Spirit AeroSystems (SPR) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 20, 2021
Cover [Abstract]
Security Exchange Name	NYSE
Title of 12(b) Security	Class A common stock, par value $0.01 per share
Entity Address, Postal Zip Code	67210
City Area Code	316
Local Phone Number	526-9000
Entity Address, State or Province	KS
Entity Address, City or Town	Wichita
Entity Address, Address Line One	3801 South Oliver
Entity Tax Identification Number	20-2436320
Entity Incorporation, State or Country Code	DE
Entity File Number	001-33160
Document Transition Report	false
Document Quarterly Report	true
Entity Registrant Name	Spirit AeroSystems Holdings, Inc.
Entity Central Index Key	0001364885
Document Type	10-Q
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Amendment Flag	false
Trading Symbol	SPR
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		105,047,298

Consolidated Statements of Oper

Consolidated Statements of Operations (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Income Statement [Abstract]
Revenues	$ 980	$ 806.3	$ 2,882.9	$ 2,528.2
Operating costs and expenses
Cost of sales	1,036.2	903.4	3,009.4	2,941
Selling, general and administrative	86.8	52.8	211.3	179.2
Restructuring Charges	0.8	19.5	8.1	68.4
Research and development	12.8	7.5	34.3	28.1
Gain (Loss) on Disposition of Property Plant Equipment	0	0	0	22.9
Total operating costs and expenses	1,136.6	983.2	3,263.1	3,239.6
Operating loss	(156.6)	(176.9)	(380.2)	(711.4)
Interest expense and financing fee amortization	(58.8)	(53)	(177.7)	(133.8)
Other income (expense), net	(94.8)	10	(138.7)	65.4
Loss before income taxes and equity in net loss of affiliate	(120.6)	(239.9)	(419.2)	(910.6)
Income tax benefit	7.9	85.2	0.6	340
Loss before equity in net loss of affiliate	(112.7)	(154.7)	(418.6)	(570.6)
Equity in net loss of affiliate	(0.9)	(0.8)	(1.9)	(3.8)
Net loss	$ (113.6)	$ (155.5)	$ (420.5)	$ (574.4)
Loss per share
Earnings Per Share, Basic	$ (1.09)	$ (1.50)	$ (4.04)	$ (5.53)
Diluted (in dollars per share)	$ (1.09)	$ (1.50)	$ (4.04)	$ (5.53)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (113.6)	$ (155.5)	$ (420.5)	$ (574.4)
Foreign currency translation adjustments	(11.6)	17.3	(7.7)	(15.6)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	7.6	23.8	3.8	(3)
Unrealized foreign exchange gain (loss) on intercompany loan, net of tax effect of $0.3 and ($0.4) for the three months ended, respectively, and $0.2 and $0.4 for the nine months ended, respectively	(0.9)	1.4	(0.6)	(1.2)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	(6.2)	0	(5.5)	(10.9)
Total other comprehensive (loss) gain	(11.2)	51.7	(9.2)	(20.4)
Total comprehensive loss	(124.8)	(103.8)	(429.7)	(594.8)
Interest Rate Swap [Member]
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0	9.2	0.9	10.3
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0	$ (9.2)	(0.9)	$ (10.3)
Foreign Exchange Forward
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.1)		(0.1)
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	$ 0.1		$ 0.1

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Unaudited) (Parentheticals) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Statement of Comprehensive Income [Abstract]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ 0.1	$ (7.4)	$ 0.4	$ 0.9
Unrealized exchange (loss) on intercompany loan, tax	0.3	(0.4)	0.2	0.4
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	0	(2.8)	(0.3)	(3.1)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, Tax	$ 0	$ 0	$ 0	$ (3.3)

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets
Cash and cash equivalents	$ 1,430.6	$ 1,873.3
Restricted Cash, Current	0.3	0.3
Accounts receivable, net	527.6	484.4
Unbilled Receivables, Current	411	368.4
Inventory, net	1,325.7	1,422.3
Other current assets	121.1	336.3
Total current assets	3,816.3	4,485
Property, plant and equipment, net	2,406.9	2,503.8
Operating Lease, Right-of-Use Asset	87.2	70.6
Unbilled Receivable, Non Current	0	4.4
Pension assets	487.2	455.9
Deferred Income Tax Assets, Net	0	0.1
Goodwill	623.6	565.3
Intangible Assets, Net (Excluding Goodwill)	216.2	215.2
Deferred income taxes	103.4	83.6
Other assets	7,740.8	8,383.9
Liabilities, Current [Abstract]
Accounts Payable, Current	644.8	558.9
Accrued Liabilities, Current	415.6	365.6
Deferred Compensation Liability, Current	39.8	57
Long-term Debt and Lease Obligation, Current	47.8	340.7
Operating Lease, Liability, Current	8.3	5.5
Customer Advances, Current	116	18.9
Contract with Customer, Liability, Current	109.9	97.6
Provision for Loss on Contracts	284	184.6
Deferred Credits and Other Liabilities, Current	95.9	22.2
Other Liabilities, Current	88.4	58.4
Liabilities Noncurrent
Long-term debt	3,546.7	3,532.9
Operating Lease, Liability, Noncurrent	80.5	66.6
Advance payments, long-term	221.7	327.4
Pension/OPEB obligation	335.6	440.2
Contract with Customer, Liability, Noncurrent	279.7	372
Provision for Loss on Contacts, Non Current	491.6	561.4
Deferred Credits and Other Liabilities, Noncurrent	34.8	38.9
Deferred grant income liability - non-current	26.7	28.1
Deferred Income Tax Liabilities, Net	26	13
Deferred income taxes	422.2	437
Additional Paid in Capital [Abstract]
Additional paid-in capital	1,140.4	1,139.8
AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract
Accumulated other comprehensive loss	(163.3)	(154.1)
Retained Earnings Accumulated Deficit [Abstract]
Retained earnings	$ 1,902.8	$ 2,326.4
Treasury Stock, Shares	41,523,470	41,523,470
Treasury Stock, Value	$ (2,456.7)	$ (2,456.7)
Total stockholders' equity	424.3	856.5
Noncontrolling interest	0.5	0.5
Total equity	424.8	857
Total liabilities and equity	7,740.8	8,383.9
Liabilities, Current	1,850.5	1,709.4
Class A [Member]
Stockholders' Equity Attributable to Parent [Abstract]
Common stock	$ 1.1	$ 1.1
Retained Earnings Accumulated Deficit [Abstract]
Common Stock, Shares Authorized	200,000,000	200,000,000
Class B [Member]
Retained Earnings Accumulated Deficit [Abstract]
Common Stock, Shares Authorized	150,000,000	150,000,000

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Shareholders' equity
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Treasury Stock, Shares	41,523,470	41,523,470
Class A [Member]
Shareholders' equity
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	105,048,226	105,542,162
Class B [Member]
Shareholders' equity
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	0	0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020
Operating activities
Net loss	$ (420.5)	$ (574.4)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	241.9	202.5
Amortization of deferred financing fees	6.4	12.6
Accretion of customer supply agreement	1.6	1.6
Employee Benefit and Share-based Payment Arrangement, Noncash	19.6	17.1
Loss on Derivative Instruments, Pretax	(0.1)	0
Gain from foreign currency transactions	(7.3)	(1.1)
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property	(2.3)	(24.9)
Deferred taxes	13.5	(34.3)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(104.5)	57.2
Grant liability amortization	(1.2)	(3.2)
Unrealized Gain (Loss) on Investments	1.9	3.8
Increase (Decrease) in Forward Provision	(1.1)	226.3
Changes in assets and liabilities
Accounts receivable, net	(4.7)	169.3
Inventory, net	83.4	(66.1)
Accounts payable and accrued liabilities	99.4	(530.6)
Profit sharing/deferred compensation	(17.7)	(46.2)
Advance payments	(1.2)	(19.9)
Income taxes receivable/payable	227.2	(252.6)
Other	(7)	44
Net cash provided by (used in) operating activities	13.3	(612.8)
Investing activities
Purchase of property, plant and equipment	(90)	(70.4)
Payments to Acquire Businesses, Net of Cash Acquired	(21.1)	(117.9)
Payments for (Proceeds from) Other Investing Activities	4.7	4.9
Net cash used in investing activities	(106.4)	(183.4)
Financing activities
Proceeds from (Repayments of) Other Debt	(7.5)	10
Proceeds from Issuance of Senior Long-term Debt	0	1,200
Principal payments of debt	(30.1)	(22.7)
Repayments of Debt	(3)	(439.7)
Repayments of Lines of Credit	0	(800)
Repayments of Senior Debt	300	0
Payment, Tax Withholding, Share-based Payment Arrangement	(5)	(14)
Proceeds from Stock Plans	3	2.6
Debt issuance and financing costs	0	(27.6)
Proceeds from (Repurchase of) Equity	0	0.1
Payments of Dividends	(3.2)	(14.4)
Proceeds from (Payments for) Other Financing Activities	0	0.1
Net cash used in financing activities	(345.8)	(105.6)
Effect of exchange rate changes on cash and cash equivalents	(3.8)	(3.3)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	(442.7)	(905.1)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning Balance	1,893.1	2,367.2
Cash, cash equivalents, and restricted cash, end of period	1,450.4	1,462.1
Cash and Cash Equivalents, at Carrying Value, Ending Balance	1,430.6	1,441.3
Reconciliation of Cash, Cash Equivalents, and Restricted Cash [Abstract]
Restricted Cash, Current	0.3	1.3
Restricted Cash, Noncurrent	19.5	19.5
Increase (Decrease) in Income Taxes Payable	227.2	(252.6)
Increase (Decrease) in Contract with Customer, Liability	(79.8)	(44.1)
Payments to Acquire Businesses, Net of Cash Acquired	21.1	117.9
Proceeds from Issuance of Senior Long-term Debt	0	1,200
Repayments of Lines of Credit	0	800
Repayments of Senior Debt	300	0
Proceeds from (Payments for) Other Financing Activities	0	0.1
Payments for Repurchase of Common Stock	0	0.1
Increase (Decrease) in Contract with Customer, Asset	$ 38.8	$ (200.4)

Condensed Statement of Changes

Condensed Statement of Changes in Stockholders' Equity Statement - USD ($) $ in Millions	Total	Class A [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock, Common [Member]	AOCI Including Portion Attributable to Noncontrolling Interest [Member]
Stockholders' Equity Attributable to Parent at Dec. 31, 2019	$ 1,761.4
Common Stock, Shares, Outstanding at Dec. 31, 2019			104,882,379
Common Stock, Value, Outstanding at Dec. 31, 2019			$ 1.1
Additional Paid in Capital, Common Stock at Dec. 31, 2019				$ 1,125
Treasury Stock, Value at Dec. 31, 2019						$ (2,456.8)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Dec. 31, 2019							$ (109.2)
Retained Earnings (Accumulated Deficit) at Dec. 31, 2019					$ 3,201.3
Net Income (Loss) Attributable to Parent	(418.9)				(418.9)
Dividends, Common Stock, Cash	(2.4)				(2.4)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			972,614
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture			$ 0
Stock Issued During Period, Value, Restricted Stock Award, Gross	13.3			13.3
Shares Issued, Shares, Share-based Payment Arrangement, Forfeited			(87,903)
Shares Granted, Value, Share-based Payment Arrangement, Forfeited			$ 0
Payment, Tax Withholding, Share-based Payment Arrangement	(13.7)		$ 0	(13.7)
Stock Issued During Period, Shares, Employee Stock Purchase Plans			55,656
Stock Issued During Period, Value, Employee Stock Purchase Plan	1.3			1.3
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation			(197,918)
Treasury Stock, Shares, Acquired			0
Treasury Stock, Value, Acquired, Cost Method	0.1		$ 0			0.1
Other Comprehensive Income (Loss), Net of Tax	(72.1)						(72.1)
Stockholders' Equity Attributable to Parent at Jul. 02, 2020	1,269
Common Stock, Shares, Outstanding at Jul. 02, 2020			105,624,828
Additional Paid in Capital, Common Stock at Jul. 02, 2020				1,125.9
Treasury Stock, Value at Jul. 02, 2020						(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Jul. 02, 2020							(181.3)
Retained Earnings (Accumulated Deficit) at Jul. 02, 2020					2,780
Common Stock, Value, Outstanding at Jul. 02, 2020			$ 1.1
Stockholders' Equity Attributable to Parent at Dec. 31, 2019	1,761.4
Common Stock, Shares, Outstanding at Dec. 31, 2019			104,882,379
Common Stock, Value, Outstanding at Dec. 31, 2019			$ 1.1
Additional Paid in Capital, Common Stock at Dec. 31, 2019				1,125
Treasury Stock, Value at Dec. 31, 2019						(2,456.8)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Dec. 31, 2019							(109.2)
Retained Earnings (Accumulated Deficit) at Dec. 31, 2019					3,201.3
Net Income (Loss) Attributable to Parent	(574.4)
Payment, Tax Withholding, Share-based Payment Arrangement	(14)
Other Comprehensive Income (Loss), Net of Tax	(20.4)
Stockholders' Equity Attributable to Parent at Oct. 01, 2020	1,171.5
Common Stock, Shares, Outstanding at Oct. 01, 2020			105,660,882
Additional Paid in Capital, Common Stock at Oct. 01, 2020				1,133.2
Treasury Stock, Value at Oct. 01, 2020						(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Oct. 01, 2020							(129.6)
Retained Earnings (Accumulated Deficit) at Oct. 01, 2020					2,623.5
Common Stock, Value, Outstanding at Oct. 01, 2020			$ 1.1
Stockholders' Equity Attributable to Parent at Jul. 02, 2020	1,269
Common Stock, Shares, Outstanding at Jul. 02, 2020			105,624,828
Additional Paid in Capital, Common Stock at Jul. 02, 2020				1,125.9
Treasury Stock, Value at Jul. 02, 2020						(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Jul. 02, 2020							(181.3)
Retained Earnings (Accumulated Deficit) at Jul. 02, 2020					2,780
Net Income (Loss) Attributable to Parent	(155.5)				(155.5)
Dividends, Common Stock, Cash	(1)				(1)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			7,657
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture			$ 0
Stock Issued During Period, Value, Restricted Stock Award, Gross	6.3			6.3
Shares Issued, Shares, Share-based Payment Arrangement, Forfeited			(30,906)
Shares Granted, Value, Share-based Payment Arrangement, Forfeited			$ 0
Payment, Tax Withholding, Share-based Payment Arrangement	(0.3)		$ 0	(0.3)
Stock Issued During Period, Shares, Employee Stock Purchase Plans			68,810
Stock Issued During Period, Value, Employee Stock Purchase Plan	1.3			1.3
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation			(9,507)
Other Comprehensive Income (Loss), Net of Tax	51.7						51.7
Stockholders' Equity Attributable to Parent at Oct. 01, 2020	1,171.5
Common Stock, Shares, Outstanding at Oct. 01, 2020			105,660,882
Additional Paid in Capital, Common Stock at Oct. 01, 2020				1,133.2
Treasury Stock, Value at Oct. 01, 2020						(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Oct. 01, 2020							(129.6)
Retained Earnings (Accumulated Deficit) at Oct. 01, 2020					2,623.5
Common Stock, Value, Outstanding at Oct. 01, 2020			$ 1.1
Stockholders' Equity Attributable to Parent at Dec. 31, 2020	856.5
Common Stock, Shares, Outstanding at Dec. 31, 2020			105,542,162
Common Stock, Value, Outstanding at Dec. 31, 2020		$ 1.1	$ 1.1
Additional Paid in Capital, Common Stock at Dec. 31, 2020	1,139.8			1,139.8
Treasury Stock, Value at Dec. 31, 2020	2,456.7					(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Dec. 31, 2020	(154.1)						(154.1)
Retained Earnings (Accumulated Deficit) at Dec. 31, 2020	2,326.4				2,326.4
Net Income (Loss) Attributable to Parent	(306.9)				(306.9)
Dividends, Common Stock, Cash	(2.2)				(2.2)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			59,538
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture			$ 0
Stock Issued During Period, Value, Restricted Stock Award, Gross	13.3			13.3
Shares Issued, Shares, Share-based Payment Arrangement, Forfeited			(105,320)
Shares Granted, Value, Share-based Payment Arrangement, Forfeited			$ 0
Payment, Tax Withholding, Share-based Payment Arrangement	(4.4)		$ 0	(4.4)
Stock Issued During Period, Shares, Employee Stock Purchase Plans			29,500
Stock Issued During Period, Value, Employee Stock Purchase Plan	1.4			1.4
Supplemental Retirement Plan Shares Issued			9,198
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation			(105,238)
Stockholders' Equity, Other	0.1				0.1
Other Comprehensive Income (Loss), Net of Tax	2						2
Stockholders' Equity Attributable to Parent at Jul. 01, 2021	559.8
Common Stock, Shares, Outstanding at Jul. 01, 2021			105,429,840
Additional Paid in Capital, Common Stock at Jul. 01, 2021				1,150.1
Treasury Stock, Value at Jul. 01, 2021						(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Jul. 01, 2021							(152.1)
Retained Earnings (Accumulated Deficit) at Jul. 01, 2021					2,017.4
Common Stock, Value, Outstanding at Jul. 01, 2021			$ 1.1
Supplemental Retirement Plan Shares Issued Value	0			0
Stockholders' Equity Attributable to Parent at Dec. 31, 2020	856.5
Common Stock, Shares, Outstanding at Dec. 31, 2020			105,542,162
Common Stock, Value, Outstanding at Dec. 31, 2020		$ 1.1	$ 1.1
Additional Paid in Capital, Common Stock at Dec. 31, 2020	1,139.8			1,139.8
Treasury Stock, Value at Dec. 31, 2020	2,456.7					(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Dec. 31, 2020	(154.1)						(154.1)
Retained Earnings (Accumulated Deficit) at Dec. 31, 2020	$ 2,326.4				2,326.4
Common Stock, Dividends, Per Share, Declared	$ 0.03
Net Income (Loss) Attributable to Parent	$ (420.5)
Payment, Tax Withholding, Share-based Payment Arrangement	(5)
Other Comprehensive Income (Loss), Net of Tax	(9.2)
Stockholders' Equity Attributable to Parent at Sep. 30, 2021	424.3
Common Stock, Shares, Outstanding at Sep. 30, 2021			105,048,226
Additional Paid in Capital, Common Stock at Sep. 30, 2021	1,140.4			1,140.4
Treasury Stock, Value at Sep. 30, 2021	2,456.7					(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Sep. 30, 2021	(163.3)						(163.3)
Retained Earnings (Accumulated Deficit) at Sep. 30, 2021	1,902.8				1,902.8
Common Stock, Value, Outstanding at Sep. 30, 2021			$ 1.1
Stockholders' Equity Attributable to Parent at Jul. 01, 2021	$ 559.8
Common Stock, Shares, Outstanding at Jul. 01, 2021			105,429,840
Additional Paid in Capital, Common Stock at Jul. 01, 2021				1,150.1
Treasury Stock, Value at Jul. 01, 2021						(2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Jul. 01, 2021							(152.1)
Retained Earnings (Accumulated Deficit) at Jul. 01, 2021					2,017.4
Common Stock, Dividends, Per Share, Declared	$ 0.01
Net Income (Loss) Attributable to Parent	$ (113.6)				(113.6)
Dividends, Common Stock, Cash	(1)				(1)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			0
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture			$ 0
Stock Issued During Period, Value, Restricted Stock Award, Gross	6.3			6.3
Shares Issued, Shares, Share-based Payment Arrangement, Forfeited			(8,898)
Shares Granted, Value, Share-based Payment Arrangement, Forfeited			$ 0
Payment, Tax Withholding, Share-based Payment Arrangement	(0.5)			(0.5)
Stock Issued During Period, Shares, Employee Stock Purchase Plans			37,023
Stock Issued During Period, Value, Employee Stock Purchase Plan	1.6			1.6
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation			(2,923)
Stockholders' Equity, Other	(17.1)				0
Other Comprehensive Income (Loss), Net of Tax	(11.2)						(11.2)
Stockholders' Equity Attributable to Parent at Sep. 30, 2021	424.3
Common Stock, Shares, Outstanding at Sep. 30, 2021			105,048,226
Additional Paid in Capital, Common Stock at Sep. 30, 2021	1,140.4			$ 1,140.4
Treasury Stock, Value at Sep. 30, 2021	2,456.7					$ (2,456.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax at Sep. 30, 2021	(163.3)						$ (163.3)
Retained Earnings (Accumulated Deficit) at Sep. 30, 2021	$ 1,902.8				$ 1,902.8
Common Stock, Value, Outstanding at Sep. 30, 2021			$ 1.1

Organization and Basis of Inter

Organization and Basis of Interim Presentation	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Interim Presentation	Organization, Basis of Interim Presentation and Recent Developments Unless the context otherwise indicates or requires, as used in this Quarterly Report on Form 10-Q ("Quarterly Report"), references to “we,” “us,” “our,” and the “Company” refer to Spirit AeroSystems Holdings, Inc. and its consolidated subsidiaries. References to “Spirit” refer only to our subsidiary, Spirit AeroSystems, Inc., and references to “Spirit Holdings” or “Holdings” refer only to Spirit AeroSystems Holdings, Inc. The Company provides manufacturing and design expertise in a wide range of fuselage, propulsion, and wing products and services for aircraft original equipment manufacturers (“OEM”) and operators through its subsidiaries including Spirit. The Company's headquarters are in Wichita, Kansas, with manufacturing and assembly facilities in Tulsa and McAlester, Oklahoma; Prestwick, Scotland; Wichita, Kansas; Kinston, North Carolina; Subang, Malaysia; Saint-Nazaire, France; Biddeford, Maine; Casablanca, Morocco; Belfast, Northern Ireland; and Dallas, Texas. The Company previously announced site consolidation activities, including the McAlester, Oklahoma and San Antonio, Texas sites. The work transfer and closure activities for the San Antonio site are complete as of September 30, 2021. The work transfer activity for the McAlester site is complete, with remaining closure activities in process as of September 30, 2021. The accompanying unaudited interim condensed consolidated financial statements include the Company’s financial statements and the financial statements of its majority-owned or controlled subsidiaries and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and the instructions to Form 10-Q and Article 10 of Regulation S-X. The Company’s fiscal quarters are 13 weeks in length. Since the Company’s fiscal year ends on December 31, the number of days in the Company’s first and fourth quarters varies slightly from year to year. All intercompany balances and transactions have been eliminated in consolidation. As part of the monthly consolidation process, the Company’s international subsidiaries that have functional currencies other than the U.S. dollar are translated to U.S. dollars using the end-of-month translation rate for balance sheet accounts and average period currency translation rates for income accounts. The subsidiaries in Prestwick, Scotland and Subang, Malaysia use the British Pound as their functional currency. All other foreign subsidiaries and branches use the U.S. dollar as their functional currency. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments (consisting of normal recurring adjustments and elimination of intercompany balances and transactions) considered necessary to fairly present the results of operations for the interim period. The results of operations for the nine months ended September 30, 2021, are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. In connection with the preparation of the condensed consolidated financial statements, the Company evaluated subsequent events through the date the financial statements were issued. The interim financial statements should be read in conjunction with the audited consolidated financial statements, including the notes thereto, included in the Company’s 2020 Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on February 25, 2021 (the “2020 Form 10-K”). The Company's significant accounting policies are described in Note 3, Summary of Significant Accounting Policies to our consolidated financial statements in the 2020 Form 10-K. COVID-19 During the three and nine months ended September 30, 2021, the COVID-19 pandemic continued to have a significant negative effect on the aviation industry, the Company's customers, and the Company's business globally. Although the aviation industry has shown signs of improvement and recovery during the three and nine months ended September 30, 2021, the length of the COVID-19 pandemic and its effect on the aviation industry and the Company’s operational and financial performance remains uncertain and outside of the Company’s control. The Company expects the pandemic and its effects to continue to have a significant negative impact on its business for the duration of the pandemic and during the subsequent economic recovery, which could be for an extended period of time. On September 9, 2021, President Biden announced new vaccination requirements applicable to federal workers and contractors, large employers and healthcare workers. Subject to limited exceptions, U.S. employees of federal contractors are required to be fully vaccinated against COVID-19 by December 8, 2021. As a federal contactor, the Company is subject to the executive order and has implemented mandatory vaccination rules for all U.S. employees to satisfy the requirements by December 8, 2021. B737 MAX The Boeing Company’s (“Boeing”) deliveries of the B737 MAX resumed in the fourth quarter of 2020 when the Federal Aviation Administration (“FAA”) rescinded the emergency order that grounded B737 MAX aircraft in the United States and issued official requirements to enable U.S. airlines to return the B737 MAX to service. Since November 2020, regulators from Brazil, Canada, the EU, U.K., India, and other countries have taken similar actions to unground the B737 MAX and permit return to service, with China remaining as the most significant country not to allow the B737 MAX to return to service. During the nine month period ended September 30, 2021, Boeing continued to receive orders for the B737 MAX, and several additional air carriers resumed flights on the aircraft.

Adoption of New Standard (Notes

Adoption of New Standard (Notes)	9 Months Ended
	Sep. 30, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update and Change in Accounting Principle [Text Block]	In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2019-12, Simplifying the Accounting for Income Taxes ("ASU 2019-12”), which modifies FASB Accounting Standards Codification (“ASC”) Topic 74 0 to simplify the accounting for income taxes. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020. The adoption of ASU 2019-12 did not have a material impact on our financial position or results of operations. In October 2020, the FASB issued ASU No. 2020-09 (“ASU 2020-09”), which revises certain SEC paragraphs of the ASC to reflect, as appropriate, the amended financial statement disclosure requirements in SEC Release 33-10762, Financial Disclosures about Guarantors and Issuers of Guaranteed Securities and Affiliates Whose Securities Collateralize a Registrant’s Securities . There is no impact to our financial position or results of operations due to the adoption of ASU 2020-09.

Changes in Estimates

Changes in Estimates	9 Months Ended
	Sep. 30, 2021
Changes in Estimates [Abstract]
Change In Estimate [Text Block]	. Changes in EstimatesThe Company has a periodic forecasting process in which management assesses the progress and performance of the Company’s programs. This process requires management to review each program’s progress by evaluating the program schedule, changes to identified risks and opportunities, changes to estimated revenues and costs for the accounting contracts, and any outstanding contract matters. Risks and opportunities include but are not limited to management’s judgment about the cost associated with the Company’s ability to achieve the schedule, technical requirements (e.g., a newly-developed product versus a mature product), and any other program requirements. Due to the span of years it may take to completely satisfy the performance obligations for the accounting contracts and the scope and nature of the work required to be performed on those contracts, the estimation of total revenue and costs is subject to many variables and, accordingly, is subject to change based upon judgment. When adjustments in estimated total consideration or estimated total cost are required, any changes from prior estimates for fully satisfied performance obligations are recognized in the current period as a cumulative catch-up adjustment for the inception-to-date effect of such changes. Cumulative catch-up adjustments are driven by several factors including production efficiencies, assumed rate of production, the rate of overhead absorption, changes to scope of work, and contract modifications. The full extent to which the effects of the COVID-19 pandemic will impact the Company's business, operations, results of operations and financial condition depends on future developments that are inherently uncertain. The Company has made reasonable estimates and judgments of the COVID-19 pandemic’s impact within its financial statements that the Company believes are reasonable, and there may be changes to those estimates in future periods related to changes in potential production volumes or timing of those production volumes. See also Note 20, Commitments, Contingencies and Guarantees . During the third quarter ended September 30, 2021, the Company recognized unfavorable changes in estimates of $73.2, which included net forward loss charges of $70.4, and unfavorable cumulative catch-up adjustments related to periods prior to the third quarter of 2021 of $2.8. The forward losses in the third quarter relate primarily to the B787 program, driven by the Company's assessment of the latest B787 program demand received from Boeing through September 2021, including the impact of reduced production volumes and the corresponding amount of fixed overhead absorption applied to lower deliveries. The loss in the current period also includes an additional loss on the A350 program related to changes in the production schedule, and a loss on the Bell V-280 OTA program, the contract for which was recently awarded to the Company . The unfavorable cumulative catch-up adjustment was driven by the impact of production schedule changes on the estimate of production costs for the B737 program, and also includes increased costs estimated on non-recurring programs. Changes in estimates are summarized below: For the Three Months Ended For the Nine Months Ended Changes in Estimates September 30, 2021 October 1, 2020 September 30, 2021 October 1, 2020 (Unfavorable) Favorable Cumulative Catch-up Adjustment by Segment Fuselage $ (1.6) $ 8.8 $ 4.9 $ (18.9) Propulsion 1.6 (4.6) (2.0) (8.6) Wing (2.9) 0.4 (5.6) (3.1) Other 0.1 — 0.2 — Total (Unfavorable) Favorable Cumulative Catch-up Adjustment $ (2.8) $ 4.6 $ (2.5) $ (30.6) Changes in Estimates on Loss Programs (Forward Loss) by Segment Fuselage $ (49.9) $ (92.0) $ (140.7) $ (260.3) Propulsion (5.9) (14.9) (19.2) (34.2) Wing (14.6) (21.5) (35.1) (47.7) Total Changes in Estimates (Forward Loss) on Loss Programs $ (70.4) $ (128.4) $ (195.0) $ (342.2) Total Changes in Estimates $ (73.2) $ (123.8) $ (197.5) $ (372.8) EPS Impact (diluted per share based upon 2021 forecasted effective tax rate) $ (0.69) $ (0.77) $ (1.86) $ (2.33)

Accounts Receivable and Allowan

Accounts Receivable and Allowance for Credit Losses Accounts Receivable and Allowance for Credit Loss (Notes)	9 Months Ended
	Sep. 30, 2021
Receivables [Abstract]
Loans, Notes, Trade and Other Receivables Disclosure [Text Block]	. Accounts Receivable and Allowance for Credit Losses Accounts Receivable, net Accounts receivable represent the Company’s unconditional rights to consideration, subject to the payment terms of the contract, for which only the passage of time is required before payment. Unbilled receivables are reflected under contract assets on the balance sheet. See also Allowance for Credit Losses, below . Accounts receivable, net consists of the following: September 30, December 31, Trade receivables $ 475.0 $ 458.9 Other 59.2 31.1 Less: allowance for credit losses (6.6) (5.6) Accounts receivable, net $ 527.6 $ 484.4 Other receivables as of September 30, 2021 in the table above includes an amount related to the Department of Transportation’s approval of the Company’s grant claim filed under the Aviation Manufacturing Jobs Protection Program, a component of the American Rescue Plan Act of 2021. As of September 30, 2021, the Company has received payment for $37.8 of the total amount approved of $75.5. The remaining $37.7, recorded in Other receivables above, is to be received through the term of the agreement, which expires in March of 2022. The full amount of the award, less an insignificant amount amortized against Cost of sales on the Condensed Consolidated Statements of Operations in the three and nine-month period ended September 30, 2021, is recorded on the Condensed Consolidated Balance Sheets line item Deferred revenue and other deferred credits, short-term. The Company has agreements (through its subsidiaries) to sell, on a revolving basis, certain trade accounts receivable balances, predominantly with Boeing, Airbus Group SE and its affiliates (collectively, “Airbus”), and Rolls-Royce PLC and its affiliates (collectively, 'Rolls-Royce") to third-party financial institutions. These programs were primarily entered into as a result of customers seeking payment term extensions with the Company and they continue to allow the Company to monetize the receivables prior to their payment date, subject to payment of a discount. No guarantees are delivered under the agreements. The Company's ability to continue using such agreements is primarily dependent upon the strength of the applicable customer’s financial condition. Transfers under these agreements are accounted for as sales of receivables resulting in the receivables being derecognized from the Company's balance sheet. For the nine months ended September 30, 2021, $1,487.7 of accounts receivable from Boeing, Airbus, and Rolls-Royce were sold via these arrangements. The proceeds from these sales of receivables are included in cash from operating activities in the Condensed Consolidated Statements of Cash Flows. The recorded net loss on sale of receivables is $4.8 for the nine months ended September 30, 2021 and is included in other income (expense), net on the Condensed Consolidated Statements of Operations. See Note 21, Other (Expense) Income, Net . Allowance for Credit Losses During the nine months ended September 30, 2021, there have been no significant changes in the factors that influenced management’s current estimate of expected credit losses, nor changes to the Company’s accounting policies or Current Expected Credit Losses methodology. The beginning balances, current period activity, and ending balances of the allocation for credit losses on accounts receivable and contract assets were not material.

Contract with customer, asset a

Contract with customer, asset and liability (Notes)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
contract with customer, asset and liability [Text Block]	Contract Assets and Contract Liabilities Contract assets primarily represent revenues recognized for performance obligations that have been satisfied but for which amounts have not been billed. Contract assets, current are those that are expected to be billed to our customer within 12 months. Contract assets, long-term are those that are expected to be billed to our customer over periods greater than 12 months. No impairments to contract assets were recorded for the period ended September 30, 2021 or the period ended October 1, 2020. See also Note 5, Accounts Receivable and Allowance for Credit Losses . Contract liabilities are established for cash received in excess of revenues recognized and are contingent upon the satisfaction of performance obligations. Contract liabilities primarily consist of cash received on contracts for which revenue has been deferred since the receipts are in excess of transaction price resulting from the allocation of consideration based on relative standalone selling price to future units (including those under option that the Company believes are likely to be exercised) with prices that are lower than standalone selling price. These contract liabilities will be recognized earlier if the options are not fully exercised, or immediately, if the contract is terminated prior to the options being fully exercised. September 30, 2021 December 31, 2020 Change Contract assets $ 411.0 $ 372.8 $ 38.2 Contract liabilities (389.6) (469.6) 80.0 Net contract assets (liabilities) $ 21.4 $ (96.8) $ 118.2 For the period ended September 30, 2021, the increase in contract assets reflects the net impact of more over time revenue recognition in relation to billed revenues during the period. The decrease in contract liabilities reflects the net impact of less deferred revenues recorded in excess of revenue recognized during the period. The Company recognized $156.1 of revenue that was included in the contract liability balance at the beginning of the period. October 1, 2020 December 31, 2019 Change Contract assets $ 337.7 $ 534.7 $ (197.0) Contract liabilities (472.6) (514.6) 42.0 Net contract assets (liabilities) $ (134.9) $ 20.1 $ (155.0) For the period ended October 1, 2020, the decrease in contract assets reflects the net impact of less over time revenue recognition in relation to billed revenues during the period. The decrease in contract liabilities reflects the net impact of less deferred revenues recorded in excess of revenue recognized during the period. The Company recognized $91.0 of revenue that was included in the contract liability balance at the beginning of the period.
Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block]	September 30, 2021 December 31, 2020 Change Contract assets $ 411.0 $ 372.8 $ 38.2 Contract liabilities (389.6) (469.6) 80.0 Net contract assets (liabilities) $ 21.4 $ (96.8) $ 118.2

Revenue (Notes)

Revenue (Notes)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Disaggregation of Revenue The Company disaggregates revenue based on the method of measuring satisfaction of the performance obligation either over time or at a point in time, based upon the location where products and services are transferred to the customer, and based upon major customer. The Company’s principal operating segments and related revenue are noted in Note 22, Segment Information . The following tables show disaggregated revenues for the periods ended September 30, 2021 and October 1, 2020: For the Three Months Ended For the Nine Revenue September 30, October 1, September 30, October 1, Contracts with performance obligations satisfied over time $ 774.9 $ 510.6 $ 2,187.3 $ 1,511.9 Contracts with performance obligations satisfied at a point in time 205.1 295.7 695.6 1,016.3 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 The following table disaggregates revenue by major customer: For the Three Months Ended For the Nine Customer September 30, October 1, September 30, October 1, Boeing $ 566.1 $ 493.8 $ 1,595.8 $ 1,539.9 Airbus 211.6 160.1 687.8 575.3 Other 202.3 152.4 599.3 413.0 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 The following table disaggregates revenue based upon the location where control of products are transferred to the customer: For the Three Months Ended For the Nine Location September 30, October 1, September 30, October 1, United States $ 715.5 $ 642.0 $ 2,048.1 $ 1,936.4 International United Kingdom 142.5 103.6 419.8 358.2 Other 122.0 60.7 415.0 233.6 Total International 264.5 164.3 834.8 591.8 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 Remaining Performance Obligations Unsatisfied, or partially unsatisfied, performance obligations that are expected to be recognized in the future are noted in the table below. The Company expects options to be exercised in addition to the amounts presented below: Remaining in 2021 2022 2023 2024 and After Unsatisfied performance obligations $ 887.7 $ 3,396.8 $ 4,146.5 $ 3,353.3

Inventory

Inventory	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Inventory	Inventory Inventory consists of raw materials used in the production process, work-in-process, which is direct material, direct labor, overhead and purchases, and capitalized pre-production costs. Raw materials are stated at lower of cost (principally on an actual or average cost basis) or net realizable value. Capitalized pre-production costs include certain contract costs, including applicable overhead, incurred before a product is manufactured on a recurring basis. These costs are typically amortized over a period that is consistent with the satisfaction of the underlying performance obligations to which these relate. September 30, December 31, Raw materials $ 306.8 $ 337.3 Work-in-process (1) 937.6 1,000.6 Finished goods 54.4 58.1 Product inventory 1,298.8 1,396.0 Capitalized pre-production 26.9 26.3 Total inventory, net $ 1,325.7 $ 1,422.3 (1) Work-in-process inventory includes direct labor, direct material, overhead, and purchases on contracts for which revenue is recognized at a point in time as well as sub-assembly parts that have not been assigned to a production unit on contracts for which revenue is recognized using the cost to cost input method. For the periods ended September 30, 2021 and December 31, 2020, work-in-process inventory includes $364.5 an d $351.2, respectively, of costs incurred in anticipation of specific contracts and no impairments were recorded in the periods. Product inventory, summarized in the table above, is shown net of valuation reserves of $52.2 and $56.8 as of September 30, 2021 and December 31, 2020, respectively. Excess capacity and abnormal production costs are excluded from inventory and recognized as expense in the period incurred. Cost of sales for three and nine months ended September 30, 2021 includes period expense of $57.1 and $172.2, respectively for excess capacity production costs related to B737 MAX, A220 and A320 production schedule changes. Cost of sales also includes abnormal costs related to workforce adjustments as a result of COVID-19 production pause, net of the U.S. employee retention credit and U.K. government subsidies for the three and nine months ended September 30, 2021 of $2.6 and $7.1 , respectively. Cost of sales for the three and nine month periods ended October 1, 2020 includes period expense of $72.6 and $228.8, respectively, of excess capacity production costs related to temporary B737 MAX and A320 production schedule changes, and abnormal costs related to temporary workforce adjustments as a result of COVID-19 production pause, net of the U.S. employee retention credit and U.K. government subsidies of ($10.9) and $33.8, respectively.

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment, net	Property, Plant and Equipment, net Property, plant and equipment, net consists of the following: September 30, December 31, Land $ 30.7 $ 30.8 Buildings (including improvements) 1,210.7 1,166.7 Machinery and equipment 2,214.1 2,120.5 Tooling 1,047.8 1,036.1 Capitalized software 292.0 282.5 Construction-in-progress 185.6 220.0 Total 4,980.9 4,856.6 Less: accumulated depreciation (2,574.0) (2,352.8) Property, plant and equipment, net $ 2,406.9 $ 2,503.8 Capitalized interest was $1.4 and $1.3 for the three months ended September 30, 2021 and October 1, 2020, respectively, and $4.5 and $3.8 for the nine months ended September 30, 2021 and October 1, 2020, respectively. Repair and maintenance costs are expensed as incurred. The Company recognized repair and maintenance costs of $36.1 and $25.7 for the three months ended September 30, 2021 and October 1, 2020, respectively, and $102.7 and $82.7 for the nine months ended September 30, 2021 and October 1, 2020, respectively. The Company capitalizes certain costs, such as software coding, installation, and testing, that are incurred to purchase or to create and implement internal-use computer software. Depreciation expense related to capitalized software was $3.8 and $4.1 for the three months ended September 30, 2021 and October 1, 2020, respectively, and $11.4 and $12.6 for the nine months ended September 30, 2021 and October 1, 2020, respectively. The Company reviews capital and amortizing intangible assets (long-lived assets) for impairment on an annual basis or whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. F or the period ended September 30, 2021, there were no events which would require the Company to update its impairment analysis.

Leases (Notes)

Leases (Notes)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Lessee, Finance Leases	The Company currently has operating and finance leases for items such as manufacturing facilities, corporate offices, manufacturing equipment, transportation equipment, and vehicles. The majority of the Company's active leases have remaining lease terms that range between less than one year to 18 years, some of which include options to extend the leases for up to 30 years, and some of which include options to terminate the leases within one year. Components of lease expense: For the Three For the Nine September 30, October 1, September 30, October 1, Operating lease cost $ 3.3 $ 2.2 $ 8.3 $ 6.6 Finance lease cost: Amortization of assets 7.2 5.7 19.6 16.0 Interest on lease liabilities 1.8 1.6 5.3 4.7 Total net lease cost $ 12.3 $ 9.5 $ 33.2 $ 27.3 Supplemental cash flow information related to leases was as follows: For the Three For the Nine September 30, October 1, September 30, October 1, Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 3.2 $ 2.1 $ 7.9 $ 6.5 Operating cash flows from finance leases $ 1.8 $ 1.6 $ 5.3 $ 4.7 Financing cash flows from finance leases $ 11.3 $ 7.7 $ 30.1 $ 21.4 ROU assets obtained in exchange for lease obligations: Operating leases $ 5.0 $ 0.1 $ 21.8 $ 0.3 Supplemental balance sheet information related to leases: September 30, 2021 December 31, 2020 Finance leases: Property and equipment, gross $ 247.2 $ 214.2 Accumulated amortization (63.7) (45.1) Property and equipment, net $ 183.5 $ 169.1 The weighted average remaining lease term as of September 30, 2021 for operating and finance leases was 35.7 years and 5.1 years, respectively. The weighted average discount rate as of September 30, 2021 for operating and finance leases was 5.6% and 4.5%, respectively. The weighted average remaining lease term as of December 31, 2020 for operating and finance leases was 42.3 years and 5.5 years, respectively. The weighted average discount rate as of December 31, 2020 for operating and finance leases was 5.5% and 4.3%, respectively. See Note 15, Debt , for current and non-current finance lease obligations. There has not been a significant impact on terms, costs, cash flows, or balance sheet value of leases, including any impairment of lease assets, as a result of the COVID-19 pandemic. As of September 30, 2021, remaining maturities of lease liabilities were as follows: 2021 2022 2023 2024 2025 2026 and thereafter Total Lease Payments Less: Imputed Interest Total Lease Obligations Operating Leases $ 3.1 $ 12.5 $ 11.7 $ 11.2 $ 10.7 $ 176.8 $ 226.0 $ (137.2) $ 88.8 Financing Leases $ 13.2 $ 47.8 $ 42.4 $ 34.3 $ 22.4 $ 36.6 $ 196.7 $ (21.3) $ 175.4 As of September 30, 2021, the Company had additional financing lease commitments that have not yet commenced of approximately $20.6 f or manufacturing equipment, software, and facilities that are in various phases of construction or customization for the Company's
Lessee, Operating Leases	The Company currently has operating and finance leases for items such as manufacturing facilities, corporate offices, manufacturing equipment, transportation equipment, and vehicles. The majority of the Company's active leases have remaining lease terms that range between less than one year to 18 years, some of which include options to extend the leases for up to 30 years, and some of which include options to terminate the leases within one year. Components of lease expense: For the Three For the Nine September 30, October 1, September 30, October 1, Operating lease cost $ 3.3 $ 2.2 $ 8.3 $ 6.6 Finance lease cost: Amortization of assets 7.2 5.7 19.6 16.0 Interest on lease liabilities 1.8 1.6 5.3 4.7 Total net lease cost $ 12.3 $ 9.5 $ 33.2 $ 27.3 Supplemental cash flow information related to leases was as follows: For the Three For the Nine September 30, October 1, September 30, October 1, Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 3.2 $ 2.1 $ 7.9 $ 6.5 Operating cash flows from finance leases $ 1.8 $ 1.6 $ 5.3 $ 4.7 Financing cash flows from finance leases $ 11.3 $ 7.7 $ 30.1 $ 21.4 ROU assets obtained in exchange for lease obligations: Operating leases $ 5.0 $ 0.1 $ 21.8 $ 0.3 Supplemental balance sheet information related to leases: September 30, 2021 December 31, 2020 Finance leases: Property and equipment, gross $ 247.2 $ 214.2 Accumulated amortization (63.7) (45.1) Property and equipment, net $ 183.5 $ 169.1 The weighted average remaining lease term as of September 30, 2021 for operating and finance leases was 35.7 years and 5.1 years, respectively. The weighted average discount rate as of September 30, 2021 for operating and finance leases was 5.6% and 4.5%, respectively. The weighted average remaining lease term as of December 31, 2020 for operating and finance leases was 42.3 years and 5.5 years, respectively. The weighted average discount rate as of December 31, 2020 for operating and finance leases was 5.5% and 4.3%, respectively. See Note 15, Debt , for current and non-current finance lease obligations. There has not been a significant impact on terms, costs, cash flows, or balance sheet value of leases, including any impairment of lease assets, as a result of the COVID-19 pandemic. As of September 30, 2021, remaining maturities of lease liabilities were as follows: 2021 2022 2023 2024 2025 2026 and thereafter Total Lease Payments Less: Imputed Interest Total Lease Obligations Operating Leases $ 3.1 $ 12.5 $ 11.7 $ 11.2 $ 10.7 $ 176.8 $ 226.0 $ (137.2) $ 88.8 Financing Leases $ 13.2 $ 47.8 $ 42.4 $ 34.3 $ 22.4 $ 36.6 $ 196.7 $ (21.3) $ 175.4 As of September 30, 2021, the Company had additional financing lease commitments that have not yet commenced of approximately $20.6 f or manufacturing equipment, software, and facilities that are in various phases of construction or customization for the Company's

Advance Payments and Deferred R

Advance Payments and Deferred Revenue/Credits	3 Months Ended
	Sep. 30, 2021
Advance Payments And Deferred Revenue Credits [Abstract]
Advance Payments	Advance Payments Advances on the B787 Program. Boeing has made advance payments to the Company under the B787 Special Business Provisions and General Terms Agreement (collectively, the “B787 Supply Agreement”) that are required to be repaid to Boeing by way of offset against the purchase price for future shipset deliveries. Advance repayments were initially scheduled to be spread evenly over the remainder of the first 1,000 B787 shipsets delivered to Boeing. On April 8, 2014, the Company signed a memorandum of agreement with Boeing that suspended advance repayments related to the B787 program for a period of twelve months beginning April 1, 2014. Repayment recommenced on April 1, 2015, and any repayments that otherwise would have become due during such twelve-month period will offset the purchase price for shipsets 1,001 through 1,120. On December 21, 2018, the Company signed a memorandum of agreement with Boeing that again suspended the advance repayments beginning with line unit 818. The advance repayments will resume at a lower rate of $0.45 per shipset at line number 1135 and continue through line number 1605. In the event Boeing does not take delivery of a sufficient number of shipsets to repay the full amount of advances prior to the termination of the B787 program or the B787 Supply Agreement, any advances not then repaid will be applied against any outstanding payments then due by Boeing to us, and any remaining balance will be repaid in annual installments of $27 due on December 15th of each year until the advance payments have been fully recovered by Boeing. As of September 30, 2021, the amount of advance payments received from Boeing under the B787 Supply Agreement and not yet repaid was approximately $212.1. Advances on the B737 Program. In an effort to minimize the disruption to the Company's operations and its supply chain, the Company and Boeing entered into a Memorandum of Agreement on April 12, 2019 (the "2019 MOA"), which included the terms and conditions for an advance payment to be made from Boeing to the Company in the amount of $123, which was received during the third quarter of 2019. The parties entered into another memorandum of agreement on February 6, 2020 (the "2020 MOA"), which extended the repayment date of the $123 advance received by the Company under the 2019 MOA to 2022. The 2020 MOA also required Boeing to pay $225 to the Company in the first quarter of 2020, consisting of (i) $70 in support of the Company's inventory and production stabilization, of which $10 will be repaid by the Company in 2021, and (ii) $155 as an incremental pre-payment for costs and shipset deliverie s over the next two years. On February 9, 2021, the Company signed a letter of agreement under which Boeing paid $38.5 to the Company in the first quarter of 2021, consisting of (i) $68.5 as additional pre-payment for the c osts and shipset deliveries less (ii) the ($30) credit owed to Boeing for rate-based pricing premium. As of September 30, 2021 , the amount of advance payments received from Boeing and not yet repaid was $125.6.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The FASB’s authoritative guidance on fair value measurements defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. It also establishes a fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The guidance discloses three levels of inputs that may be used to measure fair value: Level 1 Quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 1 assets and liabilities include debt and equity securities and derivative contracts that are traded in an active exchange market. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 2 assets and liabilities include debt securities with quoted prices that are traded less frequently than exchange-traded instruments and derivative contracts whose value is determined using a pricing model with inputs that are observable in the market or can be derived principally from or corroborated by observable market data. Observable inputs, such as current and forward interest rates and foreign exchange rates, are used in determining the fair value of the interest rate swaps and foreign currency hedge contracts. Level 3 Unobservable inputs that are supported by little or no market activity and are significant to the fair value of assets and liabilities. Level 3 assets and liabilities include financial instruments whose value is determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation. At September 30, 2021, the Company’s long-term debt includes a senior secured term loan and senior notes described further under Note 15 , Debt . The estimated fair value of the Company’s debt obligations is based on the quoted market prices for such obligations or the historical default rate for debt with similar credit ratings. The following table presents the carrying amount and estimated fair value of long-term debt: September 30, 2021 December 31, 2020 Carrying Fair Carrying Fair Senior secured term loan B (including current portion) $ 388.5 $ 389.5 (2) $ 389.6 $ 395.0 (2) Floating rate notes — — (1) 299.7 297.5 (1) Senior notes due 2023 299.2 304.5 (1) 298.8 293.8 (1) Senior secured first lien notes due 2025 494.9 524.4 (1) 493.9 521.2 (1) Senior secured second lien notes due 2025 1,186.6 1,257.6 (1) 1,184.2 1,279.1 (1) Senior notes due 2026 298.4 318.8 (1) 298.1 313.9 (1) Senior notes due 2028 695.1 691.9 (1) 694.6 689.2 (1) Total $ 3,362.7 $ 3,486.7 $ 3,658.9 $ 3,789.7 (1) Level 1 Fair Value hierarchy (2) Level 2 Fair Value hierarchy See also Note 14, Derivative and Hedging Activities.

Derivative and Hedging Activiti

Derivative and Hedging Activities	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Hedging Activities	Derivative and Hedging Activities Derivatives Accounted for as Hedges Cash Flow Hedges - Interest Rate Swaps The Company has traditionally entered into interest rate swap agreements to reduce its exposure to the variable rate portion of its long-term debt. The Company also considers counterparty credit risk and its own credit risk in its determination of all estimated fair values. As of December 31, 2020, the Company had one interest rate swap agreement, designated as cash flow hedge, with a notional value of $150. On February 24, 2021, the Company terminated the swap agreement. As of September 30, 2021, the Company had no swaps outstanding. Changes in the fair value of cash flow hedges are recorded in Accumulated Other Comprehensive Income ("AOCI") and recorded in earnings in the period in which the hedged transaction occurs. No gain or loss was recognized in AOCI for the three or nine months ended September 30, 2021. For the three and nine months ended September 30, 2021 a loss of $0.0 and $0.4, respectively, was reclassified from AOCI to earnings, and included in the interest expense line item on the Condensed Consolidated Statements of Operations, and in operating activities on the Condensed Consolidated Statements of Cash Fl ows. For the three and nine months ended September 30, 2021 a loss of $0.0 and $0.7, respectively, was reclassified from AOCI to earnings resulting from the termination of a swap agreement, and included in the other income line item on the Condensed Consolidated Statements of Operations, and in operating activities on the Condensed Consolidated Statements of Cash Flows. Cash Flow Hedges – Foreign Currency Hedge The Company has entered into currency forward contracts, each designated as a cash flow hedge upon the date of execution, for the purpose of reducing the variability of cash flows and hedging against the foreign currency exposure for forecasted payroll, pension and vendor disbursements that are expected to be made in the British Pound Sterling. The hedging program implemented is intended to reduce foreign currency exposure, and the associated forward currency contracts hedge forecasted transactions through June 2022. The following table summarizes the notional amounts (representing the gross contract/notional amount of the derivatives outstanding) and fair values of the derivative instruments in the Condensed Consolidated Balance Sheets as of September 30, 2021, and December 31, 2020. The foreign currency exchange contracts are measured within Level 1 of the Fair Value hierarchy. See Note 13, Fair Value Measurements . Notional amount Other assets Other liabilities September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 Derivatives designated as hedging instruments: Foreign currency exchange contracts $ 280.3 $ — $ — $ — $ 5.6 $ — Total derivatives at fair value $ — $ — $ 5.6 $ — Changes in the fair value of cash flow hedges are recorded in AOCI and recorded in earnings in the period in which the hedged transaction settles. The gain (loss) recognized in AOCI associated with our hedging transactions is presented in the following table: Three Months Ended Nine Months Ended September 30, 2021 October 1, 2020 September 30, 2021 October 1, 2020 Recognized in total other comprehensive loss: Foreign currency exchange contracts $ (6.2) $ — $ (5.5) $ — The following table summarizes the gains/(losses) associated with our hedging transactions reclassified from AOCI to earnings: Three Months Ended Nine Months Ended September 30, 2021 October 1, 2020 September 30, 2021 October 1, 2020 Foreign currency exchange contracts: Other income (expense) $ 0.1 $ — $ 0.1 $ — Within the next 12 months, the Company expects to recognize a loss of $5.6 in earnings related to the foreign currency forward contracts. As of September 30, 2021, the maximum term of the hedged forecasted transaction was 9 months. Generally, the Company has agreements with its counterparties that contain a provision whereby if the Company defaults on its existing credit facilities and payment of the loans extended under such facilities is accelerated, the Company could be declared in default under its agreements, which may result in the early termination of the outstanding derivatives governed by such agreements and the payment of an early termination amount.

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	Debt Total debt shown on the balance sheet is comprised of the following: September 30, 2021 December 31, 2020 Current Noncurrent Current Noncurrent Senior secured term loan B $ 3.9 $ 384.6 $ 3.9 $ 385.7 Floating rate notes — — 299.7 — Senior notes due 2023 — 299.2 — 298.8 Senior secured first lien notes due 2025 — 494.9 — 493.9 Senior secured second lien notes due 2025 — 1,186.6 — 1,184.2 Senior notes due 2026 — 298.4 — 298.1 Senior notes due 2028 — 695.1 — 694.6 Present value of finance lease obligations 42.6 132.8 35.3 121.5 Other 1.3 55.1 1.8 56.1 Total $ 47.8 $ 3,546.7 $ 340.7 $ 3,532.9 Credit Agreement On October 5, 2020, Spirit entered into a term loan credit agreement (the “Credit Agreement”) providing for a $400.0 senior secured term loan B credit facility with the lenders party thereto and Bank of America, N.A., as administrative agent and collateral agent. On October 5, 2020, Spirit borrowed the full $400.0 of initial term loans available under the Credit Agreement. The obligations under the Credit Agreement are guaranteed by Holdings and Spirit AeroSystems North Carolina, Inc., a wholly-owned subsidiary of the Company (“Spirit NC”, and together with Holdings, the "Guarantors"), and each existing and future, direct and indirect, wholly-owned material domestic subsidiary of Spirit, subject to certain customary exceptions. The obligations are secured by a first-priority lien with respect to substantially all assets of Spirit and the Guarantors, subject to certain exceptions. As of September 30, 2021 , the outstanding balance of the Credit Agreement was $397.0 and the carrying value was $388.5. As of September 30, 2021 , the Company was in compliance with all covenants in the Credit Agreement. First Lien 2025 Notes On October 5, 2020, Spirit entered into an Indenture (the “First Lien 2025 Notes Indenture”), by and among Spirit, the Guarantors, and The Bank of New York Mellon Trust Company, N.A., as trustee and collateral agent, in connection with Spirit’s offering of $500.0 aggregate principal amount of its 5.500% Senior Secured First Lien Notes due 2025 (the “First Lien 2025 Notes"). The First Lien 2025 Notes are guaranteed by the Guarantors and secured by certain real property and personal property, including certain equity interests, owned by Spirit and the Guarantors. As of September 30, 2021 , the outstanding balance of the First Lien 2025 Notes was $500.0 and the carrying value was $494.9. 2026 Notes In June 2016, Spirit issued $300.0 in aggregate principal amount of 3.850% Senior Notes due June 15, 2026 (the “2026 Notes”) with interest payable, in cash in arrears, on June 15 and December 15 of each year, beginning December 15, 2016. On October 5, 2020, Spirit entered into a Fourth Supplemental Indenture (the “Fourth Supplemental Indenture”), by and among Spirit, Spirit Holdings, Spirit NC and The Bank of New York Mellon Trust Company, N.A., as trustee in connection with 2026 Notes. Under the Fourth Supplemental Indenture, the holders of the 2026 Notes were granted security on an equal and ratable basis with the holders of the First Lien 2025 Notes and the secured parties under the Credit Agreement. As of September 30, 2021, the outstanding balance of the 2026 Notes was $300.0 and the carrying value was $298.4. Second Lien 2025 Notes On April 17, 2020, Spirit entered into an Indenture (the “Second Lien 2025 Notes Indenture”), by and among Spirit, the Guarantors, and The Bank of New York Mellon Trust Company, N.A., as trustee and collateral agent, in connection with Spirit’s offering of $1,200.0 aggregate principal amount of its 7.500% Senior Secured Second Lien Notes due 2025 (the “Second Lien 2025 Notes”). The Second Lien 2025 Notes mature on April 15, 2025 and bear interest at a rate of 7.500% per year payable semiannually in cash in arrears on April 15 and October 15 of each year. The first interest payment date was October 15, 2020. The Second Lien 2025 Notes are guaranteed by the Guarantors and secured by certain real property and personal property, including certain equity interests, owned by Spirit and the Guarantors. As of September 30, 2021 , the outstanding balance of the Second Lien 2025 Notes was $1,200.0 and the carrying value was $1,186.6. Floating Rate, 2023, and 2028 Notes On May 30, 2018, Spirit entered into an Indenture (the “2018 Indenture”) by and among Spirit, Spirit Holdings and The Bank of New York Mellon Trust Company, N.A., as trustee in connection with Spirit’s offering of $300.0 aggregate principal amount of its Senior Floating Rate Notes due 2021 (the “Floating Rate Notes”), $300.0 aggregate principal amount of its 3.950% Senior Notes due 2023 (the “2023 Notes”) and $700.0 aggregate principal amount of its 4.600% Senior Notes due 2028 (the “2028 Notes” and, together with the Floating Rate Notes and the 2023 Notes, the “2018 Notes”). Holdings guaranteed Spirit’s obligations under the 2018 Notes on a senior unsecured basis. On February 24, 2021, Spirit redeemed the outstanding $300.0 principal amount of the Floating Rate Notes. As of September 30, 2021 , the outstanding balance of the Floating Rate Notes was $0. As of September 30, 2021 , the outstanding balance of the 2023 Notes and the 2028 Notes was $300.0 and $700.0, respectively, and the carrying value was $299.2 and $695.1, respectively.

Pension and Other Post-Retireme

Pension and Other Post-Retirement Benefits Defined Benefit Plan (Notes)	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Retirement Benefits [Text Block]	Pension and Other Post-Retirement Benefits Defined Benefit Plans For the Three Months Ended For the Nine Components of Net Periodic Pension Expense (Income) September 30, October 1, September 30, October 1, Service cost $ 11.2 $ 0.2 $ 32.9 $ 0.7 Interest cost 15.8 5.4 43.3 20.1 Expected return on plan assets (40.0) (16.6) (119.0) (49.5) Amortization of net loss — — — 0.2 Curtailment loss (gain) (61.0) (1) — (2) (61.0) (1) 33.9 (2) Settlement loss — 4.2 (3) (0.1) 9.3 (3) Special termination benefits — (1.6) (4) — 31.4 (4) Net periodic pension expense (income) $ (74.0) $ (8.4) $ (103.9) $ 46.1 Other Benefits For the Three For the Nine Components of Other Benefit Expense (Income) September 30, October 1, September 30, October 1, Service cost $ 0.3 $ 0.1 $ 0.7 $ 0.5 Interest cost 0.1 0.2 0.3 0.7 Amortization of prior service cost (0.2) (0.2) (0.6) (0.6) Amortization of net gain (0.2) (0.4) (1.0) (1.3) Curtailment gain — — — (0.2) Special termination benefits — — — 12.0 Net periodic other benefit expense (income) $ — $ (0.3) $ (0.6) $ 11.1 (1) As of July 15, 2021, the Company concluded its consultation and communication with employee and Trade Union representatives on the closure of the largest of the defined benefit plans acquired as part of the Bombardier Acquisition, the Shorts Pension (as defined below). The outcome is that the Shorts Pension was amended and will close to the future accrual of benefits for all employees who are members of the plan, effective December 10, 2021. From December 11, 2021, affected employees will build up future retirement savings in a new defined contribution scheme. For the three and nine months ended September 30, 2021, the impact of the closure of the Shorts Pension resulted in a curtailment gain of $61.0. (2) F or the three and nine months ended October 1, 2020, the Company's Voluntary Retirement Program ("VRP") resulted in an estimated 16% and 12% reduction in future working lifetime for the pension value plan and postretirement medical plan resulting in a curtailment accounting charge of $0.0 and $33.7, respectively. The charges are included in other income (expense) in the Company's Condensed Consolidated Statements of Operations. (3) For the three months and nine months ended October 1, 2020, settlement accounting under ASC Topic 715 was triggered, as the lump sums paid to date as part of the VRP exceeded the estimated service cost and interest cost. The Company recognized a settlement loss of $4.2 and $9.3 for the three months and nine months ended October 1, 2020. (4) Special termination benefits for the three and nine months ended October 1, 2020 is a combination of pension value plan and postretirement medical plan changes offset by a reduction in the Company's net benefit obligation. For the three months and nine months ended October 1, 2020 special termination benefits, curtailment accounting, and the remeasurement of the pension assets and obligations resulted in a ($31.9) and $0.4 impact to other comprehensive income ("OCI"), respectively. For the three months and nine months ended October 1, 2020, retiree medical resulted in a $0.0 and $2.3 impact to OCI, respectively. This impact is included in the Company’s Condensed Consolidated Statements of Comprehensive (Loss) Income. The components of net periodic pension expense (income) and other benefit expense, other than the service cost component, are included in other income (expense) in the Company's Condensed Consolidated Statements of Operations. Employer Contributions The Company expects to contribute zero dollars to the U.S. qualified pension plan and a combined total of approximately $10.2 for the U.S. Supplemental Executive Retirement Plan (“SERP”) and U.S. post-retirement medical plans in 2021. The Company’s projected contributions to the U.K. pension plan for 2021 are $1.9. Additionally, the Company expects to contribute a combined total of $182.6 for the Shorts Pension, the Shorts Executive Benefits Scheme, and the Shorts Postretirement Medical Plan. The amount contributed can vary based on exchange rate fluctuations.

Income Taxes (Notes)

Income Taxes (Notes)	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes The process for calculating the Company’s income tax expense involves estimating actual current taxes due plus assessing temporary differences arising from differing treatment for tax and accounting purposes that are recorded as deferred tax assets and liabilities. Deferred tax assets are periodically evaluated to determine their recoverability and whether a valuation allowance is necessary. A valuation allowance, if needed, reduces deferred tax assets to the amount expected to be realized. When determining the amount of net deferred tax assets that are more likely than not to be realized, the Company assesses all available positive and negative evidence. The weight given to the positive and negative evidence is commensurate with the extent the evidence may be objectively verified. As such, it is generally difficult for positive evidence regarding projected future taxable income exclusive of reversing taxable temporary differences to outweigh objective negative evidence of recent financial reporting losses. Based on these criteria and the relative weighting of both the positive and negative evidence available, and in particular the activity surrounding our prior earnings history including the forward losses previously recognized in the U.S., the Company recorded an incremental valuation allowance of $122.5 for the nine months ended September 30, 2021. The change from December 31, 2020 is an additional valuation allowance of $104.6 recognized on the deferred tax assets generated from the 2021 activity and a $17.9 adjustment related to law changes, return to provision and other state impacts. The total valuation allowance, including the increase of $122.5 recorded for the nine-month period ended September 30, 2021, was $272.5. This results in a net U.S. deferred tax liability after valuation allowance of $13.7. The Company has determined a valuation allowance on certain U.K. deferred tax assets is needed based upon cumulative losses generated in the U.K. The Company recorded an incremental valuation allowance of $70.7 against deferred tax assets for the nine-month period ended September 30, 2021 which is comprised of $13.5 for opening balance sheet adjustments related to the Bombardier Acquisition, $0.1 related to OCI, ($0.7) from discrete items including return to provision, ($3.6) from continuing operations and a discrete tax expense of $61.4 for the change in enacted corporate tax rates from 19% to 25% effective April 1, 2023. The total valuation allowance, including the nine-month period ended September 30, 2021 increase of $70.7, was $261.5. This results in a net U.K. deferred tax liability after valuation allowance of $10.9. The Company will continue to regularly assess the potential for realization of its net deferred tax assets in future periods. Changes in future earnings projections, among other factors, may cause the Company to record a valuation allowance against some or all of its net deferred tax assets, which may materially impact its income tax expense in the period the Company determines that these factors have changed. The Company files income tax returns in all jurisdictions in which it operates. The Company establishes reserves to provide for additional income taxes that may be due upon audit. These reserves are established based on management’s assessment as to the potential exposure attributable to permanent tax adjustments and associated interest. All tax reserves are analyzed quarterly and adjustments made as events occur that warrant modification. In general, the Company records income tax expense each quarter based on its estimate as to the full year’s effective tax rate. Certain items, however, are given discrete period treatment and the tax effects for such items are therefore reported in the quarter that an event arises. Events or items that may give rise to discrete recognition include excess tax benefits with respect to share-based compensation, finalizing amounts in income tax returns filed, finalizing audit examinations for open tax years and expiration of statutes of limitations, and changes in tax law. T he 0.15% effectiv e tax rate for the nine months ended September 30, 2021 differs from the 37.3% effective tax rate for the same period of 2020 primarily due to the valuation allowance recorded in 2021. As the Company is currently reporting a pre-tax loss for the nine months ended September 30, 2021, increases to tax expense result in a decrease to the effective tax rate and decreases to tax expense result in an increase to the effective tax rate. As of September 30, 2021 , the Company had deferred $16.5 of employer payroll taxes, as allowed by the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”), which is required to be deposited by December 2022. As of September 30, 2021 , the Company has recorded an estimated pre-tax employee retention credit of approximately $18.8 related to calendar year 2020. The Company is evaluating its eligibility to continue with the pre-tax employee retention credit. In addition, as of September 30, 2021 , the Company had recorded a deferral of $15.5 of Value Added Tax payments that has the option to pay in smaller payments through the end of March 31, 2022 interest free under the United Kingdom deferral scheme. Payments under this deferral program started in June 2021.

Equity

Equity	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Equity	Equity Earnings per Share Calculation Basic net income per share is computed using the weighted-average number of outstanding shares of Common Stock during the measurement period. Diluted net income per share is computed using the weighted-average number of outstanding shares of Common Stock and, when dilutive, potential outstanding shares of Common Stock during the measurement period. Diluted earnings per share includes any dilutive impact of RSUs, DRSUs, RSAs, and PBRSUs. The Company accounts for treasury stock under the cost method and includes treasury stock as a component of stockholders’ equity. As of September 30, 2021, no treasury shares have been reissued or retired. The total authorization amount remaining under the current share repurchase program is approximately $925.0. During the nine month period ended September 30, 2021, the Company did not repurchase any shares of its Common Stock under this share repurchase program. Share repurchases are currently on hold pending the outcome of the COVID-19 pandemic. Additionally, t he Credit Agreement imposes restrictions on the Company’s ability to repurchase shares. The following table sets forth the computation of basic and diluted earnings per share: For the Three Months Ended September 30, 2021 October 1, 2020 Income Shares Per Share Income Shares Per Share Basic EPS Loss available to common stockholders $ (113.6) 104.3 $ (1.09) $ (155.5) 103.9 $ (1.50) Income allocated to participating securities — — — — Net loss $ (113.6) $ (155.5) Diluted potential common shares — — Diluted EPS Net loss $ (113.6) 104.3 $ (1.09) $ (155.5) 103.9 $ (1.50) For the Nine Months Ended September 30, 2021 October 1, 2020 Income Shares Per Share Income Shares Per Share Basic EPS Loss available to common stockholders $ (420.5) 104.2 $ (4.04) $ (574.4) 103.8 $ (5.53) Income allocated to participating securities — — — — Net loss $ (420.5) $ (574.4) Diluted potential common shares — — Diluted EPS Net loss $ (420.5) 104.2 $ (4.04) $ (574.4) 103.8 $ (5.53) Included in the outstanding Common Stock were 0.7 million and 1.6 million of issued but unvested shares at September 30, 2021 and October 1, 2020, respectively, which are excluded from the basic Earnings Per Share ("EPS") calculation. Common shares of 0.4 million and 0.5 million, respectively, were excluded from diluted EPS as a result of incurring a net loss for the three and nine months ended September 30, 2021 , as the effect would have been antidilutive. Additionally, diluted EPS for the three and nine months ended September 30, 2021 excludes 0.3 million and 0.3 million shares, respectively, that may be dilutive common shares in the future, but were not included in the computation of diluted EPS because the effect was either antidilutive or the performance condition was not met. Common shares of 0.9 million and 0.7 million, respectively, were excluded from diluted EPS as a result of incurring a net loss for the three and nine months ended October 1, 2020, as the effect would have been antidilutive. Additionally, diluted EPS for the three and nine months ended October 1, 2020 excludes 0.3 million and 0.3 million shares, respectively, that may be dilutive common shares in the future, but were not included in the computation of diluted EPS because the effect was either antidilutive or the performance condition was not met. Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Loss is summarized by component as follows: As of As of September 30, 2021 December 31, 2020 Pension $ (107.0) $ (112.0) Interest swaps — (0.9) SERP/Retiree medical 13.2 14.5 Derivatives - foreign currency hedge (5.6) — Foreign currency impact on long-term intercompany loan (12.4) (11.8) Currency translation adjustment (51.5) (43.9) Total accumulated other comprehensive loss $ (163.3) $ (154.1) Amortization or curtailment cost recognition of the pension plans’ net gain/(loss) reclassified from accumulated other comprehensive loss and realized into costs of sales and selling, general and administrative on the Condensed Consolidated Statements of Operations was $0.4 and $0.7 for the three months ended September 30, 2021 and October 1, 2020, respectively, and $1.6 and $2.0 for the nine months ended September 30, 2021 and October 1, 2020, respectively. .

Commitments, Contingencies and

Commitments, Contingencies and Guarantees	9 Months Ended
	Sep. 30, 2021
Commitments Contingencies And Guarantees [Abstract]
Commitments, Contingencies and Guarantees	Commitments, Contingencies and Guarantees Litigation On February 10, 2020, February 24, 2020, and March 24, 2020, three separate private securities class action lawsuits were filed against the Company in the U.S. District Court for the Northern District of Oklahoma, its Chief Executive Officer, Tom Gentile III, former Chief Financial Officer, Jose Garcia, and former Controller (principal accounting officer), John Gilson. On April 20, 2020, the Class Actions were consolidated by the court (the “Consolidated Class Action”), and on July 20, 2020, the plaintiffs filed a Consolidated Class Action Complaint which added Shawn Campbell, the Company’s former Vice President for the 737NG and B737 Max program, as a defendant. Allegations in the Consolidated Class Action include (i) violations of Section 10(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) and Rule 10b-5 promulgated thereunder against the Company and Messrs. Gentile, Garcia and Gilson, (ii) violations of Section 20(a) of the Exchange Act against the individual defendants, and (iii) violations of Section 10(b) of the Exchange Act and Rule 10b-5(a) and (c) promulgated thereunder against all defendants. On June 11, 2020, a shareholder derivative lawsuit (the “Derivative Action 1”) was filed against the Company (as nominal defendant), all members of the Company’s Board of Directors, and Messrs. Garcia and Gilson in the U.S. District Court for the Northern District of Oklahoma. Allegations in the Derivative Action 1 include (i) breach of fiduciary duty, (ii) abuse of control, and (iii) gross mismanagement. On October 5, 2020, a shareholder derivative lawsuit (the “Derivative Action 2” and, together with Derivative Action 1, the “Derivative Actions”) was filed against the Company (as nominal defendant), all members of the Company’s Board of Directors, and Messrs. Garcia and Gilson in the Eighteenth Judicial District, District Court of Sedgwick County, Kansas. Allegations in the Derivative Action 2 include (i) breach of fiduciary duty, (ii) waste of corporate assets, and (iii) unjust enrichment. The facts underlying the Consolidated Class Action and Derivative Actions relate to the accounting process compliance independent review (the “Accounting Review”) discussed in the Company’s January 30, 2020 press release and described under Management's Discussion and Analysis of Financial Condition and Results of Operations - Accounting Review in Part II, Item 7 of the Annual Report on Form 10-K for the year ended December 31, 2019, and its resulting conclusions. The Company voluntarily reported to the SEC the determination that, with respect to the third quarter of 2019, the Company did not comply with its established accounting processes related to potential third quarter contingent liabilities received after the quarter-end. On March 24, 2020, the Staff of the SEC Enforcement Division informed the Company that it had determined to close its inquiry without recommending any enforcement action against the Company. In addition, the facts underlying the Consolidated Class Action and Derivative Actions relate to the Company’s disclosures regarding the B737 MAX grounding and Spirit’s production rate (and related matters) after the grounding. On September 18, 2020, the Company and individual defendants filed a motion to dismiss the Consolidated Class Action. That motion is pending. The Derivative Actions have been stayed pending a decision on the Consolidated Class Action. The Company and the individual defendants deny the allegations in the Consolidated Class Action and the Derivative Actions. On October 19, 2021, the U.S. District Court for the District of Kansas ruled in favor of the Company’s former Chief Executive Officer and awarded him $44.7 for benefits withheld in connection with a disputed violation of restrictive covenants in his retirement agreement. The Company continues to evaluate the decision and future action, including an appeal. A liability for the full amount of the award has been recognized in the Condensed Consolidated Balance Sheets as of September 30, 2021. Based upon the former Chief Executive Officer's selection of cash as the sole remedy, 406,816 shares of Common Stock are no longer included in issued and outstanding shares as of September 30, 2021. These shares were recorded in prior periods to Selling, general, and administrative expense on the Condensed Consolidated Statements of Operations as stock compensation expense of $17.1, the amount of which is now included in the liability that has been recognized in the Condensed Consolidated Balance Sheets as of September 30, 2021 for the full amount of the award from the ruling, as described above, resulting in a net charge of $26.6 for the three-month and nine-month periods ended September 30, 2021, which was recorded to Selling, general and administrative expense on the Condensed Consolidated Statements of Operations. From time to time, in the ordinary course of business and similar to others in the industry, the Company receives requests for information from government agencies in connection with their regulatory or investigational authority. Such requests can include subpoenas or demand letters for documents to assist the government in audits or investigations. The Company reviews such requests and notices and takes appropriate action. Additionally, the Company is subject to federal and state requirements for protection of the environment, including those for disposal of hazardous waste and remediation of contaminated sites. As a result, the Company is required to participate in certain government investigations regarding environmental remediation actions. In addition to the items addressed above, from time to time, the Company is subject to, and is presently involved in, litigation, legal proceedings, or other claims arising in the ordinary course of business. While the final outcome of these matters cannot be predicted with certainty, considering, among other things, the meritorious legal defenses available, the Company believes that, on a basis of information presently available, none of these items, when finally resolved, will have a material adverse effect on the Company’s long-term financial position or liquidity. Customer and Vendor Claims From time to time the Company receives, or is subject to, customer and vendor claims arising in the ordinary course of business, including, but not limited to, those related to product quality and late delivery. The Company accrues for matters when losses are deemed probable and reasonably estimable. In evaluating matters for accrual and disclosure purposes, we take into consideration multiple factors including, without limitation, our historical experience with matters of a similar nature, the specific facts and circumstances asserted, the likelihood of an unfavorable outcome, and the severity of any potential loss. Any accruals deemed necessary are reevaluated at least quarterly and updated as matters progress over time. While the final outcome of these types of matters cannot be predicted with certainty, considering, among other things, the factual and legal defenses available, it is the opinion of the Company that, when finally resolved, no current claims will have a material adverse effect on the Company’s long-term financial position or liquidity. However, it is possible that the Company’s results of operations in a period could be materially affected by one or more of these other matters. The Company has evaluated and refined management’s original estimate of costs related to rework on the B787 aircraft, including a preliminary assessment related to rework on the forward section of the fuselage, for which the Company identified an additional fit and finish issue in the three month period ended July 1, 2021. The Company continues to coordinate with Boeing to ensure that all necessary rework is performed. The Company cannot reasonably estimate the amount of any potential claims related to this issue at this time due to various reasons, including, among others: (i) that there is uncertainty that any such claim could be received, (ii) that there is uncertainty as to the outcome of any such claims, (iii) that there may be significant factual and/or commercial issues to be resolved, and (iv) that there may be novel legal issues presented. Guarantees Outstanding guarantees were $16.4 and $19.6 at September 30, 2021 and December 31, 2020, respectively. Restricted Cash - Collateral Requirements The Company was required to maintain $19.5 and $19.5 of restricted cash as of September 30, 2021 and December 31, 2020, respectively, related to certain collateral requirements for obligations under its workers’ compensation programs. The restricted cash is included in "Restricted cash" and “Other assets” in the Company’s Condensed Consolidated Balance Sheets. Indemnification The Company has entered into customary indemnification agreements with its non-employee directors, and its bylaws and certain executive employment agreements include indemnification and advancement provisions. Pursuant to the terms of the bylaws and, with respect to Jose Garcia, his employment agreement, the Company is providing Messrs. Garcia and Gilson and all other individual defendants with defense costs and provisional indemnity with respect to the Consolidated Class Action and Derivative Actions, as appropriate. Under the bylaws and any applicable agreements, the Company agrees to indemnify each of these individuals against claims arising out of events or occurrences related to that individual’s service as the Company’s agent or the agent of any of its subsidiaries to the fullest extent legally permitted. The Company has agreed to indemnify parties for specified liabilities incurred, or that may be incurred, in connection with transactions they have entered into with the Company. The Company is unable to assess the potential number of future claims that may be asserted under these indemnities, nor the amounts thereof (if any). As a result, the Company cannot estimate the maximum potential amount of future payments under these indemnities and therefore, no liability has been recorded. Service and Product Warranties and Extraordinary Rework Provisions for estimated expenses related to service and product warranties and certain extraordinary rework are evaluated on a quarterly basis. These costs are accrued and are recorded to unallocated cost of goods sold. These estimates are established using historical information on the nature, frequency, and average cost of warranty claims, including the experience of industry peers. In the case of new development products or new customers, the Company considers other factors including the experience of other entities in the same business and management judgment, among others. Service warranty and extraordinary rework is reported in Current liabilities and Other liabilities on the Company's Condensed Consolidated Balance Sheets. The warranty balance presented in the table below includes unresolved warranty claims that are in dispute in regards to their value as well as their contractual liability. The Company estimated the total costs related to some of these claims; however, there is significant uncertainty surrounding the disposition of these disputed claims and as such, the ultimate determination of the provision’s adequacy requires significant management judgment. The amount of the specific provisions recorded against disputed warranty claims was $2.3 as of September 30, 2021 and $8.1 as of December 31, 2020. These specific provisions represent the Company’s best estimate of probable warranty claims. Should the Company incur higher than expected warranty costs and/or discover new or additional information related to these warranty provisions, the Company may incur additional charges that exceed these recorded provisions. The Company utilized available information to make appropriate assessments, however, the Company recognizes that data on actual claims experience is of limited duration and therefore, claims projections are subject to significant judgment. The amount of the reasonably possible disputed warranty claims in excess of the specific warranty provision was $3.4 as of September 30, 2021 and $12.1 as of December 31, 2020. The following is a roll forward of the service warranty and extraordinary rework balance at September 30, 2021: Balance, December 31, 2020 $ 76.9 Charges to costs and expenses 10.1 Payouts (13.1) Exchange rate (0.2) Balance, September 30, 2021 $ 73.7

Other Income (Expense), Net

Other Income (Expense), Net	9 Months Ended
	Sep. 30, 2021
Other Nonoperating Income (Expense) [Abstract]
Other Income (Expense), Net	Other Income (Expense), Net Other income (expense), net is summarized as follows: For the Three For the Nine September 30, October 1, September 30, October 1, Kansas Development Finance Authority bond $ 0.6 $ 0.6 $ 2.2 $ 2.3 Foreign currency (losses) gains (1) 11.3 (3.4) 3.8 1.4 Loss on foreign currency contract and interest rate swaps — (10.6) — (10.5) Loss on sale of accounts receivable (1.8) (2.0) (4.8) (6.7) Pension income (loss) (2) 84.8 9.0 137.3 (56.4) Other (0.1) (3.6) 0.2 4.5 Total $ 94.8 $ (10.0) $ 138.7 $ (65.4) (1) Foreign currency gains and losses are due to the impact of movement in foreign currency exchange rates on long-term contractual rights/obligations, as well as cash and both trade and intercompany receivables/payables that are denominated in a currency other than the entity’s functional currency. (2) Pension income for the three and nine months ended September 30, 2021 includes $74.2 and $105.3 of income re

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Segment Information	Segment Information The Company operates in three principal segments: Fuselage Systems, Propulsion Systems, and Wing Systems. Revenue from Boeing represents a substantial portion of the Company's revenues in all segments. The Wing Systems Segment also includes significant revenues from Airbus. Approximately 79% of the Company's net revenues for the three months ended September 30, 2021 came from the Company's two largest customers, Boeing and Airbus. All other activities fall within the All Other segment, principally made up of non-recurring contracts, sundry sales of miscellaneous services, tooling contracts and sales of natural gas through a tenancy-in-common with other companies that have operations in Wichita, Kansas. The Company's primary profitability measure to review a segment’s operating performance is segment operating income before corporate selling, general and administrative expenses, research and development, and unallocated cost of sales. Corporate selling, general and administrative expenses include centralized functions such as accounting, treasury, and human resources that are not specifically related to the Company's operating segments and are not allocated in measuring the operating segments’ profitability and performance and net profit margins. Research and development includes research and development efforts that benefit the Company as a whole and are not unique to a specific segment. Restructuring costs represent corporate level charges related to the closure of the San Antonio and McAlester sites. Unallocated cost of sales includes general costs not directly attributable to segment operations, such as warranty, early retirement and other incentives. All of these items are not specifically related to the Company’s operating segments and are not utilized in measuring the operating segments’ profitability and performance. The Company’s Fuselage Systems Segment includes development, production and marketing of forward, mid and rear fuselage sections and systems, primarily to aircraft OEMs (OEM refers to aircraft original equipment manufacturer). The Fuselage Systems Segment manufactures products at the Company's facilities in Wichita, Kansas; Tulsa, Oklahoma; Kinston, North Carolina; Biddeford, Maine; Casablanca, Morocco; Belfast, Northern Ireland; and Subang, Malaysia. The Fuselage Systems Segment also includes an assembly plant for the A350 XWB aircraft in Saint-Nazaire, France. The Company’s Propulsion Systems Segment includes development, production and marketing of struts/pylons, nacelles (including thrust reversers) and related engine structural components primarily to aircraft or engine OEMs, as well as related spares and maintenance, repair and overhaul ("MRO") services. The Propulsion Systems Segment manufactures products at the Company's facilities in Wichita, Kansas; Dallas, Texas; Biddeford, Maine; and Belfast, Northern Ireland. The Company’s Wing Systems Segment includes development, production and marketing of wings and wing components (including flight control surfaces) as well as other miscellaneous structural parts primarily to aircraft OEMs. These activities take place at the Company’s facilities in Tulsa, Oklahoma; Kinston, North Carolina; Prestwick, Scotland; Belfast, Northern Ireland; Casablanca, Morocco; and Subang, Malaysia. The Company’s segments are consistent with the organization and responsibilities of management reporting to the chief operating decision-maker for the purpose of assessing performance. The Company’s definition of segment operating income differs from operating income as presented in its primary financial statements and a reconciliation of the segment and consolidated results is provided in the table set forth below. While some working capital accounts are maintained on a segment basis, much of the Company’s assets are not managed or maintained on a segment basis. Property, plant and equipment, including tooling, is used in the design and production of products for each of the segments and, therefore, is not allocated to any individual segment. In addition, cash, prepaid expenses, other assets, and deferred taxes are managed and maintained on a consolidated basis and generally do not pertain to any particular segment. Raw materials and certain component parts are used in aerostructures production across all segments. Work-in-process inventory is identifiable by segment, but is managed and evaluated at the program level. As there is no segmentation of the Company’s productive assets, depreciation expense (included in fixed manufacturing costs and selling, general and administrative expenses) and capital expenditures, no allocation of these amounts has been made solely for purposes of segment disclosure requirements. The following table shows segment revenues and operating income for the three and nine months ended September 30, 2021 and October 1, 2020: Three Months Ended Nine Months Ended September 30, October 1, September 30, October 1, Segment Revenues Fuselage Systems $ 481.2 $ 421.1 $ 1,410.5 $ 1,299.7 Propulsion Systems 247.8 170.8 716.2 565.6 Wing Systems 243.0 168.3 725.9 582.2 All Other 8.0 46.1 30.3 80.7 $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 Segment Operating Income (Loss) Fuselage Systems (1) $ (53.9) $ (96.7) $ (145.5) $ (434.6) Propulsion Systems (2) 21.9 (15.6) 66.8 (38.2) Wing Systems (3) (15.8) (23.2) (50.9) (52.1) All Other 2.4 19.1 5.1 28.9 $ (45.4) $ (116.4) $ (124.5) $ (496.0) SG&A (86.8) (52.8) (211.3) (179.2) Research and development (12.8) (7.5) (34.3) (28.1) Unallocated cost of sales (11.6) (0.2) (10.1) (8.1) Total operating loss $ (156.6) $ (176.9) $ (380.2) $ (711.4) (1) The three and nine months ended September 30, 2021 includes excess capacity production costs of $36.2 and $106.4, respectively, related to the B737 MAX and A220 production schedule changes, abnormal costs of $1.4 and $3.5, respectively, for workforce adjustments as a result of COVID-19 production pause, net of U.S. employee retention credit and U.K. government subsidies, and $0.2 and $2.9, respectively, of restructuring costs. The three and nine months ended October 1, 2020 includes excess capacity production cost of $42.0 and $143.8, respectively, related to B737 MAX production schedule changes, abnormal costs of ($7.4) and $19.1, respectively, for workforce adjustments as a result of COVID-19 production pause, $6.6 and $39.1, respectively, of restructuring costs, and $0 and $22.5, respectively, from loss on disposition of assets. (2) The three and nine months ended September 30, 2021 includes excess capacity production costs of $10.8 and $25.1, respectively, related to the B737 MAX and A220 production schedule changes, abnormal costs of $0.3 and $0.7, respectively, for workforce adjustments as a result of COVID-19 production pause, net of U.S. employee retention credit, and $0.0 and ($0.2), respectively, of restructuring costs. The three and nine months ended October 1, 2020 includes excess capacity production cost of $17.5 and $50.8, respectively, related to the B737 MAX production schedule changes, abnormal costs of ($2.9) and $7.3, respectively, for workforce adjustments as a result of COVID-19 production pause, and $3.8 and $14.2, respectively, of restructuring costs. (3) The three and nine months ended September 30, 2021

Restructuring Charges (Notes)

Restructuring Charges (Notes)	9 Months Ended
	Sep. 30, 2021
Restructuring Costs [Abstract]
Restructuring and Related Activities Disclosure [Text Block]	Restructuring Costs The Company's results of operations for both the three and nine months ended September 30, 2021 and October 1, 2020 include restructuring costs related to actions the Company has taken to align costs to updated production levels that have been directed by the Company's customers (restructuring activity). Largely beginning in the first quarter of 2020, the Company's customers, including Boeing and Airbus, significantly reduced their overall production rates as a result of the COVID-19 pandemic and, in the case of Boeing, the B737 MAX grounding. The restructuring activity materially affected the scope of operations and manner in which business is conducted by the Company compared to periods prior to the restructuring activities. Restructuring costs are presented separately as a component of operating loss on the Condensed Consolidated Statements of Operations. The total restructuring costs of $0.8 and $8.1 for the three and nine months ended September 30, 2021, respectively, largely includes cost related to McAlester and San Antonio site closures. For the three and nine months ended October 1, 2020, total restructuring costs of $19.5 and $68.4, respectively, were comprised of $11.1 and $47.5, respectively, related to involuntary workforce reductions and $8.4 and $20.9, respectively, related to a VRP. Of the $8.1 total restructuring cost for the nine months ended September 30, 2021, $8.1 was paid during the nine month period ended September 30, 2021.

Acquisition (Notes)

Acquisition (Notes)	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Asco Acquisition [Text Block]

Subsequent Event (Notes)

Subsequent Event (Notes)	9 Months Ended
	Sep. 30, 2021
Subsequent Event [Line Items]
Subsequent Events [Text Block]	On September 30, 2021, the Company announced a new organizational structure to focus on growth in the key markets it serves. Under the new segment reporting structure, the Company will have three primary business divisions: Commercial, Defense & Space, and Aftermarket. The new organizational structure and leadership changes to support the new structure became effective October 1, 2021. The Company intends to report its financial performance based on the three reporting segments beginning with the 2021 fiscal year-end results. On October 19, 2021, the U.S. District Court for the District of Kansas ruled in favor of the Company’s former Chief Executive Officer and awarded him $44.7 for benefits withheld in connection with a disputed violation of restrictive covenants within his retirement agreement. The Company continues to evaluate the decision and future action, including an appeal . A liability for the amount of the award has been recognized in the Condensed Consolidated Balance Sheets as of September 30, 2021. See also Note 20, Commitments, Contingencies and Guarantees.

New Accounting Pronouncements (

New Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
New Accounting Pronouncements, Policy [Policy Text Block]	. New Accounting Pronouncements In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”), which provides temporary optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. ASU 2020-04 provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. ASU 2020-04 is effective for all entities as of March 12, 2020 through December 31, 2022, and an entity may elect to apply ASU 2020-04 for contract modifications by Topic or Industry Subtopic as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020, or prospectively from a date within an interim period that includes or is subsequent to March 12, 2020, up to the date that the financial statements are available to be issued. An entity may elect to apply ASU 2020-04 to eligible hedging relationships existing as of the beginning of the interim period that includes March 12, 2020, and to new eligible hedging relationships entered into after the beginning of the interim period that includes March 12, 2020. The Company is

Accounts Receivable and Allow_2

Accounts Receivable and Allowance for Credit Losses Allowance for Credit Losses (Policies)	9 Months Ended
	Sep. 30, 2021
Credit Loss [Abstract]
Credit Loss, Financial Instrument [Text Block]	Allowance for Credit Losses During the nine months ended September 30, 2021, there have been no significant changes in the factors that influenced management’s current estimate of expected credit losses, nor changes to the Company’s accounting policies or Current Expected Credit Losses methodology. The beginning balances, current period activity, and ending balances of the allocation for credit losses on accounts receivable and contract assets were not material.

Leases (Policies)

Leases (Policies)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Lessee, Leases [Policy Text Block]	The Company determines if an arrangement is a lease at the inception of a signed agreement. Operating leases are included in right-of-use (“ROU”) assets (long-term), short-term operating lease liabilities, and long-term operating lease liabilities on the Company’s consolidated balance sheet. Finance leases are included in Property, Plant and Equipment, current maturities of long-term debt, and long-term debt. ROU assets represent the right of the Company to use an underlying asset for the length of the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. ROU assets and liabilities are recognized at the lease commencement date based on the estimated present value of lease payments over the lease term. To determine the present value of lease payments, the Company uses its estimated incremental borrowing rate or the implicit rate, if readily determinable. The estimated incremental borrowing rate is based on information available at the lease commencement date, including any recent debt issuances and publicly available data for instruments with similar characteristics. The ROU asset also includes any lease payments made and excludes lease incentives. The Company's lease terms may include options to extend or terminate the lease and, when it is reasonably certain that an option will be exercised, those options are included in the net present value calculation. Leases with a term of 12 months or less, which are primarily related to automobiles and manufacturing equipment, are not recorded on the balance sheet. The aggregate amount of lease cost for leases with a term of 12 months or less is not material.

Other Assets goodwill (Policies

Other Assets goodwill (Policies)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets Disclosure [Text Block]	Goodwill is summarized as follows: Changes in Goodwill Balance Balance at Balance at Segment December 31, Acquisitions Adjustments/Other Currency Exchange September 30, Fuselage Systems $ 42.9 $ — $ 134.9 $ — $ 177.8 Propulsion Systems $ 33.1 $ — $ 382.0 $ — $ 415.1 Wing Systems $ 2.5 $ — $ 10.1 $ — $ 12.6 All Other $ — $ — $ — $ — $ — Not Allocated $ 486.8 (1) $ 18.1 (2) $ (486.8) (1) $ — $ 18.1 $ 565.3 $ 18.1 $ 40.2 (3) $ — $ 623.6 (1) The Bombardier Acquisition (as defined below in Note 24, Acquisitions ) on October 30, 2020 resulted in the establishment of $486.8 of goodwill that was included in the balance reported at December 31, 2020, which, given the preliminary nature of the Bombardier Acquisition purchase price allocation, had not yet been allocated to the relevant reportable segments. The amount was subsequently allocated and is included in the segments noted above. See also Note 24, Acquisitions. (2) Goodwill related to the acquisition of the assets of Applied Aerodynamics, Inc. ("Applied") during the three months ended July 1, 2021 resulted in the establishment of $17.4 of goodwill that was included in the balance reported at July 2, 2021. As a result of certain purchase price allocation adjustments recorded during the purchase price accounting measurement period based on additional information obtained, the goodwill resulting from the Applied acquisition was adjusted by $0.7 to $18.1 as of September 30, 2021. See Note 24, Acquisitions. As of September 30, 2021, given the preliminary nature of the purchase price allocation, the Company has not yet allocated goodwill for the acquisition to the relevant reportable segments. (3) As a result of certain purchase price allocation adjustments recorded during the purchase price accounting measurement period based on additional information obtained, the goodwill resulting from the Bombardier Acquisition was adjusted by $40.2, from $486.8 that was reported at December 31, 2020, to $527.0 as of September 30, 2021. See also Note 24, Acquisitions. The total goodwill value includes no a ccumulated impairment loss in any of the periods present ed. The Company assesses goodwill for impairment annually or more frequently if events or circumstances indicate that the fair value of a reporting unit that includes goodwill may be lower than its carrying value. F or the period ended September 30, 2021, there were no events or circumstances which would require the Company to update its goodwill impairment analysis. Intangible assets are summarized as follows: September 30, December 31, Intangible assets Patents $ 2.0 $ 2.0 Favorable leasehold interests 2.8 2.8 Developed technology asset (1) 92.0 94.0 Customer relationships intangible asset (2) 137.2 124.1 Total intangible assets $ 234.0 $ 222.9 Less: Accumulated amortization - patents (2.0) (2.0) Accumulated amortization - favorable leasehold interest (1.9) (1.8) Accumulated amortization - developed technology asset (7.3) (2.6) Accumulated amortization - customer relationship (6.6) (1.3) Intangible assets, net $ 216.2 $ 215.2 (1) The acquisition of Fiber Materials Inc. on January 10, 2020 resulted in the establishment of a $30.0 intangible asset for developed technology. The Bombardier Acquisition resulted in the establishment of a $64.0 intangible asset for developed technology reported at December 31, 2020, which was subsequently adjusted to $62.0 related to the goodwill adjustment described above. (2) The Bombardier Acquisition resulted in the establishment of a $124.1 intangible asset for customer relationships, which has been adjusted to $131.0 related to the goodwill adjustment described above. The acquisition of Applied on April 26, 2021 resulted in the establishment of a $6.9 intangible asset for customer relationships which has been adjusted t o $6.2 rel ated to the goodwill adjustment described above. See also Note 24, Acquisitions. The amortization for each of the five succeeding years relating to intangible assets currently recorded in the Condensed Consolidated Balance Sheets and the weighted average amortization is estimated to be the following as of September 30, 2021: Year Customer relationships Favorable leasehold interest Developed Technology Total remaining in 2021 $ 2.3 $ — $ 1.5 $ 3.8 2022 8.1 0.1 6.1 14.3 2023 8.1 0.1 6.1 14.3 2024 8.1 0.1 6.1 14.3 2025 8.1 0.1 6.1 14.3 2026 8.1 0.1 6.1 14.3 Weighted average amortization period 16.7 years 7.9 years 13.8 years 15.5 years

Changes in Estimates Changes in

Changes in Estimates Changes in Estimates (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Changes and Error Corrections [Abstract]
Schedule of Change in Accounting Estimate [Table Text Block]	Changes in estimates are summarized below: For the Three Months Ended For the Nine Months Ended Changes in Estimates September 30, 2021 October 1, 2020 September 30, 2021 October 1, 2020 (Unfavorable) Favorable Cumulative Catch-up Adjustment by Segment Fuselage $ (1.6) $ 8.8 $ 4.9 $ (18.9) Propulsion 1.6 (4.6) (2.0) (8.6) Wing (2.9) 0.4 (5.6) (3.1) Other 0.1 — 0.2 — Total (Unfavorable) Favorable Cumulative Catch-up Adjustment $ (2.8) $ 4.6 $ (2.5) $ (30.6) Changes in Estimates on Loss Programs (Forward Loss) by Segment Fuselage $ (49.9) $ (92.0) $ (140.7) $ (260.3) Propulsion (5.9) (14.9) (19.2) (34.2) Wing (14.6) (21.5) (35.1) (47.7) Total Changes in Estimates (Forward Loss) on Loss Programs $ (70.4) $ (128.4) $ (195.0) $ (342.2) Total Changes in Estimates $ (73.2) $ (123.8) $ (197.5) $ (372.8) EPS Impact (diluted per share based upon 2021 forecasted effective tax rate) $ (0.69) $ (0.77) $ (1.86) $ (2.33)

Accounts Receivable, net (Table

Accounts Receivable, net (Tables)	9 Months Ended
	Sep. 30, 2021
Accounts Receivable, after Allowance for Credit Loss, Current [Abstract]
Accounts Receivable, Net	Accounts receivable, net consists of the following: September 30, December 31, Trade receivables $ 475.0 $ 458.9 Other 59.2 31.1 Less: allowance for credit losses (6.6) (5.6) Accounts receivable, net $ 527.6 $ 484.4

Revenue (Tables)

Revenue (Tables) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 980	$ 806.3	$ 2,882.9	$ 2,528.2
Boeing [Member]
Disaggregation of Revenue [Line Items]
Revenues	566.1	493.8	1,595.8	1,539.9
Airbus [Member]
Disaggregation of Revenue [Line Items]
Revenues	211.6	160.1	687.8	575.3
Other Customer [Member]
Disaggregation of Revenue [Line Items]
Revenues	202.3	152.4	599.3	413
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues	715.5	642	2,048.1	1,936.4
UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenues	142.5	103.6	419.8	358.2
Other International [Member]
Disaggregation of Revenue [Line Items]
Revenues	122	60.7	415	233.6
Total International [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 264.5	$ 164.3	$ 834.8	$ 591.8

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Summary Of Inventories	Work-in-process inventory includes direct labor, direct material, overhead, and purchases on contracts for which revenue is recognized at a point in time as well as sub-assembly parts that have not been assigned to a production unit on contracts for which revenue is recognized using the cost to cost input method. For the periods ended September 30, 2021 and December 31, 2020, work-in-process inventory includes $364.5 an d $351.2, respectively, of costs incurred in anticipation of specific contracts and no impairments were recorded in the periods. Product inventory, summarized in the table above, is shown net of valuation reserves of $52.2 and $56.8 as of September 30, 2021 and December 31, 2020, respectively. Excess capacity and abnormal production costs are excluded from inventory and recognized as expense in the period incurred. Cost of sales for three and nine months ended September 30, 2021 includes period expense of $57.1 and $172.2, respectively for excess capacity production costs related to B737 MAX, A220 and A320 production schedule changes. Cost of sales also includes abnormal costs related to workforce adjustments as a result of COVID-19 production pause, net of the U.S. employee retention credit and U.K. government subsidies for the three and nine months ended September 30, 2021 of $2.6 and $7.1 , respectively. Cost of sales for the three and nine month periods ended October 1, 2020 includes period expense of $72.6 and $228.8, respectively, of excess capacity production costs related to temporary B737 MAX and A320 production schedule changes, and abnormal costs related to temporary workforce adjustments as a result of COVID-19 production pause, net of the U.S. employee retention credit and U.K. government subsidies of ($10.9) and $33.8, respectively.

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, plant and equipment, net	Property, plant and equipment, net consists of the following: September 30, December 31, Land $ 30.7 $ 30.8 Buildings (including improvements) 1,210.7 1,166.7 Machinery and equipment 2,214.1 2,120.5 Tooling 1,047.8 1,036.1 Capitalized software 292.0 282.5 Construction-in-progress 185.6 220.0 Total 4,980.9 4,856.6 Less: accumulated depreciation (2,574.0) (2,352.8) Property, plant and equipment, net $ 2,406.9 $ 2,503.8

Other Assets (Tables)

Other Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Other Assets, Noncurrent [Abstract]
Schedule of Other Assets	Other current assets are summarized as follows: September 30, December 31, Prepaid expenses $ 28.0 $ 16.3 Income tax receivable 88.0 315.3 Other assets - short-term 5.1 4.7 Total other current assets $ 121.1 $ 336.3 Other assets are summarized as follows: September 30, December 31, Deferred financing Deferred financing costs $ 0.9 $ 0.9 Less: Accumulated amortization - deferred financing costs (0.6) (0.5) Deferred financing costs, net $ 0.3 $ 0.4 Other Supply agreements (1) $ 9.7 $ 11.4 Equity in net assets of affiliates 1.7 3.1 Restricted cash - collateral requirements 19.5 19.5 Other 72.2 49.2 Total other long-term assets $ 103.4 $ 83.6 (1) Certain payments accounted for as consideration paid by the Company to a customer are being amortized as reductions to net revenues.

Other Assets Intangible Assets

Other Assets Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Schedule of Finite-Lived Intangible Assets [Table Text Block]	Intangible assets are summarized as follows: September 30, December 31, Intangible assets Patents $ 2.0 $ 2.0 Favorable leasehold interests 2.8 2.8 Developed technology asset (1) 92.0 94.0 Customer relationships intangible asset (2) 137.2 124.1 Total intangible assets $ 234.0 $ 222.9 Less: Accumulated amortization - patents (2.0) (2.0) Accumulated amortization - favorable leasehold interest (1.9) (1.8) Accumulated amortization - developed technology asset (7.3) (2.6) Accumulated amortization - customer relationship (6.6) (1.3) Intangible assets, net $ 216.2 $ 215.2 (1) The acquisition of Fiber Materials Inc. on January 10, 2020 resulted in the establishment of a $30.0 intangible asset for developed technology. The Bombardier Acquisition resulted in the establishment of a $64.0 intangible asset for developed technology reported at December 31, 2020, which was subsequently adjusted to $62.0 related to the goodwill adjustment described above. (2) The Bombardier Acquisition resulted in the establishment of a $124.1 intangible asset for customer relationships, which has been adjusted to $131.0 related to the goodwill adjustment described above. The acquisition of Applied on April 26, 2021 resulted in the establishment of a $6.9 intangible asset for customer relationships which has been adjusted t o $6.2 rel ated to the goodwill adjustment described above. See also Note 24, Acquisitions.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The amortization for each of the five succeeding years relating to intangible assets currently recorded in the Condensed Consolidated Balance Sheets and the weighted average amortization is estimated to be the following as of September 30, 2021: Year Customer relationships Favorable leasehold interest Developed Technology Total remaining in 2021 $ 2.3 $ — $ 1.5 $ 3.8 2022 8.1 0.1 6.1 14.3 2023 8.1 0.1 6.1 14.3 2024 8.1 0.1 6.1 14.3 2025 8.1 0.1 6.1 14.3 2026 8.1 0.1 6.1 14.3 Weighted average amortization period 16.7 years 7.9 years 13.8 years 15.5 years

Other Assets Goodwill (Tables)

Other Assets Goodwill (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill [Abstract]
Goodwill Disclosure [Text Block]	Goodwill is summarized as follows: Changes in Goodwill Balance Balance at Balance at Segment December 31, Acquisitions Adjustments/Other Currency Exchange September 30, Fuselage Systems $ 42.9 $ — $ 134.9 $ — $ 177.8 Propulsion Systems $ 33.1 $ — $ 382.0 $ — $ 415.1 Wing Systems $ 2.5 $ — $ 10.1 $ — $ 12.6 All Other $ — $ — $ — $ — $ — Not Allocated $ 486.8 (1) $ 18.1 (2) $ (486.8) (1) $ — $ 18.1 $ 565.3 $ 18.1 $ 40.2 (3) $ — $ 623.6 (1) The Bombardier Acquisition (as defined below in Note 24, Acquisitions ) on October 30, 2020 resulted in the establishment of $486.8 of goodwill that was included in the balance reported at December 31, 2020, which, given the preliminary nature of the Bombardier Acquisition purchase price allocation, had not yet been allocated to the relevant reportable segments. The amount was subsequently allocated and is included in the segments noted above. See also Note 24, Acquisitions. (2) Goodwill related to the acquisition of the assets of Applied Aerodynamics, Inc. ("Applied") during the three months ended July 1, 2021 resulted in the establishment of $17.4 of goodwill that was included in the balance reported at July 2, 2021. As a result of certain purchase price allocation adjustments recorded during the purchase price accounting measurement period based on additional information obtained, the goodwill resulting from the Applied acquisition was adjusted by $0.7 to $18.1 as of September 30, 2021. See Note 24, Acquisitions. As of September 30, 2021, given the preliminary nature of the purchase price allocation, the Company has not yet allocated goodwill for the acquisition to the relevant reportable segments. (3) As a result of certain purchase price allocation adjustments recorded during the purchase price accounting measurement period based on additional information obtained, the goodwill resulting from the Bombardier Acquisition was adjusted by $40.2, from $486.8 that was reported at December 31, 2020, to $527.0 as of September 30, 2021. See also Note 24, Acquisitions. The total goodwill value includes no a ccumulated impairment loss in any of the periods present ed. The Company assesses goodwill for impairment annually or more frequently if events or circumstances indicate that the fair value of a reporting unit that includes goodwill may be lower than its carrying value. F

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	The guidance discloses three levels of inputs that may be used to measure fair value: Level 1 Quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 1 assets and liabilities include debt and equity securities and derivative contracts that are traded in an active exchange market. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 2 assets and liabilities include debt securities with quoted prices that are traded less frequently than exchange-traded instruments and derivative contracts whose value is determined using a pricing model with inputs that are observable in the market or can be derived principally from or corroborated by observable market data. Observable inputs, such as current and forward interest rates and foreign exchange rates, are used in determining the fair value of the interest rate swaps and foreign currency hedge contracts. Level 3 Unobservable inputs that are supported by little or no market activity and are significant to the fair value of assets and liabilities. Level 3 assets and liabilities include financial instruments whose value is determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation.
Carrying Amount And Estimated Fair Value Of Long Term Debt	The following table presents the carrying amount and estimated fair value of long-term debt: September 30, 2021 December 31, 2020 Carrying Fair Carrying Fair Senior secured term loan B (including current portion) $ 388.5 $ 389.5 (2) $ 389.6 $ 395.0 (2) Floating rate notes — — (1) 299.7 297.5 (1) Senior notes due 2023 299.2 304.5 (1) 298.8 293.8 (1) Senior secured first lien notes due 2025 494.9 524.4 (1) 493.9 521.2 (1) Senior secured second lien notes due 2025 1,186.6 1,257.6 (1) 1,184.2 1,279.1 (1) Senior notes due 2026 298.4 318.8 (1) 298.1 313.9 (1) Senior notes due 2028 695.1 691.9 (1) 694.6 689.2 (1) Total $ 3,362.7 $ 3,486.7 $ 3,658.9 $ 3,789.7 (1) Level 1 Fair Value hierarchy (2) Level 2 Fair Value hierarchy See also Note 14, Derivative and Hedging Activities.

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Long Term Debt And Capital Lease Obligations Current And Non Current	Total debt shown on the balance sheet is comprised of the following: September 30, 2021 December 31, 2020 Current Noncurrent Current Noncurrent Senior secured term loan B $ 3.9 $ 384.6 $ 3.9 $ 385.7 Floating rate notes — — 299.7 — Senior notes due 2023 — 299.2 — 298.8 Senior secured first lien notes due 2025 — 494.9 — 493.9 Senior secured second lien notes due 2025 — 1,186.6 — 1,184.2 Senior notes due 2026 — 298.4 — 298.1 Senior notes due 2028 — 695.1 — 694.6 Present value of finance lease obligations 42.6 132.8 35.3 121.5 Other 1.3 55.1 1.8 56.1 Total $ 47.8 $ 3,546.7 $ 340.7 $ 3,532.9

Pension and Other Post-Retire_2

Pension and Other Post-Retirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Change in projected benefit obligations	Defined Benefit Plans For the Three Months Ended For the Nine Components of Net Periodic Pension Expense (Income) September 30, October 1, September 30, October 1, Service cost $ 11.2 $ 0.2 $ 32.9 $ 0.7 Interest cost 15.8 5.4 43.3 20.1 Expected return on plan assets (40.0) (16.6) (119.0) (49.5) Amortization of net loss — — — 0.2 Curtailment loss (gain) (61.0) (1) — (2) (61.0) (1) 33.9 (2) Settlement loss — 4.2 (3) (0.1) 9.3 (3) Special termination benefits — (1.6) (4) — 31.4 (4) Net periodic pension expense (income) $ (74.0) $ (8.4) $ (103.9) $ 46.1 Other Benefits For the Three For the Nine Components of Other Benefit Expense (Income) September 30, October 1, September 30, October 1, Service cost $ 0.3 $ 0.1 $ 0.7 $ 0.5 Interest cost 0.1 0.2 0.3 0.7 Amortization of prior service cost (0.2) (0.2) (0.6) (0.6) Amortization of net gain (0.2) (0.4) (1.0) (1.3) Curtailment gain — — — (0.2) Special termination benefits — — — 12.0 Net periodic other benefit expense (income) $ — $ (0.3) $ (0.6) $ 11.1 (1) As of July 15, 2021, the Company concluded its consultation and communication with employee and Trade Union representatives on the closure of the largest of the defined benefit plans acquired as part of the Bombardier Acquisition, the Shorts Pension (as defined below). The outcome is that the Shorts Pension was amended and will close to the future accrual of benefits for all employees who are members of the plan, effective December 10, 2021. From December 11, 2021, affected employees will build up future retirement savings in a new defined contribution scheme. For the three and nine months ended September 30, 2021, the impact of the closure of the Shorts Pension resulted in a curtailment gain of $61.0. (2) F or the three and nine months ended October 1, 2020, the Company's Voluntary Retirement Program ("VRP") resulted in an estimated 16% and 12% reduction in future working lifetime for the pension value plan and postretirement medical plan resulting in a curtailment accounting charge of $0.0 and $33.7, respectively. The charges are included in other income (expense) in the Company's Condensed Consolidated Statements of Operations. (3) For the three months and nine months ended October 1, 2020, settlement accounting under ASC Topic 715 was triggered, as the lump sums paid to date as part of the VRP exceeded the estimated service cost and interest cost. The Company recognized a settlement loss of $4.2 and $9.3 for the three months and nine months ended October 1, 2020. (4) Special termination benefits for the three and nine months ended October 1, 2020 is a combination of pension value plan and postretirement medical plan changes offset by a reduction in the Company's net benefit obligation. For the three months and nine months ended October 1, 2020 special termination benefits, curtailment accounting, and the remeasurement of the pension assets and obligations resulted in a ($31.9) and $0.4 impact to other comprehensive income ("OCI"), respectively. For the three months and nine months ended October 1, 2020, retiree medical resulted in a $0.0 and

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Basic and Diluted Earnings per share	The following table sets forth the computation of basic and diluted earnings per share: For the Three Months Ended September 30, 2021 October 1, 2020 Income Shares Per Share Income Shares Per Share Basic EPS Loss available to common stockholders $ (113.6) 104.3 $ (1.09) $ (155.5) 103.9 $ (1.50) Income allocated to participating securities — — — — Net loss $ (113.6) $ (155.5) Diluted potential common shares — — Diluted EPS Net loss $ (113.6) 104.3 $ (1.09) $ (155.5) 103.9 $ (1.50) For the Nine Months Ended September 30, 2021 October 1, 2020 Income Shares Per Share Income Shares Per Share Basic EPS Loss available to common stockholders $ (420.5) 104.2 $ (4.04) $ (574.4) 103.8 $ (5.53) Income allocated to participating securities — — — — Net loss $ (420.5) $ (574.4) Diluted potential common shares — — Diluted EPS Net loss $ (420.5) 104.2 $ (4.04) $ (574.4) 103.8 $ (5.53) Included in the outstanding Common Stock were 0.7 million and 1.6 million of issued but unvested shares at September 30, 2021 and October 1, 2020, respectively, which are excluded from the basic Earnings Per Share ("EPS") calculation. Common shares of 0.4 million and 0.5 million, respectively, were excluded from diluted EPS as a result of incurring a net loss for the three and nine months ended September 30, 2021 , as the effect would have been antidilutive. Additionally, diluted EPS for the three and nine months ended September 30, 2021 excludes 0.3 million and 0.3 million shares, respectively, that may be dilutive common shares in the future, but were not included in the computation of diluted EPS because the effect was either antidilutive or the performance condition was not met. Common shares of 0.9 million and 0.7 million, respectively, were excluded from diluted EPS as a result of incurring a net loss for the three and nine months ended October 1, 2020, as the effect would have been antidilutive. Additionally, diluted EPS for the three and nine months ended October 1, 2020 excludes 0.3 million and 0.3 million shares, respectively, that may be dilutive common shares in the future, but were not included in the computation of diluted EPS because the effect was either antidilutive or the performance condition was not met.
Schedule of Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Loss is summarized by component as follows: As of As of September 30, 2021 December 31, 2020 Pension $ (107.0) $ (112.0) Interest swaps — (0.9) SERP/Retiree medical 13.2 14.5 Derivatives - foreign currency hedge (5.6) — Foreign currency impact on long-term intercompany loan (12.4) (11.8) Currency translation adjustment (51.5) (43.9) Total accumulated other comprehensive loss $ (163.3) $ (154.1)

Commitments, Contingencies an_2

Commitments, Contingencies and Guarantees (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments Contingencies And Guarantees [Abstract]
Service warranty roll forward	The following is a roll forward of the service warranty and extraordinary rework balance at September 30, 2021: Balance, December 31, 2020 $ 76.9 Charges to costs and expenses 10.1 Payouts (13.1) Exchange rate (0.2) Balance, September 30, 2021 $ 73.7

Other Income (Expense), Net (Ta

Other Income (Expense), Net (Tables)	9 Months Ended
	Sep. 30, 2021
Other Nonoperating Income (Expense) [Abstract]
Other Income Expense Net	Other income (expense), net is summarized as follows: For the Three For the Nine September 30, October 1, September 30, October 1, Kansas Development Finance Authority bond $ 0.6 $ 0.6 $ 2.2 $ 2.3 Foreign currency (losses) gains (1) 11.3 (3.4) 3.8 1.4 Loss on foreign currency contract and interest rate swaps — (10.6) — (10.5) Loss on sale of accounts receivable (1.8) (2.0) (4.8) (6.7) Pension income (loss) (2) 84.8 9.0 137.3 (56.4) Other (0.1) (3.6) 0.2 4.5 Total $ 94.8 $ (10.0) $ 138.7 $ (65.4)

Acquisition (Tables)

Acquisition (Tables)	9 Months Ended
	Sep. 30, 2021
Acquisition [Abstract]
Asco Acquisition [Text Block]
BBD Acquisition [Text Block]	Bombardier On October 30, 2020, Spirit and Spirit AeroSystems Global Holdings Limited, wholly owned subsidiaries of the Company, completed their previously announced acquisition of the outstanding equity of Shorts and Bombardier Aerospace North Africa SAS ("BANA"), and substantially all the assets of the maintenance, repair and overhaul business in Dallas, Texas (collectively, the “Bombardier Acquired Businesses”), along with the assumption of certain liabilities of Shorts and BANA (the “Bombardier Acquisition”). The Bombardier Acquired Businesses are global leaders in aerostructures and fabrication, delivering composite and metallic wing components, nacelles, fuselages and tail assemblies, along with high-value mechanical assemblies made out of aluminum, titanium and steel. The backlog of work includes long-term contracts on the Airbus aircraft family, along with Bombardier business and regional jets. The acquisition is in line with the Company’s growth strategy of increasing Airbus content, developing a low-cost country footprint, and growing the Company’s aftermarket business. The Bombardier Acquired Businesses are included within the Fuselage Systems, Propulsion Systems, and Wing Systems reporting segments. Refer to Note 22, Segment Information for additional information about the Company’s segments. The Company, acting through certain of its subsidiaries, also assumed net pension liabilities of approximately $316. In addition, Spirit assumed financial obligations related to a repayable investment agreement with the Department for Business, Energy and Industrial Strategy of the Government of the United Kingdom. As a result of its obligation to make future payments under this agreement, the Company recorded the assumed obligation from this transaction as a liability on its Consolidated Balance Sheet that will be accounted for using the interest method over the estimated life of the agreement. As a result, the Company imputes interest on the transaction and recorded imputed interest expense at the estimated interest rate. The Company's estimate of the interest rate under the agreement is based on the amount of payments expected to be made over the remaining life of the agreement. The Company utilizes future sales projections and growth rates to further develop this estimate. The projected amount of payments expected to be made involves the use of significant estimates and assumptions with respect to the number of units expected to be sold. The Company periodically assesses the expected payments to be made using a combination of historical results and forecasts from market data sources. To the extent such payments are greater or less than its initial estimates or the timing of such payments is materially different than its original estimates, the Company will adjust the amortization of the liability prospectively. The Company determined the fair value of the liability at the acquisition date to be $304 which is included within the liabilities assumed, with a current effective annual imputed interest rate of 6.78%. Cash payments made related to the principal component of the liability will be classified as a financing outflow on the Consolidated Statements of Cash Flows, while payments made related to the interest component will be presented within operating cash flows. The $275 cash consideration, along with these assumed liabilities, results in a total enterprise value of $895 as of October 30, 2020. The Company agreed to procure payment of a special contribution of £100 million to the Shorts pension scheme (the "Shorts Pension") on October 30, 2021. In addition, included within the liabilities assumed is approximately $320 in forward loss contracts. Acquisition-related expenses were $0.0 and $1.9, respectively, and $3.3 and $6.2, respectively, for the three and nine months ended September 30, 2021 and October 1, 2020, respectively, and are included in selling, general and administrative costs on the Condensed Consolidated Statements of Operations. The acquisition was accounted for as a business combination in accordance with ASC Topic 805, Business Combinations . The purchase price has been allocated among assets acquired and liabilities assumed at fair value based on information currently available, with the excess purchase price recorded as goodwill. Determining the fair value of assets acquired and liabilities assumed requires significant judgment, including the amount and timing of expected future cash flows, long-term growth rates and discount rates. In some cases, the Company used discounted cash flow analyses, which were based on the Company's best estimate of future sales, earnings and cash flows after considering such factors as general market conditions, customer budgets, existing firm and future orders, changes in working capital, long-term business plans and recent operating performance. Use of different estimates and judgments could yield materially different results. The Company also identified contractual obligations with customers on certain contracts with economic returns that are lower than could be realized in market transactions as of the acquisition date. The Company measured these liabilities under the measurement provisions of FASB ASC Topic 820, Fair Value Measurements and Disclosures , which is based on the price to transfer the obligation to a market participant at the measurement date, assuming that the liability will remain outstanding in the marketplace. Significant assumptions were used to determine the fair value of the loss contract reserves using the discounted cash flow model including discount rates, forecasted quantities of products to be sold under the long-term contracts and market prices for respective products. These were forward looking assumptions that could be affected by future economic and market conditions. Based on the estimated net cash outflows of the programs plus a reasonable contracting profit margin required to transfer the contracts to market participants, the Company recorded assumed liabilities of approximately $320.1 in connection with the Bombardier Acquisition. These liabilities are shown within the forward loss provision on the Condensed Consolidated Balance Sheets for the period ended September 30, 2021. These liabilities will be liquidated in accordance with the underlying pattern of obligations, as reflected by the expenses incurred on the contracts, as a reduction to cost of sales. Total consumption of the contractual obligation in 2020 was $7.2. Total consumption of the contractual obligation for the next five years, based upon the assumptions referenced above is expected to be as follows: $26.6 in 2021, $53.9 in 2022, $77.2 in 2023, $86.8 in 2024, and $68.4 in 2025. As of September 30, 2021 the Company has concluded its assessment and purchase price allocation of the Bombardier Acquisition. Based on additional information obtained during the nine month period ended September 30, 2021, the Company recognized the following adjustments to its preliminary purchase price allocation, which are included in the final purchase price allocation below: intangible assets increased by $4.9, forward loss liability increased by $38.5, other non-current liabilities increased by $4.3, working capital decreased by $2.3. As a result of these adjustments, as of September 30, 2021, the recognized goodwill was adjusted from $486.8 to $527.0. There were no measurement period adjustments materially impacting earnings that would have been recorded in previous reporting periods if the adjustments had been recognized as of the acquisition date. The purchase price allocation of the assets acquired and the liabilities assumed at the acquisition date is as follows: At October 30, 2020 Cash and cash equivalents $ 4.4 Accounts receivable, net 91.9 Inventory 251.6 Other current assets 11.4 Intangible assets, net 193.0 Other non-current assets 11.7 Property and equipment, net 373.6 Right of use asset 27.7 Goodwill 527.0 Total assets acquired $ 1,492.3 Accounts payable $ 90.4 Accrued payroll and employee benefits 113.8 Forward loss provision, short-term 33.8 Other current liabilities 31.5 Forward loss provision, long-term 286.3 Other non-current liabilities 317.7 Operating lease liabilities, long-term 27.5 Retirement benefits 316.3 Total liabilities assumed $ 1,217.3 Net assets acquired $ 275.0 The amounts allocated to the intangible assets identified are as consist of the follows: Amount Amortization Period (in years) Developed Technology $ 62.0 15.0 Customer Relationships $ 131.0 18.0 Total intangible assets $ 193.0 The customer relationships intangible asset consists of estimated future revenues. The customer relationships intangible asset was valued using the excess earnings method (income approach) in which the value is derived from an estimation of the after-tax cash flows specifically attributable to the customer relationships. The analysis included assumptions for projections of revenues and expenses, contributory asset charges, discount rates, and a tax amortization benefit. The developed technology intangible asset was valued using the relief from royalty method (income approach) in which the value is derived by estimation of the after-tax royalty savings attributable to owning the assets. Assumptions in this analysis included projections of revenues, royalty rates representing costs avoided due to ownership of the assets, discount rates, and a tax amortization benefit. The goodwill recognized is attributable primarily to expected synergies and intangible assets that do not qualify for separate recognition, such as the acquired assembled workforce. We expect $24.8 of the goodwill to be deductible for income tax purposes. The Company's allocation of goodwill to our reportable segments is based on the fair value of projected earnings as of the acquisition date. The goodwill is allocated $134.9 to the Fuselage Systems Segment, $382.0 to the Propulsion Systems Segment, and $10.1 to the Wing Systems Segment. The results of operations of the Bombardier Acquired Businesses are included in the Company’s Consolidated Statements of Operations for the nine months ended September 30, 2021. The following summary, prepared on a pro-forma basis, represents the unaudited consolidated results of operations for the nine months ended October 1, 2020 as if the Bombardier Acquisition had been completed as of January 1, 2020. The pro-forma results include the impact of any post-acquisition adjustments directly attributable to the acquisition and the impact of adjustments such as the recognition of additional depreciation and amortization expense, and the related income tax effects. This pro-forma presentation does not include any impact of transaction synergies. The pro-forma results are not necessarily indicative of what the results of operations would have been had the Bombardier Acquisition occurred during the periods presented, nor does they purport to represent results for any future periods. For the Nine October 1, Revenue - as reported $ 2,528.2 Revenue - pro-forma 3,041.3 Net (loss) income - as reported $ (574.4) Net (loss) income - pro-forma (632.7) Earnings Per Share - Diluted - as reported $ (5.53) Earnings Per Share - Diluted - pro-forma (6.10) Asco On May 1, 2018, the Company and its wholly-owned subsidiary Spirit AeroSystems Belgium Holdings BVBA (“Spirit Belgium”) entered into a definitive agreement (as amended, the “Asco Purchase Agreement”) with certain private sellers providing for the purchase by Spirit Belgium of all of the issued and outstanding equity of S.R.I.F. N.V., the parent company of Asco Industries N.V. (“Asco”), subject to certain customary closing adjustments, including foreign currency adjustments (the “Asco Acquisition”). On September 25, 2020, the Company, Spirit Belgium and the private sellers entered into an amendment to the Asco Purchase Agreement (the “Termination Agreement”) pursuant to which the parties agreed to terminate the Asco Purchase Agreement, including all schedules and annexes thereto (other than certain confidentiality agreements) (collectively with the Asco Purchase Agreement, the “Transaction Documents”), effective as of September 25, 2020. Under the Termination Agreement, the parties also agreed to release each other from any and all claims, rights of action, howsoever arising, of every kind and nature, in connection with, arising out of, based upon or related to, directly or indirectly, the Transaction Documents, including any breach, non-performance, action or failure to act under the Transaction Documents. Acquisition-related expenses were $0.0 and $0.1 respectively, for the three and nine month period ended September 30, 2021 and ($0.1) and $17.3, respectively, for the three and nine month period ended October 1, 2020. Acquisition-related expenses are included in Selling, general and administrative costs on the Condensed Consolidated Statements of Operations.

Changes in Estimates (Details)

Changes in Estimates (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Change In Estimate [Line Items]
Changes in Contract Estimates, aggregate, Affecting earnings from Continuing Operations, per Share diluted	$ (0.69)	$ (0.77)	$ (1.86)	$ (2.33)
Change In Accounting Estimate, aggregate	$ (73.2)	$ (123.8)	$ (197.5)	$ (372.8)
Cumulative catch-up adjustment [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(2.8)	4.6	(2.5)	(30.6)
Forward Loss [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(70.4)	(128.4)	(195)	(342.2)
Fuselage Systems [Member] | Cumulative catch-up adjustment [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(1.6)	8.8	4.9	(18.9)
Fuselage Systems [Member] | Forward Loss [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(49.9)	(92)	(140.7)	(260.3)
Wing Systems [Member] | Cumulative catch-up adjustment [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(2.9)	0.4	(5.6)	(3.1)
Wing Systems [Member] | Forward Loss [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(14.6)	(21.5)	(35.1)	(47.7)
Propulsion Systems [Member] | Cumulative catch-up adjustment [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	1.6	(4.6)	(2)	(8.6)
Propulsion Systems [Member] | Forward Loss [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	(5.9)	(14.9)	(19.2)	(34.2)
Other Systems [Member] | Cumulative catch-up adjustment [Member]
Change In Estimate [Line Items]
Change in Accounting Estimate - Contract Accounting	$ 0.1	$ 0	$ 0.2	$ 0

Accounts Receivable, net (Detai

Accounts Receivable, net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Accounts Receivable, after Allowance for Credit Loss, Current [Abstract]
Transfer of Financial Assets Accounted for as Sales, Amount Derecognized	$ 1,487.7		$ 1,487.7
Trade receivables	475		475		$ 458.9
Other	59.2		59.2		31.1
Less: allowance for doubtful accounts	(6.6)		(6.6)		(5.6)
Accounts receivable, net	527.6		527.6		$ 484.4
Gain (Loss) on Sale of Accounts Receivable	$ 1.8	$ 2	$ 4.8	$ 6.7

Contract with customer, asset_2

Contract with customer, asset and liability (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 980	$ 806.3	$ 2,882.9	$ 2,528.2
Contract with Customer, Liability, Revenue Recognized			$ 156.1	91
Disaggregation of Revenue [Table Text Block]			Disaggregation of Revenue The Company disaggregates revenue based on the method of measuring satisfaction of the performance obligation either over time or at a point in time, based upon the location where products and services are transferred to the customer, and based upon major customer. The Company’s principal operating segments and related revenue are noted in Note 22, Segment Information . The following tables show disaggregated revenues for the periods ended September 30, 2021 and October 1, 2020: For the Three Months Ended For the Nine Revenue September 30, October 1, September 30, October 1, Contracts with performance obligations satisfied over time $ 774.9 $ 510.6 $ 2,187.3 $ 1,511.9 Contracts with performance obligations satisfied at a point in time 205.1 295.7 695.6 1,016.3 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 The following table disaggregates revenue by major customer: For the Three Months Ended For the Nine Customer September 30, October 1, September 30, October 1, Boeing $ 566.1 $ 493.8 $ 1,595.8 $ 1,539.9 Airbus 211.6 160.1 687.8 575.3 Other 202.3 152.4 599.3 413.0 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 The following table disaggregates revenue based upon the location where control of products are transferred to the customer: For the Three Months Ended For the Nine Location September 30, October 1, September 30, October 1, United States $ 715.5 $ 642.0 $ 2,048.1 $ 1,936.4 International United Kingdom 142.5 103.6 419.8 358.2 Other 122.0 60.7 415.0 233.6 Total International 264.5 164.3 834.8 591.8 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2
Contract with Customer, Liability, Revenue Recognized			$ 156.1	91
Contract with Customer, Asset, before Allowance for Credit Loss	411	337.7	411	337.7	$ 372.8	$ 534.7
change in contract asset			38.2	(197)
Contract with Customer, Liability	(389.6)	(472.6)	(389.6)	(472.6)	$ (469.6)	$ (514.6)
change in contract liability			80	42
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	774.9	510.6	2,187.3	1,511.9
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 205.1	$ 295.7	$ 695.6	$ 1,016.3

Revenue (Details)

Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Disaggregation of Revenue [Table Text Block]			Disaggregation of Revenue The Company disaggregates revenue based on the method of measuring satisfaction of the performance obligation either over time or at a point in time, based upon the location where products and services are transferred to the customer, and based upon major customer. The Company’s principal operating segments and related revenue are noted in Note 22, Segment Information . The following tables show disaggregated revenues for the periods ended September 30, 2021 and October 1, 2020: For the Three Months Ended For the Nine Revenue September 30, October 1, September 30, October 1, Contracts with performance obligations satisfied over time $ 774.9 $ 510.6 $ 2,187.3 $ 1,511.9 Contracts with performance obligations satisfied at a point in time 205.1 295.7 695.6 1,016.3 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 The following table disaggregates revenue by major customer: For the Three Months Ended For the Nine Customer September 30, October 1, September 30, October 1, Boeing $ 566.1 $ 493.8 $ 1,595.8 $ 1,539.9 Airbus 211.6 160.1 687.8 575.3 Other 202.3 152.4 599.3 413.0 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2 The following table disaggregates revenue based upon the location where control of products are transferred to the customer: For the Three Months Ended For the Nine Location September 30, October 1, September 30, October 1, United States $ 715.5 $ 642.0 $ 2,048.1 $ 1,936.4 International United Kingdom 142.5 103.6 419.8 358.2 Other 122.0 60.7 415.0 233.6 Total International 264.5 164.3 834.8 591.8 Total Revenue $ 980.0 $ 806.3 $ 2,882.9 $ 2,528.2
Revenues	$ 980	$ 806.3	$ 2,882.9	$ 2,528.2
Remaining in Current Year [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	887.7		887.7
2021 [Member] [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	3,396.8		3,396.8
2022 [Member] [Member] [Domain]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	4,146.5		4,146.5
2021 and after [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	3,353.3		3,353.3
Transferred over Time [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenues	774.9	510.6	2,187.3	1,511.9
Transferred at Point in Time [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenues	205.1	295.7	695.6	1,016.3
Boeing [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenues	566.1	493.8	1,595.8	1,539.9
Airbus [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenues	211.6	160.1	687.8	575.3
Other Customer [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenues	$ 202.3	$ 152.4	$ 599.3	$ 413

Inventory (Details)

Inventory (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Summary Of Inventories [Abstract]
Raw materials	$ 306.8		$ 306.8		$ 337.3
Work-in-process	937.6		937.6		1,000.6
Finished goods	54.4		54.4		58.1
Product inventory	1,298.8		1,298.8		1,396
Capitalized pre-production	26.9		26.9		26.3
Total inventory, net	1,325.7		1,325.7		1,422.3
Inventory Valuation Reserves	52.2		52.2		56.8
Costs Incurred in Anticipation of Contracts	364.5		364.5		$ 351.2
Excess Capacity Costs- B737MAX and A320 Production Schedules	57.1	$ 72.6	172.2	$ 228.8
Abnormal Costs- COVID19 production suspension	2.6	(10.9)	7.1	33.8
Inventories [Line Items]
Excess Capacity Costs- B737MAX and A320 Production Schedules	57.1	72.6	172.2	228.8
Abnormal Costs- COVID19 production suspension	$ 2.6	$ (10.9)	$ 7.1	$ 33.8

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Property, plant and equipment, net
Land	$ 30.7	$ 30.8
Buildings (including improvements)	1,210.7	1,166.7
Machinery and equipment	2,214.1	2,120.5
Tooling	1,047.8	1,036.1
Capitalized software	292	282.5
Construction-in-progress	185.6	220
Total	4,980.9	4,856.6
Less: accumulated depreciation	(2,574)	(2,352.8)
Property, plant and equipment, net	$ 2,406.9	$ 2,503.8

Property, Plant and Equipment_3

Property, Plant and Equipment (Details Textual) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment	$ 0	$ 0	$ 0	$ 22.9
Property Plant And Equipment Textuals [Abstract]
Capitalized interest related to construction-in-progress	1.4	1.3	4.5	3.8
Repair and maintenance costs	36.1	25.7	102.7	82.7
Depreciation expense related to capitalized software	$ 3.8	4.1	$ 11.4	12.6
Fuselage Systems [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment		0		(22.5)
Wing Systems [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment		$ 0		$ (0.4)

Leases (Details)

Leases (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Lessee Disclosure [Abstract]
Operating Lease, Weighted Average Remaining Lease Term	35 years 8 months 12 days		35 years 8 months 12 days		42 years 3 months 18 days
Finance Lease, Weighted Average Remaining Lease Term	5 years 1 month 6 days		5 years 1 month 6 days		5 years 6 months
Assets and Liabilities, Lessee [Abstract]
Operating Lease, Liability, Current	$ 8.3		$ 8.3		$ 5.5
Operating Lease, Liability, Noncurrent	80.5		80.5		66.6
Operating Lease, Liability	88.8		88.8
finance lease, Right-of-Use Asset, gross	247.2		247.2		214.2
Finance Lease, Right-of-Use Asset, Accumulated Amortization	(63.7)		(63.7)		(45.1)
Finance Lease, Right-of-Use Asset, after Accumulated Amortization	183.5		183.5		169.1
Finance Lease, Liability, Current	42.6		42.6		35.3
Finance Lease, Liability, Noncurrent	132.8		132.8		$ 121.5
Finance Lease, Liability	175.4		175.4
Lessee, Finance Lease, Lease Not yet Commenced, Description	$ 20.6		$ 20.6
Operating Lease, Weighted Average Discount Rate, Percent	5.60%		5.60%		5.50%
Finance Lease, Weighted Average Discount Rate, Percent	4.50%		4.50%		4.30%
Finance Lease, Liability, Payment, Due [Abstract]
Finance Lease, Liability, to be Paid, Remainder of Fiscal Year	$ 13.2		$ 13.2
Finance Lease, Liability, to be Paid, Year Two	47.8		47.8
Finance Lease, Liability, to be Paid, Year Three	42.4		42.4
Finance Lease, Liability, to be Paid, Year Four	34.3		34.3
Finance Lease, Liability, to be Paid, Year Five	22.4		22.4
Finance Lease, Liability, to be Paid, after Year Five	36.6		36.6
Finance Lease, Liability, Payment, Due	196.7		196.7
Lease Imputed Interest Due- Financing	(21.3)		(21.3)
Cash Flow, Operating Activities, Lessee [Abstract]
Operating lease cost	3.2	$ 2.1	7.9	$ 6.5
Finance Lease, Interest Payment on Liability	1.8	1.6	5.3	4.7
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	5	0.1	21.8	0.3
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year	3.1		3.1
Lessee, Operating Lease, Liability, to be Paid, Year Two	12.5		12.5
Lessee, Operating Lease, Liability, to be Paid, Year Three	11.7		11.7
Lessee, Operating Lease, Liability, to be Paid, Year Four	11.2		11.2
Lessee, Operating Lease, Liability, to be Paid, Year Five	10.7		10.7
Lessee, Operating Lease, Liability, to be Paid, after Year Five	176.8		176.8
Lessee, Operating Lease, Liability, to be Paid	226		226
Lease Imputed Interest Due- Operating	(137.2)		(137.2)
Lease, Cost [Abstract]
Operating Lease, Cost	3.3	2.2	8.3	6.6
Finance Lease, Right-of-Use Asset, Amortization	7.2	5.7	19.6	16
Finance Lease, Interest Expense	1.8	1.6	5.3	4.7
Lease, Cost	12.3	9.5	33.2	27.3
Cash Flow, Financing Activities, Lessee [Abstract]
Finance Lease, Principal Payments	$ 11.3	$ 7.7	$ 30.1	$ 21.4

Other Assets (Details)

Other Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Oct. 01, 2020	Dec. 31, 2019
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 234	$ 222.9
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	3.8
Finite-Lived Intangible Asset, Expected Amortization, Year One	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Two	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Three	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Four	14.3
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 14.3
Finite-Lived Intangible Assets, Remaining Amortization Period	15 years 6 months
Intangible assets
Deferred financing costs, net	$ 0.3	0.4
Goodwill	623.6	565.3
Equity in net assets of affiliates	1.7	3.1
Customer Supply Agreement	9.7	11.4
Restricted Cash, Noncurrent	19.5	19.5	$ 19.5	$ 16.4
Other	72.2	49.2
Total other long-term assets	103.4	83.6
Prepaid Expense, Current	28	16.3
Income Taxes Receivable, Current	88	315.3
Other Assets, Miscellaneous, Current	5.1	4.7
Intangible Assets, Net (Excluding Goodwill)	216.2	215.2
Other Assets, Current	121.1	336.3
Patents [Member]
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	2	2
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	2.3
Finite-Lived Intangible Asset, Expected Amortization, Year One	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Two	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Three	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Four	8.1
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 8.1
Finite-Lived Intangible Assets, Remaining Amortization Period	16 years 8 months 12 days
Intangible assets
Less: Accumulated amortization	$ (2)	(2)
Favorable Leasehold [Member]
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	2.8	2.8
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	0
Finite-Lived Intangible Asset, Expected Amortization, Year One	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Two	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Three	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Four	0.1
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 0.1
Finite-Lived Intangible Assets, Remaining Amortization Period	7 years 10 months 24 days
Intangible assets
Less: Accumulated amortization	$ (1.9)	(1.8)
Debt issuance costs [Member]
Intangible assets
Deferred financing costs	0.9	0.9
Less: Accumulated amortization-deferred financing costs	(0.6)	(0.5)
Developed Technology [Member]
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	92	94
Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year	1.5
Finite-Lived Intangible Asset, Expected Amortization, Year One	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Two	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Three	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Four	6.1
Finite-Lived Intangible Asset, Expected Amortization, Year Five	$ 6.1
Finite-Lived Intangible Assets, Remaining Amortization Period	13 years 9 months 18 days
Intangible assets
Less: Accumulated amortization	$ (7.3)	(2.6)
Customer Relationships
Other Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	137.2	124.1
Intangible assets
Less: Accumulated amortization	$ (6.6)	$ (1.3)

Other Assets (Details Textuals)

Other Assets (Details Textuals) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Goodwill [Line Items]
Goodwill	$ 623.6	$ 565.3
Goodwill, Acquired During Period	18.1
Goodwill, Other Increase (Decrease)	40.2
Goodwill, Period Increase (Decrease)	0
Wing Systems [Member]
Goodwill [Line Items]
Goodwill	12.6	2.5
Goodwill, Acquired During Period	0
Goodwill, Other Increase (Decrease)	10.1
Goodwill, Period Increase (Decrease)	0
Propulsion Systems [Member]
Goodwill [Line Items]
Goodwill	415.1	33.1
Goodwill, Acquired During Period	0
Goodwill, Other Increase (Decrease)	382
Goodwill, Period Increase (Decrease)	0
Fuselage Systems [Member]
Goodwill [Line Items]
Goodwill	177.8	42.9
Goodwill, Acquired During Period	0
Goodwill, Other Increase (Decrease)	134.9
Goodwill, Period Increase (Decrease)	0
Unallocated
Goodwill [Line Items]
Goodwill	18.1	486.8
Goodwill, Acquired During Period	18.1
Goodwill, Other Increase (Decrease)	(486.8)
Goodwill, Period Increase (Decrease)	0
Other Segments
Goodwill [Line Items]
Goodwill, Other Increase (Decrease)	0
Bombardier Acquisition
Goodwill [Line Items]
Goodwill	$ 527	$ 486.8

Advance Payments and Deferred_2

Advance Payments and Deferred Revenue/Credits (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
advance payments [Line Items]
Customer advances- B787 program	$ 212.1
Customer advances- B737 program	125.6
Total Payment [Member]
advance payments [Line Items]
Customer advances- B737 program		$ 123
Total Payment [Member]
advance payments [Line Items]
Customer advances- B737 program		225
Production Stabilization [Member]
advance payments [Line Items]
Customer advances- B737 program		70
To be repaid in 2021 [Member]
advance payments [Line Items]
Customer advances- B737 program		10
Prepayment of shipset deliveries [Member]
advance payments [Line Items]
Customer advances- B737 program	$ 68.5	$ 155

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Carrying amount and estimated fair value of long term debt
Carrying Amount	$ 3,362.7	$ 3,658.9
Fair Value	3,486.7	3,789.7
Secured Debt Term B [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	384.6	385.7
Carrying amount and estimated fair value of long term debt
Carrying Amount	388.5	389.6
Fair Value	389.5	395
Senior Unsecured Notes Due 2023 [Domain]
Carrying amount and estimated fair value of long term debt
Carrying Amount	299.2	298.8
Fair Value	304.5	293.8
Senior Unsecured Notes Due 2026 [Member]
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	298.4	298.1
Carrying amount and estimated fair value of long term debt
Carrying Amount	298.4	298.1
Fair Value	318.8	313.9
Senior Unsecured Notes Due 2021 [Domain]
Carrying amount and estimated fair value of long term debt
Carrying Amount	0	299.7
Fair Value	0	297.5
Senior Secured Second Lien Notes Due 2025
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	1,186.6	1,184.2
Carrying amount and estimated fair value of long term debt
Carrying Amount	1,186.6	1,184.2
Fair Value	1,257.6	1,279.1
Senior Unsecured Notes Due 2028 [Member]
Carrying amount and estimated fair value of long term debt
Carrying Amount	695.1	694.6
Fair Value	691.9	689.2
Senior Secured Notes Due 2025
Debt Instrument [Line Items]
Secured Long-term Debt, Noncurrent	494.9	493.9
Carrying amount and estimated fair value of long term debt
Carrying Amount	494.9	493.9
Fair Value	$ 524.4	$ 521.2

Derivative and Hedging Activi_2

Derivative and Hedging Activities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Sep. 26, 2019	Dec. 31, 2020
Interest Rate Swaps
Foreign Currency Cash Flow Hedge Asset at Fair Value	$ 0		$ 0		$ 0
Foreign Currency Cash Flow Hedge Liability at Fair Value	5.6		5.6		0
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	(6.2)	$ 0	(5.5)	$ 0
Derivative, Notional Amount	280.3		280.3		$ 0
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ 0.1	$ 0	0.1	$ 0
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ (5.6)
Maximum Length of Time Hedged in Cash Flow Hedge			9 months
Derivative, Credit Risk Related Contingent Features, Existence and Nature			Generally, the Company has agreements with its counterparties that contain a provision whereby if the Company defaults on its existing credit facilities and payment of the loans extended under such facilities is accelerated, the Company could be declared in default under its agreements, which may result in the early termination of the outstanding derivatives governed by such agreements and the payment of an early termination amount.
General Cash Flow Hedge Information [Abstract]
Objectives for Using Cash Flow Hedging Instruments			The Company has entered into currency forward contracts, each designated as a cash flow hedge upon the date of execution, for the purpose of reducing the variability of cash flows and hedging against the foreign currency exposure for forecasted payroll, pension and vendor disbursements that are expected to be made in the British Pound Sterling. The hedging program implemented is intended to reduce foreign currency exposure, and the associated forward currency contracts hedge forecasted transactions through June 2022.

Derivative and Hedging Activi_3

Derivative and Hedging Activities (Details 1) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Derivative [Line Items]
Maximum Length of Time Hedged in Cash Flow Hedge		9 months
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	$ 0

Derivative and Hedging Activi_4

Derivative and Hedging Activities (Details Textual) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Derivatives Fair Value [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ (5.6)
Maximum Length of Time Hedged in Cash Flow Hedge		9 months
Interest Rate Swap [Member]
Derivatives Fair Value [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	$ 0	$ 0.4
Loss on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring	0	$ 0.7
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	$ 0

Debt (Details)

Debt (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Long Term Debt And Capital Lease Obligations Current And Non Current [Abstract]
Other Long-term Debt, Current	$ 1.3	$ 1.8
Other Long-term Debt, Noncurrent	55.1	56.1
Long-term Debt and Lease Obligation, Current	47.8	340.7
Long-term Debt and Lease Obligation	3,546.7	3,532.9
Total Debt [Member]
Long Term Debt And Capital Lease Obligations Current And Non Current [Abstract]
Long-term Debt and Lease Obligation, Current	47.8	340.7
Long-term Debt and Lease Obligation	$ 3,546.7	$ 3,532.9

Debt (Details Textual)

Debt (Details Textual) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Proceeds from (Payments for) Other Financing Activities	$ 0	$ 0.1
Proceeds from Issuance of Senior Long-term Debt	0	1,200
Repayments of Lines of Credit	0	$ 800
Long-term Debt	3,362.7		$ 3,658.9
Finance Lease, Liability, Noncurrent	132.8		121.5
Finance Lease, Liability, Current	42.6		35.3
Other Long-term Debt, Current	1.3		1.8
Other Long-term Debt, Noncurrent	$ 55.1		56.1
Senior Unsecured Notes Due 2023 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.95%
Long-term Debt	$ 299.2		298.8
Long-term Debt, Current Maturities	0		0
Unsecured Long-term Debt, Noncurrent	$ 299.2		298.8
Senior Unsecured Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.85%
Long-term Debt	$ 298.4		298.1
Long-term Debt, Current Maturities	0		0
Secured Long-term Debt, Noncurrent	298.4		298.1
Senior Unsecured Notes Due 2021 [Domain]
Debt Instrument [Line Items]
Long-term Debt	0		299.7
Long-term Debt, Current Maturities	0		299.7
Unsecured Long-term Debt, Noncurrent	$ 0		0
Senior Secured Second Lien Notes Due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	7.50%
Long-term Debt	$ 1,186.6		1,184.2
Long-term Debt, Current Maturities	0		0
Secured Long-term Debt, Noncurrent	$ 1,186.6		1,184.2
Senior Unsecured Notes Due 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.60%
Long-term Debt	$ 695.1		694.6
Long-term Debt, Current Maturities	0		0
Unsecured Long-term Debt, Noncurrent	695.1		694.6
Secured Debt Term B [Member]
Debt Instrument [Line Items]
Long-term Debt	388.5		389.6
Long-term Debt, Current Maturities	3.9		3.9
Secured Long-term Debt, Noncurrent	384.6		385.7
Senior Secured Notes Due 2025
Debt Instrument [Line Items]
Long-term Debt	494.9		493.9
Long-term Debt, Current Maturities	0		0
Secured Long-term Debt, Noncurrent	$ 494.9		$ 493.9

Pension and Other Post-Retire_3

Pension and Other Post-Retirement Benefits Pension and Other Post-Retirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment		$ 0		$ (33.7)
Defined Benefit Plan Estimated Future Employer Contributions Remainder Of Year			$ 10.2
Expected UK Pension Plan Contribution For Year			1.9
Expected UK-Belfast Pension Plan Contribution For Year			182.6
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax		0		2.3
Defined Benefit Plan, Service Cost	$ 0.3	0.1	0.7	0.5
Defined Benefit Plan, Interest Cost	0.1	0.2	0.3	0.7
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(0.2)	(0.2)	(0.6)	(0.6)
Defined Benefit Plan, Amortization of Gain (Loss)	(0.2)	(0.4)	(1)	(1.3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	0	0	(0.2)
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits	0	0	0	12
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	0	(0.3)	(0.6)	11.1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax		(31.9)		0.4
Defined Benefit Plan, Service Cost	11.2	0.2	32.9	0.7
Defined Benefit Plan, Interest Cost	15.8	5.4	43.3	20.1
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(40)	(16.6)	(119)	(49.5)
Defined Benefit Plan, Amortization of Gain (Loss)	0	0	0	0.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	(61)	0	(61)	33.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	4.2	(0.1)	9.3
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits	0	(1.6)	0	31.4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ (74)	$ (8.4)	$ (103.9)	$ 46.1

Stock Compensation (Details)

Stock Compensation (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
LTIA AND Prior Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company recognized total stock compensation expense, net of forfeitures	$ 6,200,000	$ 6,200,000	$ 19,600,000	$ 17,100,000
Class A [Member] | Long Term Incentive Plan RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted			557,851
Class A [Member] | Board of Directors Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value Of Shares Granted			$ 1,600,000
Class A [Member] | Board of Directors Plan [Member] | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Vested			11,133
Number of shares granted			6,055
Grant date value of shares vested			$ 0.2
Class A [Member] | Board of Directors Plan [Member] | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Vested			53,617
Number of shares granted			29,514
Grant date value of shares vested			$ 1,000,000
Class A [Member] | Service Based LTIA [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted			30,024
Class A [Member] | Performance Based LTIP RSU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted			161,954
Fair Value Of Shares Granted			$ 9,800,000
Class A [Member] | Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Vested			270,343
Fair Value Of Shares Granted			$ 26,400,000
Grant date value of shares vested			$ 18,800,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	0.15%	37.30%
Valuation Allowance [Line Items]
Deferred Income Tax Liabilities, Net	$ 26		$ 13
Domestic Tax Authority
Valuation Allowance [Line Items]
Deferred Tax Assets, Valuation Allowance	272.5
Deferred Income Tax Liabilities, Net	13.7
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	122.5
Foreign Tax Authority
Valuation Allowance [Line Items]
Deferred Tax Assets, Valuation Allowance	261.5
Deferred Income Tax Liabilities, Net	10.9
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 70.7

Equity (Details)

Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Jul. 01, 2021	Jul. 02, 2020	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 925				$ 925
Common Stock, Dividends, Per Share, Declared	$ 0.01				$ 0.03
Basic EPS
Income available to common shareholders	$ (113.6)	$ (155.5)			$ (420.5)	$ (574.4)
Income available to common shareholders, shares	104,300,000	103,900,000			104,200,000	103,800,000
Income available to common shareholders, per share amount	$ (1.09)	$ (1.50)			$ (4.04)	$ (5.53)
Income allocated to participating securities, shares	0	0			0	0
Net Income (Loss) Attributable to Parent	$ (113.6)	$ (155.5)	$ (306.9)	$ (418.9)	$ (420.5)	$ (574.4)
Diluted potential common shares	0	0			0	0
Diluted EPS
Net Income (Loss) Attributable to Parent	$ (113.6)	$ (155.5)	$ (306.9)	$ (418.9)	$ (420.5)	$ (574.4)
Shares	104,300,000	103,900,000			104,200,000	103,800,000
Diluted (in dollars per share)	$ (1.09)	$ (1.50)			$ (4.04)	$ (5.53)
Equity Textuals [Abstract]
Noncontrolling interest	$ 0.5				$ 0.5		$ 0.5
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(163.3)				(163.3)		(154.1)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax	$ 0.4	$ 0.7			$ 1.6	$ 2
Class of Stock [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	400,000	900,000			500,000	700,000
Earnings Per Share, Potentially Dilutive Securities		0.3				0.3
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	$ 0	$ 0			$ 0	$ 0
Pension [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(107)				(107)		(112)
Accumulated Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	0				0		(0.9)
SERP and Retiree medical [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	13.2				13.2		14.5
Foreign currency impact on long term intercompany loan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(12.4)				(12.4)		(11.8)
Currency translation adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(51.5)				(51.5)		(43.9)
Accumulated Foreign Exchange Forward [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (5.6)				$ (5.6)		$ 0

Commitments, Contingencies an_3

Commitments, Contingencies and Guarantees (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Oct. 01, 2020	Dec. 31, 2019
Commitments Contingencies And Guarantees [Abstract]
Restricted Cash, Noncurrent	$ 19.5	$ 19.5	$ 19.5	$ 16.4
Service warranty roll forward
Product Warranty And Extraordinary Rework	76.9
Charges to costs and expenses	(10.1)
Product Warranty Accrual, Payments	(13.1)
Product Warranty And Extraordinary Rework	73.7	76.9
Product Warranty Extraordinary Rework Accrual Currency Translation Increase Decrease	(0.2)
Commitments Contingencies And Guarantees Textuals [Abstract]
Outstanding amount of guarantees	16.4	19.6
Product Liability Accrual, Component Amount	2.3	8.1
Product Liability Contingency, Loss Exposure in Excess of Accrual, Best Estimate	$ 3.4	$ 12.1

Other Income (Expense), Net (De

Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Other Income (Loss) [Line Items]
UK Belfast Pension income	$ 74.2		$ 105.3
Kansas Development Finance Authority bond	0.6	$ 0.6	2.2	$ 2.3
Foreign currency (losses) gains (1)	11.3	(3.4)	3.8	1.4
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	0	(10.6)	0	(10.5)
Gain (Loss) on Sale of Accounts Receivable	(1.8)	(2)	(4.8)	(6.7)
Pension Income (Expense) without Service Cost	84.8	9	137.3	(56.4)
Other Nonoperating Expense	(0.1)	(3.6)
Other Nonoperating Income			0.2	4.5
VRP pension expense		2.6		86.4
Total	$ 94.8	$ (10)	$ 138.7	$ (65.4)

Segment Information (Details)

Segment Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Oct. 01, 2020USD ($)	Sep. 30, 2021USD ($)segment	Oct. 01, 2020USD ($)
Segment Reporting Information [Line Items]
Restructuring Charges	$ 800,000	$ 19,500,000	$ 8,100,000	$ 68,400,000
Excess Capacity Costs- B737MAX and A320 Production Schedules	57,100,000	72,600,000	172,200,000	228,800,000
Abnormal Costs- COVID19 production suspension	2,600,000	(10,900,000)	7,100,000	33,800,000
Cost of Goods and Services Sold	1,036,200,000	903,400,000	3,009,400,000	2,941,000,000
Gain (Loss) on Disposition of Property Plant Equipment	0	0	0	(22,900,000)
Segment Revenues
Segment Revenues	980,000,000	806,300,000	2,882,900,000	2,528,200,000
Segment Operating Income
Business Segment Operating Income	(45,400,000)	(116,400,000)	(124,500,000)	(496,000,000)
Segment Information Unallocated Corporate Selling General And Administrative	(86,800,000)	(52,800,000)	(211,300,000)	(179,200,000)
Segment Information Unallocated Research And Development	(12,800,000)	(7,500,000)	(34,300,000)	(28,100,000)
Segment Information Unallocated Cost Of Sales	(11,600,000)	(200,000)	(10,100,000)	(8,100,000)
Operating loss	(156,600,000)	(176,900,000)	$ (380,200,000)	(711,400,000)
Segment Reporting Information, Additional Information [Abstract]
Number Of Principal Segments | segment			3
Fuselage Systems [Member]
Segment Reporting Information [Line Items]
Restructuring Charges	200,000	6,600,000	$ 2,900,000	39,100,000
Excess Capacity Costs- B737MAX and A320 Production Schedules	36,200,000	42,000,000	106,400,000	143,800,000
Abnormal Costs- COVID19 production suspension	1,400,000	7,400,000	3,500,000	19,100,000
Gain (Loss) on Disposition of Property Plant Equipment		0		22,500,000
Segment Revenues
Segment Revenues	481,200,000	421,100,000	1,410,500,000	1,299,700,000
Segment Operating Income
Business Segment Operating Income	(53,900,000)	(96,700,000)	(145,500,000)	(434,600,000)
Propulsion Systems [Member]
Segment Reporting Information [Line Items]
Restructuring Charges	0	3,800,000	(200,000)	14,200,000
Excess Capacity Costs- B737MAX and A320 Production Schedules	10,800,000	17,500,000	25,100,000	50,800,000
Abnormal Costs- COVID19 production suspension	300,000	2,900,000	700,000	7,300,000
Segment Revenues
Segment Revenues	247,800,000	170,800,000	716,200,000	565,600,000
Segment Operating Income
Business Segment Operating Income	21,900,000	(15,600,000)	66,800,000	(38,200,000)
Wing Systems [Member]
Segment Reporting Information [Line Items]
Restructuring Charges	600,000	9,100,000	5,400,000	15,100,000
Excess Capacity Costs- B737MAX and A320 Production Schedules	10,100,000	13,100,000	40,700,000	34,200,000
Abnormal Costs- COVID19 production suspension	900,000	600,000	2,900,000	7,400,000
Gain (Loss) on Disposition of Property Plant Equipment		0		400,000
Segment Revenues
Segment Revenues	243,000,000	168,300,000	725,900,000	582,200,000
Segment Operating Income
Business Segment Operating Income	(15,800,000)	(23,200,000)	(50,900,000)	(52,100,000)
Other Systems [Member]
Segment Revenues
Segment Revenues	8,000,000	46,100,000	30,300,000	80,700,000
Segment Operating Income
Business Segment Operating Income	$ 2,400,000	$ 19,100,000	$ 5,100,000	$ 28,900,000

Restructuring Charges (Details)

Restructuring Charges (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Sep. 30, 2021	Oct. 01, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 800,000	$ 19,500,000	$ 8,100,000	$ 68,400,000
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges		11,100,000		47,500,000
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Costs		8,400,000		20,900,000
Fuselage Systems [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	200,000	6,600,000	2,900,000	39,100,000
Propulsion Systems [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0	3,800,000	(200,000)	14,200,000
Wing Systems [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 600,000	$ 9,100,000	$ 5,400,000	$ 15,100,000

Acquisition (Details)

Acquisition (Details) - USD ($)	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2021	Oct. 01, 2020	Jul. 01, 2021	Jul. 02, 2020	Sep. 30, 2021	Oct. 01, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Revenues	$ 980,000,000	$ 806,300,000			$ 2,882,900,000	$ 2,528,200,000
Net Income (Loss) Attributable to Parent	(113,600,000)	$ (155,500,000)	$ (306,900,000)	$ (418,900,000)	(420,500,000)	$ (574,400,000)
Goodwill	$ 623,600,000				$ 623,600,000		$ 565,300,000
Earnings Per Share, Diluted	$ (1.09)	$ (1.50)			$ (4.04)	$ (5.53)
Restructuring Charges	$ 800,000	$ 19,500,000			$ 8,100,000	$ 68,400,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount	24,800,000				24,800,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles					4,900,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities					38,500,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Assets					(2,300,000)
Business Combination Provisional Information Initial Accounting Incomplete Adjustment Other non-current liabilities					4,300,000
Retained Earnings [Member]
Business Acquisition [Line Items]
Net Income (Loss) Attributable to Parent	(113,600,000)	(155,500,000)	$ (306,900,000)	$ (418,900,000)
Asco [Member]
Business Acquisition [Line Items]
Business Acquisition, Transaction Costs	100,000	17,300,000			100,000	17,300,000
Bombardier Acquisition
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)						(632,700,000)
Business Acquisition, Pro Forma Revenue						3,041,300,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	4,400,000				4,400,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	91,900,000				$ 91,900,000
Business Acquisition, Effective Date of Acquisition					Oct. 30, 2020
Business Combination, Consideration Transferred					$ 895,000,000
Business Combination, Reason for Business Combination					The acquisition is in line with the Company’s growth strategy of increasing Airbus content, developing a low-cost country footprint, and growing the Company’s aftermarket business.
Business Acquisition, Description of Acquired Entity					The Bombardier Acquired Businesses are global leaders in aerostructures and fabrication, delivering composite and metallic wing components, nacelles, fuselages and tail assemblies, along with high-value mechanical assemblies made out of aluminum, titanium and steel.
Business Acquisition, Transaction Costs	1,900,000	6,200,000			$ 1,900,000	$ 6,200,000
Goodwill	527,000,000				527,000,000		486,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	251,600,000				251,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets	11,400,000				11,400,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	373,600,000				373,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	193,000,000				193,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	11,700,000				11,700,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	1,492,300,000				1,492,300,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	90,400,000				90,400,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	31,500,000				31,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	317,700,000				317,700,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	1,217,300,000				1,217,300,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	275,000,000				275,000,000
Business Acquisition, Pro Forma Earnings Per Share, Diluted						$ (6.10)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets, Right of Use	27,700,000				27,700,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accrued payroll and employee benefits	113,800,000				113,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, forward loss provisions, short term	33,800,000				33,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Forward Loss Provisions	286,300,000				286,300,000
Business Combination, Recognized Identifiable Asset Acquired and Liability Assumed, Lease Obligation	27,500,000				27,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Retirement benefits	316,300,000				316,300,000
Business Combination, Consideration Transferred, Liabilities Incurred					316,000,000
Business Combination, Consideration Transferred, Other					304,000,000
Payments to Acquire Businesses, Gross					275,000,000
Applied Aerodynamics [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred					29,600,000
Business Acquisition, Transaction Costs	600,000				600,000
Goodwill	18,100,000				18,100,000
Technology-Based Intangible Assets [Member] | Bombardier Acquisition
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	62,000,000				$ 62,000,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					15 years
Customer Relationships | Bombardier Acquisition
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	131,000,000				$ 131,000,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					18 years
Customer Relationships | Applied Aerodynamics [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	3,000,000				$ 3,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	6,200,000				6,200,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	2,300,000				2,300,000
Fuselage Systems [Member]
Business Acquisition [Line Items]
Revenues	481,200,000	421,100,000			1,410,500,000	$ 1,299,700,000
Goodwill	177,800,000				177,800,000		42,900,000
Restructuring Charges	200,000	6,600,000			2,900,000	39,100,000
Propulsion Systems [Member]
Business Acquisition [Line Items]
Revenues	247,800,000	170,800,000			716,200,000	565,600,000
Goodwill	415,100,000				415,100,000		33,100,000
Restructuring Charges	0	3,800,000			(200,000)	14,200,000
Wing Systems [Member]
Business Acquisition [Line Items]
Revenues	243,000,000	168,300,000			725,900,000	582,200,000
Goodwill	12,600,000				12,600,000		$ 2,500,000
Restructuring Charges	$ 600,000	$ 9,100,000			$ 5,400,000	$ 15,100,000