American Axle & Manufacturing (AXL) 10-Q 30 Jul 21 2021 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2021	Jul. 27, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
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
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
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	AXL
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding (in shares)		114,047,028
Entity Central Index Key	0001062231
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net sales	$ 1,283.3	$ 515.3	$ 2,708.4	$ 1,858.8
Cost of goods sold	1,093.3	614.2	2,291.3	1,762.4
Gross profit (loss)	190	(98.9)	417.1	96.4
Selling, general and administrative expenses	86.2	73.8	176.2	164.1
Amortization of intangible assets	21.4	21.6	42.9	43.4
Impairment charges	0	0	0	510
Restructuring and acquisition-related costs	15.9	11.3	33.4	28.9
Loss on sale of business	0.1	0	2.7	1
Operating income (loss)	66.4	(205.6)	161.9	(651)
Interest expense	(49.9)	(54.6)	(101)	(106.1)
Interest income	2.6	3	5.5	5.8
Debt refinancing and redemption costs	(1.3)	0	(2.4)	(1.5)
Other income (expense), net	0.6	0.1	1.8	(2.2)
Income (loss) before income taxes	18.4	(257.1)	65.8	(755)
Income tax expense (benefit)	2.4	(43.9)	11.2	(40.6)
Net income (loss)	16	(213.2)	54.6	(714.4)
Net income attributable to noncontrolling interests	0	0	0	(0.1)
Net income (loss) attributable to AAM	$ 16	$ (213.2)	$ 54.6	$ (714.5)
Basic earnings (loss) per share	$ 0.13	$ (1.88)	$ 0.46	$ (6.33)
Diluted earnings (loss) per share	$ 0.13	$ (1.88)	$ 0.46	$ (6.33)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net income (loss)		$ 16	$ (213.2)	$ 54.6	$ (714.4)
Other comprehensive income (loss)
Defined benefit plans, net of tax	[1]	2.2	1.7	4.3	3.3
Foreign currency translation adjustments		12.2	4.8	1.2	(44)
Changes in cash flow hedges, net of tax	[2]	5.1	8.7	4.8	(26)
Other comprehensive income (loss)		19.5	15.2	10.3	(66.7)
Comprehensive income (loss)		35.5	(198)	64.9	(781.1)
Net income attributable to noncontrolling interests		0	0	0	(0.1)
Foreign currency translation adjustments attributable to noncontrolling interests		0	0	0	0.3
Comprehensive income (loss) attributable to AAM		$ 35.5	$ (198)	$ 64.9	$ (780.9)
[1]	Amounts are net of tax of $(0.5) million and $(1.1) million for the three and six months ended June 30, 2021, and $(0.4) million and $(0.8) million for the three and six months ended June 30, 2020, respectively.
[2]	Amounts are net of tax of $(0.7) million and $(2.0) million for the three and six months ended June 30, 2021, and $(0.5) million and $1.8 million for the three and six months ended June 30, 2020, respectively.

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Other comprehensive income (loss), pension and other postretirement benefit plans, tax	$ (0.5)	$ (0.4)	$ (1.1)	$ (0.8)
Other comprehensive income (loss), derivatives qualifying as hedges, tax	$ (0.7)	$ (0.5)	$ (2)	$ 1.8

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 587.7	$ 557
Accounts receivable, net	798.1	793.2
Inventories, net	395	323.2
Prepaid expenses and other	169.7	203.6
Total current assets	1,950.5	1,877
Property, plant and equipment, net	2,067	2,163.8
Deferred income taxes	115.1	107.8
Goodwill	185.1	185.7
Other intangible assets, net	738.4	780.7
GM postretirement cost sharing asset	235.9	237
Operating lease right-of-use assets	123.2	116.6
Other assets and deferred charges	429.7	447.7
Total assets	5,844.9	5,916.3
Current liabilities
Current portion of long-term debt	116.5	13.7
Accounts payable	647.4	578.9
Accrued compensation and benefits	173.2	170.9
Deferred revenue	24.5	23.4
Current portion of operating lease liabilities	23.8	22.6
Accrued expenses and other	166.7	169.8
Total current liabilities	1,152.1	979.3
Long-term debt, net	3,118.5	3,441.3
Deferred revenue	89.9	91
Deferred income taxes	14	13.2
Long-term portion of operating lease liabilities	100.2	94.4
Postretirement benefits and other long-term liabilities	928.9	923.9
Total liabilities	5,403.6	5,543.1
Stockholders' equity
Common stock, par value $0.01 per share; 150.0 million shares authorized; 122.5 million shares issued as of June 30, 2021 and 121.3 million shares issued as of December 31, 2020	1.3	1.2
Paid-in capital	1,343.3	1,333.3
Accumulated deficit	(265.2)	(319.8)
Treasury stock at cost, 8.4 million shares as of June 30, 2021 and 8.0 million shares as of December 31, 2020	(216.2)	(212)
Accumulated other comprehensive loss
Defined benefit plans, net of tax	(306.7)	(311)
Foreign currency translation adjustments	(99.9)	(101.1)
Unrecognized loss on cash flow hedges, net of tax	(15.3)	(20.1)
Total AAM stockholders' equity	441.3	370.5
Noncontrolling interests in subsidiaries	0	2.7
Total stockholders' equity	441.3	373.2
Total liabilities and stockholders' equity	$ 5,844.9	$ 5,916.3

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Millions	Jun. 30, 2021	Dec. 31, 2020
Common stock, par or stated value per share	$ 0.01	$ 0.01
Common stock, shares authorized	150	150
Common stock, shares, issued	122.5	121.3
Treasury stock, shares	8.4	8

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Net income (loss)	$ 54.6	$ (714.4)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Depreciation and amortization	285.6	268.7
Impairment charges	0	510
Deferred income taxes	(6.8)	(11.2)
Stock-based compensation	10	9.3
Pensions and other postretirement benefits, net of contributions	(5.6)	(2.5)
Loss on sale of business	2.7	1
Loss (gain) on disposal of property, plant and equipment, net	1.7	11.9
Debt refinancing and redemption costs	2.4	1.5
Changes in operating assets and liabilities
Accounts receivable	(8.1)	256.6
Inventories	(67.5)	10.3
Accounts payable and accrued expenses	82.8	(298)
Deferred revenue	2.3	(1.5)
Other assets and liabilities	(7.9)	(44.8)
Net cash provided by (used in) operating activities	346.2	(3.1)
Investing activities
Purchases of property, plant and equipment	(82.4)	(105.6)
Proceeds from sale of property, plant and equipment	1.6	1.4
Purchase buyouts of leased equipment	0	(0.2)
Proceeds (payments) for sale of business, net of cash divested	(0.7)	(4.4)
Acquisition of business	(4.9)	0
Proceeds from insurance claim	12.1	0
Net cash used in investing activities	(74.3)	(108.8)
Financing activities
Proceeds from Revolving Credit Facility	0	350
Payments of Revolving Credit Facility	0	(150)
Proceeds from issuance of long-term debt	22.8	408.8
Payments of long-term debt	(256.6)	(115.6)
Debt issuance costs	0	(10.6)
Purchase of treasury stock	(4.2)	(2.7)
Other financing activities	(2.2)	0.3
Net cash provided by (used in) financing activities	(240.2)	480.2
Effect of exchange rate changes on cash	(1)	(7)
Net increase in cash and cash equivalents	30.7	361.3
Cash and cash equivalents at beginning of period	557	532
Cash and cash equivalents at end of period	587.7	893.3
Supplemental cash flow information
Interest paid	95.1	102
Income taxes paid, net	8	17.6
Non-cash investing activities: Deferred consideration for acquisition of business	$ 10	$ 0

Condensed Consolidated Statem_5

Condensed 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
Common stock, shares, outstanding at Dec. 31, 2019		112.6
Total AAM stockholders' equity at Dec. 31, 2019				$ 1.2	$ 1,313.9	$ 248.6	$ (209.3)	$ (376.8)	$ 2.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM						(501.3)
Net income (loss) attributable to noncontrolling interest									0.1
Stock issued during period, shares, share-based compensation, net of forfeitures		0.8
Stock-based compensation					4.6
New accounting pronouncement, effect of adoption | ASU 2016-13 [Member]						(7.1)
Treasury stock, shares, acquired		(0.4)
Purchase of treasury stock							(2.4)
Changes in cash flow hedges, net of tax								(34.7)
Foreign currency translation adjustments								(48.5)
Foreign currency translation adjustments attributable to noncontrolling interests									(0.3)
Defined benefit plans, net of tax								1.6
Common stock, shares, outstanding at Mar. 31, 2020		113
Total AAM stockholders' equity at Mar. 31, 2020				1.2	1,318.5	(259.8)	(211.7)	(458.4)	2.6
Common stock, shares, outstanding at Dec. 31, 2019		112.6
Total AAM stockholders' equity at Dec. 31, 2019				1.2	1,313.9	248.6	(209.3)	(376.8)	2.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM		$ (714.5)
Net income (loss) attributable to noncontrolling interest		0.1
Purchase of treasury stock		2.7
Changes in cash flow hedges, net of tax	[1]	(26)
Foreign currency translation adjustments		(44)
Foreign currency translation adjustments attributable to noncontrolling interests		(0.3)
Defined benefit plans, net of tax	[2]	$ 3.3
Common stock, shares, outstanding at Jun. 30, 2020		113.3
Total AAM stockholders' equity at Jun. 30, 2020				1.2	1,323.2	(473)	(212)	(443.2)	2.6
Common stock, shares, outstanding at Mar. 31, 2020		113
Total AAM stockholders' equity at Mar. 31, 2020				1.2	1,318.5	(259.8)	(211.7)	(458.4)	2.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM		$ (213.2)				(213.2)
Net income (loss) attributable to noncontrolling interest		$ 0							0
Stock issued during period, shares, share-based compensation, net of forfeitures		0.3
Stock-based compensation					4.7
Treasury stock, shares, acquired		0
Purchase of treasury stock							(0.3)
Changes in cash flow hedges, net of tax		$ 8.7	[1]					8.7
Foreign currency translation adjustments		4.8						4.8
Foreign currency translation adjustments attributable to noncontrolling interests		0
Defined benefit plans, net of tax		$ 1.7	[2]					1.7
Common stock, shares, outstanding at Jun. 30, 2020		113.3
Total AAM stockholders' equity at Jun. 30, 2020				1.2	1,323.2	(473)	(212)	(443.2)	2.6
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM						38.6
Net income (loss) attributable to noncontrolling interest									0
Stock issued during period, shares, share-based compensation, net of forfeitures		1
Exercise of stock options		$ 0.1
Stock-based compensation					5.3
Treasury stock, shares, acquired		(0.4)
Purchase of treasury stock							(4)
Changes in cash flow hedges, net of tax								(0.3)
Foreign currency translation adjustments								(11)
Foreign currency translation adjustments attributable to noncontrolling interests									0
Defined benefit plans, net of tax								2.1
Loss on sale of business									(2.7)
Common stock, shares, outstanding at Mar. 31, 2021		113.9
Total AAM stockholders' equity at Mar. 31, 2021				1.3	1,338.6	(281.2)	(216)	(441.4)	0
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM		54.6
Net income (loss) attributable to noncontrolling interest		0
Purchase of treasury stock		4.2
Changes in cash flow hedges, net of tax	[1]	4.8
Foreign currency translation adjustments		1.2
Foreign currency translation adjustments attributable to noncontrolling interests		0
Defined benefit plans, net of tax	[2]	$ 4.3
Common stock, shares, outstanding at Jun. 30, 2021		114.1
Total AAM stockholders' equity at Jun. 30, 2021		$ 441.3		1.3	1,343.3	(265.2)	(216.2)	(421.9)	0
Common stock, shares, outstanding at Mar. 31, 2021		113.9
Total AAM stockholders' equity at Mar. 31, 2021				1.3	1,338.6	(281.2)	(216)	(441.4)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to AAM		$ 16				16
Net income (loss) attributable to noncontrolling interest		$ 0							0
Stock issued during period, shares, share-based compensation, net of forfeitures		0.2
Stock-based compensation					4.7
Treasury stock, shares, acquired		0
Purchase of treasury stock							(0.2)
Changes in cash flow hedges, net of tax		$ 5.1	[1]					5.1
Foreign currency translation adjustments		12.2						12.2
Foreign currency translation adjustments attributable to noncontrolling interests		0
Defined benefit plans, net of tax		$ 2.2	[2]					2.2
Common stock, shares, outstanding at Jun. 30, 2021		114.1
Total AAM stockholders' equity at Jun. 30, 2021		$ 441.3		$ 1.3	$ 1,343.3	$ (265.2)	$ (216.2)	$ (421.9)	$ 0
[1]	Amounts are net of tax of $(0.7) million and $(2.0) million for the three and six months ended June 30, 2021, and $(0.5) million and $1.8 million for the three and six months ended June 30, 2020, respectively.
[2]	Amounts are net of tax of $(0.5) million and $(1.1) million for the three and six months ended June 30, 2021, and $(0.4) million and $(0.8) million for the three and six months ended June 30, 2020, respectively.

Organization and Basis of Prese

Organization and Basis of Presentation (Notes)	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	1. ORGANIZATION AND BASIS OF PRESENTATION Organization We are a global Tier 1 supplier to the automotive industry. We design, engineer and manufacture driveline and metal forming technologies 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 quality, operational excellence and technology leadership. Basis of Presentation We have prepared the accompanying interim condensed consolidated financial statements in accordance with the instructions to Form 10-Q under the Securities Exchange Act of 1934. These condensed consolidated financial statements are unaudited but include all normal recurring adjustments, which we consider necessary for a fair presentation of the information set forth herein. Results of operations for the periods presented are not necessarily indicative of the results for the full fiscal year. The balance sheet at December 31, 2020 presented herein has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America (GAAP) for complete consolidated financial statements. In order to prepare the accompanying interim condensed consolidated financial statements, we are required to make estimates and assumptions that affect the reported amounts and disclosures in our interim condensed consolidated financial statements. These estimates and assumptions are impacted by risks and uncertainties, including those associated with the Novel Coronavirus (COVID-19) pandemic and the semiconductor supply shortage that is impacting the automotive industry. While we have made estimates and assumptions based on the facts and circumstances available as of the date of this report, the full impact of COVID-19 and the semiconductor shortage cannot be predicted, and actual results could differ materially from those estimates and assumptions. For further information, refer to the audited consolidated financial statements and notes included in our Annual Report on Form 10-K for the year ended December 31, 2020. Commencement of Lease of European Headquarters and Engineering Center (EHEC) In the first six months of 2021, the lease of our new EHEC in Langen, Germany commenced. This lease has a term of 20 years and is classified as a finance lease. We recognized a right-of-use (ROU) asset and finance lease liability of approximately $49 million upon commencement of this lease. The ROU asset is presented in Property, plant and equipment, net and the finance lease liability is presented in Accrued expenses and other (current portion), and Postretirement benefits and other long-term liabilities (long-term portion) in our Condensed Consolidated Balance Sheet at June 30, 2021. Effect of New Accounting Standards and Other Regulatory Pronouncements Accounting Standard Update 2020-04 On March 12, 2020, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) 2020-04 - Reference Rate Reform (Topic 848), and has subsequently issued ASU 2021-01 - 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 expect to utilize certain of the optional expedients and exceptions available under ASU 2020-04 and ASU 2021-01 and we do not expect the adoption of this guidance to have a material impact on our financial statements. Accounting Standard 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 on current tax expense be included in the annual effective tax rate computation in the interim period of the enactment. This guidance became effective and we adopted this guidance on January 1, 2021. The adoption of this guidance did not have a material impact on our consolidated financial statements. 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 they remain applicable to AAM, include 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 received an income tax refund of approximately $6.0 million during the first quarter of 2021 as a result of this provision of the CARES Act. • 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. At June 30, 2021, we had deferred $15.2 million of social security taxes, 50% of which will be paid in the fourth quarter of 2021 and the remainder to be paid in the fourth quarter of 2022.

Restructuring and Acquisition-R

Restructuring and Acquisition-Related Costs (Notes)	6 Months Ended
	Jun. 30, 2021
Restructuring and Related Activities [Abstract]
Business Acquisition, Integration, Restructuring and Other Related Costs [Text Block]	2. RESTRUCTURING AND ACQUISITION-RELATED COSTS In the first quarter of 2020, we initiated a new global restructuring program (the 2020 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 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 first six months of 2021 and 2020 is shown below: Severance Charges Implementation Costs Total (in millions) Accrual at December 31, 2019 $ 4.8 $ 7.4 $ 12.2 Charges 16.3 7.7 24.0 Cash utilization (16.0) (8.9) (24.9) Accrual at June 30, 2020 $ 5.1 $ 6.2 $ 11.3 Accrual at December 31, 2020 $ 1.7 $ 9.8 $ 11.5 Charges 2.0 28.8 30.8 Cash utilization (3.7) (32.9) (36.6) Accrual at June 30, 2021 $ — $ 5.7 $ 5.7 As part of our restructuring actions, we incurred total severance charges of approximately $2.0 million and $16.3 million during the six months ended June 30, 2021 and 2020, respectively. We also incurred total implementation costs of approximately $28.8 million and $7.7 million during the six months ended June 30, 2021 and 2020, respectively. Implementation costs consist primarily of professional fees and plant exit costs. Substantially all of the restructuring costs incurred during the six months ended June 30, 2021 were under the 2020 Program. Approximately $2.3 million and $1.4 million of our total restructuring costs for the six months ended June 30, 2021 related to our Driveline and Metal Forming segments, respectively, while the remainder were corporate costs. Approximately $9.9 million and $10.4 million of our total restructuring costs for the six months ended June 30, 2020 related to our Driveline and Metal Forming 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 expected to be under the 2020 Program. During the three months ended June 30, 2021 we completed our acquisition of a manufacturing facility in Emporium, Pennsylvania, and we continue to incur integration costs related to our acquisition of MPG. The following table represents a summary of charges incurred in the six months ended June 30, 2021 and 2020 associated with acquisition and integration costs: Acquisition-Related Costs Integration Expenses Total (in millions) Charges for the six months ended June 30, 2021 $ 0.2 $ 2.4 $ 2.6 Charges for the six months ended June 30, 2020 — 4.9 4.9 Acquisition-related costs primarily consist of valuation fees incurred. Integration expenses primarily reflect costs incurred for information technology infrastructure and enterprise resource planning systems. Total restructuring charges and acquisition-related charges are presented on a separate line item titled Restructuring and acquisition-related costs in our Condensed Consolidated Statements of Operations, and totaled $15.9 million and $33.4 million for the three and six months ended June 30, 2021, respectively, and $11.3 million and $28.9 million for the three and six months ended June 30, 2020, respectively.

Inventories (Notes)

Inventories (Notes)	6 Months Ended
	Jun. 30, 2021
Inventory Disclosure [Abstract]
Inventory Disclosure [Text Block]	3. 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 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: June 30, 2021 December 31, 2020 (in millions) Raw materials and work-in-progress $ 334.3 $ 276.2 Finished goods 83.8 70.4 Gross inventories 418.1 346.6 Inventory valuation reserves (23.1) (23.4) Inventories, net $ 395.0 $ 323.2

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Notes)	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets Disclosure [Text Block]	4. GOODWILL AND OTHER INTANGIBLE ASSETS Goodwill The following table provides a reconciliation of changes in goodwill for the six months ended June 30, 2021: Consolidated (in millions) Balance at December 31, 2020 $ 185.7 Foreign currency translation (0.6) Balance at June 30, 2021 $ 185.1 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. 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 $510.0 million in the first quarter of 2020, of which $210.8 million was associated with our Driveline reporting unit and $299.2 million was associated with our Metal Forming reporting unit. The Metal Forming impairment charge represented a full impairment of the goodwill associated with that reporting unit. As a result, all remaining goodwill is attributable to our Driveline 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 June 30, 2021, 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. 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: June 30, December 31, 2021 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (in millions) Capitalized computer software $ 48.2 $ (36.8) $ 11.4 $ 47.6 $ (33.9) $ 13.7 Customer platforms 856.2 (269.6) 586.6 856.2 (237.9) 618.3 Customer relationships 53.0 (14.5) 38.5 53.0 (12.8) 40.2 Technology and other 156.5 (54.6) 101.9 156.7 (48.2) 108.5 Total $ 1,113.9 $ (375.5) $ 738.4 $ 1,113.5 $ (332.8) $ 780.7

Long-Term Debt (Notes)

Long-Term Debt (Notes)	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Long-term Debt [Text Block]	5. LONG-TERM DEBT Long-term debt consists of the following: June 30, 2021 December 31, 2020 (in millions) Revolving Credit Facility $ — $ — Term Loan A Facility due 2024 314.5 323.0 Term Loan B Facility due 2024 850.0 1,088.8 6.875% Notes due 2028 400.0 400.0 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 108.7 88.8 Total debt 3,273.2 3,500.6 Less: Current portion of long-term debt 116.5 13.7 Long-term debt 3,156.7 3,486.9 Less: Debt issuance costs 38.2 45.6 Long-term debt, net $ 3,118.5 $ 3,441.3 Senior Secured Credit Facilities In 2017, American Axle & Manufacturing Holdings, Inc. (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, as amended in July 2019 (First Amendment), includes a $340 million term loan A facility (the Term Loan A Facility due 2024), a $1.55 billion term loan B facility (the Term Loan B Facility due 2024) and a $925 million multi-currency revolving credit facility (the Revolving Credit Facility, and together with the Term Loan A Facility due 2024 and the Term Loan B Facility due 2024, the Senior Secured Credit Facilities). The Term Loan A Facility due 2024 and the Term Loan B Facility due 2024 have been paid down from the original amounts through both scheduled and voluntary payments. There are no scheduled payments under the Term Loan B due 2024 until maturity. In April 2020, Holdings, AAM, Inc., and certain subsidiaries of Holdings entered into the Second Amendment (Second Amendment) to the Credit Agreement. 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. In June 2021, Holdings, AAM, Inc., and certain subsidiaries of Holdings entered into an agreement (the Agreement) amending the Second Amendment to the Credit Agreement. For the Amendment Period, the Agreement modified a covenant in the Second Amendment restricting the ability of Holdings, AAM and certain subsidiaries of Holdings to make certain voluntary payments and distributions of, or in respect of, certain senior unsecured notes of AAM during the Amendment Period, which modification permits voluntary payments and redemptions of the 6.25% senior notes due 2025 issued by AAM. In the first quarter of 2021, we made a voluntary prepayment of $100.0 million on our Term Loan B Facility due 2024 and $4.3 million on our Term Loan A Facility due 2024. As a result, we expensed approximately $1.1 million for the write-off of a portion of the unamortized debt issuance costs that we had been amortizing over the expected life of these borrowings. In the second quarter of 2021, we made voluntary prepayments totaling $138.8 million on our Term Loan B Facility due 2024 and $4.2 million on our Term Loan A Facility due 2024. As a result, we expensed approximately $1.3 million for the write-off of a portion of the unamortized debt issuance costs that we had been amortizing over the expected life of these borrowings. At June 30, 2021, we had $895.2 million available under the Revolving Credit Facility. This availability reflects a reduction of $29.8 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 Condensed Consolidated Balance Sheet. Subsequent Event In the second quarter of 2021, we issued an irrevocable notice to the holders of our 6.25% Notes due 2025 to voluntarily redeem a portion of our 6.25% Notes due 2025 in the third quarter of 2021. As a result, we made a principal payment of $100 million and $1.8 million in accrued interest in July 2021. Subsequent to June 30, 2021, we expensed approximately $1.4 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 $3.1 million for the payment of an early redemption premium. 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 $6.0 million in the six months ended June 30, 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 a portion 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. We voluntarily redeemed the remaining $350 million that was outstanding under our 6.625% Notes due 2022 in the third quarter of 2020. Foreign credit facilities We utilize local currency credit facilities to finance the operations of certain foreign subsidiaries. At June 30, 2021, $108.7 million was outstanding under our foreign credit facilities, as compared to $88.8 million at December 31, 2020. At June 30, 2021, an additional $60.7 million was available under our foreign credit facilities.

Derivatives (Notes)

Derivatives (Notes)	6 Months Ended
	Jun. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	6. DERIVATIVES Our business and financial results are affected by fluctuations in global financial markets, including interest rates and currency exchange rates. Our hedging policy has been developed to manage these risks to an acceptable level based on management’s judgment of the appropriate trade-off between risk, opportunity and cost. We do not hold financial instruments for trading or speculative purposes. 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. As of June 30, 2021 and December 31, 2020, we had currency forward contracts outstanding with a total notional amount of $172.1 million and $178.2 million, respectively, that hedge our exposure to changes in foreign currency exchange rates for certain payroll expenses into the first quarter of 2024 and the purchase of certain direct and indirect inventory and other working capital items into the first quarter of 2022. 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. The notional amount of the fixed-to-fixed cross-currency swap is €200.0 million, which was equivalent to $237.1 million and $244.2 million at June 30, 2021 and December 31, 2020, respectively. The fixed-to-fixed cross-currency swap 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 2019, 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. We have the following notional amounts hedged in relation to our variable-to-fixed interest rate swap: $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 and losses into net income (loss) from accumulated other comprehensive income (loss) for those derivative instruments designated as cash flow hedges under ASC 815 - Derivatives and Hedging : Location Gain (Loss) Reclassified During Total of Financial Gain (Loss) Expected of Gain (Loss) Three Months Ended Six Months Ended Statement to be Reclassified Reclassified into June 30, June 30, Line Item During the Net Income 2021 2020 2021 2020 2021 Next 12 Months (in millions) Currency forward contracts Cost of Goods Sold $ 1.8 $ (2.3) $ 4.1 $ (1.0) $ 2,291.3 $ 4.1 Fixed-to-fixed cross-currency swap Other Income (Expense), net (2.1) (3.7) 8.0 — 1.8 1.7 Variable-to-fixed interest rate swap Interest Expense (3.7) (4.0) (7.9) (6.0) (101.0) (13.9) See Note 12 - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (AOCI) for amounts recognized in other comprehensive income (loss) during the three and six months ended June 30, 2021 and 2020. The following table summarizes the amount and location of gains and losses recognized in the Condensed Consolidated Statements of Operations for those derivative instruments not designated as hedging instruments under ASC 815: Gain (Loss) Recognized During Total of Financial Location of Gain (Loss) Three Months Ended Six Months Ended Statement Line Recognized in June 30, June 30, Item Net Income 2021 2020 2021 2020 2021 (in millions) Currency forward contracts Cost of Goods Sold $ — $ 0.8 $ — $ (7.6) $ 2,291.3 Currency forward contracts Other Income (Expense), net 0.5 (0.1) 0.4 (0.5) 1.8

Fair Value (Notes)

Fair Value (Notes)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	7. FAIR VALUE ASC 820 - Fair Value Measurement 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 carrying value 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: June 30, 2021 December 31, 2020 Fair Value Fair Value Input (in millions) Balance Sheet Classification Cash equivalents $ 237.8 $ 206.7 Level 1 Prepaid expenses and other Cash flow hedges - currency forward contracts 4.1 5.8 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 2.7 4.9 Level 2 Nondesignated - currency forward contracts 0.2 0.2 Level 2 Other assets and deferred charges Cash flow hedges - currency forward contracts 1.9 3.3 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 6.3 8.6 Level 2 Accrued expenses and other Cash flow hedges - currency forward contracts — 0.1 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 10.0 17.8 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 13.1 20.6 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 26.4 32.1 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 value due to the frequent resetting of the interest rates. Subsequent Event At June 30, 2021, we have a $3.0 million cost method investment in REE Automotive, an e-mobility company that had previously announced entry into a merger agreement with a Special Purpose Acquisition Company in an effort to become publicly traded. In July 2021, REE completed its merger and, as a result, the form of our investment in REE changed from a cost method investment to an investment in the equity securities of the publicly traded entity. These equity securities will be measured at fair value each reporting period with changes in fair value reported through an unrealized holding gain or loss within Other income (expense), net in our Condensed Consolidated Statement of Operations. We are subject to a customary restriction on transferring any of our shares of the publicly traded entity for 180 days following the closing of the merger. As of July 29, 2021, our investment in REE shares was valued at approximately $41 million based on a closing price on that date of $8.35 per share. We estimated the fair value of the amounts outstanding on our debt using available market information and other observable data, to be as follows: June 30, 2021 December 31, 2020 Carrying Amount Fair Value Carrying Amount Fair Value Input (in millions) Revolving Credit Facility $ — $ — $ — $ — Level 2 Term Loan A Facility due 2024 314.5 315.7 323.0 318.6 Level 2 Term Loan B Facility due 2024 850.0 845.8 1,088.8 1,071.1 Level 2 6.875% Notes due 2028 400.0 436.0 400.0 426.0 Level 2 6.50% Notes due 2027 500.0 527.5 500.0 523.8 Level 2 6.25% Notes due 2026 400.0 411.0 400.0 411.0 Level 2 6.25% Notes due 2025 700.0 721.9 700.0 724.3 Level 2

Employee Benefit Plans (Notes)

Employee Benefit Plans (Notes)	6 Months Ended
	Jun. 30, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	8. EMPLOYEE BENEFIT PLANS The components of net periodic benefit cost (credit) are as follows: Pension Benefits Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions) Service cost $ 0.5 $ 0.5 $ 1.0 $ 1.0 Interest cost 4.3 5.4 8.6 10.8 Expected asset return (9.7) (9.7) (19.4) (19.3) Amortized loss 2.7 2.2 5.4 4.3 Net periodic benefit credit $ (2.2) $ (1.6) $ (4.4) $ (3.2) Other Postretirement Benefits Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions) Service cost $ 0.1 $ 0.1 $ 0.2 $ 0.2 Interest cost 2.1 2.5 4.2 5.1 Amortized loss 0.4 0.3 0.8 0.5 Amortized prior service credit (0.4) (0.4) (0.8) (0.8) Net periodic benefit cost $ 2.2 $ 2.5 $ 4.4 $ 5.0 The noncurrent liabilities associated with our pension and other postretirement benefit plans are classified as Postretirement benefits and other long-term liabilities on our Condensed Consolidated Balance Sheets. As of June 30, 2021 and December 31, 2020, we have a noncurrent pension liability of $130.4 million and $141.2 million, respectively. As of June 30, 2021 and December 31, 2020, we have a noncurrent other postretirement benefits liability of $552.8 million and $556.7 million, respectively. 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 million. We expect our cash payments for other postretirement benefit obligations in 2021, net of GM cost sharing, to be approximately $17 million.

Product Warranties (Notes)

Product Warranties (Notes)	6 Months Ended
	Jun. 30, 2021
Product Warranties Disclosures [Abstract]
Product Warranty Disclosure [Text Block]	9. 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. The following table provides a reconciliation of changes in the product warranty liability: Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions) Beginning balance $ 69.1 $ 64.2 $ 66.7 $ 62.0 Accruals 4.1 0.6 8.4 4.8 Payments (1.8) (0.7) (2.6) (2.0) Adjustment to prior period accruals (7.3) (0.4) (8.0) (0.5) Foreign currency translation 0.2 0.2 (0.2) (0.4) Ending balance $ 64.3 $ 63.9 $ 64.3 $ 63.9

Income Taxes (Notes)

Income Taxes (Notes)	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	10. INCOME TAXES We adjust our effective tax rate each quarter based on our estimated annual effective tax rate. We also record the tax impact of certain discrete, unusual or infrequently occurring items, including changes in judgment about valuation allowances and the effects of changes in tax laws or rates on deferred tax balances, in the interim period in which they occur. In addition, jurisdictions with a projected loss for the year or a year-to-date loss where no tax benefit can be recognized are excluded from the estimated annual effective tax rate. The impact of such an exclusion could result in a higher or lower effective tax rate during a particular quarter, based upon the mix and timing of actual earnings versus annual projections. Income tax expense was $2.4 million for the three months ended June 30, 2021, an effective income tax rate of 13.0%, as compared to income tax benefit of $43.9 million for the three months ended June 30, 2020, an effective income tax rate of 17.1%. Income tax expense was $11.2 million for the six months ended June 30, 2021, an effective income tax rate of 17.0%, as compared to income tax benefit of $40.6 million for the six months ended June 30, 2020, an effective income tax rate of 5.4%. During the three months ended June 30, 2020, we finalized an advance pricing agreement in a foreign jurisdiction, which resulted in a tax benefit of approximately $6.8 million and we recognized a tax benefit of approximately $7.0 million related to our ability to carry back projected current year losses under the CARES Act. In addition, during the three months ended June 30, 2020, we recognized a tax expense of approximately $36 million to establish a partial valuation allowance in the U.S. This partial valuation allowance was released in the third quarter of 2020 as a result of final regulations issued on July 28, 2020 by the Internal Revenue Service and the U.S. Department of Treasury. During the six months ended June 30, 2020, in addition to the items noted above for the three months ended June 30, 2020, we recognized a net tax benefit of approximately $7.5 million related to our ability to carry back losses from prior years under the CARES Act. This income tax benefit was the result of our ability to carry back losses to tax years with the higher 35% corporate income tax rate. Our effective income tax rate for the three and six months ended June 30, 2021 varies from our effective income tax rate for the three and six months ended June 30, 2020 primarily as a result of the items discussed above. In addition, our effective income tax rate for the six months ended June 30, 2021 varies from our effective income tax rate for the six months ended June 30, 2020 as a result of the impact of the goodwill impairment charge recorded during the first quarter of 2020, which had no corresponding income tax benefit. For the three and six months ended June 30, 2021 and 2020, our effective income tax rates vary from the U.S. federal statutory rate of 21% primarily due to favorable foreign tax rates, the impact of tax credits, and the effect of the goodwill impairment charge in the first six months of 2020. In accordance with the guidance in ASC 740 - 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 the available evidence. Due to the uncertainty associated with the extent and ultimate impact of COVID-19 and the semiconductor shortage on global automotive production volumes, we may experience lower than projected earnings in certain jurisdictions in future periods, and as a result, it is reasonably possible that changes in valuation allowances could be recognized in future periods.

Earnings Per Share (Notes)

Earnings Per Share (Notes)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	11. 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): Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions, except per share data) Numerator Net income (loss) attributable to AAM $ 16.0 $ (213.2) $ 54.6 $ (714.5) Less: Net income attributable to participating securities (0.6) — (2.2) — Net income (loss) attributable to common shareholders - Basic and Dilutive $ 15.4 $ (213.2) $ 52.4 $ (714.5) Denominators Basic common shares outstanding - Weighted-average shares outstanding 118.7 118.4 118.5 117.4 Less: Participating securities (4.7) (5.3) (4.7) (4.5) Weighted-average common shares outstanding 114.0 113.1 113.8 112.9 Effect of dilutive securities - Dilutive stock-based compensation 0.4 — 0.2 — Diluted shares outstanding - Adjusted weighted-average shares after assumed conversions 114.4 113.1 114.0 112.9 Basic EPS $ 0.13 $ (1.88) $ 0.46 $ (6.33) Diluted EPS $ 0.13 $ (1.88) $ 0.46 $ (6.33)

Reclassifications out of Accumu

Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Notes)	6 Months Ended
	Jun. 30, 2021
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Disclosure of Reclassification Amount [Text Block]	12. RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) Reclassification adjustments and other activity impacting accumulated other comprehensive income (loss) during the three months ended June 30, 2021 and June 30, 2020 are as follows (in millions) : Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at March 31, 2021 $ (308.9) $ (112.1) $ (20.4) $ (441.4) Other comprehensive income (loss) before reclassifications — 12.2 1.8 14.0 Income tax effect of other comprehensive income (loss) before reclassifications — — 0.4 0.4 Amounts reclassified from accumulated other comprehensive loss 2.7 (a) — 4.0 (b) 6.7 Income taxes reclassified into net income (0.5) — (1.1) (1.6) Net change in accumulated other comprehensive loss 2.2 12.2 5.1 19.5 Balance at June 30, 2021 $ (306.7) $ (99.9) $ (15.3) $ (421.9) Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at March 31, 2020 $ (258.3) $ (149.7) $ (50.4) $ (458.4) Other comprehensive income (loss) before reclassifications — 4.8 (0.8) 4.0 Income tax effect of other comprehensive income (loss) before reclassifications — — 1.2 1.2 Amounts reclassified from accumulated other comprehensive loss 2.1 (a) — 10.0 (b) 12.1 Income taxes reclassified into net income (0.4) — (1.7) (2.1) Net change in accumulated other comprehensive loss 1.7 4.8 8.7 15.2 Balance at June 30, 2020 $ (256.6) $ (144.9) $ (41.7) $ (443.2) (a) These amounts were reclassified from AOCI to Other income (expense), net for the three months ended June 30, 2021 and June 30, 2020. (b) The amounts reclassified from AOCI included $(1.8) million in cost of goods sold (COGS), $3.7 million in interest expense and $2.1 million in Other income (expense), net for the three months ended June 30, 2021 and $2.3 million in COGS, $4.0 million in interest expense and $3.7 million in Other income (expense), net for the three months ended June 30, 2020. Reclassification adjustments and other activity impacting accumulated other comprehensive income (loss) during the six months ended June 30, 2021 and June 30, 2020 are as follows (in millions) : Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at December 31, 2020 $ (311.0) $ (101.1) $ (20.1) $ (432.2) Other comprehensive income (loss) before reclassifications — 0.7 11.0 11.7 Income tax effect of other comprehensive income (loss) before reclassifications — — (2.1) (2.1) Amounts reclassified from accumulated other comprehensive loss 5.4 (a) 0.5 (4.2) (b) 1.7 Income taxes reclassified into net income (1.1) — 0.1 (1.0) Net change in accumulated other comprehensive loss 4.3 1.2 4.8 10.3 Balance at June 30, 2021 $ (306.7) $ (99.9) $ (15.3) $ (421.9) Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at December 31, 2019 $ (259.9) $ (101.2) $ (15.7) $ (376.8) Other comprehensive income (loss) before reclassifications — (43.7) (34.8) (78.5) Income tax effect of other comprehensive income (loss) before reclassifications — — 3.1 3.1 Amounts reclassified from accumulated other comprehensive loss 4.1 (a) — 7.0 (b) 11.1 Income taxes reclassified into net income (0.8) — (1.3) (2.1) Net change in accumulated other comprehensive loss 3.3 (43.7) (26.0) (66.4) Balance at June 30, 2020 $ (256.6) $ (144.9) $ (41.7) $ (443.2) (a) These amounts were reclassified from AOCI to Other income (expense), net for the six months ended June 30, 2021 and June 30, 2020. (b) The amounts reclassified from AOCI included $(4.1) million in cost of goods sold (COGS), $7.9 million in interest expense and $(8.0) million in Other income (expense), net for the six months ended June 30, 2021 and $1.0 million in COGS and $6.0 million in interest expense for the six months ended June 30, 2020.

Revenue from Contracts with Cus

Revenue from Contracts with Customers (Notes)	6 Months Ended
	Jun. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	13. REVENUE FROM CONTRACTS WITH CUSTOMERS Net sales recognized from contracts with customers, disaggregated by segment and geographical location, are presented in the following table for the three and six months ended June 30, 2021 and 2020. Net sales are attributed to regions based on the location of production. Intersegment sales have been excluded from the table. In the first quarter of 2021, we reorganized our segments and moved certain of our Driveline facilities to our Metal Forming segment. The amounts previously reported in the tables below for the three and six months ended June 30, 2020 have been retrospectively restated to reflect this change. Three Months Ended June 30, 2021 Driveline Metal Forming Total North America $ 722.0 $ 276.3 $ 998.3 Asia 100.9 11.4 112.3 Europe 93.8 57.9 151.7 South America 18.2 2.8 21.0 Total $ 934.9 $ 348.4 $ 1,283.3 Three Months Ended June 30, 2020 Driveline Metal Forming Total North America $ 239.7 $ 104.4 $ 344.1 Asia 88.1 10.0 98.1 Europe 46.3 24.5 70.8 South America 1.7 0.6 2.3 Total $ 375.8 $ 139.5 $ 515.3 Six Months Ended June 30, 2021 Driveline Metal Forming Total North America $ 1,495.8 $ 596.7 $ 2,092.5 Asia 222.1 24.2 246.3 Europe 203.8 122.1 325.9 South America 38.2 5.5 43.7 Total $ 1,959.9 $ 748.5 $ 2,708.4 Six Months Ended June 30, 2020 Driveline Metal Forming Total North America $ 964.8 $ 432.2 $ 1,397.0 Asia 191.2 16.1 207.3 Europe 145.2 85.7 230.9 South America 20.4 3.2 23.6 Total $ 1,321.6 $ 537.2 $ 1,858.8 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, 2020 $ 793.2 $ 23.4 $ 91.0 June 30, 2021 798.1 24.5 89.9 Increase/(decrease) $ 4.9 $ 1.1 $ (1.1) Contract liabilities relate to deferred revenue associated with various settlements and commercial agreements for which we have a future performance obligation 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 six months ended June 30, 2021, we amortized approximately $10.0 million of previously recorded contract liabilities into revenue as we satisfied performance obligations with our customers.

Acquisitions and Divestitures (

Acquisitions and Divestitures (Notes)	6 Months Ended
	Jun. 30, 2021
Acquisitions and Divestitures [Abstract]
Acquisitions and Divestitures [Text Block]	14. ACQUISITIONS AND DISPOSITIONS Acquisition of Manufacturing Facility in Emporium, Pennsylvania In May 2021, AAM completed our acquisition of a manufacturing facility in Emporium, Pennsylvania, under which we acquired $14.9 million of net assets that consisted of $5.9 million of inventory and $9.0 million of property, plant and equipment. The purchase price was $14.9 million, which consisted of $4.9 million of cash and $10.0 million of a deferred consideration liability that will be paid to seller at $2.5 million annually over the period 2022 through 2025. As the value of the net assets acquired was equal to the purchase price, no goodwill or gain on bargain purchase was recognized for this acquisition for the period ended June 30, 2021. The operating results of this manufacturing facility for the period from our acquisition date through June 30, 2021 were insignificant to AAM's Condensed Consolidated Statement of Operations for this period. Further we have not disclosed pro forma revenue and earnings for the six months ended June 30, 2021 and 2020 as the operating results of this manufacturing facility would be insignificant to AAM's consolidated results for these periods. Sale of Interest in Consolidated Joint Venture In the six months ended June 30, 2021, we completed the sale of our ownership interest in a consolidated joint venture and received cash proceeds of approximately $2.6 million. As a result of the sale and deconsolidation of this joint venture, we recognized a loss of $2.7 million. Subsequent to the sale of this joint venture, we no longer present noncontrolling interest in our condensed consolidated financial statements as all consolidated entities are wholly-owned.

Manufacturing Facility Fire and

Manufacturing Facility Fire and Insurance Recovery (Notes)	6 Months Ended
	Jun. 30, 2021
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 and we were able to maintain continuity of supply to our customers without any significant disruptions. 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 the six months ended June 30, 2021, we recorded $12.2 million of charges primarily related to transportation and freight, asset repairs and other costs incurred to resume or relocate operations and ensure continuity of supply to our customers. We also recorded an estimated insurance recovery of $17.6 million and received reimbursements and advances under our insurance policies of approximately $40.1 million, of which approximately $28.0 million is presented as an operating cash flow and approximately $12.1 million is presented as an investing cash flow in our Condensed Consolidated Statement of Cash Flows. This resulted in net pre-tax income in our Condensed Consolidated Statement of Operations of approximately $5.4 million in Cost of goods sold for the six months ended June 30, 2021. At June 30, 2021, $20.6 million of insurance recovery receivable is included in Prepaid expenses and other in our Condensed Consolidated Balance Sheet. Since the date of the Malvern Fire and the establishment of the insurance claim, we have incurred $48.7 million of total charges primarily related to site services and clean-up, transportation and freight, asset repairs and other costs incurred to resume or relocate operations and ensure continuity of supply to our customers. In addition, we have recorded a total of $27.0 million of costs primarily associated with the write-down of property, plant and equipment as a result of damage from the fire. We have recorded total estimated insurance recoveries of $71.8 million and have received total reimbursements and advances under our insurance policies of $51.2 million, of which $11.1 million was received in 2020 and $40.1 million was received in the first six months of 2021. 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 June 30, 2021, we have estimated the amount of expected insurance proceeds recoverable in consideration of the policy provisions, estimated repair costs or actual cash value of damaged assets, and claim eligible expenses incurred from the date of the fire. We expect the claim settlement process to continue through 2021 and, 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.

Segment Reporting (Notes)

Segment Reporting (Notes)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Segment Reporting Disclosure [Text Block]	16. SEGMENT REPORTING Our business is organized into Driveline and Metal Forming segments, with each representing a reportable segment under ASC 280 Segment Reporting . In the first quarter of 2021, we completed a reorganization of our segments, which included moving certain locations that were previously reported under our Driveline segment to our Metal Forming segment in order to better align our product and process technologies. The amounts in the tables below for the three and six months ended June 30, 2020 have been retrospectively restated to reflect this reorganization. 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 to the segments. 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, 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 Original Equipment Manufacturers 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. We define EBITDA to be earnings before interest expense, income taxes, depreciation and amortization. Segment Adjusted EBITDA is defined as EBITDA for our reportable segments excluding the impact of restructuring and acquisition-related costs, debt refinancing and redemption costs, loss on the sale of a business, impairment charges, pension settlements and non-recurring items. The following tables represent information by reportable segment for the three months ended June 30, 2021 and 2020 (in millions) : Three Months Ended June 30, 2021 Driveline Metal Forming Total Sales $ 935.4 $ 440.1 $ 1,375.5 Less: intersegment sales 0.5 91.7 92.2 Net external sales $ 934.9 $ 348.4 $ 1,283.3 Segment Adjusted EBITDA $ 151.3 $ 71.3 $ 222.6 Three Months Ended June 30, 2020 Driveline Metal Forming Total Sales $ 375.9 $ 168.2 $ 544.1 Less: intersegment sales 0.1 28.7 28.8 Net external sales $ 375.8 $ 139.5 $ 515.3 Segment Adjusted EBITDA $ (25.0) $ (27.1) $ (52.1) The following tables represent information by reportable segment for the six months ended June 30, 2021 and 2020 (in millions) : Six Months Ended June 30, 2021 Driveline Metal Forming Total Sales $ 1,961.5 $ 929.4 $ 2,890.9 Less: intersegment sales 1.6 180.9 182.5 Net external sales $ 1,959.9 $ 748.5 $ 2,708.4 Segment Adjusted EBITDA $ 321.8 $ 163.7 $ 485.5 Six Months Ended June 30, 2020 Driveline Metal Forming Total Sales $ 1,321.8 $ 650.3 $ 1,972.1 Less: intersegment sales 0.2 113.1 113.3 Net external sales $ 1,321.6 $ 537.2 $ 1,858.8 Segment Adjusted EBITDA $ 109.5 $ 51.7 $ 161.2 The following table represents a reconciliation of Total Segment Adjusted EBITDA to consolidated income (loss) before income taxes for the three and six months ended June 30, 2021 and 2020 (in millions) : Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Total segment adjusted EBITDA $ 222.6 $ (52.1) $ 485.5 $ 161.2 Interest expense (49.9) (54.6) (101.0) (106.1) Depreciation and amortization (143.6) (139.1) (285.6) (268.7) Restructuring and acquisition-related costs (15.9) (11.3) (33.4) (28.9) Loss on sale of business (0.1) — (2.7) (1.0) Debt refinancing and redemption costs (1.3) — (2.4) (1.5) Impairment charges — — — (510.0) Non-recurring items: Malvern Fire charges, net of recoveries 6.6 — 5.4 — Income (loss) before income taxes $ 18.4 $ (257.1) $ 65.8 $ (755.0)

Organization and Basis of Pre_2

Organization and Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of Presentation We have prepared the accompanying interim condensed consolidated financial statements in accordance with the instructions to Form 10-Q under the Securities Exchange Act of 1934. These condensed consolidated financial statements are unaudited but include all normal recurring adjustments, which we consider necessary for a fair presentation of the information set forth herein. Results of operations for the periods presented are not necessarily indicative of the results for the full fiscal year. The balance sheet at December 31, 2020 presented herein has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America (GAAP) for complete consolidated financial statements. In order to prepare the accompanying interim condensed consolidated financial statements, we are required to make estimates and assumptions that affect the reported amounts and disclosures in our interim condensed consolidated financial statements. These estimates and assumptions are impacted by risks and uncertainties, including those associated with the Novel Coronavirus (COVID-19) pandemic and the semiconductor supply shortage that is impacting the automotive industry. While we have made estimates and assumptions based on the facts and circumstances available as of the date of this report, the full impact of COVID-19 and the semiconductor shortage cannot be predicted, and actual results could differ materially from those estimates and assumptions. For further information, refer to the audited consolidated financial statements and notes included in our Annual Report on Form 10-K for the year ended December 31, 2020.
New Accounting Pronouncements and Other Regulatory Pronouncements, Policy [Policy Text Block]	Effect of New Accounting Standards and Other Regulatory Pronouncements Accounting Standard Update 2020-04 On March 12, 2020, the Financial Accounting Standards Board (FASB) issued Accounting Standard Update (ASU) 2020-04 - Reference Rate Reform (Topic 848), and has subsequently issued ASU 2021-01 - 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 expect to utilize certain of the optional expedients and exceptions available under ASU 2020-04 and ASU 2021-01 and we do not expect the adoption of this guidance to have a material impact on our financial statements. Accounting Standard 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 on current tax expense be included in the annual effective tax rate computation in the interim period of the enactment. This guidance became effective and we adopted this guidance on January 1, 2021. The adoption of this guidance did not have a material impact on our consolidated financial statements. 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 they remain applicable to AAM, include 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 received an income tax refund of approximately $6.0 million during the first quarter of 2021 as a result of this provision of the CARES Act. • 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. At June 30, 2021, we had deferred $15.2 million of social security taxes, 50% of which will be paid in the fourth quarter of 2021 and the remainder to be paid in the fourth quarter of 2022.

Restructuring and Acquisition_2

Restructuring and Acquisition-Related Costs (Tables)	6 Months Ended
	Jun. 30, 2021
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs [Table Text Block]	A summary of our restructuring activity for the first six months of 2021 and 2020 is shown below: Severance Charges Implementation Costs Total (in millions) Accrual at December 31, 2019 $ 4.8 $ 7.4 $ 12.2 Charges 16.3 7.7 24.0 Cash utilization (16.0) (8.9) (24.9) Accrual at June 30, 2020 $ 5.1 $ 6.2 $ 11.3 Accrual at December 31, 2020 $ 1.7 $ 9.8 $ 11.5 Charges 2.0 28.8 30.8 Cash utilization (3.7) (32.9) (36.6) Accrual at June 30, 2021 $ — $ 5.7 $ 5.7
Business Combination, Separately Recognized Transactions [Table Text Block]	During the three months ended June 30, 2021 we completed our acquisition of a manufacturing facility in Emporium, Pennsylvania, and we continue to incur integration costs related to our acquisition of MPG. The following table represents a summary of charges incurred in the six months ended June 30, 2021 and 2020 associated with acquisition and integration costs: Acquisition-Related Costs Integration Expenses Total (in millions) Charges for the six months ended June 30, 2021 $ 0.2 $ 2.4 $ 2.6 Charges for the six months ended June 30, 2020 — 4.9 4.9

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Jun. 30, 2021
Inventory Disclosure [Abstract]
Schedule of Inventory, Current [Table Text Block]	Inventories consist of the following: June 30, 2021 December 31, 2020 (in millions) Raw materials and work-in-progress $ 334.3 $ 276.2 Finished goods 83.8 70.4 Gross inventories 418.1 346.6 Inventory valuation reserves (23.1) (23.4) Inventories, net $ 395.0 $ 323.2

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill [Table Text Block]	The following table provides a reconciliation of changes in goodwill for the six months ended June 30, 2021: Consolidated (in millions) Balance at December 31, 2020 $ 185.7 Foreign currency translation (0.6) Balance at June 30, 2021 $ 185.1
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: June 30, December 31, 2021 2020 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (in millions) Capitalized computer software $ 48.2 $ (36.8) $ 11.4 $ 47.6 $ (33.9) $ 13.7 Customer platforms 856.2 (269.6) 586.6 856.2 (237.9) 618.3 Customer relationships 53.0 (14.5) 38.5 53.0 (12.8) 40.2 Technology and other 156.5 (54.6) 101.9 156.7 (48.2) 108.5 Total $ 1,113.9 $ (375.5) $ 738.4 $ 1,113.5 $ (332.8) $ 780.7

Long-Term Debt (Tables)

Long-Term Debt (Tables)	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	Long-term debt consists of the following: June 30, 2021 December 31, 2020 (in millions) Revolving Credit Facility $ — $ — Term Loan A Facility due 2024 314.5 323.0 Term Loan B Facility due 2024 850.0 1,088.8 6.875% Notes due 2028 400.0 400.0 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 108.7 88.8 Total debt 3,273.2 3,500.6 Less: Current portion of long-term debt 116.5 13.7 Long-term debt 3,156.7 3,486.9 Less: Debt issuance costs 38.2 45.6 Long-term debt, net $ 3,118.5 $ 3,441.3

Derivatives (Tables)

Derivatives (Tables)	6 Months Ended
	Jun. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block]	The following table summarizes the reclassification of pre-tax derivative gains and losses into net income (loss) from accumulated other comprehensive income (loss) for those derivative instruments designated as cash flow hedges under ASC 815 - Derivatives and Hedging : Location Gain (Loss) Reclassified During Total of Financial Gain (Loss) Expected of Gain (Loss) Three Months Ended Six Months Ended Statement to be Reclassified Reclassified into June 30, June 30, Line Item During the Net Income 2021 2020 2021 2020 2021 Next 12 Months (in millions) Currency forward contracts Cost of Goods Sold $ 1.8 $ (2.3) $ 4.1 $ (1.0) $ 2,291.3 $ 4.1 Fixed-to-fixed cross-currency swap Other Income (Expense), net (2.1) (3.7) 8.0 — 1.8 1.7 Variable-to-fixed interest rate swap Interest Expense (3.7) (4.0) (7.9) (6.0) (101.0) (13.9) See Note 12 - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (AOCI) for amounts recognized in other comprehensive income (loss) during the three and six months ended June 30, 2021 and 2020. The following table summarizes the amount and location of gains and losses recognized in the Condensed Consolidated Statements of Operations for those derivative instruments not designated as hedging instruments under ASC 815: Gain (Loss) Recognized During Total of Financial Location of Gain (Loss) Three Months Ended Six Months Ended Statement Line Recognized in June 30, June 30, Item Net Income 2021 2020 2021 2020 2021 (in millions) Currency forward contracts Cost of Goods Sold $ — $ 0.8 $ — $ (7.6) $ 2,291.3 Currency forward contracts Other Income (Expense), net 0.5 (0.1) 0.4 (0.5) 1.8

Fair Value (Tables)

Fair Value (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The estimated carrying value 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: June 30, 2021 December 31, 2020 Fair Value Fair Value Input (in millions) Balance Sheet Classification Cash equivalents $ 237.8 $ 206.7 Level 1 Prepaid expenses and other Cash flow hedges - currency forward contracts 4.1 5.8 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 2.7 4.9 Level 2 Nondesignated - currency forward contracts 0.2 0.2 Level 2 Other assets and deferred charges Cash flow hedges - currency forward contracts 1.9 3.3 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 6.3 8.6 Level 2 Accrued expenses and other Cash flow hedges - currency forward contracts — 0.1 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 10.0 17.8 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 13.1 20.6 Level 2 Cash flow hedges - variable-to-fixed interest rate swap 26.4 32.1 Level 2
Fair Value, Financial Instruments not Carried at Fair Value [Table Text Block]	We estimated the fair value of the amounts outstanding on our debt using available market information and other observable data, to be as follows: June 30, 2021 December 31, 2020 Carrying Amount Fair Value Carrying Amount Fair Value Input (in millions) Revolving Credit Facility $ — $ — $ — $ — Level 2 Term Loan A Facility due 2024 314.5 315.7 323.0 318.6 Level 2 Term Loan B Facility due 2024 850.0 845.8 1,088.8 1,071.1 Level 2 6.875% Notes due 2028 400.0 436.0 400.0 426.0 Level 2 6.50% Notes due 2027 500.0 527.5 500.0 523.8 Level 2 6.25% Notes due 2026 400.0 411.0 400.0 411.0 Level 2 6.25% Notes due 2025 700.0 721.9 700.0 724.3 Level 2

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Schedule of Net Benefit (Credits) Costs [Table Text Block]	The components of net periodic benefit cost (credit) are as follows: Pension Benefits Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions) Service cost $ 0.5 $ 0.5 $ 1.0 $ 1.0 Interest cost 4.3 5.4 8.6 10.8 Expected asset return (9.7) (9.7) (19.4) (19.3) Amortized loss 2.7 2.2 5.4 4.3 Net periodic benefit credit $ (2.2) $ (1.6) $ (4.4) $ (3.2) Other Postretirement Benefits Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions) Service cost $ 0.1 $ 0.1 $ 0.2 $ 0.2 Interest cost 2.1 2.5 4.2 5.1 Amortized loss 0.4 0.3 0.8 0.5 Amortized prior service credit (0.4) (0.4) (0.8) (0.8) Net periodic benefit cost $ 2.2 $ 2.5 $ 4.4 $ 5.0

Product Warranties (Tables)

Product Warranties (Tables)	6 Months Ended
	Jun. 30, 2021
Product Warranties Disclosures [Abstract]
Schedule of Product Warranty Liability [Table Text Block]	The following table provides a reconciliation of changes in the product warranty liability: Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions) Beginning balance $ 69.1 $ 64.2 $ 66.7 $ 62.0 Accruals 4.1 0.6 8.4 4.8 Payments (1.8) (0.7) (2.6) (2.0) Adjustment to prior period accruals (7.3) (0.4) (8.0) (0.5) Foreign currency translation 0.2 0.2 (0.2) (0.4) Ending balance $ 64.3 $ 63.9 $ 64.3 $ 63.9

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2021
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): Three Months Ended Six Months Ended June 30, June 30, 2021 2020 2021 2020 (in millions, except per share data) Numerator Net income (loss) attributable to AAM $ 16.0 $ (213.2) $ 54.6 $ (714.5) Less: Net income attributable to participating securities (0.6) — (2.2) — Net income (loss) attributable to common shareholders - Basic and Dilutive $ 15.4 $ (213.2) $ 52.4 $ (714.5) Denominators Basic common shares outstanding - Weighted-average shares outstanding 118.7 118.4 118.5 117.4 Less: Participating securities (4.7) (5.3) (4.7) (4.5) Weighted-average common shares outstanding 114.0 113.1 113.8 112.9 Effect of dilutive securities - Dilutive stock-based compensation 0.4 — 0.2 — Diluted shares outstanding - Adjusted weighted-average shares after assumed conversions 114.4 113.1 114.0 112.9 Basic EPS $ 0.13 $ (1.88) $ 0.46 $ (6.33) Diluted EPS $ 0.13 $ (1.88) $ 0.46 $ (6.33)

Reclassifications out of Accu_2

Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2021
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Abstract]
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	Reclassification adjustments and other activity impacting accumulated other comprehensive income (loss) during the three months ended June 30, 2021 and June 30, 2020 are as follows (in millions) : Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at March 31, 2021 $ (308.9) $ (112.1) $ (20.4) $ (441.4) Other comprehensive income (loss) before reclassifications — 12.2 1.8 14.0 Income tax effect of other comprehensive income (loss) before reclassifications — — 0.4 0.4 Amounts reclassified from accumulated other comprehensive loss 2.7 (a) — 4.0 (b) 6.7 Income taxes reclassified into net income (0.5) — (1.1) (1.6) Net change in accumulated other comprehensive loss 2.2 12.2 5.1 19.5 Balance at June 30, 2021 $ (306.7) $ (99.9) $ (15.3) $ (421.9) Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at March 31, 2020 $ (258.3) $ (149.7) $ (50.4) $ (458.4) Other comprehensive income (loss) before reclassifications — 4.8 (0.8) 4.0 Income tax effect of other comprehensive income (loss) before reclassifications — — 1.2 1.2 Amounts reclassified from accumulated other comprehensive loss 2.1 (a) — 10.0 (b) 12.1 Income taxes reclassified into net income (0.4) — (1.7) (2.1) Net change in accumulated other comprehensive loss 1.7 4.8 8.7 15.2 Balance at June 30, 2020 $ (256.6) $ (144.9) $ (41.7) $ (443.2) (a) These amounts were reclassified from AOCI to Other income (expense), net for the three months ended June 30, 2021 and June 30, 2020. (b) The amounts reclassified from AOCI included $(1.8) million in cost of goods sold (COGS), $3.7 million in interest expense and $2.1 million in Other income (expense), net for the three months ended June 30, 2021 and $2.3 million in COGS, $4.0 million in interest expense and $3.7 million in Other income (expense), net for the three months ended June 30, 2020. Reclassification adjustments and other activity impacting accumulated other comprehensive income (loss) during the six months ended June 30, 2021 and June 30, 2020 are as follows (in millions) : Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at December 31, 2020 $ (311.0) $ (101.1) $ (20.1) $ (432.2) Other comprehensive income (loss) before reclassifications — 0.7 11.0 11.7 Income tax effect of other comprehensive income (loss) before reclassifications — — (2.1) (2.1) Amounts reclassified from accumulated other comprehensive loss 5.4 (a) 0.5 (4.2) (b) 1.7 Income taxes reclassified into net income (1.1) — 0.1 (1.0) Net change in accumulated other comprehensive loss 4.3 1.2 4.8 10.3 Balance at June 30, 2021 $ (306.7) $ (99.9) $ (15.3) $ (421.9) Defined Benefit Plans Foreign Currency Translation Adjustments Unrecognized Gain (Loss) on Cash Flow Hedges Total Balance at December 31, 2019 $ (259.9) $ (101.2) $ (15.7) $ (376.8) Other comprehensive income (loss) before reclassifications — (43.7) (34.8) (78.5) Income tax effect of other comprehensive income (loss) before reclassifications — — 3.1 3.1 Amounts reclassified from accumulated other comprehensive loss 4.1 (a) — 7.0 (b) 11.1 Income taxes reclassified into net income (0.8) — (1.3) (2.1) Net change in accumulated other comprehensive loss 3.3 (43.7) (26.0) (66.4) Balance at June 30, 2020 $ (256.6) $ (144.9) $ (41.7) $ (443.2) (a) These amounts were reclassified from AOCI to Other income (expense), net for the six months ended June 30, 2021 and June 30, 2020. (b) The amounts reclassified from AOCI included $(4.1) million in cost of goods sold (COGS), $7.9 million in interest expense and $(8.0) million in Other income (expense), net for the six months ended June 30, 2021 and $1.0 million in COGS and $6.0 million in interest expense for the six months ended June 30, 2020.

Disaggregation of Revenue (Tabl

Disaggregation of Revenue (Tables)	6 Months Ended
	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers	Net sales recognized from contracts with customers, disaggregated by segment and geographical location, are presented in the following table for the three and six months ended June 30, 2021 and 2020. Net sales are attributed to regions based on the location of production. Intersegment sales have been excluded from the table. In the first quarter of 2021, we reorganized our segments and moved certain of our Driveline facilities to our Metal Forming segment. The amounts previously reported in the tables below for the three and six months ended June 30, 2020 have been retrospectively restated to reflect this change. Three Months Ended June 30, 2021 Driveline Metal Forming Total North America $ 722.0 $ 276.3 $ 998.3 Asia 100.9 11.4 112.3 Europe 93.8 57.9 151.7 South America 18.2 2.8 21.0 Total $ 934.9 $ 348.4 $ 1,283.3 Three Months Ended June 30, 2020 Driveline Metal Forming Total North America $ 239.7 $ 104.4 $ 344.1 Asia 88.1 10.0 98.1 Europe 46.3 24.5 70.8 South America 1.7 0.6 2.3 Total $ 375.8 $ 139.5 $ 515.3 Six Months Ended June 30, 2021 Driveline Metal Forming Total North America $ 1,495.8 $ 596.7 $ 2,092.5 Asia 222.1 24.2 246.3 Europe 203.8 122.1 325.9 South America 38.2 5.5 43.7 Total $ 1,959.9 $ 748.5 $ 2,708.4 Six Months Ended June 30, 2020 Driveline Metal Forming Total North America $ 964.8 $ 432.2 $ 1,397.0 Asia 191.2 16.1 207.3 Europe 145.2 85.7 230.9 South America 20.4 3.2 23.6 Total $ 1,321.6 $ 537.2 $ 1,858.8 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, 2020 $ 793.2 $ 23.4 $ 91.0 June 30, 2021 798.1 24.5 89.9 Increase/(decrease) $ 4.9 $ 1.1 $ (1.1)

Segment Reporting (Tables)

Segment Reporting (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	The following tables represent information by reportable segment for the three months ended June 30, 2021 and 2020 (in millions) : Three Months Ended June 30, 2021 Driveline Metal Forming Total Sales $ 935.4 $ 440.1 $ 1,375.5 Less: intersegment sales 0.5 91.7 92.2 Net external sales $ 934.9 $ 348.4 $ 1,283.3 Segment Adjusted EBITDA $ 151.3 $ 71.3 $ 222.6 Three Months Ended June 30, 2020 Driveline Metal Forming Total Sales $ 375.9 $ 168.2 $ 544.1 Less: intersegment sales 0.1 28.7 28.8 Net external sales $ 375.8 $ 139.5 $ 515.3 Segment Adjusted EBITDA $ (25.0) $ (27.1) $ (52.1) The following tables represent information by reportable segment for the six months ended June 30, 2021 and 2020 (in millions) : Six Months Ended June 30, 2021 Driveline Metal Forming Total Sales $ 1,961.5 $ 929.4 $ 2,890.9 Less: intersegment sales 1.6 180.9 182.5 Net external sales $ 1,959.9 $ 748.5 $ 2,708.4 Segment Adjusted EBITDA $ 321.8 $ 163.7 $ 485.5 Six Months Ended June 30, 2020 Driveline Metal Forming Total Sales $ 1,321.8 $ 650.3 $ 1,972.1 Less: intersegment sales 0.2 113.1 113.3 Net external sales $ 1,321.6 $ 537.2 $ 1,858.8 Segment Adjusted EBITDA $ 109.5 $ 51.7 $ 161.2
Reconciliation of Total Segment Adjusted EBITDA to Income Before Income Taxes [Table Text Block]	The following table represents a reconciliation of Total Segment Adjusted EBITDA to consolidated income (loss) before income taxes for the three and six months ended June 30, 2021 and 2020 (in millions) : Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Total segment adjusted EBITDA $ 222.6 $ (52.1) $ 485.5 $ 161.2 Interest expense (49.9) (54.6) (101.0) (106.1) Depreciation and amortization (143.6) (139.1) (285.6) (268.7) Restructuring and acquisition-related costs (15.9) (11.3) (33.4) (28.9) Loss on sale of business (0.1) — (2.7) (1.0) Debt refinancing and redemption costs (1.3) — (2.4) (1.5) Impairment charges — — — (510.0) Non-recurring items: Malvern Fire charges, net of recoveries 6.6 — 5.4 — Income (loss) before income taxes $ 18.4 $ (257.1) $ 65.8 $ (755.0)

Organization and Basis of Pre_3

Organization and Basis of Presentation (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Jun. 30, 2021USD ($)EmployeesCountriesFacilities
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Entity Number of Employees | Employees			20,000
Number of Facilities | Facilities			80
Number of Countries in which Entity Operates | Countries			17
Finance Lease, Right-of-Use Asset, before Accumulated Amortization	$ 49
Deferred payments of social security tax			$ 15.2
CARES Act [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Refundable payroll tax credit			$ 6.7
CARES Act [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Proceeds from Income Tax Refunds	6
Loss carryback related to the CARES Act
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Other Tax Expense (Benefit)		$ 14.4
GERMANY
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Finance Lease, Liability	$ 49

Restructuring and Acquisition_3

Restructuring and Acquisition-Related Costs (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Restructuring Reserve [Roll Forward]
Restructuring reserve	$ 11.5	$ 12.2
Charges	30.8	24
Cash utilization	(36.6)	(24.9)
Restructuring reserve	5.7	11.3
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve	1.7	4.8
Charges	2	16.3
Cash utilization	(3.7)	(16)
Restructuring reserve	0	5.1
Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve	9.8	7.4
Charges	28.8	7.7
Cash utilization	(32.9)	(8.9)
Restructuring reserve	$ 5.7	$ 6.2

Restructuring Reserve Narrative

Restructuring Reserve Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 30.8	$ 24
Minimum [Member] | Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost			$ 50
Maximum [Member] | Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost			$ 65
Driveline [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	2.3	9.9
Metal Forming [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	1.4	10.4
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	2	16.3
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 28.8	$ 7.7

Business Combinations, Separate

Business Combinations, Separately Recognized Transactions Table (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Restructuring and Related Activities [Abstract]
Business Combination, Acquisition Related Costs			$ 0.2	$ 0
Integration expenses			2.4	4.9
Total acquisition and integration charges			2.6	4.9
Restructuring and acquisition-related costs	$ 15.9	$ 11.3	$ 33.4	$ 28.9

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Inventory [Line Items]
Raw materials and work-in-progress	$ 334.3	$ 276.2
Finished goods	83.8	70.4
Gross inventories	418.1	346.6
Inventory valuation reserves	(23.1)	(23.4)
Inventories, net	$ 395	$ 323.2

Goodwill Rollforward (Details)

Goodwill Rollforward (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Goodwill [Roll Forward]
Goodwill	$ 185.7
Foreign currency translation	(0.6)
Goodwill	$ 185.1

Goodwill Narrative (Details)

Goodwill Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Jun. 30, 2021
Goodwill [Line Items]
Goodwill impairment charge	$ 510
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.
Goodwill, Impaired, Accumulated Impairment Loss		$ 1,435.5
Driveline [Member]
Goodwill [Line Items]
Goodwill impairment charge	$ 210.8
Metal Forming [Member]
Goodwill [Line Items]
Goodwill impairment charge	$ 299.2

Intangible Assets Table (Detail

Intangible Assets Table (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,113.9		$ 1,113.9		$ 1,113.5
Accumulated Amortization	(375.5)		(375.5)		(332.8)
Net Carrying Amount	738.4		738.4		780.7
Amortization of intangible assets	21.4	$ 21.6	42.9	$ 43.4
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Current Fiscal Year	80		80
Finite-Lived Intangible Assets, Amortization Expense, Year Two	80		80
Finite-Lived Intangible Assets, Amortization Expense, Year Three	80		80
Finite-Lived Intangible Assets, Amortization Expense, Year Four	80		80
Finite-Lived Intangible Assets, Amortization Expense, Year Five	80		80
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Current Fiscal Year	85		85
Finite-Lived Intangible Assets, Amortization Expense, Year Two	85		85
Finite-Lived Intangible Assets, Amortization Expense, Year Three	85		85
Finite-Lived Intangible Assets, Amortization Expense, Year Four	85		85
Finite-Lived Intangible Assets, Amortization Expense, Year Five	85		85
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	48.2		48.2		47.6
Accumulated Amortization	(36.8)		(36.8)		(33.9)
Net Carrying Amount	11.4		11.4		13.7
Customer Platforms - Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	856.2		856.2		856.2
Accumulated Amortization	(269.6)		(269.6)		(237.9)
Net Carrying Amount	586.6		586.6		618.3
Customer Relationships - Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	53		53		53
Accumulated Amortization	(14.5)		(14.5)		(12.8)
Net Carrying Amount	38.5		38.5		40.2
Technology-Based Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	156.5		156.5		156.7
Accumulated Amortization	(54.6)		(54.6)		(48.2)
Net Carrying Amount	$ 101.9		$ 101.9		$ 108.5

Schedule of Long-Term Debt (Det

Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jul. 29, 2019
Debt Instrument [Line Items]
Foreign credit facilities and other	$ 108.7	$ 88.8
Total debt	3,273.2	3,500.6
Current portion of long-term debt	116.5	13.7
Long-term debt	3,156.7	3,486.9
Long-term debt, net	3,118.5	3,441.3
Total Debt Instruments excluding Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt Issuance Costs	38.2	45.6
Revolving 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	314.5	323	$ 340
Secured Debt [Member] | Term Loan B due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt	850	1,088.8	$ 1,550
Unsecured Debt [Member] | 6.875% Notes [Member]
Debt Instrument [Line Items]
Long-term Debt	400	400
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
Unsecured Debt [Member] | 6.25% Notes due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 700	$ 700

Senior Secured Credit Facilitie

Senior Secured Credit Facilities Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Jul. 29, 2019
Debt Instrument [Line Items]
Repayments of Long-term Debt			$ 256.6	$ 115.6
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 925		925
Secured Debt [Member] | Term Loan A Due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt	314.5		314.5		$ 323	$ 340
Repayments of Long-term Debt	4.2	$ 4.3
Secured Debt [Member] | Term Loan B due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt	850		850		1,088.8	$ 1,550
Repayments of Long-term Debt	138.8	100
Secured Debt [Member] | Term Loan A & Term Loan B
Debt Instrument [Line Items]
Write off of Deferred Debt Issuance Cost	1.3	$ 1.1
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	895.2		895.2
Line of Credit Facility, Standby Letters of Credit Issued Against the Facility	29.8		29.8
Unsecured Debt [Member] | 6.25% Notes due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 700		$ 700		$ 700
Debt Instrument, Interest Rate, Stated Percentage	6.25%		6.25%

Other Debt Disclosures Narrativ

Other Debt Disclosures Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Sep. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Sep. 30, 2020
Debt Instrument [Line Items]
Payments of Debt Issuance Costs				$ 0	$ 10.6
Long-term Debt, Weighted Average Interest Rate, at Point in Time				5.90%		5.80%
Proceeds from issuance of long-term debt				$ 22.8	$ 408.8
Unsecured Debt [Member] | 6.25% Notes due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.25%
Long-term Debt				$ 700		$ 700
Unsecured Debt [Member] | 6.25% Notes due 2025 [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchase Amount	$ 100
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	1.8
Write off of Deferred Debt Issuance Cost	1.4
Redemption Premium	$ 3.1
Unsecured Debt [Member] | 6.875% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.875%			6.875%
Long-term Debt				400		400
Payments of Debt Issuance Costs					$ 6
Proceeds from issuance of long-term debt		$ 400
Unsecured Debt [Member] | 6.625% Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.625%				6.625%
Debt Instrument, Repurchase Amount			$ 100				$ 350
Interest Paid, Including Capitalized Interest, Operating and Investing Activities			2
Write off of Deferred Debt Issuance Cost			0.4
Redemption Premium			$ 1.1
Foreign Credit Facilities [Member]
Debt Instrument [Line Items]
Long-term Line of Credit				108.7		$ 88.8
Debt Instrument, Unused Borrowing Capacity, Amount				$ 60.7

Derivatives Narrative (Details)

Derivatives Narrative (Details) € in Millions, $ in Millions	Jun. 30, 2021USD ($)	Jun. 30, 2021EUR (€)	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Mar. 09, 2020USD ($)
Foreign Currency Forward & Foreign Currency Option Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 172.1		$ 178.2
Currency Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	237.1	€ 200	$ 244.2	€ 200
Fair value asset at date of dedesignation					$ 9.8
Interest Rate Swap [Member] | Debt [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
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

Schedule of Derivatives (Detail

Schedule of Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Cost of goods sold	$ 1,093.3	$ 614.2	$ 2,291.3	$ 1,762.4
Other income (expense), net	0.6	0.1	1.8	(2.2)
Interest expense	(49.9)	(54.6)	$ (101)	(106.1)
Foreign Exchange Forward [Member] | Cost of Sales [Member]
Derivative Instruments, Gain (Loss) [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
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0	0.8	$ 0	(7.6)
Foreign Exchange Forward [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Income Statement Location Gain (Loss) Reclassified from Accumulated OCI			Cost of Goods Sold
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	1.8	(2.3)	$ 4.1	(1)
Foreign Exchange Forward [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member] | Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					$ 4.1
Foreign Exchange Forward [Member] | Nonoperating Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Description of Location of Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments in Financial Statements			Other Income (Expense), net
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0.5	(0.1)	$ 0.4	(0.5)
Currency Swap [Member] | Nonoperating Income (Expense) [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Income Statement Location Gain (Loss) Reclassified from Accumulated OCI			Other Income (Expense), net
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(2.1)	(3.7)	$ 8	0
Currency Swap [Member] | Nonoperating Income (Expense) [Member] | Cash Flow Hedging [Member] | Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					1.7
Interest Rate Swap [Member] | Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Income Statement Location Gain (Loss) Reclassified from Accumulated OCI			Interest Expense
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (3.7)	$ (4)	$ (7.9)	$ (6)
Interest Rate Swap [Member] | Interest Expense [Member] | Cash Flow Hedging [Member] | Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					$ (13.9)

Fair Value of Assets and Liabil

Fair Value of Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 29, 2021	Jun. 30, 2021	Dec. 31, 2020
REE Automotive Ltd.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments		$ 3
Subsequent Event [Member] | REE Automotive Ltd.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Share Price	$ 8.35
Equity Securities, FV-NI	$ 41
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, at Carrying Value		237.8	$ 206.7
Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Carrying and Fair Value Disclosure		4.1	5.8
Foreign Exchange Forward [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, Carrying and Fair Value Disclosure		1.9	3.3
Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member] | Accrued expenses and other [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contracts, Liability, Carrying and Fair Value Disclosure		0	0.1
Foreign Exchange Forward [Member] | Designated as Hedging Instrument [Member] | Postretirement benefits and other long-term 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, Carrying and Fair Value Disclosure		0.1	0.1
Foreign Exchange Forward [Member] | Not Designated as Hedging Instrument [Member] | Prepaid expenses and other [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Carrying and Fair Value Disclosure		0.2	0.2
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Prepaid expenses and other [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 Carrying and Fair Value		2.7	4.9
Interest Rate Swap [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 Carrying and Fair Value		6.3	8.6
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Accrued expenses and other [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 Carrying and Fair Value		10	17.8
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Postretirement benefits and other long-term 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 Carrying and Fair Value		26.4	32.1
Currency Swap [Member] | Designated as Hedging Instrument [Member] | Postretirement benefits and other long-term 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, Carrying and Fair Value Disclosure		$ 13.1	$ 20.6

Fair Value of Debt (Details)

Fair Value of Debt (Details) - Fair Value, Inputs, Level 2 [Member] - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Revolving Credit Facility [Member] | Carrying (Reported) Amount, Fair Value Disclosure [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, Fair Value Disclosure [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] | Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	314.5	323
Term Loan A Due 2024 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	315.7	318.6
Term Loan B due 2024 [Member] | Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	850	1,088.8
Term Loan B due 2024 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	845.8	1,071.1
6.875% Notes [Member] | Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	400	400
6.875% Notes [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	436	426
6.50% Notes [Member] | Carrying (Reported) Amount, Fair Value Disclosure [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, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	527.5	523.8
6.25% Notes Due 2026 [Member] | Carrying (Reported) Amount, Fair Value Disclosure [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, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	411	411
6.25% Notes due 2025 [Member] | Carrying (Reported) Amount, Fair Value Disclosure [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, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt	$ 721.9	$ 724.3

Schedule of Employee Benefit Pl

Schedule of Employee Benefit Plans Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0.5	$ 0.5	$ 1	$ 1
Interest cost	4.3	5.4	8.6	10.8
Expected asset return	(9.7)	(9.7)	(19.4)	(19.3)
Amortized loss	2.7	2.2	5.4	4.3
Net periodic benefit credit	(2.2)	(1.6)	(4.4)	(3.2)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.1	0.1	0.2	0.2
Interest cost	2.1	2.5	4.2	5.1
Amortized loss	0.4	0.3	0.8	0.5
Amortized prior service credit	(0.4)	(0.4)	(0.8)	(0.8)
Net periodic benefit cost	$ 2.2	$ 2.5	$ 4.4	$ 5

Employee Benefit Plans and Othe

Employee Benefit Plans and Other Postretirement Benefit Plans Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Liability, Defined Benefit Pension Plan, Noncurrent	$ 130.4	$ 141.2
Liability, Other Postretirement Defined Benefit Plan, Noncurrent	552.8	$ 556.7
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	1
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year	$ 17

Product Warranties (Details)

Product Warranties (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Product Warranty Rollforward
Beginning balance	$ 69.1	$ 64.2	$ 66.7	$ 62
Accruals	4.1	0.6	8.4	4.8
Payments	(1.8)	(0.7)	(2.6)	(2)
Adjustment to prior period accruals	(7.3)	(0.4)	(8)	(0.5)
Foreign currency translation	0.2	0.2	(0.2)	(0.4)
Ending balance	$ 64.3	$ 63.9	$ 64.3	$ 63.9

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Income tax expense (benefit)	$ 2.4	$ (43.9)	$ 11.2	$ (40.6)
Effective income tax rate, continuing operations	13.00%	17.10%	17.00%	5.40%
Unrecognized tax benefit liability, including penalties and accrued interest	$ 22.5		$ 22.5		$ 22.2
UNITED STATES
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		$ 36
Settlement with Taxing Authority [Member]
Other Tax Expense (Benefit)		(6.8)
CARES Act [Member]
Other Tax Expense (Benefit)		$ (7)		$ (7.5)

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator
Net income (loss) attributable to AAM	$ 16	$ (213.2)	$ 54.6	$ (714.5)
Less: Net income attributable to participating securities	(0.6)	0	(2.2)	0
Net income (loss) attributable to common shareholders - Basic and Dilutive	$ 15.4	$ (213.2)	$ 52.4	$ (714.5)
Denominators
Basic - Weighted-average shares outstanding	118.7	118.4	118.5	117.4
Basic - Less: Participating securities	(4.7)	(5.3)	(4.7)	(4.5)
Basic - Weighted-average common shares outstanding	114	113.1	113.8	112.9
Effect of dilutive securities - dilutive stock-based compensation	0.4	0	0.2	0
Diluted - Adjusted weighted-average shares after assumed conversions	114.4	113.1	114	112.9
Basic EPS	$ 0.13	$ (1.88)	$ 0.46	$ (6.33)
Diluted EPS	$ 0.13	$ (1.88)	$ 0.46	$ (6.33)

Reclassifications out of Accu_3

Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended
		Jun. 30, 2021		Mar. 31, 2021	Jun. 30, 2020		Mar. 31, 2020	Jun. 30, 2021		Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), derivatives qualifying as hedges, tax		$ (0.7)			$ (0.5)			$ (2)		$ 1.8
Defined benefit plans, net current period other comprehensive income (loss)	[1]	2.2			1.7			4.3		3.3
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax		12.2			4.8			1.2		(44)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	[2]	5.1			8.7			4.8		(26)
Other comprehensive income (loss)		19.5			15.2			10.3		(66.7)
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		(1.8)			2.3			(4.1)		1
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		3.7			4			7.9		6
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		2.1			3.7			(8)
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		(308.9)		$ (311)	(258.3)		$ (259.9)	(311)		(259.9)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax		0			0			0		0
Income tax effect of other comprehensive income (loss) before reclassifications		0			0			0		0
Defined benefit plans, amounts reclassified from accumulated other comprehensive income (loss)		2.7	[3]		2.1	[3]		5.4	[4]	4.1	[4]
Income taxes reclassified into net income		(0.5)			(0.4)			(1.1)		(0.8)
Defined benefit plans, net current period other comprehensive income (loss)		2.2			1.7			4.3		3.3
Accumulated other comprehensive income (loss), net of tax - Ending balance		(306.7)		(308.9)	(256.6)		(258.3)	(306.7)		(256.6)
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		(112.1)		(101.1)	(149.7)		(101.2)	(101.1)		(101.2)
Foreign currency translation adjustments, other comprehensive income (loss) arising during period		12.2			4.8			0.7		(43.7)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax		0			0			0		0
Foreign currency translation adjustments, amounts reclassified from accumulated other comprehensive income (loss)		0			0			0.5		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax		0			0			0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax		12.2			4.8			1.2		(43.7)
Accumulated other comprehensive income (loss), net of tax - Ending balance		(99.9)		(112.1)	(144.9)		(149.7)	(99.9)		(144.9)
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		(20.4)		(20.1)	(50.4)		(15.7)	(20.1)		(15.7)
Unrecognized gain (loss) on cash flow hedges, other comprehensive income (loss) arising during period		1.8			(0.8)			11		(34.8)
Other comprehensive income (loss), derivatives qualifying as hedges, tax		0.4			1.2			(2.1)		3.1
Unrecognized gain (loss) on cash flow hedges, amounts reclassified from accumulated other comprehensive income (loss)		4	[5]		10	[5]		(4.2)	[6]	7	[6]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax		(1.1)			(1.7)			0.1		(1.3)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		5.1			8.7			4.8		(26)
Accumulated other comprehensive income (loss), net of tax - Ending balance		(15.3)		(20.4)	(41.7)		(50.4)	(15.3)		(41.7)
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		(441.4)		(432.2)	(458.4)		(376.8)	(432.2)		(376.8)
Other comprehensive income (loss) arising during period, total		14			4			11.7		(78.5)
Other Comprehensive Income (Loss) before Reclassifications, Tax		0.4			1.2			(2.1)		3.1
Other comprehensive income (loss), reclassification before tax		6.7			12.1			1.7		11.1
Reclassification from AOCI, Current Period, Tax		(1.6)			(2.1)			(1)		(2.1)
Other comprehensive income (loss)		19.5			15.2			10.3		(66.4)
Accumulated other comprehensive income (loss), net of tax - Ending balance		$ (421.9)		$ (441.4)	$ (443.2)		$ (458.4)	$ (421.9)		$ (443.2)
[1]	Amounts are net of tax of $(0.5) million and $(1.1) million for the three and six months ended June 30, 2021, and $(0.4) million and $(0.8) million for the three and six months ended June 30, 2020, respectively.
[2]	Amounts are net of tax of $(0.7) million and $(2.0) million for the three and six months ended June 30, 2021, and $(0.5) million and $1.8 million for the three and six months ended June 30, 2020, respectively.
[3]	These amounts were reclassified from AOCI to Other income (expense), net for the three months ended June 30, 2021 and June 30, 2020.
[4]	These amounts were reclassified from AOCI to Other income (expense), net for the six months ended June 30, 2021 and June 30, 2020.
[5]	The amounts reclassified from AOCI included $(1.8) million in cost of goods sold (COGS), $3.7 million in interest expense and $2.1 million in Other income (expense), net for the three months ended June 30, 2021 and $2.3 million in COGS, $4.0 million in interest expense and $3.7 million in Other income (expense), net for the three months ended June 30, 2020.
[6]	The amounts reclassified from AOCI included $(4.1) million in cost of goods sold (COGS), $7.9 million in interest expense and $(8.0) million in Other income (expense), net for the six months ended June 30, 2021 and $1.0 million in COGS and $6.0 million in interest expense for the six months ended June 30, 2020.

Revenue from Contracts with C_2

Revenue from Contracts with Customers Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Net sales	$ 1,283.3	$ 515.3	$ 2,708.4	$ 1,858.8
North America [Member]
Disaggregation of Revenue [Line Items]
Net sales	998.3	344.1	2,092.5	1,397
Asia [Member]
Disaggregation of Revenue [Line Items]
Net sales	112.3	98.1	246.3	207.3
Europe [Member]
Disaggregation of Revenue [Line Items]
Net sales	151.7	70.8	325.9	230.9
South America [Member]
Disaggregation of Revenue [Line Items]
Net sales	21	2.3	43.7	23.6
Driveline [Member]
Disaggregation of Revenue [Line Items]
Net sales	934.9	375.8	1,959.9	1,321.6
Driveline [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Net sales	722	239.7	1,495.8	964.8
Driveline [Member] | Asia [Member]
Disaggregation of Revenue [Line Items]
Net sales	100.9	88.1	222.1	191.2
Driveline [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Net sales	93.8	46.3	203.8	145.2
Driveline [Member] | South America [Member]
Disaggregation of Revenue [Line Items]
Net sales	18.2	1.7	38.2	20.4
Metal Forming [Member]
Disaggregation of Revenue [Line Items]
Net sales	348.4	139.5	748.5	537.2
Metal Forming [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Net sales	276.3	104.4	596.7	432.2
Metal Forming [Member] | Asia [Member]
Disaggregation of Revenue [Line Items]
Net sales	11.4	10	24.2	16.1
Metal Forming [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Net sales	57.9	24.5	122.1	85.7
Metal Forming [Member] | South America [Member]
Disaggregation of Revenue [Line Items]
Net sales	$ 2.8	$ 0.6	$ 5.5	$ 3.2

Revenue from Contracts with C_3

Revenue from Contracts with Customers Contract Assets and Liabilities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Accounts receivable, net	$ 798.1	$ 793.2
Deferred revenue, current	24.5	23.4
Deferred revenue, noncurrent	89.9	$ 91
Increase (decrease) in accounts receivable	4.9
Contract liability, current, increase (decrease)	1.1
Contract liability, noncurrent, increase (decrease)	(1.1)
Contract with customer, liability, revenue recognized	$ 10

Acquisitions and Divestitures_2

Acquisitions and Divestitures (Details) - USD ($) $ in Millions	May 17, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Asset Acquisition [Line Items]
Proceeds from Divestiture of Businesses				$ 2.6
Loss on sale of business		$ 0.1	$ 0	$ 2.7	$ 1
Emporium, Pennsylvannia
Asset Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 14.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	5.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Equipment	9
Business Combination, Consideration Transferred	14.9
Business Combination, Consideration Transferred, Cash Paid	4.9
Business Combination, Consideration Transferred, Liabilities Incurred	10
Business Combination, Consideration Transferred, Liabilities Incurred, Annual Amount	$ 2.5

Manufacturing Facility Fire a_2

Manufacturing Facility Fire and Insurance Recovery (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		9 Months Ended
	Dec. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021
Insurance Recoveries [Abstract]
Insurance Deductible Expense		$ 1
Business interruption charges		12.2		$ 48.7
Insurance Recoveries Estimated		17.6		71.8
Proceeds from Insurance Settlement, Operating and Investing Activities	$ 11.1	40.1		51.2
Proceeds from Insurance Settlement, Operating Activities		28
Proceeds from Insurance Settlement, Investing Activities		12.1	$ 0
Gain (Loss) Related to Insurance Settlement		5.4
Loss Contingency, Receivable		$ 20.6		20.6
Tangible Asset Impairment Charges				$ 27

Sales and Segment Adjusted EBIT

Sales and Segment Adjusted EBITDA (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Sales	$ 1,375.5	$ 544.1	$ 2,890.9	$ 1,972.1
Less: intersegment sales	92.2	28.8	182.5	113.3
Net external sales	1,283.3	515.3	2,708.4	1,858.8
Segment Adjusted EBITDA	222.6	(52.1)	485.5	161.2
Driveline [Member]
Segment Reporting Information [Line Items]
Sales	935.4	375.9	1,961.5	1,321.8
Less: intersegment sales	0.5	0.1	1.6	0.2
Net external sales	934.9	375.8	1,959.9	1,321.6
Segment Adjusted EBITDA	151.3	(25)	321.8	109.5
Metal Forming [Member]
Segment Reporting Information [Line Items]
Sales	440.1	168.2	929.4	650.3
Less: intersegment sales	91.7	28.7	180.9	113.1
Net external sales	348.4	139.5	748.5	537.2
Segment Adjusted EBITDA	$ 71.3	$ (27.1)	$ 163.7	$ 51.7

Reconciliation of Total Segment

Reconciliation of Total Segment Adjusted EBITDA to Income Before Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Total segment adjusted EBITDA	$ 222.6	$ (52.1)	$ 485.5	$ 161.2
Interest expense	(49.9)	(54.6)	(101)	(106.1)
Depreciation and amortization	(143.6)	(139.1)	(285.6)	(268.7)
Restructuring and acquisition-related costs	(15.9)	(11.3)	(33.4)	(28.9)
Loss on sale of business	(0.1)	0	(2.7)	(1)
Debt refinancing and redemption costs	(1.3)	0	(2.4)	(1.5)
Impairment charges	0	0	0	(510)
Malvern Fire charges, net of recoveries	6.6	0	5.4	0
Income (loss) before income taxes	$ 18.4	$ (257.1)	$ 65.8	$ (755)