP, we made an accounting policy election to provide for the tax expense related to GILTI in the year the tax is incurred as a period expense. As of December 31, 2020, we have refundable income taxes of approximately $14 million classified as Prepaid expenses and other on our Consolidated Balance Sheet, as compared to approximately $25 million as of December 31, 2019. We also have income taxes payable of approximately $6 million and $3 million classified as Accrued expenses and other on our Consolidated Balance Sheets as of December 31, 2020 and 2019, respectively. The approximate tax effect of each significant type of temporary difference and carryforward that results in a deferred tax asset or liability is as follows: December 31, 2020 2019 (in millions) Deferred tax assets Employee benefits $ 162.4 $ 149.4 Inventory 32.9 27.3 Net operating loss (NOL) carryforwards 221.4 201.7 Tax credit carryforwards 88.6 47.8 Capital allowance carryforwards 10.2 9.3 Capitalized expenditures 45.9 42.9 Interest carryforward 10.4 43.9 Operating lease liabilities 25.7 27.1 Other 50.6 42.7 Valuation allowances (208.0) (196.0) Deferred tax assets $ 440.1 $ 396.1 Deferred tax liabilities Other intangible assets (179.9) (199.7) Fixed assets (137.5) (120.7) Operating lease right-of-use assets (25.6) (27.1) Other (2.5) (4.1) Deferred tax liabilities $ (345.5) $ (351.6) Deferred tax assets, net $ 94.6 $ 44.5 Deferred tax assets and liabilities recognized in our Consolidated Balance Sheets are as follows: December 31, 2020 2019 (in millions) U.S. federal and state deferred tax asset, net $ 44.1 $ 5.0 Other foreign deferred tax asset, net 50.5 39.5 Deferred tax asset, net $ 94.6 $ 44.5 DEFERRED INCOME TAX ASSETS AND LIABILITIES AND VALUATION ALLOWANCES The deferred income tax assets and liabilities summarized above reflect the impact of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the basis of such assets and liabilities for income tax purposes. ASC 740 - Income Taxes states that companies must measure deferred tax amounts at the rate at which they are expected to be realized. As of December 31, 2020 and December 31, 2019, we had deferred tax assets from domestic and foreign net operating loss and tax credit carryforwards of $320.2 million and $258.8 million, respectively. Approximately $107.7 million of the deferred tax assets at December 31, 2020 relate to NOL and tax credits that can be carried forward indefinitely with the remainder expiring between 2021 and 2040. Accounting guidance for income taxes requires a deferred tax liability to be established for the U.S. tax impact of undistributed earnings of foreign subsidiaries unless it can be shown that these earnings will be permanently reinvested outside the U.S. We have provided deferred income taxes for the estimated U.S. federal income tax, foreign income tax, and applicable withholding taxes on earnings of subsidiaries expected to be distributed. In accordance with the accounting guidance for income taxes, we review the likelihood that we will realize the benefit of deferred tax assets and estimate whether recoverability of our deferred tax assets is “more likely than not,” based on forecasts of taxable income in the related tax jurisdictions. In determining the requirement for a valuation allowance, the historical results, projected future operating results based upon approved business plans, eligible carry forward periods, and tax planning opportunities are considered, along with other relevant positive and negative evidence. If, based upon available evidence, it is more likely than not the deferred tax assets will not be realized, a valuation allowance is recorded. During 2020, we determined that a portion of our deferred tax assets related to certain U.S. federal income tax attributes that are being carried forward were not more likely than not to be realized and, as such, we recorded a valuation allowance resulting in tax expense of approximately $5.3 million during the year ended December 31, 2020. Due to the uncertainty associated with the extent and ultimate impact of COVID-19 on global automotive production volumes, we may experience lower than projected earnings in certain jurisdictions in future periods, and it is reasonably possible that changes in valuation allowances could be recognized in the next twelve months as a result. During 2020, 2019 and 2018, we recorded a net tax expense of $14.5 million, $25.4 million and $16.0 million, respectively, resulting from net losses in certain foreign and U.S. state and local jurisdictions with no corresponding tax benefit due to increases in our valuation allowance. These income tax expenses were increased in 2020 and partially offset in 2019 and 2018 by a net tax expense of $5.3 million, and a net tax benefit of $12.8 million and $3.1 million, respectively, resulting from changes in determinations relating to the potential realization of deferred tax assets, the resulting establishment of a partial valuation allowance in the U.S., and the resulting release of valuation allowances in foreign jurisdictions. As of December 31, 2020 and December 31, 2019, we have a valuation allowance of $208.0 million and $196.0 million, respectively, related to net deferred tax assets in several foreign jurisdictions and U.S. federal, state and local jurisdictions. UNRECOGNIZED INCOME TAX BENEFITS To the extent that we have uncertain tax positions, a determination is made as to whether such positions meet the “more likely than not” threshold. This threshold must be met in order to record any tax benefit and, to the extent that an uncertain tax position meets the "more likely than not" threshold, we have measured and recorded the highest probable benefit, and have established appropriate reserves for benefits that exceed the amount likely to be sustained upon examination. A reconciliation of the beginning and ending amounts of unrecognized income tax benefits is as follows: Unrecognized Income Tax Interest and Benefits Penalties (in millions) Balance at January 1, 2018 $ 47.7 $ 7.5 Increase in prior year tax positions 5.6 3.5 Decrease in prior year tax positions (16.9) (2.5) Increase in current year tax positions 6.0 — Settlement (3.7) (1.6) Balance at December 31, 2018 $ 38.7 $ 6.9 Increase in prior year tax positions 0.2 4.5 Decrease in prior year tax positions (3.1) (0.1) Increase in current year tax positions 4.4 — Foreign currency remeasurement adjustment 0.9 0.2 Balance at December 31, 2019 $ 41.1 $ 11.5 Increase in prior year tax positions 0.2 — Decrease in prior year tax positions (6.6) (1.7) Increase in current year tax positions 0.7 — Settlement (12.2) (6.3) Foreign currency remeasurement adjustment (3.0) (1.5) Balance at December 31, 2020 $ 20.2 $ 2.0 At December 31, 2020 and December 31, 2019, we had $20.2 million and $41.1 million of gross unrecognized income tax benefits, respectively. In 2020, 2019, and 2018, we recognized a tax (benefit)/expense of $(1.7) million, $4.4 million and $1.0 million, respectively, related to interest and penalties in Income tax benefit on our Consolidated Statements of Operations. We have a liability of $2.0 million and $11.5 million related to the estimated future payment of interest and penalties at December 31, 2020 and 2019, respectively. The amount of the unrecognized income tax benefits, including interest and penalties, as of December 31, 2020 that, if recognized, would affect the effective tax rate is $19.0 million. We operate in multiple jurisdictions throughout the world and the income tax returns of several subsidiaries in various tax jurisdictions are currently under examination. We are currently under a U.S. federal income tax examination for the years 2015 through 2018. Generally, we are no longer subject to U.S. federal, state and local, or non-U.S. income tax examinations by tax authorities for years prior to 2013. In the second quarter of 2020, we finalized an advance pricing agreement in a foreign jurisdiction, which resulted in a cash payment to the tax authorities of $18.5 million and a reduction of our liability for unrecognized tax benefits and related interest and penalties of $25.3 million.

Earnings Per Share (EPS)

Earnings Per Share (EPS)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	10. EARNINGS (LOSS) PER SHARE (EPS) We present EPS using the two-class method. This method allocates undistributed earnings between common shares and non-vested share based payment awards that entitle the holder to non-forfeitable dividend rights. Our participating securities include non-vested restricted stock units. The following table sets forth the computation of our basic and diluted EPS available to shareholders of common stock (excluding participating securities): 2020 2019 2018 (in millions, except per share data) Numerator Net loss attributable to AAM $ (561.3) $ (484.5) $ (57.5) Less: Net loss allocated to participating securities — — — Net loss attributable to common shareholders - Basic and Dilutive $ (561.3) $ (484.5) $ (57.5) Denominators Basic common shares outstanding - Weighted-average shares outstanding 117.9 115.6 115.0 Less: Participating securities (4.8) (3.3) (3.4) Weighted-average common shares outstanding 113.1 112.3 111.6 Effect of dilutive securities - Dilutive stock-based compensation — — — Diluted shares outstanding - Adjusted weighted-average shares after assumed conversions 113.1 112.3 111.6 Basic EPS $ (4.96) $ (4.31) $ (0.51) Diluted EPS $ (4.96) $ (4.31) $ (0.51)

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure [Text Block]	11. COMMITMENTS AND CONTINGENCIES PURCHASE COMMITMENTS Obligated purchase commitments for capital expenditures and related project expenses were approximately $90.8 million at December 31, 2020 and $131.9 million at December 31, 2019. LEGAL PROCEEDINGS We are involved in, or potentially subject to, various legal proceedings or claims incidental to our business. These include, but are not limited to, matters arising out of product warranties, tax or contractual matters, and environmental obligations. Although the outcome of these matters cannot be predicted with certainty, we do not believe that any of these matters, individually or in the aggregate, will have a material effect on our financial condition, results of operations or cash flows. We are subject to various federal, state, local and foreign environmental and occupational safety and health laws, regulations and ordinances, including those regulating air emissions, water discharge, waste management and environmental cleanup. We will continue to closely monitor our environmental conditions to ensure that we are in compliance with all laws, regulations and ordinances. We have made, and anticipate continuing to make, capital and other expenditures (including recurring administrative costs) to comply with environmental requirements at our current and former facilities. Such expenditures were not significant in 2020, 2019 and 2018. ENVIRONMENTAL OBLIGATIONS Due to the nature of our manufacturing operations, we have legal obligations to perform asset retirement activities pursuant to federal, state, and local requirements at our current and former facilities. The process of estimating environmental liabilities is complex. Significant uncertainty may exist related to the timing and method of the settlement of these obligations. Therefore, these liabilities are not reasonably estimable until a triggering event occurs that allows us to estimate a range and assess the probabilities of potential settlement dates and the potential methods of settlement. In the future, we will update our estimated costs and potential settlement dates and methods and their associated probabilities based on available information. Any update may change our estimate and could result in a material adjustment to this liability. PRODUCT WARRANTIES We record a liability for estimated warranty obligations at the dates our products are sold. These estimates are established using sales volumes and internal and external warranty data where there is no payment history and historical information about the average cost of warranty claims for customers with prior claims. We estimate our costs based on the contractual arrangements with our customers, existing customer warranty terms and internal and external warranty data, which includes a determination of our warranty claims and actions taken to improve product quality and minimize warranty claims. We continuously evaluate these estimates and our customers' administration of their warranty programs. We monitor actual warranty claim data and adjust the liability, as necessary, on a quarterly basis. During 2020 and 2019, we also made adjustments to our warranty accrual to reflect revised estimates regarding our projected future warranty obligations. The following table provides a reconciliation of changes in the product warranty liability: December 31, 2020 2019 (in millions) Beginning balance $ 62.0 $ 57.7 Accruals 21.9 18.5 Settlements (14.1) (10.4) Adjustments to prior period accruals (3.5) (3.9) Foreign currency translation 0.4 0.1 Ending balance $ 66.7 $ 62.0

Reclassifications out of Accumu

Reclassifications out of Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2020
Reclassifications out of Accumulated Other Comprehensive Income [Abstract]
Disclosure of Reclassification Amount [Text Block]	12. RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Reclassification adjustments and other activity impacting accumulated other comprehensive income (loss) (AOCI) during the year ended December 31, 2020, December 31, 2019 and December 31, 2018 are as follows (in millions) : Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Loss on Cash Flow Hedges Total Balance at January 1, 2018 $ (252.0) $ (34.1) $ (6.6) $ (292.7) Other comprehensive income (loss) before reclassifications 41.9 (62.7) 5.4 (15.4) Income tax effect of other comprehensive income (loss) before reclassifications (8.4) — (0.2) (8.6) Amounts reclassified from accumulated other comprehensive loss into net loss 6.0 (a) 0.2 (0.4) (b) 5.8 Income taxes reclassified into net loss (1.4) — 0.7 (0.7) Net current period other comprehensive income (loss) 38.1 (62.5) 5.5 (18.9) Balance at December 31, 2018 $ (213.9) $ (96.6) $ (1.1) $ (311.6) Other comprehensive loss before reclassifications (61.5) (c) (4.6) (19.0) (85.1) Income tax effect of other comprehensive loss before reclassifications 5.6 — 6.3 11.9 Amounts reclassified from accumulated other comprehensive loss into net loss 12.5 (a) — (1.7) (b) 10.8 Income taxes reclassified into net loss (2.6) — (0.2) (2.8) Net current period other comprehensive loss (46.0) (4.6) (14.6) (65.2) Balance at December 31, 2019 $ (259.9) $ (101.2) $ (15.7) $ (376.8) Other comprehensive income (loss) before reclassifications (72.0) 0.1 (41.5) (113.4) Income tax effect of other comprehensive income (loss) before reclassifications 14.2 — 8.2 22.4 Amounts reclassified from accumulated other comprehensive loss into net loss 8.2 (a) — 35.8 (b) 44.0 Income taxes reclassified into net loss (1.5) — (6.9) (8.4) Net current period other comprehensive income (loss) (51.1) 0.1 (4.4) (55.4) Balance at December 31, 2020 $ (311.0) $ (101.1) $ (20.1) $ (432.2) (a) Subsequent to the adoption of ASU 2017-07 effective January 1, 2018, these amounts were reclassified from AOCI to Other, net for the years ended December 31, 2020, 2019 and 2018. The amount reclassified for 2019 includes a credit to AOCI of $7.4 million related to the net effect of the AAM Pension Payout Offer and the Casting Sale. See Note 7 - Employee Benefit Plans and Note 16 - Acquisitions and Dispositions for more detail. (b) The amounts reclassified from AOCI included $2.9 million in COGS, $14.2 million in interest expense and $18.7 million in other expense, net for the year ended December 31, 2020, $(2.4) million in COGS, $2.0 million in interest expense and $(1.3) million in other expense, net for the year ended December 31, 2019 and $2.8 million in COGS and $(3.2) million in interest expense for the year ended December 31, 2018. (c) ASU 2018-02 became effective on January 1, 2019, and we elected to reclassify the stranded tax effects caused by the 2017 Tax Cuts and Jobs Act, resulting in a decrease in Accumulated other comprehensive income (loss) of $27.7 million at January 1, 2019.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customers [Abstract]
Revenue from Contract with Customer [Text Block]	13. REVENUE FROM CONTRACTS WITH CUSTOMERS The guidance in ASC 606 - Revenue from Contracts with Customers is based on the principle that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. We are obligated under our contracts with customers to manufacture and supply products for use in our customers’ operations. We satisfy these performance obligations at the point in time that the customer obtains control of the products, which is the point in time that the customer is able to direct the use of, and obtain substantially all of the remaining benefits from, the products. This typically occurs upon shipment to the customer in accordance with purchase orders and delivery releases issued by our customers. There is judgment involved in determining when the customer obtains control of the products and we have utilized the following indicators of control in our assessment: • We have the present right to payment for the asset; • The customer has legal title to the asset; • We have transferred physical possession of the asset; • The customer has the significant risks and rewards of ownership of the asset; and • The customer has accepted the asset. Our product offerings by segment are as follows: • Driveline products consist primarily of front and rear axles, driveshafts, differential assemblies, clutch modules, balance shaft systems, disconnecting driveline technology, and electric and hybrid driveline products and systems for light trucks, sport utility vehicles (SUVs), crossover vehicles (CUVs), passenger cars and commercial vehicles; and • Metal Forming products consist primarily of axle and transmission shafts, ring and pinion gears, differential gears and assemblies, connecting rods and variable valve timing products for OEMs and Tier 1 automotive suppliers. Our contracts with customers, which are comprised of purchase orders and delivery releases issued by our customers, generally state the terms of the sale, including the quantity and price of each product purchased. Trade accounts receivable from our customers are generally due approximately 50 days from the date our customers receive our product. Our contracts typically do not contain variable consideration as the contracts include stated prices. We provide our customers with assurance type warranties, which are not separate performance obligations and are outside the scope of ASC 606. Refer to Note 11 - Commitments and Contingencies for further information on our product warranties. Disaggregation of Net Sales Net sales recognized from contracts with customers, disaggregated by segment and geographical location, are presented in the following table for the years ended December 31, 2020, 2019 and 2018. Net sales are attributed to regions based on the location of production. Intersegment sales have been excluded from the table. In 2019, we finalized the Casting Sale. The Casting Sale did not qualify for classification as discontinued operations, as it did not represent a strategic shift in our business that has had, or will have, a major effect on our operations and financial results. As such, we continue to present Casting as a segment in the tables below, which is comprised entirely of the U.S. casting operations that were included in the sale. Twelve Months Ended December 31, 2020 Driveline Metal Forming Casting Total North America $ 2,770.1 $ 855.0 $ — $ 3,625.1 Asia 433.7 43.8 — 477.5 Europe 352.5 198.0 — 550.5 South America 49.2 8.5 — 57.7 Total $ 3,605.5 $ 1,105.3 $ — $ 4,710.8 Twelve Months Ended December 31, 2019 Driveline Metal Forming Casting Total North America $ 3,466.3 $ 1,153.1 $ 627.7 $ 5,247.1 Asia 533.6 37.6 — 571.2 Europe 351.0 256.3 — 607.3 South America 98.8 6.5 — 105.3 Total $ 4,449.7 $ 1,453.5 $ 627.7 $ 6,530.9 Twelve Months Ended December 31, 2018 Driveline Metal Forming Casting Total North America $ 3,823.1 $ 1,275.9 $ 741.3 $ 5,840.3 Asia 634.4 43.9 — 678.3 Europe 329.0 293.1 — 622.1 South America 124.9 4.8 — 129.7 Total $ 4,911.4 $ 1,617.7 $ 741.3 $ 7,270.4 Contract Assets and Liabilities The following table summarizes our beginning and ending balances for accounts receivable and contract liabilities associated with our contracts with customers: Accounts Receivable, Net Contract Liabilities (Current) Contract Liabilities (Long-term) December 31, 2019 $ 815.4 $ 18.9 $ 83.7 December 31, 2020 793.2 23.4 91.0 Increase/(decrease) $ (22.2) $ 4.5 $ 7.3 Contract liabilities relate to deferred revenue associated with various settlements and commercial agreements for which we have future performance obligations to the customer. We recognize this deferred revenue into revenue over the life of the associated program as we satisfy our performance obligations to the customer. We do not have contract assets as defined in ASC 606. During the twelve months ended December 31, 2020 and December 31, 2019 we amortized $22.7 million and $48.6 million, respectively, of previously recorded contract liabilities into revenue as we satisfied performance obligations with our customers. Sales and Other Taxes ASC 606 provides a practical expedient that allows companies to exclude from the transaction price any amounts collected from customers for all sales (and other similar) taxes. We do not include sales and other taxes in our transaction price and thus do not recognize these amounts as revenue.

Leasing

Leasing	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases of Lessor Disclosure [Text Block]	14. LEASING When an agreement grants us the right to substantially all of the economic benefits associated with an identified asset, and we are able to direct the use of that asset throughout the term of the agreement, we have a lease. We lease certain facilities, manufacturing machinery and equipment, and furniture under finance leases, and we also lease certain commercial office and production facilities, manufacturing machinery and equipment, vehicles and other assets under operating leases. Some of our leases include options to extend or terminate the leases and these options have been included in the relevant lease term to the extent that they are reasonably certain to be exercised. The lease consideration for some of our facilities and machinery and equipment is variable, as it is based on various indices or usage of the underlying assets, respectively. Variable lease payments based on indices have been included in the related right-of-use assets and lease liabilities on our Consolidated Balance Sheets, while variable lease payments based on usage of the underlying asset have been excluded as they do not represent present rights or obligations. Lease cost consists of the following: Twelve Months Ended December 31, 2020 2019 (in millions) Finance lease cost Amortization of right-of-use assets $ 1.8 $ 1.0 Interest on lease liabilities 0.4 0.3 Total finance lease cost 2.2 1.3 Operating lease cost 32.7 28.9 Short-term lease cost 3.0 5.9 Variable lease cost 2.9 7.2 Total lease cost $ 40.8 $ 43.3 For the year ended December 31, 2020, $28.4 million and $10.2 million were recorded to Cost of goods sold (COGS) and Selling, general and administrative expenses (SG&A), respectively, related to our operating leases, on our Consolidated Statements of Operations, as compared to $31.9 million and $10.1 million, respectively, for the year ended December 31, 2019 and $28.4 million and $10.0 million, respectively, for the year ended December 31, 2018. The following table summarizes additional information related to our lease agreements. Twelve Months Ended December 31, 2020 2019 (in millions, except lease term and rate) Cash paid for amounts included in measurement of lease liabilities Operating cash flows from finance leases $ 0.3 $ 0.3 Operating cash flows from operating leases 35.1 29.0 Financing cash flows from finance leases 3.0 1.0 Weighted-average remaining lease term - finance leases 15.8 years 2.8 years Weighted-average remaining lease term - operating leases 8.7 years 9.2 years Weighted-average discount rate - finance leases 4.2 % 5.1 % Weighted-average discount rate - operating leases 5.7 % 6.1 % As the rate implicit in the lease is typically unknown, the discount rate used to determine the lease liability for the majority of our leases is the collateralized incremental borrowing rate in the applicable geographic area for a similar term and amount as the lease agreement. Future undiscounted minimum payments under non-cancelable leases are as follows: Finance Leases Operating Leases (in millions) 2021 $ 3.9 $ 27.9 2022 3.1 23.8 2023 1.6 17.3 2024 1.1 12.8 2025 1.1 10.4 Thereafter 18.4 57.4 Total future undiscounted minimum lease payments 29.2 149.6 Less: Impact of discounting (7.6) (32.6) Total $ 21.6 $ 117.0 The right-of-use assets and lease liabilities recorded on our Consolidated Balance Sheets are as follows: December 31, 2020 December 31, 2019 Finance Leases Operating Leases Finance Leases Operating Leases (in millions) (in millions) Property, plant and equipment, net $ 24.9 $ — $ 7.3 $ — Operating lease right-of-use assets — 116.6 — 118.5 Total $ 24.9 $ 116.6 $ 7.3 $ 118.5 Current portion of operating lease liabilities $ — $ 22.6 $ — $ 21.8 Accrued expenses and other 3.3 — 3.3 — Long-term portion of operating lease liabilities — 94.4 — 96.7 Postretirement benefits and other long-term liabilities 18.3 — 4.0 — Total $ 21.6 $ 117.0 $ 7.3 $ 118.5 ASC 842 Adoption of Practical Expedients We have elected to adopt, for all classes of underlying assets, a package of practical expedients provided under ASC 842 that allow us to 1) not reassess whether existing or expired contracts contain or contained a lease; 2) not reassess the lease classification (operating or financing) of our existing leases at adoption; and 3) not reassess initial direct costs for existing leases. ASC 842 also provides a practical expedient that allows companies to exclude balance sheet recognition of right-of-use assets and associated liabilities for lease terms of 12 months or less, which we have elected as part of our adoption of ASC 842 for all classes of underlying assets. We do not include right-of-use assets and operating lease liabilities on our Consolidated Balance Sheet for leases with a term of 12 months or less. We have also elected to adopt the practical expedient under ASC 842 to not separate lease and non-lease components in contracts that contain both. These lease agreements are accounted for as a single lease component for all classes of underlying assets. Leases Not Yet Commenced

Manufacturing Facility Fire and

Manufacturing Facility Fire and Insurance Recovery	12 Months Ended
	Dec. 31, 2020
Insurance Recoveries [Abstract]
Manufacturing Facility Fire and Insurance Recovery	15. MANUFACTURING FACILITY FIRE AND INSURANCE RECOVERY On September 22, 2020, a significant industrial fire occurred at our Malvern Manufacturing Facility in Ohio (Malvern Fire). All associates were evacuated safely and without injury. We continue to focus on managing this disruption and protecting continuity of supply to our customers, including utilizing production capacity and resources at other AAM facilities. Our insurance policies are expected to cover the repair, replacement or actual cash value of the assets that incurred loss or damage, less our applicable deductible of $1.0 million. In addition, our insurance policies are expected to provide coverage for interruption to our business, including lost or reduced profits and reimbursement for certain expenses and costs that are incurred relating to the fire. In 2020, we recorded $36.5 million of charges primarily related to site services and clean-up, expediting, asset repairs and other costs incurred to resume or relocate operations and ensure continuity of supply to our customers. In addition, we recorded $27.0 million of costs primarily associated with the write-down of PP&E as a result of damage from the fire. We also recorded an estimated insurance recovery of $54.2 million in the twelve months ended December 31, 2020, of which $43.1 million is included in Prepaid expenses and other in our Consolidated Balance Sheet as of December 31, 2020. This receivable is net of cash received in the fourth quarter of 2020 as an advance under our insurance policies of $11.1 million. This resulted in a net pre-tax impact to our Consolidated Statement of Operations of approximately $9.3 million in Cost of goods sold for the twelve months ended December 31, 2020, which includes our applicable deductible. In the fourth quarter of 2020, we determined that we will cease production at the Malvern Manufacturing Facility and relocate production capacity to other AAM manufacturing facilities during 2021. As such, we cannot estimate the total claim eligible costs that we will incur as a result of the Malvern Fire and the associated relocation of production capacity to other AAM manufacturing facilities. At December 31, 2020, we have estimated the amount of expected insurance proceeds recoverable in consideration of the policy provisions, carrying amount of the PP&E that was written-down, and claim eligible expenses incurred from the date of the fire. We expect the claim settlement process to continue through 2021, however, based on the provisions of the policy the process could continue into 2022. We will update our estimates as additional information becomes available, however, the actual impact on our results of operations, financial position or cash flows, or the timing of such impact, could differ from our estimates.

Acquisitions and Dispositions

Acquisitions and Dispositions	12 Months Ended
	Dec. 31, 2020
Mergers, Acquisitions and Dispositions [Abstract]
Mergers, Acquisitions and Dispositions Disclosures	16. ACQUISITIONS AND DISPOSITIONS Acquisition of Mitec In December 2019, AAM completed our acquisition of certain operations of Mitec Automotive AG (Mitec), under which we acquired $20.2 million of net assets for a purchase price of $9.4 million, which was funded entirely with available cash. We recognized a gain on bargain purchase of $10.8 million, which was primarily the result of Mitec's insolvency prior to the acquisition. This gain is presented in the Gain on bargain purchase of business line item in our Consolidated Statement of Operations for the year ended December 31, 2019. The operating results of Mitec for the period from our acquisition date through December 31, 2019, were insignificant to AAM's Consolidated Statement of Operations for this period. Further we have not disclosed pro forma revenue and earnings for the years ended December 31, 2019 and December 31, 2018, as the operating results of Mitec would be insignificant to AAM's consolidated results for these periods. Sale of U.S. Casting Operations In December 2019, we completed the Casting Sale. Upon closing the sale, we received net cash proceeds of $141.2 million subsequent to customary closing adjustments. Upon reclassification of the U.S. casting operations to held-for-sale in 2019, we recorded a pre-tax impairment charge of $225.0 million to reduce the carrying value of this business to fair value less cost to sell. The sale of the U.S. operations of our Casting segment did not qualify for classification as discontinued operations, as the sale did not represent a strategic shift in our business that has had, or will have, a major effect on our operations and financial results. Upon finalizing the sale, we recorded a loss on deconsolidation of the U.S. Casting entities of $21.3 million. During 2020, we finalized certain customary post-closing calculations associated with the Casting Sale, resulting in an additional loss on sale of $1.0 million. These losses are presented in Loss (gain) on sale of business in our Consolidated Statements of Operations for the years ended December 31, 2020 and 2019. Sale of Powertrain Aftermarket

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2020
Segments, Geographical Areas [Abstract]
Segment Reporting Disclosure [Text Block]	17. SEGMENT AND GEOGRAPHIC INFORMATION Our business is organized into Driveline and Metal Forming segments, with each representing a reportable segment under ASC 280 - Segment Reporting . In the fourth quarter of 2019, we completed the Casting Sale. The Casting Sale did not qualify for classification as discontinued operations, as it did not represent a strategic shift in our business that has had, or will have, a major effect on our operations and financial results. As such, we continue to present Casting as a segment in the tables below, which is comprised entirely of the U.S. casting operations that were included in the sale. The results of each segment are regularly reviewed by the chief operating decision maker to assess the performance of the segment and make decisions regarding the allocation of resources. Our product offerings by segment are as follows: • Driveline products consist primarily of front and rear axles, driveshafts, differential assemblies, clutch modules, balance shaft systems, disconnecting driveline technology, and electric and hybrid driveline products and systems for light trucks, SUVs, crossover vehicles (CUVs), passenger cars and commercial vehicles; and • Metal Forming products consist primarily of axle and transmission shafts, ring and pinion gears, differential gears and assemblies, connecting rods and variable valve timing products for OEMs and Tier 1 automotive suppliers. We use Segment Adjusted EBITDA as the measure of earnings to assess the performance of each segment and determine the resources to be allocated to the segments. Segment Adjusted EBITDA is defined as earnings before interest expense, income taxes, depreciation and amortization for our reportable segments, excluding the impact of restructuring and acquisition-related costs, debt refinancing and redemption costs, gain (loss) on the sale of a business, impairment charges, pension settlements, and non-recurring items. Year Ended December 31, 2020 Driveline Metal Forming Casting Corporate and Eliminations Total (in millions) Sales $ 3,635.6 $ 1,439.2 $ — $ — $ 5,074.8 Less: Intersegment sales 30.1 333.9 — — 364.0 Net external sales $ 3,605.5 $ 1,105.3 $ — $ — $ 4,710.8 Segment adjusted EBITDA $ 501.7 $ 218.1 $ — $ — $ 719.8 Depreciation and amortization $ 332.7 $ 189.2 $ — $ — $ 521.9 Capital expenditures $ 133.5 $ 73.7 $ — $ 8.4 $ 215.6 Total assets $ 3,231.3 $ 1,484.7 $ — $ 1,200.3 $ 5,916.3 Year Ended December 31, 2019 Driveline Metal Forming Casting Corporate and Eliminations Total Sales $ 4,550.2 $ 1,845.2 $ 669.2 $ — $ 7,064.6 Less: Intersegment sales 100.5 391.7 41.5 — 533.7 Net external sales $ 4,449.7 $ 1,453.5 $ 627.7 $ — $ 6,530.9 Segment adjusted EBITDA $ 610.8 $ 316.5 $ 43.0 $ — $ 970.3 Depreciation and amortization $ 307.7 $ 186.9 $ 42.3 $ — $ 536.9 Capital expenditures $ 283.8 $ 105.5 $ 28.5 $ 15.5 $ 433.3 Total assets $ 3,778.8 $ 1,900.0 $ — $ 965.8 $ 6,644.6 Year Ended December 31, 2018 Driveline Metal Forming Casting Corporate and Eliminations Total Sales $ 5,001.2 $ 2,046.0 $ 780.6 $ — $ 7,827.8 Less: Intersegment sales 89.8 428.3 39.3 — 557.4 Net external sales $ 4,911.4 $ 1,617.7 $ 741.3 $ — $ 7,270.4 Segment adjusted EBITDA $ 754.5 $ 376.5 $ 52.9 $ — $ 1,183.9 Depreciation and amortization $ 272.0 $ 192.6 $ 64.2 $ — $ 528.8 Capital expenditures $ 339.4 $ 138.3 $ 35.0 $ 12.0 $ 524.7 Total assets $ 3,796.6 $ 2,607.2 $ 521.5 $ 585.4 $ 7,510.7 Assets included in the Corporate and Eliminations column of the tables above represent AAM corporate assets, as well as eliminations of intercompany assets. The following table represents a reconciliation of Segment Adjusted EBITDA to consolidated loss before income taxes for the years ended December 31, 2020, 2019 and 2018: Year Ended December 31, 2020 2019 2018 (in millions) Segment adjusted EBITDA $ 719.8 $ 970.3 $ 1,183.9 Interest expense (212.3) (217.3) (216.3) Depreciation and amortization (521.9) (536.9) (528.8) Impairment charges (510.0) (665.0) (485.5) Restructuring and acquisition-related costs (67.2) (57.8) (78.9) Pension settlements (0.5) (9.8) — Gain (loss) on sale of business (1.0) (21.3) 15.5 Gain on bargain purchase of business — 10.8 — Gain on settlement of capital lease — — 15.6 Debt refinancing and redemption costs (7.9) (8.4) (19.4) Malvern Fire charges, net of recoveries (9.3) — — Other — 2.4 — Loss before income taxes $ (610.3) $ (533.0) $ (113.9) Financial information relating to our operations by geographic area is presented in the following table. Net sales are attributed to countries based upon location of production. Long-lived assets exclude deferred income taxes. December 31, 2020 2019 2018 (in millions) Net sales United States $ 1,816.7 $ 2,894.0 $ 3,293.2 Mexico 1,808.5 2,353.1 2,547.1 South America 57.6 105.3 129.7 China 317.1 315.4 373.4 All other Asia 160.4 255.8 304.9 Europe 550.5 607.3 622.1 Total net sales $ 4,710.8 $ 6,530.9 $ 7,270.4 Long-lived assets United States $ 2,099.4 $ 2,805.8 $ 3,612.3 Mexico 1,021.6 1,117.4 1,117.9 South America 49.7 61.9 70.6 China 185.1 191.4 177.6 All other Asia 84.2 106.8 101.0 Europe 491.5 439.4 356.0 Total long-lived assets $ 3,931.5 $ 4,722.7 $ 5,435.4

Unaudited Quarterly Financial D

Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	18. UNAUDITED QUARTERLY FINANCIAL DATA Three Months Ended, March 31 June 30 September 30 December 31 (in millions, except per share data) 2020 Net sales $ 1,343.5 $ 515.3 (3) $ 1,414.1 $ 1,437.9 Gross profit 195.3 (98.9) (3) 249.8 236.5 Net income (loss) (501.2) (2) (213.2) (3) 117.2 36.1 Net income (loss) attributable to AAM (501.3) (2) (213.2) (3) 117.2 36.0 Basic EPS (1) $ (4.45) (2) $ (1.88) (3) $ 0.99 $ 0.30 Diluted EPS (1) $ (4.45) (2) $ (1.88) (3) $ 0.99 $ 0.30 2019 Net sales $ 1,719.2 $ 1,704.3 $ 1,677.4 $ 1,430.0 Gross profit 222.2 248.3 248.7 183.4 Net income (loss) 41.7 52.7 (124.1) (4) (454.4) (5) Net income (loss) attributable to AAM 41.6 52.5 (124.2) (4) (454.4) (5) Basic EPS (1) $ 0.36 $ 0.45 $ (1.10) (4) $ (4.04) (5) Diluted EPS (1) $ 0.36 $ 0.45 $ (1.10) (4) $ (4.04) (5) (1) Full year basic and diluted EPS will not necessarily agree to the sum of the four quarters because each quarter is a separate calculation. (2) In the first quarter of 2020, we recorded a goodwill impairment charge of $510 million that was not subject to tax effect as a result of the significant decline in automotive production volumes due to the impact of COVID-19. (3) Many of our plant locations temporarily suspended production or experienced a significant reduction in production volumes during the second quarter of 2020 as a result of the impact of COVID-19. (4) In the third quarter of 2019, we recorded an impairment charge of approximately $178 million, net of tax, to reduce the carrying value of our U.S. Casting operations to fair value less cost to sell upon reclassification of the assets and liabilities to held-for-sale. (5) In the fourth quarter of 2019, we recorded a goodwill impairment charge of $440 million that was not subject to tax effect associated with the annual goodwill impairment test for our Metal Forming reporting unit. We also recorded a loss on the Casting Sale of approximately $17 million, net of tax, recognized a gain on bargain purchase of approximately $10.8 million, which was not subject to tax effect, associated with the acquisition of Mitec, and recognized a loss of approximately $8 million, net of tax, related to pension settlements.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	Schedule II - VALUATION AND QUALIFYING ACCOUNTS Additions - Balance at Charged to Acquisitions Balance Beginning of Costs and and At End of Period Expenses Disposals (a) Deductions Period (in millions) Year Ended December 31, 2018: Allowance for credit losses (1) $ 7.0 $ 6.6 $ — $ 5.2 $ 8.4 Allowance for deferred taxes (3) 180.4 12.9 — 10.0 183.3 Inventory valuation allowance (2) 17.3 22.2 — 25.1 14.4 Year Ended December 31, 2019: Allowance for credit losses (1) 8.4 13.2 (0.8) 12.8 8.0 Allowance for deferred taxes (4) 183.3 25.4 — 12.7 196.0 Inventory valuation allowance (2) 14.4 31.0 1.4 26.3 20.5 Year Ended December 31, 2020: Allowance for credit losses (1) 8.0 7.0 — 10.5 4.5 Allowance for deferred taxes (5) 196.0 19.8 — 7.8 208.0 Inventory valuation allowance (2) 20.5 31.7 — 28.8 23.4 (a ) Amounts represent reserves recognized in conjunction with our acquisition of Mitec as well as reserves derecognized in conjunction with the Casting Sale in 2019. (1) Uncollectible accounts charged off, net of recoveries. (2) Primarily relates to write-offs of excess and obsolete inventories, as well as adjustments for physical quantity discrepancies. (3) Primarily reflects a reduction in deferred tax assets at various foreign locations due to foreign currency translation. (4) Primarily reflects the reversal of a valuation allowance against certain deferred tax assets in foreign locations, as well as changes due to foreign currency translation. (5) Primarily reflects new net operating losses established with a corresponding valuation allowance at certain foreign locations, partially offset by adjustments to previously established valuation allowances and foreign currency translation.

Organization and Basis of Prese

Organization and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidation, Policy [Policy Text Block]	PRINCIPLES OF CONSOLIDATION We include the accounts of American Axle & Manufacturing Holdings, Inc. (Holdings) and its subsidiaries in our consolidated financial statements. We eliminate the effects of all intercompany transactions, balances and profits in our consolidation.
Cash and Cash Equivalents, Policy [Policy Text Block]	CASH AND CASH EQUIVALENTS Cash and cash equivalents include all cash balances, savings accounts, sweep accounts, and highly liquid investments in money market funds and certificates of deposit with maturities of 90 days or less at the time of purchase.
Revenue [Policy Text Block]	REVENUE RECOGNITION We are obligated under our contracts with customers to manufacture and supply products for use in our customers’ operations. We satisfy these performance obligations at the point in time that the customer obtains control of the products, which is the point in time that the customer is able to direct the use of, and obtain substantially all of the remaining benefits from, the products. This typically occurs upon shipment to the customer in accordance with purchase orders and delivery releases issued by our customers. See Note 13 - Revenue from Contracts with Customers for more detail on our revenue.
Accounts Receivable [Policy Text Block]	ACCOUNTS RECEIVABLE The majority of our accounts receivable are due from original equipment manufacturers (OEMs) in the automotive industry and are considered past due when payment is not received within the terms stated within the contract. Trade accounts receivable for our customers are generally due within approximately 50 days from the date our customers receive our product. Amounts due from customers are stated net of allowances for credit losses. We determine our allowances by considering our expected credit losses, in addition to factors such as our previous loss history, customers' ability to pay their obligations to us, and the condition of the general economy and industry as a whole. The allowance for credit losses was $4.5 million and $8.0 million as of December 31, 2020 and 2019, respectively. We write-off accounts receivable when they become uncollectible. We have agreements in place with factoring companies to sell customer receivables on a nonrecourse basis from certain of our locations in Europe. The factoring companies collect payment for the sold receivables and AAM has no continuing involvement with such receivables.
Property, Plant and Equipment, Preproduction Design and Development Costs [Policy Text Block]	CUSTOMER TOOLING AND PRE-PRODUCTION COSTS RELATED TO LONG-TERM SUPPLY AGREEMENTS Engineering, research and development (R&D), and other pre-production design and development costs for products sold on long-term supply arrangements are expensed as incurred unless we have a contractual guarantee for reimbursement from the customer. Reimbursements received for pre-production costs relating to awarded programs are deferred and recognized into revenue over the life of the associated program. Reimbursements received for pre-production costs relating to future programs that have not been awarded, or amounts received for programs that become discontinued prior to production, are recorded as a reduction of expense.
Inventory, Policy [Policy Text Block]	INVENTORIES We state our inventories at the lower of cost or net realizable value. The cost of our inventories is determined using the first-in-first-out (FIFO) method.  When we determine that our gross inventories exceed usage requirements, or if inventories become obsolete or otherwise not saleable, we record a provision for such loss as a component of our inventory accounts.
Maintenance, Repair & Operations (MRO) [Policy Text Block]	MAINTENANCE, REPAIR AND OPERATIONS (MRO) MATERIALS We include all spare parts and other durable materials for machinery and equipment that are consumed in the manufacturing process in MRO, which is included in Other assets and deferred charges in our Consolidated Balance Sheets. MRO assets are capitalized at actual cost and amortized on a straight-line basis over a useful life of six years, beginning from their purchase date. Repair costs for MRO assets are expensed in the period incurred. Amortization expense related to MRO was $62.4 million, $67.7 million and $62.4 million for 2020, 2019 and 2018, respectively.
Property, Plant and Equipment, Policy [Policy Text Block]	PROPERTY, PLANT AND EQUIPMENT (PP&E) We state property, plant and equipment, including amortizable tooling, at historical cost, as adjusted for impairments. Construction in progress includes costs incurred for the construction of buildings and building improvements, and machinery and equipment in process. Repair and maintenance costs that do not extend the useful life or otherwise improve the utility of the asset beyond its existing useful state are expensed in the period incurred. We record depreciation and tooling amortization using the straight-line method over the estimated useful lives of the depreciable assets. Depreciation and tooling amortization amounted to $372.9 million, $373.8 million and $367.0 million in 2020, 2019 and 2018, respectively.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	IMPAIRMENT OF LONG-LIVED ASSETS When impairment indicators exist, we evaluate the carrying value of long-lived assets for potential impairment. We consider projected future undiscounted cash flows, trends and other circumstances in making such estimates and evaluations. If impairment is deemed to exist, the carrying amount of the asset is adjusted based on its fair value. Recoverability of assets “held for use” is determined by comparing the forecasted undiscounted cash flows of the operations to which the assets relate to their carrying amount. When the carrying value of an asset group exceeds its fair value and is therefore nonrecoverable, those assets are written down to fair value. Fair value is determined based on market prices, when available, or a discounted cash flow analysis is performed using management estimates.
Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block]	GOODWILL We record goodwill when the purchase price of acquired businesses exceeds the value of their identifiable net tangible and intangible assets acquired. We test our goodwill annually as of October 1, or more frequently if necessary, for impairment in accordance with the accounting guidance for goodwill and other indefinite-lived intangibles. See Note 3 - Goodwill and Other Intangible Assets, for more detail on our goodwill.
Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block]	OTHER INTANGIBLE ASSETS Intangible assets are valued using primarily the relief from royalty method or the multi-period excess earnings method, both of which utilize significant unobservable inputs. These inputs are defined in the fair value hierarchy as Level 3 inputs, which require management to make estimates and assumptions regarding certain financial measures using forecasted or projected information. See Note 3 - Goodwill and Other Intangible Assets, for more detail on our intangible assets.
Lessee, Leases [Policy Text Block]	LEASING We record a right of use asset and lease liability when an agreement grants us the right to substantially all of the economic benefits associated with an identified asset, and we are able to direct the use of that asset throughout the term of the agreement, if such term exceeds 12 months. Options to extend or terminate the agreements have been included in the relevant lease term to the extent that they are reasonably certain to be exercised. For agreements that contain both lease and non-lease components, we account for these agreements as a single lease component for all classes of underlying assets. See Note 14 - Leasing for more detail on our leases
Debt, Policy [Policy Text Block]	DEBT ISSUANCE COSTS
Derivatives, Policy [Policy Text Block]	DERIVATIVES We recognize all derivatives on the balance sheet at fair value and we are not subject to master netting agreements. If a derivative qualifies under the accounting guidance as a hedge, depending on the nature of the hedge, changes in the fair value of the derivative are either offset against the change in fair value of the hedged asset, liability or firm commitment through earnings or recognized in other comprehensive income until the hedged item is recognized in earnings. Changes in the fair value of derivatives that do not qualify as hedges, are immediately recognized in earnings. See Note 5 - Derivatives and Risk Management, for more detail on our derivatives.
Foreign Currency Transactions and Translations Policy [Policy Text Block]	CURRENCY TRANSLATION AND REMEASUREMENT We translate the assets and liabilities of our foreign subsidiaries to United States (U.S.) dollars at end-of-period exchange rates. We translate the income statement elements of our foreign subsidiaries to U.S. dollars at average-period exchange rates. We report the effect of translation for our foreign subsidiaries that use the local currency as their functional currency as a separate component of stockholders' equity. Gains and losses resulting from the remeasurement of assets and liabilities in a currency other than the functional currency of a subsidiary are reported in current period income. We also report any gains and losses arising from transactions denominated in a currency other than the functional currency of a subsidiary in current period income. These foreign currency gains and losses resulted in net losses of $0.5 million, $6.5 million and $0.2 million for the years 2020, 2019 and 2018, respectively, in Other expense, net.
Postemployment Benefit Plans, Policy [Policy Text Block]	PENSION AND OTHER POSTRETIREMENT DEFINED BENEFIT PLANS Net pension and postretirement benefit expenses and the related liabilities are determined on an actuarial basis. These plan expenses and obligations are dependent on management's assumptions developed in consultation with our actuaries. We review these actuarial assumptions at least annually and make modifications when appropriate. See Note 7 - Employee Benefit Plans, for more detail on our pension and other postretirement defined benefit plans.
Share-based Payment Arrangement [Policy Text Block]	STOCK-BASED COMPENSATION AND OTHER INCENTIVE COMPENSATION We award stock-based compensation in the form of restricted stock units (RSUs) and performance shares. For non-performance based awards, the grant date fair value is measured as the stock price at the date of grant. For certain performance based awards, fair value is estimated using valuation techniques that require management to use estimates and assumptions. Certain awards require that management's estimates and assumptions be evaluated at each reporting date to determine if compensation expense related to the award should be adjusted, both on a catch-up and go-forward basis. Compensation expense is recognized over the period during which the requisite service is provided, referred to as the vesting period. We also award incentive compensation in the form of performance units (PU). We grant PU payable in cash to officers and certain other associates which vest in full over a three-year performance period and are based primarily on AAM's three-year cumulative free cash flow. See Note 8 - Stock-Based Compensation and Other Incentive Compensation, for more detail on our accounting for stock-based compensation and other incentive compensation.
Research and Development Expense, Policy [Policy Text Block]	RESEARCH AND DEVELOPMENT COSTS We expense R&D, as incurred, in selling, general and administrative expenses on our Consolidated Statements of Operations. R&D spending was $117.4 million, $144.7 million and $146.2 million in 2020, 2019 and 2018, respectively.
Income Tax, Policy [Policy Text Block]	DEFERRED INCOME TAX ASSETS AND LIABILITIES AND VALUATION ALLOWANCES Our deferred income tax assets and liabilities reflect the impact of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the basis of such assets and liabilities for income tax purposes. In accordance with the accounting guidance for income taxes, we review the likelihood that we will realize the benefit of deferred tax assets and estimate whether recoverability of our deferred tax assets is “more likely than not,” based on forecasts of taxable income in the related tax jurisdictions. In determining the requirement for a valuation allowance, the historical results, projected future operating results based upon approved business plans, eligible carry forward periods, and tax planning opportunities are considered, along with other relevant positive and negative evidence. If, based upon available evidence, it is more likely than not the deferred tax assets will not be realized, a valuation allowance is recorded. We record uncertain tax positions on the basis of a two-step process whereby: (1) we determine whether it is "more likely than not" that the tax positions will be sustained based on the technical merits of the position: and (2) for those positions that meet the "more likely than not" recognition threshold, we recognize the largest amount of tax benefit that is greater than 50% likely to be realized upon ultimate settlement with the related tax authority. We record interest and penalties on uncertain tax positions in income tax expense (benefit).
Earnings Per Share, Policy [Policy Text Block]	EARNINGS (LOSS) PER SHARE (EPS) We present EPS using the two-class method. This method allocates undistributed earnings between common shares and non-vested share based payment awards that entitle the holder to non-forfeitable dividend rights. Our participating securities include non-vested restricted stock units. See Note 10 - Earnings (Loss) Per Share (EPS), for more detail on our accounting for EPS.
Standard Product Warranty, Policy [Policy Text Block]	PRODUCT WARRANTY We record estimated warranty obligation liabilities at the dates our products are sold, using sales volumes and internal and external warranty data where there is no payment history and historical information about the average cost of warranty claims for customers with prior claims. We estimate our costs based on the contractual arrangements with our customers, existing customer warranty terms and internal and external warranty data, which includes a determination of our warranty claims and actions taken to improve product quality and minimize warranty claims. See Note 11 - Commitments and Contingencies, for detail on our accounting for product warranties.
Use of Estimates, Policy [Policy Text Block]	USE OF ESTIMATES In order to prepare consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP), we are required to make estimates and assumptions that affect the reported amounts and disclosures in our consolidated financial statements. Actual results could differ from those estimates.
New Accounting Pronouncements, Policy [Policy Text Block]	EFFECT OF NEW ACCOUNTING STANDARDS Standards Recently Adopted Accounting Standards Update 2018-15 On August 15, 2018, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) 2018-15 - Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract (Topic 350-40). ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a cloud computing or hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This guidance became effective at the beginning of our 2020 fiscal year and we adopted this guidance prospectively on January 1, 2020. The adoption of this standard did not have a material impact on our consolidated financial statements. Accounting Standards Update 2016-13 On June 16, 2016, the FASB issued 2016-13 - Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . ASU 2016-13 replaces the incurred loss model under previous guidance, and requires entities to consider expected credit losses, in addition to past events and current conditions when measuring credit losses. This guidance applies to certain of our financial instruments and is primarily applicable to our trade accounts receivable. We adopted this guidance on January 1, 2020, using a modified-retrospective transition method and the adoption of this standard did not have a material impact on our condensed consolidated financial statements. See the Statement of Stockholders' Equity for the implementation impact of ASU 2016-13. Standards Not Yet Adopted Accounting Standard Update 2020-04 On March 12, 2020, the FASB issued ASU 2020-04 - Reference Rate Reform (Topic 848) . This guidance provides optional expedients and exceptions that are intended to ease the burden of updating contracts to contain a new reference rate due to the discontinuation of the London Inter-Bank Offered Rate (LIBOR). This guidance is available immediately and may be implemented in any period prior to the guidance expiration on December 31, 2022. We are currently assessing which of our various contracts could require an update for a new reference rate and will determine the timing for our implementation of this guidance at the completion of that analysis. We expect to utilize certain of the optional expedients and exceptions available under ASU 2020-04 and we do not expect the adoption of this guidance to have a material impact on our financial statements. Accounting Standards Update 2019-12 On December 18, 2019, the FASB issued ASU 2019-12 - Income Taxes (Topic 740) . This guidance is intended to simplify the accounting and disclosure requirements for income taxes by removing various exceptions, and requires that the effect of an enacted change in tax laws or rates be included in the annual effective tax rate computation in the interim period of the enactment. This guidance becomes effective at the beginning of our 2021 fiscal year. We expect to adopt this guidance on January 1, 2021 and we do not expect that this standard will have a material impact on our consolidated financial statements. Other Regulatory Standards Adopted Securities and Exchange Commission (SEC) Rule In the first quarter of 2020, the SEC adopted "Financial Disclosures about Guarantors and Issuers of Guaranteed Securities and Affiliates Whose Securities Collateralize a Registrant's Securities," a rule that amends the financial disclosure requirements for guarantors and issuers of registered guaranteed securities. This rule eliminates the previous requirement to present guarantor financial statement information in the notes to the financial statements and allows for the disclosure of summarized financial information for the most recent year and interim period, as well as expanded non-financial disclosures, in Management's Discussion and Analysis (MD&A). The effective date for this rule is January 4, 2021, however, the SEC permitted voluntary compliance prior to this date and we elected to adopt the new disclosure requirements in the first quarter of 2020. As such, we no longer present guarantor financial statement information in the notes to the consolidated financial statements, but instead present the required information within MD&A. Coronavirus Aid, Relief, and Economic Security Act The Coronavirus Aid, Relief, and Economic Security Act (the CARES Act) was enacted on March 27, 2020 in the United States. The key provisions of the CARES Act, as applicable to AAM, included the following: • The ability to use net operating losses (NOLs) to offset income without the 80% taxable income limitation enacted as part of the Tax Cuts and Jobs Act (TCJA) of 2017, and to carry back NOLs to offset prior year income for five years. These are temporary provisions that apply to NOLs incurred in 2018, 2019 or 2020 tax years. We recognized a tax benefit of $14.4 million for the year ended December 31, 2020 related to our ability to carry back prior year losses, as well as projected current year losses, under the CARES Act to years with the previous 35% tax rate. We also received an income tax refund of approximately $31.0 million during 2020 as a result of the provisions of the CARES Act. • The ability to claim a current deduction for interest expense up to 50% of Adjusted Taxable Income (ATI) for tax years 2019 and 2020. This limitation was previously 30% of ATI pursuant to the TCJA, and will revert to 30% after 2020. • The ability to defer the payment of the employer portion of social security taxes incurred between March 27, 2020 and December 31, 2020, with 50% of the deferred amount to be paid by December 31, 2021 and the remaining 50% to be paid by December 31, 2022. For the year ended December 31, 2020, we deferred $15.2 million of social security taxes that will be paid in 2021 and 2022. • The ability to claim an Employee Retention Credit (ERC), which is a refundable payroll tax credit, for 50% of qualified wages or benefits, subject to certain limitations, that are paid to an employee when they are not providing services due to Novel Coronavirus (COVID-19). The ERC applies to qualified wages paid or incurred during the period March 13, 2020 through December 31, 2020 and is available to eligible employers whose operations were fully or partially suspended due to COVID-19, or whose gross receipts declined by more than 50% when compared to the applicable period in the prior year.

Organization and Basis of Pre_2

Organization and Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Inventory, Current [Table Text Block]	Inventories consist of the following: December 31, 2020 2019 (in millions) Raw materials and work-in-progress $ 276.2 $ 310.4 Finished goods 70.4 83.7 Gross inventories 346.6 394.1 Inventory valuation reserves (23.4) (20.5) Inventories, net $ 323.2 $ 373.6
Property, Plant and Equipment [Table Text Block]	Property, plant and equipment consists of the following: Estimated December 31, Useful Lives 2020 2019 (years) (in millions) Land Indefinite $ 49.2 $ 45.1 Land improvements 10-15 26.3 24.4 Buildings and building improvements 15-40 554.3 512.7 Machinery and equipment 3-12 3,703.7 3,645.6 Construction in progress 122.1 219.5 4,455.6 4,447.3 Accumulated depreciation and amortization (2,291.8) (2,088.9) Property, plant and equipment, net $ 2,163.8 $ 2,358.4

Restructuring and Acquisition_2

Restructuring and Acquisition-Related Costs (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs [Table Text Block]	A summary of our restructuring activity for the years 2020, 2019 and 2018 is shown below: Severance Charges Implementation Costs Asset Impairment Charges Total (in millions) Accrual at January 1, 2018 $ 0.3 $ — $ — $ 0.3 Charges 2.5 11.7 30.0 44.2 Cash utilization (0.4) (10.1) — (10.5) Non-cash utilization — — (30.0) (30.0) Accrual at December 31, 2018 2.4 1.6 — 4.0 Charges 19.4 20.4 — 39.8 Cash utilization (17.0) (14.6) — (31.6) Non-cash utilization — — — — Accrual at December 31, 2019 4.8 7.4 — 12.2 Charges 22.3 36.1 — 58.4 Cash utilization (25.4) (33.7) — (59.1) Non-cash utilization — — — — Accrual at December 31, 2020 $ 1.7 $ 9.8 $ — $ 11.5
Business Combination, Separately Recognized Transactions [Table Text Block]	The following table represents a summary of charges incurred in 2020, 2019 and 2018 associated with acquisition and integration costs: Acquisition-Related Costs Severance Charges Integration Expenses Total 2020 Charges $ — $ — $ 8.8 $ 8.8 2019 Charges 1.8 — 16.2 18.0 2018 Charges 1.2 0.5 33.0 34.7

Schedule of Goodwill and Finite

Schedule of Goodwill and Finite Lived Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets [Abstract]
Schedule of Goodwill [Table Text Block]	Goodwill The following table provides a reconciliation of changes in goodwill for the year ended December 31, 2020 and the year ended December 31, 2019: Driveline Metal Forming Powertrain Consolidated (in millions) Balance as of January 1, 2019 $ 212.1 $ 552.4 $ 377.3 $ 1,141.8 Reorganization 187.2 190.1 (377.3) — Impairment charge — (440.0) — (440.0) Foreign currency translation (1.0) (1.7) — (2.7) Balance as of December 31, 2019 $ 398.3 $ 300.8 $ — $ 699.1 Impairment charge (210.8) (299.2) — (510.0) Foreign currency translation (1.8) (1.6) — (3.4) Balance as of December 31, 2020 $ 185.7 $ — $ — $ 185.7
Schedule of Finite-Lived Intangible Assets [Table Text Block]	The following table provides a reconciliation of the gross carrying amount and associated accumulated amortization for AAM's other intangible assets, which are all subject to amortization, as of December 31, 2020 and December 31, 2019: December 31, December 31, 2020 2019 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (in millions) Capitalized computer software $ 47.6 $ (33.9) $ 13.7 $ 45.8 $ (27.6) $ 18.2 Customer platforms 856.2 (237.9) 618.3 856.2 (174.4) 681.8 Customer relationships 53.0 (12.8) 40.2 53.0 (9.4) 43.6 Technology and other 156.7 (48.2) 108.5 156.0 (35.1) 120.9 Total $ 1,113.5 $ (332.8) $ 780.7 $ 1,111.0 $ (246.5) $ 864.5

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	Long-term debt, net consists of the following: December 31, 2020 2019 (in millions) Revolving credit facility $ — $ — Term Loan A Facility 323.0 340.0 Term Loan B Facility 1,088.8 1,188.8 6.875% Notes due 2028 400.0 — 6.625% Notes due 2022 — 450.0 6.50% Notes due 2027 500.0 500.0 6.25% Notes due 2026 400.0 400.0 6.25% Notes due 2025 700.0 700.0 Foreign credit facilities and other 88.8 113.4 Total debt 3,500.6 3,692.2 Less: Current portion of long-term debt 13.7 28.7 Long-term debt 3,486.9 3,663.5 Less: Debt issuance costs 45.6 51.2 Long-term debt, net $ 3,441.3 $ 3,612.3
Schedule of Maturities of Long-term Debt [Table Text Block]	DEBT MATURITIES Aggregate maturities of long-term debt are as follows (in millions) : 2021 $ 32.2 2022 34.2 2023 73.4 2024 1,360.8 2025 700.0 Thereafter 1,300.0 Total $ 3,500.6

Gain (Loss) on Derivative Instr

Gain (Loss) on Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) [Table Text Block]	The following table summarizes the reclassification of pre-tax derivative gains (losses) into net income (loss) from accumulated other comprehensive income (loss) for those derivative instruments designated as cash flow hedges under Accounting Standards Codification 815 - Derivatives and Hedging (ASC 815): Location of Gain (Loss) Reclassified into Net Income (Loss) Gain (Loss) Reclassified During the Twelve Months Ended December 31, Total of Financial Statement Line Item Gain (Loss) Expected to be Reclassified During the Next 12 Months 2020 2019 2018 2020 (in millions) Currency forward contracts Cost of Goods Sold $ (2.9) $ 2.4 $ (2.8) $ 4,128.1 $ 5.7 Fixed-to-fixed cross-currency swap Other Expense, net (18.7) 1.3 — (5.2) 1.7 Variable-to-fixed interest rate swap Interest Expense (14.2) (2.0) 3.2 (212.3) (15.3)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) [Table Text Block]	The following table summarizes the amount and location of gains (losses) recognized in the Consolidated Statements of Operations for those derivative instruments not designated as hedging instruments under ASC 815: Location of Gain (Loss) Recognized in Net Income (Loss) Gain (Loss) Recognized During the Twelve Months Ended December 31, Total of Financial Statement Line Item 2020 2019 2018 2020 (in millions) Currency forward contracts Cost of Goods Sold $ (6.7) $ 3.9 $ 1.6 $ 4,128.1 Currency forward contracts Other Expense, Net 0.6 — 1.4 (5.2)

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	FINANCIAL INSTRUMENTS The estimated fair values of our financial assets and liabilities that are recognized at fair value on a recurring basis, using available market information and other observable data are as follows: December 31, 2020 December 31, 2019 Carrying Amount Fair Value Carrying Amount Fair Value Input (in millions) Balance Sheet Classification Cash equivalents $ 206.7 $ 206.7 $ 271.3 $ 271.3 Level 1 Prepaid expenses and other Cash flow hedges - currency forward contracts 5.8 5.8 5.0 5.0 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 4.9 4.9 0.9 0.9 Level 2 Nondesignated - currency forward contracts 0.2 0.2 1.9 1.9 Level 2 Other assets and deferred charges Cash flow hedges - currency forward contracts 3.3 3.3 3.4 3.4 Level 2 Cash flow hedges - fixed-to-fixed cross-currency swap — — 1.1 1.1 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 8.6 8.6 2.2 2.2 Level 2 Accrued expenses and other Cash flow hedges - currency forward contracts 0.1 0.1 — — Level 2 Cash flow hedges - variable-to-fixed interest rate swap 17.8 17.8 7.9 7.9 Level 2 Postretirement benefits and other long-term liabilities Cash flow hedges - currency forward contracts 0.1 0.1 — — Level 2 Cash flow hedges - fixed-to-fixed cross-currency swap 20.6 20.6 — — Level 2 Cash flow hedges - variable-to-fixed interest rate swap 32.1 32.1 18.4 18.4 Level 2
Fair Value, by Balance Sheet Grouping [Table Text Block]	We estimated the fair value of our outstanding debt using available market information and other observable data to be as follows: December 31, 2020 December 31, 2019 Carrying Amount Fair Value Carrying Amount Fair Value Input (in millions) Revolving Credit Facility $ — $ — $ — $ — Level 2 Term Loan A Facility 323.0 318.6 340.0 337.9 Level 2 Term Loan B Facility 1,088.8 1,071.1 1,188.8 1,174.0 Level 2 6.875% Notes due 2028 400.0 426.0 — — Level 2 6.625% Notes due 2022 — — 450.0 455.4 Level 2 6.50% Notes due 2027 500.0 523.8 500.0 516.3 Level 2 6.25% Notes due 2026 400.0 411.0 400.0 409.0 Level 2 6.25% Notes due 2025 700.0 724.3 700.0 716.6 Level 2

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined Benefit Plan, Assumptions [Table Text Block]	Pension Benefits OPEB 2020 2019 2018 2020 2019 2018 U.S. U.K. U.S. U.K. U.S. U.K. Discount rate 2.50 % 1.55 % 3.40 % 2.05 % 4.30 % 2.95 % 2.55 % 3.35 % 4.35 % Expected return on plan assets 7.25 % 4.00 % 7.25 % 4.00 % 7.50 % 5.10 % N/A N/A N/A Rate of compensation increase N/A 3.15 % N/A 3.15 % 4.00 % 3.40 % 4.00 % 4.00 % 4.00 %
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan [Table Text Block]	The following table summarizes the changes in projected benefit obligations and plan assets and reconciles the funded status of the benefit plans, which is the net benefit plan liability: Pension Benefits OPEB December 31, December 31, 2020 2019 2020 2019 (in millions) Change in benefit obligation Benefit obligation at beginning of year $ 740.2 $ 734.5 $ 549.1 $ 537.3 Service cost 2.0 1.5 0.4 0.3 Interest cost 21.4 28.0 10.2 12.8 Actuarial loss 63.5 71.5 25.3 11.9 Change in GM portion of OPEB obligation — — 14.0 3.1 Participant contributions 0.2 0.2 — — Curtailments — (1.9) — — Settlements (3.3) (28.8) — — Benefit payments (34.4) (44.1) (12.5) (15.5) Sale of business — (26.2) — (0.8) Currency fluctuations 8.7 5.5 — — Other 0.6 — — — Net change 58.7 5.7 37.4 11.8 Benefit obligation at end of year $ 798.9 $ 740.2 $ 586.5 $ 549.1 Change in plan assets Fair value of plan assets at beginning of year $ 636.6 $ 625.8 $ — $ — Actual return on plan assets 55.7 87.5 — — Employer contributions 8.5 10.0 12.5 15.5 Participant contributions 0.2 0.2 — — Benefit payments (34.4) (44.1) (12.5) (15.5) Settlements (3.3) (28.8) — — Sale of business — (20.7) — — Currency fluctuations 6.6 6.7 — — Net change 33.3 10.8 — — Fair value of plan assets at end of year $ 669.9 $ 636.6 $ — $ —
Schedule of Amounts Recognized in Balance Sheet [Table Text Block]	Amounts recognized in our Consolidated Balance Sheets are as follows: Pension Benefits OPEB December 31, December 31, 2020 2019 2020 2019 (in millions) Noncurrent assets $ 20.2 $ 21.2 $ — $ — Current liabilities (8.0) (6.6) (29.8) (29.1) Noncurrent liabilities (141.2) (118.2) (556.7) (520.0) Net liability $ (129.0) $ (103.6) $ (586.5) $ (549.1)
Schedule of Pre-tax Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]	Pre-tax amounts recorded in accumulated other comprehensive income (loss) (AOCI), not yet recognized in net periodic benefit cost (credit) as of December 31, 2020 and 2019, consists of: Pension Benefits OPEB December 31, December 31, 2020 2019 2020 2019 (in millions) Net actuarial gain (loss) $ (278.0) $ (239.2) $ (4.9) $ 19.3 Net prior service credit (cost) (1.8) (1.2) 3.1 4.7 Total amounts recorded $ (279.8) $ (240.4) $ (1.8) $ 24.0
Schedule of Net Benefit Costs [Table Text Block]	The components of net periodic benefit cost (credit) are as follows: Pension Benefits OPEB 2020 2019 2018 2020 2019 2018 (in millions) Service cost $ 2.0 $ 1.5 $ 2.6 $ 0.4 $ 0.3 $ 0.4 Interest cost 21.4 28.0 27.3 10.2 12.8 12.4 Expected asset return (38.4) (41.1) (45.8) — — — Amortized actuarial loss 8.6 6.4 7.8 1.0 0.1 0.8 Amortized prior service cost (credit) 0.1 — 0.1 (1.5) (1.5) (2.7) Curtailment loss (gain) — — 3.2 — — (0.6) Settlement charge 0.5 10.4 0.4 — — — Net periodic benefit cost (credit) $ (5.8) $ 5.2 $ (4.4) $ 10.1 $ 11.7 $ 10.3
Schedule of Allocation of Plan Assets [Table Text Block]	U.S. U.K. Target Target 2020 2019 Allocation 2020 2019 Allocation Equity securities 34.7 % 35.2 % 25% - 40% 21.8 % 22.7 % 15% - 30% Fixed income securities 57.3 52.9 50% - 70% 65.9 66.8 60% - 80% Alternative assets 7.3 10.4 5% - 15% 8.9 9.4 5% - 15% Cash 0.7 1.5 0% - 5% 3.4 1.1 0% - 5% Total 100.0 % 100.0 % 100.0 % 100.0 % The primary objective of our pension plan assets is to provide a source of retirement income for participants and beneficiaries. Our primary financial objectives for the pension plan assets have been established in conjunction with a comprehensive review of our current and projected financial requirements. These objectives include having the ability to pay all future benefits and expenses when due, maintaining flexibility and minimizing volatility. These objectives are based on a long-term investment horizon. Defined Benefit Pension Plan Assets Investments in our defined benefit plans are stated at fair value. Level 1 assets are valued using quoted market prices that represent the asset value of the shares held by the trusts. The level 2 assets are investments in pooled funds, which are valued using a model to reflect the valuation of their underlying assets that are publicly traded with observable values. The fair values of our pension plan assets are as follows: December 31, 2020 Asset Categories Level 1 Level 2 Level 3 Total (in millions) Cash and Cash Equivalents $ 7.4 $ 2.9 $ — $ 10.3 Equity U.S. Large Cap 88.1 2.7 — 90.8 U.S. Small/Mid Cap 20.5 — — 20.5 World Equity 87.0 7.8 — 94.8 Fixed Income Securities Government & Agencies 84.1 45.9 — 130.0 Corporate Bonds - Investment Grade 219.0 2.7 — 221.7 Corporate Bonds - Non-investment Grade 22.4 0.7 — 23.1 Emerging Market Debt 21.1 1.1 — 22.2 Other 3.6 0.3 — 3.9 Other Property Funds (a) — — — 44.2 Liquid Alternatives Fund (a) — — — 1.8 Structured Credit Fund (a) — — — 6.6 Total Plan Assets $ 553.2 $ 64.1 $ — $ 669.9 December 31, 2019 Asset Categories Level 1 Level 2 Level 3 Total (in millions) Cash and Cash Equivalents $ 7.3 $ 2.0 $ — $ 9.3 Equity U.S. Large Cap 82.4 3.0 — 85.4 U.S. Small/Mid Cap 22.7 — — 22.7 World Equity 88.1 4.7 — 92.8 Fixed Income Securities Government & Agencies 74.3 45.0 — 119.3 Corporate Bonds - Investment Grade 185.8 0.6 — 186.4 Corporate Bonds - Non-investment Grade 21.7 1.1 — 22.8 Emerging Market Debt 20.4 0.7 — 21.1 Other 6.9 4.8 — 11.7 Other Property Funds (a) — — — 57.3 Liquid Alternatives Fund (a) — — — 1.6 Structured Credit Fund (a) — — — 6.2 Total Plan Assets $ 509.6 $ 61.9 $ — $ 636.6 (a) In accordance with ASC 820 - Fair Value Measurement certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the Consolidated Balance Sheets.

Stock Based Compensation and _2

Stock Based Compensation and Other Incentive Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]	The following table summarizes activity relating to our RSUs: Weighted-Average Number of Grant Date Fair Shares/Units Value per Share/Unit (in millions, except per share data) Outstanding at January 1, 2018 2.5 $ 18.35 Granted 1.7 14.57 Vested (0.4) 24.16 Canceled (0.3) 15.84 Outstanding at December 31, 2018 3.5 $ 16.00 Granted 1.0 15.78 Vested (0.7) 15.53 Canceled (0.7) 16.05 Outstanding at December 31, 2019 3.1 $ 16.03 Granted 3.2 5.08 Vested (0.8) 18.22 Canceled (0.6) 10.33 Outstanding at December 31, 2020 4.9 $ 9.20
Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block]	The following table summarizes activity relating to our performance shares: Weighted Average Number of Grant Date Fair Shares Value per Share EBITDA Awards (in millions, except per share data) Outstanding at January 1, 2018 0.6 $ 33.91 Granted — — Vested (0.1) 37.67 Canceled — — Outstanding at December 31, 2018 0.5 $ 34.49 Granted — — Vested (0.4) 31.21 Canceled — — Outstanding at December 31, 2019 0.1 $ 39.09 Granted — — Vested (0.1) 39.09 Canceled — — Outstanding at December 31, 2020 — $ — TSR Awards Outstanding at January 1, 2018 0.6 $ 20.93 Granted 0.3 13.91 Vested (0.1) 31.21 Canceled — — Outstanding at December 31, 2018 0.8 $ 16.25 Granted 0.3 24.36 Vested (0.2) 17.54 Canceled (0.1) 20.49 Outstanding at December 31, 2019 0.8 $ 20.13 Granted — — Vested (0.2) 24.63 Canceled — — Outstanding at December 31, 2020 0.6 $ 18.86 Free Cash Flow Awards Outstanding at January 1, 2018 — $ — Granted 0.3 14.28 Vested — — Canceled — — Outstanding at December 31, 2018 0.3 $ 14.28 Granted — — Vested — — Canceled — — Outstanding at December 31, 2019 0.3 $ 14.28 Granted 0.9 5.18 Vested — — Canceled — — Outstanding at December 31, 2020 1.2 $ 7.50

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	The components of income (loss) before income taxes are as follows: 2020 2019 2018 (in millions) U.S. loss $ (721.6) $ (889.0) $ (549.4) Non - U.S. income 111.3 356.0 435.5 Total loss before income taxes $ (610.3) $ (533.0) $ (113.9)
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The following is a summary of the components of our provision for income taxes: 2020 2019 2018 (in millions) Current Federal $ 2.0 $ (11.9) $ (81.5) State and local 0.5 0.1 3.2 Foreign 20.2 49.3 46.5 Total current $ 22.7 $ 37.5 $ (31.8) Deferred Federal $ (60.0) $ (73.5) $ (5.1) State and local (0.7) (1.5) (6.7) Foreign (11.2) (11.4) (13.5) Total deferred (71.9) (86.4) (25.3) Total income tax benefit $ (49.2) $ (48.9) $ (57.1)
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following is a reconciliation of income taxes calculated at the U.S. federal statutory income tax rate of 21% in 2020, 2019 and 2018 to our provision for income taxes: 2020 2019 2018 (in millions) Federal statutory $ (128.2) $ (111.9) $ (23.9) Foreign income taxes (21.5) (40.2) (39.7) Change in enacted tax rate 2.1 0.2 (8.3) Transition tax — (7.5) 5.8 State and local (5.0) (20.0) (12.8) Tax credits (9.7) (9.6) (20.1) Valuation allowance 19.8 12.6 12.9 Goodwill impairment 107.1 92.4 21.6 Withholding taxes 5.6 4.0 6.6 U.S. tax on unremitted foreign earnings — (2.8) 4.1 Tax benefit on loss carryback (14.4) — — Global intangible low-taxed income 2.3 31.1 8.0 Uncertain tax positions (8.8) 5.9 (9.8) Other 1.5 (3.1) (1.5) Effective income tax benefit $ (49.2) $ (48.9) $ (57.1)
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The approximate tax effect of each significant type of temporary difference and carryforward that results in a deferred tax asset or liability is as follows: December 31, 2020 2019 (in millions) Deferred tax assets Employee benefits $ 162.4 $ 149.4 Inventory 32.9 27.3 Net operating loss (NOL) carryforwards 221.4 201.7 Tax credit carryforwards 88.6 47.8 Capital allowance carryforwards 10.2 9.3 Capitalized expenditures 45.9 42.9 Interest carryforward 10.4 43.9 Operating lease liabilities 25.7 27.1 Other 50.6 42.7 Valuation allowances (208.0) (196.0) Deferred tax assets $ 440.1 $ 396.1 Deferred tax liabilities Other intangible assets (179.9) (199.7) Fixed assets (137.5) (120.7) Operating lease right-of-use assets (25.6) (27.1) Other (2.5) (4.1) Deferred tax liabilities $ (345.5) $ (351.6) Deferred tax assets, net $ 94.6 $ 44.5 Deferred tax assets and liabilities recognized in our Consolidated Balance Sheets are as follows: December 31, 2020 2019 (in millions) U.S. federal and state deferred tax asset, net $ 44.1 $ 5.0 Other foreign deferred tax asset, net 50.5 39.5 Deferred tax asset, net $ 94.6 $ 44.5
Schedule of Unrecognized Income Tax Benefits [Table Text Block]	A reconciliation of the beginning and ending amounts of unrecognized income tax benefits is as follows: Unrecognized Income Tax Interest and Benefits Penalties (in millions) Balance at January 1, 2018 $ 47.7 $ 7.5 Increase in prior year tax positions 5.6 3.5 Decrease in prior year tax positions (16.9) (2.5) Increase in current year tax positions 6.0 — Settlement (3.7) (1.6) Balance at December 31, 2018 $ 38.7 $ 6.9 Increase in prior year tax positions 0.2 4.5 Decrease in prior year tax positions (3.1) (0.1) Increase in current year tax positions 4.4 — Foreign currency remeasurement adjustment 0.9 0.2 Balance at December 31, 2019 $ 41.1 $ 11.5 Increase in prior year tax positions 0.2 — Decrease in prior year tax positions (6.6) (1.7) Increase in current year tax positions 0.7 — Settlement (12.2) (6.3) Foreign currency remeasurement adjustment (3.0) (1.5) Balance at December 31, 2020 $ 20.2 $ 2.0

Earnings Per Share (EPS) (Table

Earnings Per Share (EPS) (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table sets forth the computation of our basic and diluted EPS available to shareholders of common stock (excluding participating securities): 2020 2019 2018 (in millions, except per share data) Numerator Net loss attributable to AAM $ (561.3) $ (484.5) $ (57.5) Less: Net loss allocated to participating securities — — — Net loss attributable to common shareholders - Basic and Dilutive $ (561.3) $ (484.5) $ (57.5) Denominators Basic common shares outstanding - Weighted-average shares outstanding 117.9 115.6 115.0 Less: Participating securities (4.8) (3.3) (3.4) Weighted-average common shares outstanding 113.1 112.3 111.6 Effect of dilutive securities - Dilutive stock-based compensation — — — Diluted shares outstanding - Adjusted weighted-average shares after assumed conversions 113.1 112.3 111.6 Basic EPS $ (4.96) $ (4.31) $ (0.51) Diluted EPS $ (4.96) $ (4.31) $ (0.51)

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Schedule of Product Warranty Liability [Table Text Block]	The following table provides a reconciliation of changes in the product warranty liability: December 31, 2020 2019 (in millions) Beginning balance $ 62.0 $ 57.7 Accruals 21.9 18.5 Settlements (14.1) (10.4) Adjustments to prior period accruals (3.5) (3.9) Foreign currency translation 0.4 0.1 Ending balance $ 66.7 $ 62.0

Reclassifications out of Accu_2

Reclassifications out of Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2020
Reclassifications out of Accumulated Other Comprehensive Income [Abstract]
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	Reclassification adjustments and other activity impacting accumulated other comprehensive income (loss) (AOCI) during the year ended December 31, 2020, December 31, 2019 and December 31, 2018 are as follows (in millions) : Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Loss on Cash Flow Hedges Total Balance at January 1, 2018 $ (252.0) $ (34.1) $ (6.6) $ (292.7) Other comprehensive income (loss) before reclassifications 41.9 (62.7) 5.4 (15.4) Income tax effect of other comprehensive income (loss) before reclassifications (8.4) — (0.2) (8.6) Amounts reclassified from accumulated other comprehensive loss into net loss 6.0 (a) 0.2 (0.4) (b) 5.8 Income taxes reclassified into net loss (1.4) — 0.7 (0.7) Net current period other comprehensive income (loss) 38.1 (62.5) 5.5 (18.9) Balance at December 31, 2018 $ (213.9) $ (96.6) $ (1.1) $ (311.6) Other comprehensive loss before reclassifications (61.5) (c) (4.6) (19.0) (85.1) Income tax effect of other comprehensive loss before reclassifications 5.6 — 6.3 11.9 Amounts reclassified from accumulated other comprehensive loss into net loss 12.5 (a) — (1.7) (b) 10.8 Income taxes reclassified into net loss (2.6) — (0.2) (2.8) Net current period other comprehensive loss (46.0) (4.6) (14.6) (65.2) Balance at December 31, 2019 $ (259.9) $ (101.2) $ (15.7) $ (376.8) Other comprehensive income (loss) before reclassifications (72.0) 0.1 (41.5) (113.4) Income tax effect of other comprehensive income (loss) before reclassifications 14.2 — 8.2 22.4 Amounts reclassified from accumulated other comprehensive loss into net loss 8.2 (a) — 35.8 (b) 44.0 Income taxes reclassified into net loss (1.5) — (6.9) (8.4) Net current period other comprehensive income (loss) (51.1) 0.1 (4.4) (55.4) Balance at December 31, 2020 $ (311.0) $ (101.1) $ (20.1) $ (432.2) (a) Subsequent to the adoption of ASU 2017-07 effective January 1, 2018, these amounts were reclassified from AOCI to Other, net for the years ended December 31, 2020, 2019 and 2018. The amount reclassified for 2019 includes a credit to AOCI of $7.4 million related to the net effect of the AAM Pension Payout Offer and the Casting Sale. See Note 7 - Employee Benefit Plans and Note 16 - Acquisitions and Dispositions for more detail. (b) The amounts reclassified from AOCI included $2.9 million in COGS, $14.2 million in interest expense and $18.7 million in other expense, net for the year ended December 31, 2020, $(2.4) million in COGS, $2.0 million in interest expense and $(1.3) million in other expense, net for the year ended December 31, 2019 and $2.8 million in COGS and $(3.2) million in interest expense for the year ended December 31, 2018. (c) ASU 2018-02 became effective on January 1, 2019, and we elected to reclassify the stranded tax effects caused by the 2017 Tax Cuts and Jobs Act, resulting in a decrease in Accumulated other comprehensive income (loss) of $27.7 million at January 1, 2019.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customers [Abstract]
Disaggregation of Revenue [Table Text Block]	Disaggregation of Net Sales Net sales recognized from contracts with customers, disaggregated by segment and geographical location, are presented in the following table for the years ended December 31, 2020, 2019 and 2018. Net sales are attributed to regions based on the location of production. Intersegment sales have been excluded from the table. In 2019, we finalized the Casting Sale. The Casting Sale did not qualify for classification as discontinued operations, as it did not represent a strategic shift in our business that has had, or will have, a major effect on our operations and financial results. As such, we continue to present Casting as a segment in the tables below, which is comprised entirely of the U.S. casting operations that were included in the sale. Twelve Months Ended December 31, 2020 Driveline Metal Forming Casting Total North America $ 2,770.1 $ 855.0 $ — $ 3,625.1 Asia 433.7 43.8 — 477.5 Europe 352.5 198.0 — 550.5 South America 49.2 8.5 — 57.7 Total $ 3,605.5 $ 1,105.3 $ — $ 4,710.8 Twelve Months Ended December 31, 2019 Driveline Metal Forming Casting Total North America $ 3,466.3 $ 1,153.1 $ 627.7 $ 5,247.1 Asia 533.6 37.6 — 571.2 Europe 351.0 256.3 — 607.3 South America 98.8 6.5 — 105.3 Total $ 4,449.7 $ 1,453.5 $ 627.7 $ 6,530.9 Twelve Months Ended December 31, 2018 Driveline Metal Forming Casting Total North America $ 3,823.1 $ 1,275.9 $ 741.3 $ 5,840.3 Asia 634.4 43.9 — 678.3 Europe 329.0 293.1 — 622.1 South America 124.9 4.8 — 129.7 Total $ 4,911.4 $ 1,617.7 $ 741.3 $ 7,270.4 Contract Assets and Liabilities The following table summarizes our beginning and ending balances for accounts receivable and contract liabilities associated with our contracts with customers: Accounts Receivable, Net Contract Liabilities (Current) Contract Liabilities (Long-term) December 31, 2019 $ 815.4 $ 18.9 $ 83.7 December 31, 2020 793.2 23.4 91.0 Increase/(decrease) $ (22.2) $ 4.5 $ 7.3

Leasing (Tables)

Leasing (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Components of lease cost [Table Text Block]	Lease cost consists of the following: Twelve Months Ended December 31, 2020 2019 (in millions) Finance lease cost Amortization of right-of-use assets $ 1.8 $ 1.0 Interest on lease liabilities 0.4 0.3 Total finance lease cost 2.2 1.3 Operating lease cost 32.7 28.9 Short-term lease cost 3.0 5.9 Variable lease cost 2.9 7.2 Total lease cost $ 40.8 $ 43.3
Supplemental lease information [Table Text Block]	The following table summarizes additional information related to our lease agreements. Twelve Months Ended December 31, 2020 2019 (in millions, except lease term and rate) Cash paid for amounts included in measurement of lease liabilities Operating cash flows from finance leases $ 0.3 $ 0.3 Operating cash flows from operating leases 35.1 29.0 Financing cash flows from finance leases 3.0 1.0 Weighted-average remaining lease term - finance leases 15.8 years 2.8 years Weighted-average remaining lease term - operating leases 8.7 years 9.2 years Weighted-average discount rate - finance leases 4.2 % 5.1 % Weighted-average discount rate - operating leases 5.7 % 6.1 %
Future minimum lease payments [Table Text Block]	Future undiscounted minimum payments under non-cancelable leases are as follows: Finance Leases Operating Leases (in millions) 2021 $ 3.9 $ 27.9 2022 3.1 23.8 2023 1.6 17.3 2024 1.1 12.8 2025 1.1 10.4 Thereafter 18.4 57.4 Total future undiscounted minimum lease payments 29.2 149.6 Less: Impact of discounting (7.6) (32.6) Total $ 21.6 $ 117.0
Right of use assets and lease liabilities [Table Text Block]	The right-of-use assets and lease liabilities recorded on our Consolidated Balance Sheets are as follows: December 31, 2020 December 31, 2019 Finance Leases Operating Leases Finance Leases Operating Leases (in millions) (in millions) Property, plant and equipment, net $ 24.9 $ — $ 7.3 $ — Operating lease right-of-use assets — 116.6 — 118.5 Total $ 24.9 $ 116.6 $ 7.3 $ 118.5 Current portion of operating lease liabilities $ — $ 22.6 $ — $ 21.8 Accrued expenses and other 3.3 — 3.3 — Long-term portion of operating lease liabilities — 94.4 — 96.7 Postretirement benefits and other long-term liabilities 18.3 — 4.0 — Total $ 21.6 $ 117.0 $ 7.3 $ 118.5

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2020
Segments, Geographical Areas [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Year Ended December 31, 2020 Driveline Metal Forming Casting Corporate and Eliminations Total (in millions) Sales $ 3,635.6 $ 1,439.2 $ — $ — $ 5,074.8 Less: Intersegment sales 30.1 333.9 — — 364.0 Net external sales $ 3,605.5 $ 1,105.3 $ — $ — $ 4,710.8 Segment adjusted EBITDA $ 501.7 $ 218.1 $ — $ — $ 719.8 Depreciation and amortization $ 332.7 $ 189.2 $ — $ — $ 521.9 Capital expenditures $ 133.5 $ 73.7 $ — $ 8.4 $ 215.6 Total assets $ 3,231.3 $ 1,484.7 $ — $ 1,200.3 $ 5,916.3 Year Ended December 31, 2019 Driveline Metal Forming Casting Corporate and Eliminations Total Sales $ 4,550.2 $ 1,845.2 $ 669.2 $ — $ 7,064.6 Less: Intersegment sales 100.5 391.7 41.5 — 533.7 Net external sales $ 4,449.7 $ 1,453.5 $ 627.7 $ — $ 6,530.9 Segment adjusted EBITDA $ 610.8 $ 316.5 $ 43.0 $ — $ 970.3 Depreciation and amortization $ 307.7 $ 186.9 $ 42.3 $ — $ 536.9 Capital expenditures $ 283.8 $ 105.5 $ 28.5 $ 15.5 $ 433.3 Total assets $ 3,778.8 $ 1,900.0 $ — $ 965.8 $ 6,644.6 Year Ended December 31, 2018 Driveline Metal Forming Casting Corporate and Eliminations Total Sales $ 5,001.2 $ 2,046.0 $ 780.6 $ — $ 7,827.8 Less: Intersegment sales 89.8 428.3 39.3 — 557.4 Net external sales $ 4,911.4 $ 1,617.7 $ 741.3 $ — $ 7,270.4 Segment adjusted EBITDA $ 754.5 $ 376.5 $ 52.9 $ — $ 1,183.9 Depreciation and amortization $ 272.0 $ 192.6 $ 64.2 $ — $ 528.8 Capital expenditures $ 339.4 $ 138.3 $ 35.0 $ 12.0 $ 524.7 Total assets $ 3,796.6 $ 2,607.2 $ 521.5 $ 585.4 $ 7,510.7
Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block]	The following table represents a reconciliation of Segment Adjusted EBITDA to consolidated loss before income taxes for the years ended December 31, 2020, 2019 and 2018: Year Ended December 31, 2020 2019 2018 (in millions) Segment adjusted EBITDA $ 719.8 $ 970.3 $ 1,183.9 Interest expense (212.3) (217.3) (216.3) Depreciation and amortization (521.9) (536.9) (528.8) Impairment charges (510.0) (665.0) (485.5) Restructuring and acquisition-related costs (67.2) (57.8) (78.9) Pension settlements (0.5) (9.8) — Gain (loss) on sale of business (1.0) (21.3) 15.5 Gain on bargain purchase of business — 10.8 — Gain on settlement of capital lease — — 15.6 Debt refinancing and redemption costs (7.9) (8.4) (19.4) Malvern Fire charges, net of recoveries (9.3) — — Other — 2.4 — Loss before income taxes $ (610.3) $ (533.0) $ (113.9)
Schedule of Disclosure on Geographic Areas, Revenue and Long-Lived Assets by Country [Table Text Block]	Financial information relating to our operations by geographic area is presented in the following table. Net sales are attributed to countries based upon location of production. Long-lived assets exclude deferred income taxes. December 31, 2020 2019 2018 (in millions) Net sales United States $ 1,816.7 $ 2,894.0 $ 3,293.2 Mexico 1,808.5 2,353.1 2,547.1 South America 57.6 105.3 129.7 China 317.1 315.4 373.4 All other Asia 160.4 255.8 304.9 Europe 550.5 607.3 622.1 Total net sales $ 4,710.8 $ 6,530.9 $ 7,270.4 Long-lived assets United States $ 2,099.4 $ 2,805.8 $ 3,612.3 Mexico 1,021.6 1,117.4 1,117.9 South America 49.7 61.9 70.6 China 185.1 191.4 177.6 All other Asia 84.2 106.8 101.0 Europe 491.5 439.4 356.0 Total long-lived assets $ 3,931.5 $ 4,722.7 $ 5,435.4

Unaudited Quarterly Financial_2

Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]	Three Months Ended, March 31 June 30 September 30 December 31 (in millions, except per share data) 2020 Net sales $ 1,343.5 $ 515.3 (3) $ 1,414.1 $ 1,437.9 Gross profit 195.3 (98.9) (3) 249.8 236.5 Net income (loss) (501.2) (2) (213.2) (3) 117.2 36.1 Net income (loss) attributable to AAM (501.3) (2) (213.2) (3) 117.2 36.0 Basic EPS (1) $ (4.45) (2) $ (1.88) (3) $ 0.99 $ 0.30 Diluted EPS (1) $ (4.45) (2) $ (1.88) (3) $ 0.99 $ 0.30 2019 Net sales $ 1,719.2 $ 1,704.3 $ 1,677.4 $ 1,430.0 Gross profit 222.2 248.3 248.7 183.4 Net income (loss) 41.7 52.7 (124.1) (4) (454.4) (5) Net income (loss) attributable to AAM 41.6 52.5 (124.2) (4) (454.4) (5) Basic EPS (1) $ 0.36 $ 0.45 $ (1.10) (4) $ (4.04) (5) Diluted EPS (1) $ 0.36 $ 0.45 $ (1.10) (4) $ (4.04) (5) (1) Full year basic and diluted EPS will not necessarily agree to the sum of the four quarters because each quarter is a separate calculation. (2) In the first quarter of 2020, we recorded a goodwill impairment charge of $510 million that was not subject to tax effect as a result of the significant decline in automotive production volumes due to the impact of COVID-19. (3) Many of our plant locations temporarily suspended production or experienced a significant reduction in production volumes during the second quarter of 2020 as a result of the impact of COVID-19. (4) In the third quarter of 2019, we recorded an impairment charge of approximately $178 million, net of tax, to reduce the carrying value of our U.S. Casting operations to fair value less cost to sell upon reclassification of the assets and liabilities to held-for-sale. (5) In the fourth quarter of 2019, we recorded a goodwill impairment charge of $440 million that was not subject to tax effect associated with the annual goodwill impairment test for our Metal Forming reporting unit. We also recorded a loss on the Casting Sale of approximately $17 million, net of tax, recognized a gain on bargain purchase of approximately $10.8 million, which was not subject to tax effect, associated with the acquisition of Mitec, and recognized a loss of approximately $8 million, net of tax, related to pension settlements.

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	Schedule II - VALUATION AND QUALIFYING ACCOUNTS Additions - Balance at Charged to Acquisitions Balance Beginning of Costs and and At End of Period Expenses Disposals (a) Deductions Period (in millions) Year Ended December 31, 2018: Allowance for credit losses (1) $ 7.0 $ 6.6 $ — $ 5.2 $ 8.4 Allowance for deferred taxes (3) 180.4 12.9 — 10.0 183.3 Inventory valuation allowance (2) 17.3 22.2 — 25.1 14.4 Year Ended December 31, 2019: Allowance for credit losses (1) 8.4 13.2 (0.8) 12.8 8.0 Allowance for deferred taxes (4) 183.3 25.4 — 12.7 196.0 Inventory valuation allowance (2) 14.4 31.0 1.4 26.3 20.5 Year Ended December 31, 2020: Allowance for credit losses (1) 8.0 7.0 — 10.5 4.5 Allowance for deferred taxes (5) 196.0 19.8 — 7.8 208.0 Inventory valuation allowance (2) 20.5 31.7 — 28.8 23.4 (a ) Amounts represent reserves recognized in conjunction with our acquisition of Mitec as well as reserves derecognized in conjunction with the Casting Sale in 2019. (1) Uncollectible accounts charged off, net of recoveries. (2) Primarily relates to write-offs of excess and obsolete inventories, as well as adjustments for physical quantity discrepancies. (3) Primarily reflects a reduction in deferred tax assets at various foreign locations due to foreign currency translation. (4) Primarily reflects the reversal of a valuation allowance against certain deferred tax assets in foreign locations, as well as changes due to foreign currency translation. (5) Primarily reflects new net operating losses established with a corresponding valuation allowance at certain foreign locations, partially offset by adjustments to previously established valuation allowances and foreign currency translation.

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies - Organization (Details)	Dec. 31, 2020EmployeesCountriesFacilities
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Entity Number of Employees | Employees	20,000
Number of Facilities | Facilities	80
Number of Countries in which Entity Operates | Countries	17

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies - Accounts Receivable Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue, Performance Obligation, Description of Payment Terms	50 days
Accounts Receivable, Allowance for Credit Loss	$ 4.5	$ 8

Organization and Summary of S_4

Organization and Summary of Significant Accounting Policies - Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Raw materials and work-in-progress	$ 276.2	$ 310.4
Finished goods	70.4	83.7
Gross inventories	346.6	394.1
Inventory valuation reserves	(23.4)	(20.5)
Inventories, net	$ 323.2	$ 373.6

Organization and Summary of S_5

Organization and Summary of Significant Accounting Policies - Maintenance, Repair and Operations (MRO) Materials (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Maintenance, Repair and Operations (MRO) Materials [Abstract]
Maintenance, Repair and Operations (MRO) Materials Amortization	$ 62.4	$ 67.7	$ 62.4

Organization and Summary of S_6

Organization and Summary of Significant Accounting Policies - Property, Plant, & Equipment Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Depreciation and tooling amortization	$ 372.9	$ 373.8	$ 367
Noncash or part noncash acquisition, fixed assets acquired	$ 20.4	$ 46	$ 84.1

Organization and Summary of S_7

Organization and Summary of Significant Accounting Policies - Schedule of Property, Plant & Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Land	$ 49.2	$ 45.1
Land improvements	26.3	24.4
Buildings and building improvements	554.3	512.7
Machinery and equipment	3,703.7	3,645.6
Construction in progress	122.1	219.5
Property, plant and equipment, gross	4,455.6	4,447.3
Accumulated depreciation and amortization	(2,291.8)	(2,088.9)
Property, plant and equipment, net	$ 2,163.8	$ 2,358.4
Land [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	Indefinite	Indefinite
Minimum [Member] | Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	10	10
Minimum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	15	15
Minimum [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3	3
Maximum [Member] | Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	15	15
Maximum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	40	40
Maximum [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	12	12

Organization and Summary of S_8

Organization and Summary of Significant Accounting Policies - Debt Issuance Costs Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 57.8	$ 63.3
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 12.2	$ 12.1

Organization and Summary of S_9

Organization and Summary of Significant Accounting Policies - Currency Translation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Foreign currency transaction gain (loss), before tax	$ (0.5)	$ (6.5)	$ (0.2)

Organization and Summary of _10

Organization and Summary of Significant Accounting Policies - Research and Development Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Research and development expense	$ 117.4	$ 144.7	$ 146.2

Organization and Summary of _11

Organization and Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred payments of social security tax	$ 15.2
Loss carryback related to the CARES Act [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Tax Expense (Benefit)	(14.4)
CARES Act [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Proceeds from Income Tax Refunds	$ 31

Restructuring and Acquisition_3

Restructuring and Acquisition-Related Costs - Restructuring Reserve Table (Details) - USD ($) $ in Millions	12 Months Ended			39 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019
Restructuring Reserve [Roll Forward]
Restructuring reserve	$ 12.2	$ 4	$ 0.3
Restructuring charges	58.4	39.8	44.2
Cash utilization	(59.1)	(31.6)	(10.5)
Non-cash utilization	0	0	(30)
Restructuring reserve	11.5	12.2	4	$ 12.2
2016 Restructuring Plan - Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges				2.8
2016 Restructuring Plan - Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges				29.6
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve	4.8	2.4	0.3
Restructuring charges	22.3	19.4	2.5
Cash utilization	(25.4)	(17)	(0.4)
Non-cash utilization	0	0	0
Restructuring reserve	1.7	4.8	2.4	4.8
Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve	7.4	1.6	0
Restructuring charges	36.1	20.4	11.7
Cash utilization	(33.7)	(14.6)	(10.1)
Non-cash utilization	0	0	0
Restructuring reserve	9.8	7.4	1.6	7.4
Asset Impairment [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve	0	0	0
Restructuring charges	0	0	30
Cash utilization	0	0	0
Non-cash utilization	0	0	(30)
Restructuring reserve	$ 0	$ 0	$ 0	$ 0

Restructuring and Acquisition_4

Restructuring and Acquisition-Related Costs - Restructuring Reserve Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 58.4	$ 39.8	$ 44.2
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost remaining	50
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost remaining	65
Driveline [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	19.3	6.4	3.4
Metal Forming [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	16	21.5	37.6
Casting [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		0.7	0.1
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	22.3	19.4	2.5
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	36.1	20.4	11.7
2020 Restructuring Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	47.8
Asset Impairment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 0	$ 0	$ 30

Restructuring and Acquisition_5

Restructuring and Acquisition-Related Costs - Business Combinations, Separately Recognized Transactions Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Acquisition-Related Costs	$ 0	$ 1.8	$ 1.2
Severance Costs	0	0	0.5
Integration Expenses	8.8	16.2	33
Total acquisition-related charges	8.8	18	34.7
Restructuring and acquisition-related costs	$ 67.2	$ 57.8	$ 78.9

Goodwill and Intangible Assets

Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning balance	$ 699.1	$ 1,141.8
Reorganization		0
Impairment charge	(510)	(440)
Foreign currency translation	(3.4)	(2.7)
Ending balance	185.7	699.1	$ 1,141.8
Driveline [Member]
Goodwill [Roll Forward]
Beginning balance	398.3	212.1
Reorganization		187.2
Impairment charge	(210.8)	0
Foreign currency translation	(1.8)	(1)
Ending balance	185.7	398.3	212.1
Metal Forming [Member]
Goodwill [Roll Forward]
Beginning balance	300.8	552.4
Reorganization		190.1
Impairment charge	(299.2)	(440)
Foreign currency translation	(1.6)	(1.7)
Ending balance	0	300.8	552.4
Powertrain [Member]
Goodwill [Roll Forward]
Beginning balance	0	377.3
Reorganization		(377.3)
Impairment charge	0	0	(80)
Foreign currency translation	0	0
Ending balance	$ 0	$ 0	$ 377.3

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Goodwill Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 510	$ 440
Goodwill, Impaired, Facts and Circumstances Leading to Impairment	These impairment charges were primarily the result of a decline in the projected cash flows of these reporting units under our revised long-range plan completed in the first quarter of 2020. The revision to our long-range plan was driven by lower forecasted sales volumes in the internal and external data sources used to form our projections primarily due to the reduction in global automotive production volumes caused by the impact of COVID-19. The impairment charges were also the result of changes in certain market-related inputs to the analysis to reflect macro-economic changes caused by the impact of COVID-19, including increased discount rates and lower pricing multiples for comparable public companies.	This impairment was primarily the result of a decline in the projected cash flows of this reporting unit under our long-range plan completed in the fourth quarter of 2019, as compared to the long-range plan completed in the fourth quarter of 2018. This was driven, in part, by lower forecasted sales volumes in the internal and external data sources used to form our projections.	These impairments were primarily the result of a general contraction of pricing multiples associated with capital intensive businesses such as the business conducted by our former Casting and Powertrain reporting units, as well as a decline in the projected cash flows of these reporting units under our long-range plan completed in the fourth quarter of 2018, as compared to the long-range plan completed in the fourth quarter of 2017.
Goodwill, Impaired, Accumulated Impairment Loss	$ 1,435.5
Driveline [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss	210.8	$ 0
Metal Forming [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss	299.2	440
Casting [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss			$ 405.5
Powertrain [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 0	$ 0	$ 80

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Acquired Finite Lived Intangible Assets by Major Class (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 1,113.5	$ 1,111
Finite-Lived Intangible Assets, Accumulated Amortization	(332.8)	(246.5)
Finite-Lived Intangible Assets, Net	780.7	864.5
Amortization of intangible assets	86.6	95.4	$ 99.4
Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Expected Amortization, Year One	80
Finite-Lived Intangible Asset, Expected Amortization, Year Two	80
Finite-Lived Intangible Asset, Expected Amortization, Year Three	80
Finite-Lived Intangible Asset, Expected Amortization, Year Four	80
Finite-Lived Intangible Asset, Expected Amortization, Year Five	80
Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Expected Amortization, Year One	85
Finite-Lived Intangible Asset, Expected Amortization, Year Two	85
Finite-Lived Intangible Asset, Expected Amortization, Year Three	85
Finite-Lived Intangible Asset, Expected Amortization, Year Four	85
Finite-Lived Intangible Asset, Expected Amortization, Year Five	85
Computer Software, Intangible Asset [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	47.6	45.8
Finite-Lived Intangible Assets, Accumulated Amortization	(33.9)	(27.6)
Finite-Lived Intangible Assets, Net	13.7	18.2
Customer Platforms - Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	856.2	856.2
Finite-Lived Intangible Assets, Accumulated Amortization	(237.9)	(174.4)
Finite-Lived Intangible Assets, Net	618.3	681.8
Customer Relationships - Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	53	53
Finite-Lived Intangible Assets, Accumulated Amortization	(12.8)	(9.4)
Finite-Lived Intangible Assets, Net	40.2	43.6
Technology-Based Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	156.7	156
Finite-Lived Intangible Assets, Accumulated Amortization	(48.2)	(35.1)
Finite-Lived Intangible Assets, Net	$ 108.5	$ 120.9

Long-Term Debt - Long-term Debt

Long-Term Debt - Long-term Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019	Jul. 29, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Total debt	$ 3,500.6		$ 3,692.2
Current portion of long-term debt	13.7		28.7
Long-term debt and capital lease obligations	3,486.9		3,663.5
Unamortized debt issuance costs	57.8		63.3
Long-term debt, net	3,441.3		3,612.3
Total Debt Instruments excluding Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	45.6		51.2
Multi-Currency Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	0		0
Secured Debt [Member] | Term Loan A Due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	323		340	$ 340
Secured Debt [Member] | Term Loan B [Member]
Debt Instrument [Line Items]
Long-term debt	1,088.8		1,188.8
Unsecured Debt [Member] | 6.875% Notes [Member]
Debt Instrument [Line Items]
Long-term debt	400	$ 400	0
Unsecured Debt [Member] | 6.625% Notes [Member]
Debt Instrument [Line Items]
Long-term debt	0		450
Unsecured Debt [Member] | 6.50% Notes [Member]
Debt Instrument [Line Items]
Long-term debt	500		500
Unsecured Debt [Member] | 6.25% Notes Due 2026 [Member]
Debt Instrument [Line Items]
Long-term debt	400		400		$ 400
Unsecured Debt [Member] | 6.25% Notes due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	700		700
Foreign Credit Facilities and Other [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	$ 88.8		$ 113.4

Long-Term Debt - Senior Secured

Long-Term Debt - Senior Secured Credit Facilities (Details) - USD ($) $ in Millions	Apr. 06, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 29, 2019
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt		$ 408	$ 356.3	$ 509.6
Repayments of Long-term Debt		610.5	545.5	681.2
Payments of Debt Issuance Costs		11	3.3	$ 6.9
Term Loan A [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt	$ 100
Term Loan B [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt	1,550
Multi-Currency Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 932				$ 925
Multi-Currency Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity		891.2
Letters of Credit Outstanding, Amount		33.8
Secured Debt [Member] | Term Loan B [Member]
Debt Instrument [Line Items]
Long-term debt		1,088.8	1,188.8
Write off of Deferred Debt Issuance Cost			1
Repayments of Long-term Debt		100	59.8
Interest Paid, Including Capitalized Interest, Operating and Investing Activities			0.4
Secured Debt [Member] | Term Loan A Due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt		323	340		$ 340
Repayments of Long-term Debt		15
Prepayment of 2021 Amount		12.8
Secured Debt [Member] | Term Loan A & Term Loan B [Member]
Debt Instrument [Line Items]
Write off of Deferred Debt Issuance Cost		1.2	$ 5.1
Secured Debt [Member] | Second Amendment to the Credit Amendments [Member]
Debt Instrument [Line Items]
Payments of Debt Issuance Costs		$ 4.6

Long-Term Debt - Long-Term De_2

Long-Term Debt - Long-Term Debt Notes Payable Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018
Debt Instrument [Line Items]
Payments of Debt Issuance Costs			$ 11	$ 3.3	$ 6.9
6.875% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						6.875%
6.625% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.625%	6.625%						6.625%
7.75% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					7.75%		7.75%
6.25% Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage									6.25%
6.25% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage									6.25%
Unsecured Debt [Member] | 6.875% Notes [Member]
Debt Instrument [Line Items]
Long-term debt			400	0		$ 400
Payments of Debt Issuance Costs			6.4
Unsecured Debt [Member] | 6.625% Notes [Member]
Debt Instrument [Line Items]
Long-term debt			0	450
Debt Instrument, Repurchase Amount	$ 350	$ 100						$ 100
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	5.7	2			$ 0.8
Write off of Deferred Debt Issuance Cost	1.3	0.4			0.8
Redemption Premium	$ 3.9	$ 1.1			3.3
Unsecured Debt [Member] | 7.75% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount					100		$ 100
Interest Paid, Including Capitalized Interest, Operating and Investing Activities				0.3	3.9
Write off of Deferred Debt Issuance Cost				0.1	0.3
Redemption Premium				2.2	4.5
Unsecured Debt [Member] | 6.25% Notes Due 2026 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 400	$ 400					$ 400
Payments of Debt Issuance Costs					6.6
Unsecured Debt [Member] | 6.25% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount									$ 400
Write off of Deferred Debt Issuance Cost					2.5
Gain (Loss) on Extinguishment of Debt, before Write off of Debt Issuance Cost					$ 8

Long-Term Debt - Foreign Credit

Long-Term Debt - Foreign Credit Facilities Narrative (Details) - Foreign Credit Facilities [Member] - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	$ 88.8	$ 106
Foreign Credit Facilities, Remaining Borrowing Capacity	$ 72.8	$ 89.1

Long-Term Debt - Long-term De_3

Long-Term Debt - Long-term Debt Maturity Schedule (Details) $ in Millions	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
2021	$ 32.2
2022	34.2
2023	73.4
2024	1,360.8
2025	700
Thereafter	1,300
Debt	$ 3,500.6

Long-Term Debt - Interest Expen

Long-Term Debt - Interest Expense and Interest Income Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Interest Expense	$ 212.3	$ 217.3	$ 216.3
Interest Costs Capitalized	$ 7.9	$ 15.5	$ 28.4
Long-term Debt, Weighted Average Interest Rate, at Point in Time	5.80%	5.80%	5.90%
Investment Income, Interest	$ 11.6	$ 5.8	$ 2

Derivatives and Risk Manageme_2

Derivatives and Risk Management - Derivatives and Risk Management Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Mar. 09, 2020	Dec. 31, 2019	May 28, 2019
Foreign Currency Forward & Foreign Currency Option Contracts [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 178.2		$ 180.1
Currency Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		244.2		$ 224.2
Fair value asset at the date of dedesignation			$ 9.8
Interest Rate Swap [Member] | Debt [Member]
Derivative [Line Items]
Derivative, Liquidation Proceeds, Monetary Amount	$ 5.6
Fair Value Liability At Date Of Dedesignation					$ 9.7
Derivative, Amount of Hedged Item, Through May 2021		900
Derivative, Amount of Hedged Item, Through May 2022		750
Derivative, Amount of Hedged Item, Through May 2023		600
Derivative, Amount of Hedged Item, Through May 2024		$ 500

Derivatives and Risk Manageme_3

Derivatives and Risk Management - Gain (Loss) Recognized for Designated and Undesignated Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Cost of Goods and Services Sold	$ 4,128.1	$ 5,628.3	$ 6,130
Other Nonoperating Income (Expense)	(5.2)	(12.5)	(2.2)
Interest expense	$ (212.3)	$ (217.3)	$ (216.3)
Cost of Sales [Member] | Foreign Exchange Forward [Member]
Derivative [Line Items]
Description of Location of Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments in Financial Statements	Cost of Goods Sold	Cost of Goods Sold	Cost of Goods Sold
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ (6.7)	$ 3.9	$ 1.6
Cost of Sales [Member] | Cash Flow Hedging [Member] | Foreign Exchange Forward [Member]
Derivative [Line Items]
Derivative Instruments, Income Statement Location of Gain (Loss) Reclassified from Accumulated OCI	Cost of Goods Sold	Cost of Goods Sold	Cost of Goods Sold
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (2.9)	$ 2.4	$ (2.8)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 5.7
Other Nonoperating Income (Expense) [Member] | Foreign Exchange Forward [Member]
Derivative [Line Items]
Description of Location of Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments in Financial Statements	Other Expense, Net	Other Expense, Net	Other Expense, Net
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 0.6	$ 0	$ 1.4
Other Nonoperating Income (Expense) [Member] | Cash Flow Hedging [Member] | Currency Swap [Member]
Derivative [Line Items]
Derivative Instruments, Income Statement Location of Gain (Loss) Reclassified from Accumulated OCI	Other Expense, net	Other Expense, net	Other Expense, net
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (18.7)	$ 1.3	$ 0
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 1.7
Interest Expense [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Instruments, Income Statement Location of Gain (Loss) Reclassified from Accumulated OCI	Interest Expense	Interest Expense	Interest Expense
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (14.2)	$ (2)	$ 3.2
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ (15.3)

Derivatives and Risk Manageme_4

Derivatives and Risk Management - Sales, Receivables and Postretirement Cost Sharing Asset by Major Customer Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue, Major Customer [Line Items]
Total GM postretirement cost sharing asset	$ 250	$ 236
General Motors [Member]
Revenue, Major Customer [Line Items]
Entity-wide revenue, major customer, percentage	39.00%	37.00%	41.00%
Fair value, concentration of risk, accounts receivable	$ 297.5	$ 328.5
FCA [Member]
Revenue, Major Customer [Line Items]
Entity-wide revenue, major customer, percentage	19.00%	17.00%	13.00%
Fair value, concentration of risk, accounts receivable	$ 157	$ 154.8
Ford [Member]
Revenue, Major Customer [Line Items]
Entity-wide revenue, major customer, percentage	12.00%	9.00%	8.00%
Fair value, concentration of risk, accounts receivable	$ 116.5	$ 111.7

Fair Value - Fair Value of Asse

Fair Value - Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents, at carrying value	$ 206.7	$ 271.3
Reported Value Measurement [Member] | Not Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0.2	1.9
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents, at fair value	206.7	271.3
Estimate of Fair Value Measurement [Member] | Not Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0.2	1.9
Foreign Exchange Forward [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	5.8	5
Foreign Exchange Forward [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	3.3	3.4
Foreign Exchange Forward [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	0.1	0
Foreign Exchange Forward [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	0.1	0
Foreign Exchange Forward [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	5.8	5
Foreign Exchange Forward [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	3.3	3.4
Foreign Exchange Forward [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	0.1	0
Foreign Exchange Forward [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	0.1	0
Currency Swap [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	1.1
Currency Swap [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	20.6	0
Currency Swap [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	1.1
Currency Swap [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Fair Value Disclosure	20.6	0
Interest Rate Swap [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Assets, at Fair Value	4.9	0.9
Interest Rate Swap [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Assets, at Fair Value	8.6	2.2
Interest Rate Swap [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Liabilities, at Fair Value	17.8	7.9
Interest Rate Swap [Member] | Reported Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Liabilities, at Fair Value	32.1	18.4
Interest Rate Swap [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Assets, at Fair Value	4.9	0.9
Interest Rate Swap [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Assets, at Fair Value	8.6	2.2
Interest Rate Swap [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Accrued Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Liabilities, at Fair Value	17.8	7.9
Interest Rate Swap [Member] | Estimate of Fair Value Measurement [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest Rate Derivative Liabilities, at Fair Value	$ 32.1	$ 18.4

Fair Value - Fair Value of Debt

Fair Value - Fair Value of Debt (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Revolving Credit Facility [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Line of credit facility, amount outstanding	$ 0	$ 0
Revolving Credit Facility [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Line of credit facility, amount outstanding	0	0
Term Loan A Due 2024 [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	323	340
Term Loan A Due 2024 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	318.6	337.9
Term Loan B [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	1,088.8	1,188.8
Term Loan B [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	1,071.1	1,174
6.875% Notes [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	400	0
6.875% Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	426	0
6.625% Notes [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	0	450
6.625% Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	0	455.4
6.50% Notes [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	500	500
6.50% Notes [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	523.8	516.3
6.25% Notes Due 2026 [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	400	400
6.25% Notes Due 2026 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	411	409
6.25% Notes due 2025 [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	700	700
6.25% Notes due 2025 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	$ 724.3	$ 716.6

Employee Benefit Plans - Define

Employee Benefit Plans - Defined Benefit Plan, Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.50%	3.40%	4.30%
Expected return on plan assets	7.25%	7.25%	7.50%
Rate of compensation increase			4.00%
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.55%	2.05%	2.95%
Expected return on plan assets	4.00%	4.00%	5.10%
Rate of compensation increase	3.15%	3.15%	3.40%
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.55%	3.35%	4.35%
Rate of compensation increase	4.00%	4.00%	4.00%

Employee Benefit Plans - Accumu

Employee Benefit Plans - Accumulated Benefit Obligation and Underfunded Pension Plan Detail Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Defined benefit plan, accumulated benefit obligation	$ 796.6	$ 737.8
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	618.8
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	618.8
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets	$ 469.6

Employee Benefit Plans - GM Cos

Employee Benefit Plans - GM Cost Sharing Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Total GM postretirement cost sharing asset	$ 250	$ 236
Current GM postretirement cost sharing asset	13
Noncurrent GM postretirement cost sharing asset	$ 237	$ 223.3

Employee Benefit Plans - Change

Employee Benefit Plans - Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 636.6
Fair value of plan assets at end of year	669.9	$ 636.6
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	740.2	734.5
Service cost	2	1.5	$ 2.6
Interest cost	21.4	28	27.3
Actuarial loss	63.5	71.5
Change in GM portion of OPEB obligation	0	0
Participant contributions	0.2	0.2
Curtailments	0	(1.9)
Settlements	(3.3)	(28.8)
Benefit payments	(34.4)	(44.1)
Sale of business	0	(26.2)
Currency fluctuations	8.7	5.5
Other	0.6	0
Net change	58.7	5.7
Benefit obligation at end of year	798.9	740.2	734.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	636.6	625.8
Actual return on plan assets	55.7	87.5
Employer contributions	8.5	10
Participant contributions	0.2	0.2
Benefit payments	(34.4)	(44.1)
Settlements	(3.3)	(28.8)
Sale of business	0	(20.7)
Currency fluctuations	6.6	6.7
Net change	33.3	10.8
Fair value of plan assets at end of year	669.9	636.6	625.8
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	549.1	537.3
Service cost	0.4	0.3	0.4
Interest cost	10.2	12.8	12.4
Actuarial loss	25.3	11.9
Change in GM portion of OPEB obligation	14	3.1
Participant contributions	0	0
Curtailments	0	0
Settlements	0	0
Benefit payments	(12.5)	(15.5)
Sale of business	0	(0.8)
Currency fluctuations	0	0
Other	0	0
Net change	37.4	11.8
Benefit obligation at end of year	586.5	549.1	537.3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	12.5	15.5
Participant contributions	0	0
Benefit payments	(12.5)	(15.5)
Settlements	0	0
Sale of business	0	0
Currency fluctuations	0	0
Net change	0	0
Fair value of plan assets at end of year	$ 0	$ 0	$ 0

Employee Benefit Plans - Amount

Employee Benefit Plans - Amounts Recognized in the Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Noncurrent assets	$ 20.2	$ 21.2
Liability, Defined Benefit Pension Plan, Current	(8)	(6.6)
Defined benefit pension plan, liabilities, noncurrent	(141.2)	(118.2)
Defined benefit plan, amounts recognized in balance sheet	(129)	(103.6)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Noncurrent assets	0	0
Postemployment Benefits Liability, Current	(29.8)	(29.1)
Other postretirement defined benefit plan, liabilities, noncurrent	(556.7)	(520)
Other postretirement defined benefit plan, liabilities	$ (586.5)	$ (549.1)

Employee Benefit Plans - Pre-ta

Employee Benefit Plans - Pre-tax Amounts Recorded in AOCI (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial gain (loss)	$ (278)	$ (239.2)
Net prior service credit (cost)	(1.8)	(1.2)
Total amounts recorded	(279.8)	(240.4)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial gain (loss)	(4.9)	19.3
Net prior service credit (cost)	3.1	4.7
Total amounts recorded	$ (1.8)	$ 24

Employee Benefit Plans - Compon

Employee Benefit Plans - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment loss (gain)	$ 0.5	$ 9.8	$ 0
Settlement charge	0.5	9.8	0
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	2	1.5	2.6
Interest cost	21.4	28	27.3
Expected asset return	(38.4)	(41.1)	(45.8)
Amortized actuarial loss	8.6	6.4	7.8
Amortized prior service cost (credit)	0.1	0	0.1
Curtailment loss (gain)	0	0	3.2
Settlement charge	0.5	10.4	0.4
Net periodic benefit cost (credit)	(5.8)	5.2	(4.4)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.4	0.3	0.4
Interest cost	10.2	12.8	12.4
Expected asset return	0	0	0
Amortized actuarial loss	1	0.1	0.8
Amortized prior service cost (credit)	(1.5)	(1.5)	(2.7)
Curtailment loss (gain)	0	0	(0.6)
Settlement charge	0	0	0
Other postretirement benefit expense	$ 10.1	$ 11.7	$ 10.3

Employee Benefit Plans - All Ot

Employee Benefit Plans - All Other Relevant Defined Benefit Pension and Other Postretirement Benefit Disclosures Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	6.25%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2026
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 59.7
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	55.2
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	55.1
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	56.4
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	57.2
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	287.4
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	1
Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Payment for Pension and Other Postretirement Benefits	4.2
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 17

Employee Benefit Plans - Termin

Employee Benefit Plans - Terminated vested lump sum payment offer (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)Employees	Dec. 31, 2018USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	$ (0.5)	$ (9.8)	$ 0
Terminated vested lump sum payment offer [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, number of plan participants eligible for settlement | Employees		2,000
Defined benefit plan, number of plan participants included in settlement | Employees		616
Defined Benefit Plan, Benefit Obligation, Payment for Settlement		$ 28.4
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		32.5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment		$ (9.8)

Employee Benefit Plans - Defi_2

Employee Benefit Plans - Defined Benefit Pension Plan Assets by Category and Fair Value Hierarchy (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 669.9	$ 636.6
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	553.2	509.6
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64.1	61.9
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10.3	9.3
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.4	7.3
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.9	2
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	90.8	85.4
U.S. Large Cap [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	88.1	82.4
U.S. Large Cap [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.7	3
U.S. Large Cap [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. Small/Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20.5	22.7
U.S. Small/Mid Cap [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20.5	22.7
U.S. Small/Mid Cap [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. Small/Mid Cap [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
World Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	94.8	92.8
World Equity [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	87	88.1
World Equity [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.8	4.7
World Equity [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Government & Agencies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	130	119.3
Government & Agencies [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	84.1	74.3
Government & Agencies [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.9	45
Government & Agencies [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate Bonds - Investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	221.7	186.4
Corporate Bonds - Investment Grade [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	219	185.8
Corporate Bonds - Investment Grade [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.7	0.6
Corporate Bonds - Investment Grade [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate Bonds - Non-investment Grade [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23.1	22.8
Corporate Bonds - Non-investment Grade [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.4	21.7
Corporate Bonds - Non-investment Grade [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.7	1.1
Corporate Bonds - Non-investment Grade [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Emerging Market Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.2	21.1
Emerging Market Debt [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21.1	20.4
Emerging Market Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.1	0.7
Emerging Market Debt [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed Income Securities - Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.9	11.7
Fixed Income Securities - Other [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.6	6.9
Fixed Income Securities - Other [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3	4.8
Fixed Income Securities - Other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Property Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44.2	57.3
Property Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Property Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Property Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Liquid Alternatives Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.8	1.6
Liquid Alternatives Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Liquid Alternatives Fund [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Liquid Alternatives Fund [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Structured Credit Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.6	6.2
Structured Credit Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Structured Credit Fund [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Structured Credit Fund [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	100.00%	100.00%
Domestic Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	34.70%	35.20%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	25% - 40%
Domestic Plan [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	57.30%	52.90%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	50% - 70%
Domestic Plan [Member] | Alternative assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	7.30%	10.40%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	5% - 15%
Domestic Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	0.70%	1.50%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	0% - 5%
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	100.00%	100.00%
Foreign Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	21.80%	22.70%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	15% - 30%
Foreign Plan [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	65.90%	66.80%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	60% - 80%
Foreign Plan [Member] | Alternative assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.90%	9.40%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	5% - 15%
Foreign Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	3.40%	1.10%
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	0% - 5%

Employee Benefit Plans - Defi_3

Employee Benefit Plans - Defined Contribution Plans Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%
Defined contribution plans, ARC, maximum employee contribution percentage	10.00%
Defined contribution plans, salaried voluntary savings plan, matching contributions during the period	$ 7.9	$ 11.5	$ 12.4
Annual Retirement Contribution (ARC) [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 8	$ 10.3	$ 7.3
Minimum [Member] | Annual Retirement Contribution (ARC) [Member]
Defined Contribution Plan, Employer Discretionary Contribution Percentage		3.00%
Maximum [Member] | Annual Retirement Contribution (ARC) [Member]
Defined Contribution Plan, Employer Discretionary Contribution Percentage		5.00%

Stock Based Compensation and _3

Stock Based Compensation and Other Incentive Compensation - Stock Based Compensation Narrative (Details) shares in Millions	Dec. 31, 2020shares
Share-based Payment Arrangement [Abstract]
Share-based compensation arrangement by share-based payment award, number of shares available for grant	2.1

Stock Based Compensation and _4

Stock Based Compensation and Other Incentive Compensation - Restricted Stock Units Activity (Details) - Restricted Stock Units (RSUs) [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning balance	3.1	3.5	2.5
Restricted stock units granted	3.2	1	1.7
Restricted stock units vested	(0.8)	(0.7)	(0.4)
Restricted stock units canceled	(0.6)	(0.7)	(0.3)
Ending balance	4.9	3.1	3.5
Weighted-average grant date fair value outstanding	$ 9.20	$ 16.03	$ 16	$ 18.35
Weighted-average grant date fair value granted	5.08	15.78	14.57
Weighted-average grant date fair value vested	18.22	15.53	24.16
Weighted-average grant date fair value canceled	$ 10.33	$ 16.05	$ 15.84
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 15.5
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years
Share-based compensation arrangement by share-based payment award, equity instruments other than options, vested in period, total fair value	$ 5	$ 10.9

Stock Based Compensation and _5

Stock Based Compensation and Other Incentive Compensation - Performance Shares Activity (Details) - Performance Shares [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 5.3
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years
EBITDA Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning balance	0.1	0.5	0.6
Performance shares granted	0	0	0
Performance shares vested	(0.1)	(0.4)	(0.1)
Performance shares canceled	0	0	0
Ending balance	0	0.1	0.5
Weighted-average grant date fair value outstanding	$ 0	$ 39.09	$ 34.49	$ 33.91
Weighted-average grant date fair value granted	0	0	0
Weighted-average grant date fair value vested	39.09	31.21	37.67
Weighted-average grant date fair value canceled	$ 0	$ 0	$ 0
Total Shareholder Return (TSR) Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning balance	0.8	0.8	0.6
Performance shares granted	0	0.3	0.3
Performance shares vested	(0.2)	(0.2)	(0.1)
Performance shares canceled	0	(0.1)	0
Ending balance	0.6	0.8	0.8
Weighted-average grant date fair value outstanding	$ 18.86	$ 20.13	$ 16.25	20.93
Weighted-average grant date fair value granted	0	24.36	13.91
Weighted-average grant date fair value vested	24.63	17.54	31.21
Weighted-average grant date fair value canceled	$ 0	$ 20.49	$ 0
Free Cash Flow (FCF) Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Beginning balance	0.3	0.3	0
Performance shares granted	0.9	0	0.3
Performance shares vested	0	0	0
Performance shares canceled	0	0	0
Ending balance	1.2	0.3	0.3
Weighted-average grant date fair value outstanding	$ 7.50	$ 14.28	$ 14.28	$ 0
Weighted-average grant date fair value granted	5.18	0	14.28
Weighted-average grant date fair value vested	0	0	0
Weighted-average grant date fair value canceled	$ 0	$ 0	$ 0

Stock Based Compensation and _6

Stock Based Compensation and Other Incentive Compensation - Performance Units (Details) - Performance Units [Member] - Free Cash Flow (FCF) Awards [Member] - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive compensation arrangement, by award, grants in period	13.6	14.2
Incentive compensation arrangement, cost not yet recognized, amount	$ 13.7
Incentive compensation arrangement, cost not yet recognized, period for recognition	2 years

Income Taxes - Income Before In

Income Taxes - Income Before Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S. loss	$ (721.6)	$ (889)	$ (549.4)
Non - U.S. income	111.3	356	435.5
Loss before income taxes	$ (610.3)	$ (533)	$ (113.9)

Income Taxes - Components of Pr

Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current
Federal	$ 2	$ (11.9)	$ (81.5)
State and local	0.5	0.1	3.2
Foreign	20.2	49.3	46.5
Total current	22.7	37.5	(31.8)
Deferred
Federal	(60)	(73.5)	(5.1)
State and local	(0.7)	(1.5)	(6.7)
Foreign	(11.2)	(11.4)	(13.5)
Total deferred	(71.9)	(86.4)	(25.3)
Total income tax benefit	$ (49.2)	$ (48.9)	$ (57.1)

Income Taxes - Rate Reconciliat

Income Taxes - Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory	$ (128.2)	$ (111.9)	$ (23.9)
Foreign income taxes	(21.5)	(40.2)	(39.7)
Change in enacted tax rate	2.1	0.2	(8.3)
Transition tax	0	(7.5)	5.8
State and local	(5)	(20)	(12.8)
Tax credits	(9.7)	(9.6)	(20.1)
Valuation allowance	19.8	12.6	12.9
Goodwill impairment	107.1	92.4	21.6
Withholding taxes	5.6	4	6.6
U.S. tax on unremitted foreign earnings	0	(2.8)	4.1
Tax benefit on loss carryback	(14.4)	0	0
Global intangible low-taxed income	2.3	31.1	8
Uncertain tax positions	(8.8)	5.9	(9.8)
Other	1.5	(3.1)	(1.5)
Total income tax benefit	$ (49.2)	$ (48.9)	$ (57.1)

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation allowance, deferred tax asset, increase (decrease), amount		$ 14.5	$ 25.4	$ 16
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	$ 25.3	12.2		3.7
Income tax benefit of goodwill impairment loss				85
United States
Valuation allowance, deferred tax asset, increase (decrease), amount		5.3
Foreign Tax Authority [Member]
Valuation allowance, deferred tax asset, increase (decrease), amount			12.8	3.1
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities				$ 20
Settlement with Taxing Authority [Member]
Other Tax Expense (Benefit)		6.8
Loss carryback related to the CARES Act [Member]
Other Tax Expense (Benefit)		$ (14.4)
Transition tax [Member]
Other Tax Expense (Benefit)			$ 9.3

Income Taxes - Refundable Incom

Income Taxes - Refundable Income Taxes and Income Taxes Payable Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Prepaid Expenses and Other Current Assets [Member]
Refundable income taxes and income taxes payable [Line Items]
Refundable income taxes	$ 14	$ 25
Accrued Liabilities [Member]
Refundable income taxes and income taxes payable [Line Items]
Taxes Payable, Current	$ 6	$ 3

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Valuation allowances	$ (208)	$ (196)
Deferred tax assets, net	94.6	44.5
Domestic [Member]
Deferred tax assets, net	44.1	5
Foreign [Member]
Deferred tax assets, net	50.5	39.5
Deferred Tax Assets [Member]
Employee benefits	162.4	149.4
Inventory	32.9	27.3
Net operating loss (NOL) carryforwards	221.4	201.7
Tax credit carryforwards	88.6	47.8
Capital allowance carryforwards	10.2	9.3
Capitalized expenditures	45.9	42.9
Interest carryforward	10.4	43.9
Operating lease liabilities	25.7	27.1
Other	50.6	42.7
Valuation allowances	(208)	(196)
Deferred tax assets	440.1	396.1
Deferred Tax Liabilities [Member]
Other intangible assets	(179.9)	(199.7)
Fixed assets	(137.5)	(120.7)
Operating lease right-of-use assets	(25.6)	(27.1)
Other	(2.5)	(4.1)
Deferred tax liabilities	$ (345.5)	$ (351.6)

Income Taxes - Deferred Income

Income Taxes - Deferred Income Tax Assets and Liabilities and Valuation Allowances Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Operating Loss and Tax Credit Carryforwards	$ 320.2	$ 258.8
Deferred Tax Assets, Operating Loss and Tax Credit Carryforwards, Not Subject to Expiration	107.7
Valuation allowance, deferred tax asset, increase (decrease), amount	14.5	25.4	$ 16
Deferred Tax Assets, Valuation Allowance	208	196
United States
Tax Credit Carryforward [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	$ 5.3
Foreign Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount		$ 12.8	$ 3.1

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefts (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning balance		$ 41.1	$ 38.7	$ 47.7
Increase in prior year tax positions		0.2	0.2	5.6
Decrease in prior year tax positions		(6.6)	(3.1)	(16.9)
Increase in current year tax positions		0.7	4.4	6
Settlement	$ (25.3)	(12.2)		(3.7)
Foreign currency remeasurement adjustment		(3)	(0.9)
Unrecognized tax benefits, ending balance		20.2	41.1	38.7
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Unrecognized tax benefits, interest and penalties, beginning balance		11.5	6.9	7.5
Increase in prior year tax positions		0	4.5	3.5
Decrease in prior year tax positions		(1.7)	(0.1)	(2.5)
Increase in current year tax positions		0	0	0
Settlement		(6.3)		(1.6)
Foreign currency remeasurement adjustment		(1.5)	0.2
Unrecognized tax benefits, interest and penalties, ending balance		$ 2	$ 11.5	$ 6.9

Income Taxes - Other Tax Disclo

Income Taxes - Other Tax Disclosure Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits		$ 20.2	$ 41.1	$ 38.7	$ 47.7
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		(1.7)	4.4	1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		2	$ 11.5	6.9	$ 7.5
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		19
Tax Adjustments, Settlements, and Unusual Provisions	$ 18.5
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	$ 25.3	$ 12.2		$ 3.7

Earnings Per Share (EPS) (Detai

Earnings Per Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended														12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020	[1]	Mar. 31, 2020	[2]	Dec. 31, 2019	[3]	Sep. 30, 2019	[4]	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator [Abstract]
Net Loss Attributable to AAM	$ 36		$ 117.2		$ (213.2)		$ (501.3)		$ (454.4)		$ (124.2)		$ 52.5	$ 41.6	$ (561.3)	$ (484.5)	$ (57.5)
Less: Net income allocated to participating securities															0	0	0
Net loss attributable to common shareholders - Basic and Dilutive															$ (561.3)	$ (484.5)	$ (57.5)
Denominator [Abstract]
Weighted-average shares outstanding															117.9	115.6	115
Less: Participating securities															(4.8)	(3.3)	(3.4)
Weighted-average common shares outstanding															113.1	112.3	111.6
Dilutive stock-based compensation															0	0	0
Diluted shares outstanding - adjusted weighted-average shares after assumed conversions															113.1	112.3	111.6
Basic loss per share	$ 0.30	[5]	$ 0.99	[5]	$ (1.88)	[5]	$ (4.45)	[5]	$ (4.04)		$ (1.10)		$ 0.45	$ 0.36	$ (4.96)	$ (4.31)	$ (0.51)
Diluted loss per share	$ 0.30	[5]	$ 0.99	[5]	$ (1.88)	[5]	$ (4.45)	[5]	$ (4.04)		$ (1.10)		$ 0.45	$ 0.36	$ (4.96)	$ (4.31)	$ (0.51)
[1]	Many of our plant locations temporarily suspended production or experienced a significant reduction in production volumes during the second quarter of 2020 as a result of the impact of COVID-19.
[2]	In the first quarter of 2020, we recorded a goodwill impairment charge of $510 million that was not subject to tax effect as a result of the significant decline in automotive production volumes due to the impact of COVID-19.
[3]	In the fourth quarter of 2019, we recorded a goodwill impairment charge of $440 million that was not subject to tax effect associated with the annual goodwill impairment test for our Metal Forming reporting unit. We also recorded a loss on the Casting Sale of approximately $17 million, net of tax, recognized a gain on bargain purchase of approximately $10.8 million, which was not subject to tax effect, associated with the acquisition of Mitec, and recognized a loss of approximately $8 million, net of tax, related to pension settlements.
[4]	In the third quarter of 2019, we recorded an impairment charge of approximately $178 million, net of tax, to reduce the carrying value of our U.S. Casting operations to fair value less cost to sell upon reclassification of the assets and liabilities to held-for-sale.
[5]	Full year basic and diluted EPS will not necessarily agree to the sum of the four quarters because each quarter is a separate calculation.

Earnings Per Share (EPS) - Anti

Earnings Per Share (EPS) - Antidilutive Shares (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0.4	0.8

Commitments and Contingencies -

Commitments and Contingencies - Purchase Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Obligated purchase commitments	$ 90.8	$ 131.9

Commitments and Contingencies_2

Commitments and Contingencies - Product Liability (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Movement in Standard Product Warranty Accrual [Roll Forward]
Beginning balance	$ 62	$ 57.7
Accruals	21.9	18.5
Settlements	(14.1)	(10.4)
Adjustments to prior period accruals	(3.5)	(3.9)
Foreign currency translation	0.4	0.1
Ending balance	$ 66.7	$ 62

Reclassifications out of Accu_3

Reclassifications out of Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Defined benefit plans, net of $12.7 million, $3.0 million and $(9.8) million of tax in 2020, 2019 and 2018, respectively		$ (51.1)	$ (18.3)		$ 38.1
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax		(0.2)	(4.6)		(62.5)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(4.4)	(14.6)		5.5
Other Comprehensive Income (Loss), Net of Tax		(55.7)	(37.5)		(18.9)
ASU 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
New accounting pronouncement, effect of adoption			27.7
Cost of Sales [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		2.9	(2.4)		2.8
Interest Expense [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		14.2	2		(3.2)
Other Income [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		18.7	(1.3)
Net effect of AAM Pension Payout and the Casting Sale [Member] | Other Income [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax			7.4
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax - Beginning Balance		(259.9)	(213.9)		(252)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax		(72)	(61.5)	[1]	41.9
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, Tax		14.2	5.6		(8.4)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	[2]	8.2	12.5		6
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax		(1.5)	(2.6)		(1.4)
Defined benefit plans, net of $12.7 million, $3.0 million and $(9.8) million of tax in 2020, 2019 and 2018, respectively		(51.1)	(46)		38.1
Accumulated Other Comprehensive Income (Loss), Net of Tax - Ending Balance		(311)	(259.9)		(213.9)
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax - Beginning Balance		(101.2)	(96.6)		(34.1)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax		0.1	(4.6)		(62.7)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax		0	0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax		0	0		0.2
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax		0	0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax		0.1	(4.6)		(62.5)
Accumulated Other Comprehensive Income (Loss), Net of Tax - Ending Balance		(101.1)	(101.2)		(96.6)
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax - Beginning Balance		(15.7)	(1.1)		(6.6)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax		(41.5)	(19)		5.4
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax		8.2	6.3		(0.2)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[3]	35.8	(1.7)		(0.4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax		(6.9)	(0.2)		0.7
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(4.4)	(14.6)		5.5
Accumulated Other Comprehensive Income (Loss), Net of Tax - Ending Balance		(20.1)	(15.7)		(1.1)
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax - Beginning Balance		(376.8)	(311.6)		(292.7)
Other Comprehensive Income (Loss) Arising During Period, Total, Before Tax		(113.4)	(85.1)		(15.4)
Other Comprehensive Income (Loss), Defined Benefit Plans, before Reclassification Adjustments, Tax		22.4	11.9		(8.6)
Other Comprehensive Income (Loss), Reclassification Adjustments, Total, Before Tax		44	10.8		5.8
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Defined Benefit Plans, Tax		(8.4)	(2.8)		(0.7)
Other Comprehensive Income (Loss), Net of Tax		(55.4)	(65.2)		(18.9)
Accumulated Other Comprehensive Income (Loss), Net of Tax - Ending Balance		$ (432.2)	$ (376.8)		$ (311.6)
[1]	ASU 2018-02 became effective on January 1, 2019, and we elected to reclassify the stranded tax effects caused by the 2017 Tax Cuts and Jobs Act, resulting in a decrease in Accumulated other comprehensive income (loss) of $27.7 million at January 1, 2019.
[2]	Subsequent to the adoption of ASU 2017-07 effective January 1, 2018, these amounts were reclassified from AOCI to Other, net for the years ended December 31, 2020, 2019 and 2018. The amount reclassified for 2019 includes a credit to AOCI of $7.4 million related to the net effect of the AAM Pension Payout Offer and the Casting Sale. See Note 7 - Employee Benefit Plans and Note 16 - Acquisitions and Dispositions for more detail.
[3]	The amounts reclassified from AOCI included $2.9 million in COGS, $14.2 million in interest expense and $18.7 million in other expense, net for the year ended December 31, 2020, $(2.4) million in COGS, $2.0 million in interest expense and $(1.3) million in other expense, net for the year ended December 31, 2019 and $2.8 million in COGS and $(3.2) million in interest expense for the year ended December 31, 2018.

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details)	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customers [Abstract]
Revenue, Performance Obligation, Description of Payment Terms	50 days

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	[1]	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 1,437.9	$ 1,414.1	$ 515.3		$ 1,343.5	$ 1,430	$ 1,677.4	$ 1,704.3	$ 1,719.2	$ 4,710.8	$ 6,530.9	$ 7,270.4
North America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										3,625.1	5,247.1	5,840.3
Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										477.5	571.2	678.3
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										550.5	607.3	622.1
South America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										57.7	105.3	129.7
Driveline [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										3,605.5	4,449.7	4,911.4
Driveline [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										2,770.1	3,466.3	3,823.1
Driveline [Member] | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										433.7	533.6	634.4
Driveline [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										352.5	351	329
Driveline [Member] | South America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										49.2	98.8	124.9
Metal Forming [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										1,105.3	1,453.5	1,617.7
Metal Forming [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										855	1,153.1	1,275.9
Metal Forming [Member] | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										43.8	37.6	43.9
Metal Forming [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										198	256.3	293.1
Metal Forming [Member] | South America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										8.5	6.5	4.8
Casting [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0	627.7	741.3
Casting [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0	627.7	741.3
Casting [Member] | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0	0	0
Casting [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										0	0	0
Casting [Member] | South America [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax										$ 0	$ 0	$ 0
[1]	Many of our plant locations temporarily suspended production or experienced a significant reduction in production volumes during the second quarter of 2020 as a result of the impact of COVID-19.

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Contract Asset and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Receivables, net, current	$ 793.2	$ 815.4
Increase (decrease) in receivables	(22.2)
Contract Liabilities, current	23.4	18.9
Contract Liabilities, noncurrent	91	83.7
Deferred revenue	5.5	(17.9)	$ 10.7
Contract with customer, liability, revenue recognized	22.7	$ 48.6
Other Current Liabilities [Member]
Deferred revenue	4.5
Other Noncurrent Liabilities [Member]
Deferred revenue	$ 7.3

Leasing - Components of Lease C

Leasing - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of lease expense [Line Items]
Amortization of right-of-use assets	$ 1.8	$ 1
Interest on lease liabilities	0.4	0.3
Total finance lease cost	2.2	1.3
Operating lease cost	32.7	28.9
Short-term lease cost	3	5.9
Variable lease cost	2.9	7.2
Total lease cost	40.8	43.3
Cost of Sales [Member]
Components of lease expense [Line Items]
Lease expense	28.4	31.9	$ 28.4
Selling, General and Administrative Expenses [Member]
Components of lease expense [Line Items]
Lease expense	$ 10.2	$ 10.1	$ 10

Leasing - Supplemental Lease In

Leasing - Supplemental Lease Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Supplemental lease information [Line Items]
Operating cash flows from finance leases	$ 0.3	$ 0.3
Operating cash flows from operating leases	35.1	29
Financing cash flows from finance leases	$ 3	$ 1
Weighted-average remaining lease term - finance leases	15 years 9 months 18 days	2 years 9 months 18 days
Weighted-average remaining lease term - operating leases	8 years 8 months 12 days	9 years 2 months 12 days
Weighted-average discount rate - finance leases	4.20%	5.10%
Weighted-average discount rate - operating leases	5.70%	6.10%

Leasing - Future Minimum Lease

Leasing - Future Minimum Lease Payments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Future minimum lease payments [Line Items]
Finance Lease, Liability	$ 21.6	$ 7.3
Operating Lease, Liability	117	$ 118.5
Finance Lease [Member]
Future minimum lease payments [Line Items]
Finance Lease, Liability, to be Paid, Year One	3.9
Finance Lease, Liability, Payments, Due Year Two	3.1
Finance Lease, Liability, Payments, Due Year Three	1.6
Finance Lease, Liability, Payments, Due Year Four	1.1
Finance Lease, Liability, Payments, Due Year Five	1.1
Finance Lease, Liability, Payments, Due after Year Five	18.4
Finance Lease, Liability, Payment, Due	29.2
Finance Lease, Liability, Undiscounted Excess Amount	(7.6)
Finance Lease, Liability	21.6
Operating lease [Member]
Future minimum lease payments [Line Items]
Lessee, Operating Lease, Liability, to be Paid, Year One	27.9
Lessee, Operating Lease, Liability, Payments, Due Year Two	23.8
Lessee, Operating Lease, Liability, Payments, Due Year Three	17.3
Lessee, Operating Lease, Liability, Payments, Due Year Four	12.8
Lessee, Operating Lease, Liability, Payments, Due Year Five	10.4
Lessee, Operating Lease, Liability, Payments, Due after Year Five	57.4
Lessee, Operating Lease, Liability, Payments, Due	149.6
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(32.6)
Operating Lease, Liability	$ 117

Leasing - Right of Use Assets a

Leasing - Right of Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Right of use assets and lease liabilities [Line Items]
Finance Lease, Right-of-Use Asset	$ 24.9	$ 7.3
Operating lease right-of-use assets	116.6	118.5
Finance Lease, Liability	21.6	7.3
Operating Lease, Liability	117	118.5
Property, plant and equipment, net [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Right-of-Use Asset	24.9	7.3
Operating lease right-of-use assets	0	0
Operating lease right-of-use assets [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Right-of-Use Asset	0	0
Operating lease right-of-use assets	116.6	118.5
Current portion of operating lease liabilities
Right of use assets and lease liabilities [Line Items]
Finance Lease, Liability	0	0
Operating Lease, Liability	22.6	21.8
Accrued expenses and other [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Liability	3.3	3.3
Operating Lease, Liability	0	0
Long-term portion of operating lease liabilities
Right of use assets and lease liabilities [Line Items]
Finance Lease, Liability	0	0
Operating Lease, Liability	94.4	96.7
Postretirement benefits and other long-term liabilities [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Liability	18.3	4
Operating Lease, Liability	$ 0	$ 0

Leasing - Leases Not Yet Commen

Leasing - Leases Not Yet Commenced (Details) $ in Millions	Dec. 31, 2020USD ($)
Leases not yet commenced [Line Items]
Lessee, Operating and financing leases, Leases not yet commenced	$ 85.2

Manufacturing Facility Fire a_2

Manufacturing Facility Fire and Insurance Recovery (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Insurance Recoveries [Abstract]
Insurance Deductible Expense	$ 1
Business Interruption Charges	36.5
Tangible Asset Impairment Charges	27
Estimated Insurance Recoveries	54.2
Loss Contingency, Receivable	43.1
Insurance Recoveries	11.1
Loss from Fire	$ 9.3

Acquisitions and Dispositions (

Acquisitions and Dispositions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 02, 2019
Business Acquisition [Line Items]
Gain on bargain purchase of business	$ 0	$ 10.8	$ 0
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of business, net	0	141.2	47.1
Gain (loss) on sale of business	(1)	(21.3)	15.5
Sale of U.S. Casting Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of business, net		141.2
Impairment of Long-Lived Assets to be Disposed of		225
Gain (loss) on sale of business	$ (1)	(21.3)
Sale of Powertrain Aftermarket [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of business			15.5
Proceeds from Divestiture of Businesses			$ 50
Mitec Automotive AG [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets				$ 20.2
Business Combination, Consideration Transferred		9.4
Gain on bargain purchase of business		$ 10.8

Segment and Geographic Inform_3

Segment and Geographic Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Sales	$ 5,074.8	$ 7,064.6	$ 7,827.8
Less: Intersegment sales	364	533.7	557.4
Net external sales	4,710.8	6,530.9	7,270.4
Segment adjusted EBITDA	719.8	970.3	1,183.9
Depreciation and amortization	521.9	536.9	528.8
Capital expenditures	215.6	433.3	524.7
Total assets	5,916.3	6,644.6	7,510.7
Driveline [Member]
Segment Reporting Information [Line Items]
Sales	3,635.6	4,550.2	5,001.2
Less: Intersegment sales	30.1	100.5	89.8
Net external sales	3,605.5	4,449.7	4,911.4
Segment adjusted EBITDA	501.7	610.8	754.5
Depreciation and amortization	332.7	307.7	272
Capital expenditures	133.5	283.8	339.4
Total assets	3,231.3	3,778.8	3,796.6
Metal Forming [Member]
Segment Reporting Information [Line Items]
Sales	1,439.2	1,845.2	2,046
Less: Intersegment sales	333.9	391.7	428.3
Net external sales	1,105.3	1,453.5	1,617.7
Segment adjusted EBITDA	218.1	316.5	376.5
Depreciation and amortization	189.2	186.9	192.6
Capital expenditures	73.7	105.5	138.3
Total assets	1,484.7	1,900	2,607.2
Casting [Member]
Segment Reporting Information [Line Items]
Sales	0	669.2	780.6
Less: Intersegment sales	0	41.5	39.3
Net external sales	0	627.7	741.3
Segment adjusted EBITDA	0	43	52.9
Depreciation and amortization	0	42.3	64.2
Capital expenditures	0	28.5	35
Total assets	0	0	521.5
Corporate and Eliminations [Member]
Segment Reporting Information [Line Items]
Sales	0	0	0
Less: Intersegment sales	0	0	0
Net external sales	0	0	0
Segment adjusted EBITDA	0	0	0
Depreciation and amortization	0	0	0
Capital expenditures	8.4	15.5	12
Total assets	$ 1,200.3	$ 965.8	$ 585.4

Segment and Geographic Inform_4

Segment and Geographic Information - Reconciliation of Operating Profit Loss from Segments to Consolidated (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment adjusted EBITDA	$ 719.8	$ 970.3	$ 1,183.9
Interest expense	(212.3)	(217.3)	(216.3)
Depreciation and amortization	(521.9)	(536.9)	(528.8)
Impairment charges	(510)	(665)	(485.5)
Restructuring and acquisition-related costs	(67.2)	(57.8)	(78.9)
Pension settlements	(0.5)	(9.8)	0
Gain (loss) on sale of business	(1)	(21.3)	15.5
Gain on bargain purchase of business	0	10.8	0
Gain on settlement of capital lease	0	0	15.6
Debt refinancing and redemption costs	(7.9)	(8.4)	(19.4)
Malvern Fire charges, net of recoveries	(9.3)	0	0
Other	0	2.4	0
Loss before income taxes	$ (610.3)	$ (533)	$ (113.9)

Segment and Geographic Inform_5

Segment and Geographic Information - Schedule of Disclosure on Geographic Areas (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 4,710.8	$ 6,530.9	$ 7,270.4
Long-lived assets	3,931.5	4,722.7	5,435.4
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	1,816.7	2,894	3,293.2
Long-lived assets	2,099.4	2,805.8	3,612.3
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	1,808.5	2,353.1	2,547.1
Long-lived assets	1,021.6	1,117.4	1,117.9
South America
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	57.6	105.3	129.7
Long-lived assets	49.7	61.9	70.6
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	317.1	315.4	373.4
Long-lived assets	185.1	191.4	177.6
Asia, excluding China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	160.4	255.8	304.9
Long-lived assets	84.2	106.8	101
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	550.5	607.3	622.1
Long-lived assets	$ 491.5	$ 439.4	$ 356

Unaudited Quarterly Financial_3

Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended														12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020	[1]	Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net sales	$ 1,437.9		$ 1,414.1		$ 515.3		$ 1,343.5		$ 1,430		$ 1,677.4		$ 1,704.3	$ 1,719.2	$ 4,710.8	$ 6,530.9	$ 7,270.4
Gross profit (loss)	236.5		249.8		(98.9)		195.3		183.4		248.7		248.3	222.2	582.7	902.6	1,140.4
Net Income (loss)	36.1		117.2		(213.2)		(501.2)	[2]	(454.4)	[3]	(124.1)	[4]	52.7	41.7	(561.1)	(484.1)	(56.8)
Net Income (Loss) Attributable to AAM	$ 36		$ 117.2		$ (213.2)		$ (501.3)	[2]	$ (454.4)	[3]	$ (124.2)	[4]	$ 52.5	$ 41.6	$ (561.3)	$ (484.5)	$ (57.5)
Basic earnings (loss) per share	$ 0.30	[5]	$ 0.99	[5]	$ (1.88)	[5]	$ (4.45)	[2],[5]	$ (4.04)	[3]	$ (1.10)	[4]	$ 0.45	$ 0.36	$ (4.96)	$ (4.31)	$ (0.51)
Diluted earnings (loss) per share	$ 0.30	[5]	$ 0.99	[5]	$ (1.88)	[5]	$ (4.45)	[2],[5]	$ (4.04)	[3]	$ (1.10)	[4]	$ 0.45	$ 0.36	$ (4.96)	$ (4.31)	$ (0.51)
Impairment charges															$ 510	$ 665	$ 485.5
Impairment of long-lived assets to be disposed of, net of tax											$ 178
Gain (Loss) on disposition of business, net of tax									$ 17
Gain on bargain purchase of business															0	10.8	0
Defined benefit plan, net periodic benefit cost (credit), loss (gain) due to settlement or curtailment, net of tax									8
Driveline and Metal Forming [Member]
Impairment charges							$ 510
Metal Forming [Member]
Net sales															$ 1,105.3	$ 1,453.5	$ 1,617.7
Impairment charges									$ 440
[1]	Many of our plant locations temporarily suspended production or experienced a significant reduction in production volumes during the second quarter of 2020 as a result of the impact of COVID-19.
[2]	In the first quarter of 2020, we recorded a goodwill impairment charge of $510 million that was not subject to tax effect as a result of the significant decline in automotive production volumes due to the impact of COVID-19.
[3]	In the fourth quarter of 2019, we recorded a goodwill impairment charge of $440 million that was not subject to tax effect associated with the annual goodwill impairment test for our Metal Forming reporting unit. We also recorded a loss on the Casting Sale of approximately $17 million, net of tax, recognized a gain on bargain purchase of approximately $10.8 million, which was not subject to tax effect, associated with the acquisition of Mitec, and recognized a loss of approximately $8 million, net of tax, related to pension settlements.
[4]	In the third quarter of 2019, we recorded an impairment charge of approximately $178 million, net of tax, to reduce the carrying value of our U.S. Casting operations to fair value less cost to sell upon reclassification of the assets and liabilities to held-for-sale.
[5]	Full year basic and diluted EPS will not necessarily agree to the sum of the four quarters because each quarter is a separate calculation.

Schedule II - Valuation and Q_3

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowances and reserves, balance	$ 8	$ 8.4	$ 7
Additions, charged to costs and expenses	7	13.2	6.6
Acquisitions and other	0	(0.8)	0
Deductions	10.5	12.8	5.2
Valuation allowances and reserves, balance	4.5	8	8.4
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowances and reserves, balance	196	183.3	180.4
Additions, charged to costs and expenses	19.8	25.4	12.9
Acquisitions and other	0	0	0
Deductions	7.8	12.7	10
Valuation allowances and reserves, balance	208	196	183.3
SEC Schedule, 12-09, Reserve, Inventory [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowances and reserves, balance	20.5	14.4	17.3
Additions, charged to costs and expenses	31.7	31	22.2
Acquisitions and other	0	1.4	0
Deductions	28.8	26.3	25.1
Valuation allowances and reserves, balance	$ 23.4	$ 20.5	$ 14.4