Condensed Consolidating Financial Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Apr. 02, 2015	Mar. 31, 2016	Dec. 31, 2015
Condensed Consolidating Statements of Operations [Abstract]
Net revenues	$ 1,681.6	$ 1,742.2
Operating costs and expenses
Cost of sales	1,359.0	1,448.3
Selling, general and administrative	50.0	51.6
Research and development	6.1	7.0
Total operating costs and expenses	1,415.1	1,506.9
Operating income	266.5	235.3
Interest expense and financing fee amortization	(11.4)	(17.9)
Other expense, net	(2.2)	(6.4)
Income (loss) before income taxes and equity in net loss of affiliates and subsidiaries	252.9	211.0
Income tax provision	(81.9)	(29.4)
Income (loss) Before Equity In Net Income (Loss) Of Affiliates and Subsidiaries	171.0	181.6
Equity in net income of affiliate	0.6	0.3
Equity in net income of subsidiaries	0.0
Net income	171.6	181.9
Total other comprehensive income (loss)	(8.0)	(14.0)
Comprehensive Income, Net of Tax, Attributable to Parent	163.6	167.9
Current assets
Cash and cash equivalents	957.3	377.9	$ 822.9	$ 957.3
Accounts receivable, net			683.2	537.0
Inventory			1,808.0	1,774.4
Other current assets			27.5	30.4
Total current assets			3,341.6	3,299.1
Property, plant and equipment, net			1,947.2	1,950.7
Pension assets			242.7	246.9
Other assets			255.4	280.8
Total assets			5,786.9	5,777.5
Current liabilities
Accounts payable			645.8	618.2
Accrued expenses			225.5	230.2
Profit sharing			18.4	61.6
Current portion of long-term debt			42.9	35.6
Advance payments, short-term			192.5	178.3
Deferred revenue, short-term			312.1	285.5
Deferred grant income liability - current			12.6	11.9
Other current liabilities			88.7	37.7
Total current liabilities			1,538.5	1,459.0
Long-term debt			1,083.4	1,097.6
Advance payments, long-term			452.9	507.4
Pension/OPEB obligation			70.2	67.7
Deferred grant income liability - non-current			78.2	82.3
Deferred revenue and other deferred credits			172.4	170.0
Other liabilities			270.6	273.5
Total equity			2,120.7	2,120.0
Total liabilities and equity			5,786.9	5,777.5
Operating activities
Net cash (used in) operating activities	93.8	423.7
Investing activities
Purchase of property, plant and equipment	(50.4)	(40.3)
Net cash used in investing activities	(50.4)	(40.3)
Financing activities
Principal payments of debt	(7.5)	(7.5)
Repayments of Debt	0.0	(534.9)
Payments Related to Tax Withholding for Share-based Compensation	(2.9)	0.0
Proceeds from Issuance of Long-term Debt	0.0	535.0
Debt issuance and financing costs	0.0	(4.7)
Proceeds from (Payments for) Other Financing Activities	0.0
Payments for Repurchase of Common Stock	165.2	0.0
Excess tax benefit of share-based payment arrangements	0.2	0.0
Net cash used in financing activities	(175.4)	(12.1)
Effect of exchange rate changes on cash and cash equivalents	(2.4)	0.3
Net (decrease) increase in cash and cash equivalents for the period	(134.4)	371.6
Cash and cash equivalents, beginning of period	957.3	377.9
Cash and cash equivalents, end of period	822.9	749.5
Holdings [Member]
Operating costs and expenses
Selling, general and administrative	1.5	2.6
Total operating costs and expenses	1.5	2.6
Operating income	(1.5)	(2.6)
Income (loss) before income taxes and equity in net loss of affiliates and subsidiaries	(1.5)	(2.6)
Income tax provision	0.5	0.3
Income (loss) Before Equity In Net Income (Loss) Of Affiliates and Subsidiaries	(1.0)	(2.3)
Equity in net income of affiliate	0.6	0.3
Equity in net income of subsidiaries	172.0	183.9
Net income	171.6	181.9
Total other comprehensive income (loss)	(8.0)	(14.0)
Comprehensive Income, Net of Tax, Attributable to Parent	163.6	167.9
Current assets
Investment in subsidiary			460.8	623.6
Equity In Net Assets Of Subsidiaries			1,659.9	1,496.4
Total assets			2,120.7	2,120.0
Current liabilities
Total equity			2,120.7	2,120.0
Total liabilities and equity			2,120.7	2,120.0
Financing activities
Repayments of Debt		0.0
Payments Related to Tax Withholding for Share-based Compensation	0.0
Proceeds from (Payments for) Other Financing Activities	165.2
Payments for Repurchase of Common Stock	165.2
Spirit [Member]
Condensed Consolidating Statements of Operations [Abstract]
Net revenues	1,510.5	1,619.0
Operating costs and expenses
Cost of sales	1,214.4	1,352.0
Selling, general and administrative	44.2	45.2
Research and development	5.0	6.3
Total operating costs and expenses	1,263.6	1,403.5
Operating income	246.9	215.5
Interest expense and financing fee amortization	(11.3)	(17.8)
Other expense, net	3.9	1.4
Income (loss) before income taxes and equity in net loss of affiliates and subsidiaries	239.5	199.1
Income tax provision	(78.7)	(27.1)
Income (loss) Before Equity In Net Income (Loss) Of Affiliates and Subsidiaries	160.8	172.0
Equity in net income of subsidiaries	11.2	11.9
Net income	172.0	183.9
Total other comprehensive income (loss)	(8.0)	1.1
Comprehensive Income, Net of Tax, Attributable to Parent	164.0	185.0
Current assets
Cash and cash equivalents	894.2	354.6	796.3	894.2
Accounts receivable, net			798.0	686.3
Inventory			1,281.2	1,229.0
Other current assets			21.4	24.4
Total current assets			2,896.9	2,833.9
Property, plant and equipment, net			1,393.0	1,393.1
Pension assets			229.5	233.3
Investment in subsidiary			283.7	283.7
Equity In Net Assets Of Subsidiaries			257.1	254.1
Other assets			480.5	517.7
Total assets			5,540.7	5,515.8
Current liabilities
Accounts payable			573.8	538.2
Accrued expenses			190.4	195.0
Profit sharing			17.7	58.3
Current portion of long-term debt			39.9	32.9
Advance payments, short-term			192.5	178.3
Deferred revenue, short-term			309.2	281.7
Other current liabilities			85.9	34.7
Total current liabilities			1,409.4	1,319.1
Long-term debt			1,074.3	1,088.0
Advance payments, long-term			452.9	507.4
Pension/OPEB obligation			70.2	67.7
Deferred revenue and other deferred credits			167.7	165.6
Other liabilities			325.5	328.2
Total equity			2,040.7	2,039.8
Total liabilities and equity			5,540.7	5,515.8
Operating activities
Net cash (used in) operating activities	101.5	408.4
Investing activities
Purchase of property, plant and equipment	(37.3)	(26.1)
Net cash used in investing activities	(37.3)	(26.1)
Financing activities
Principal payments of debt	(6.7)	(6.7)
Repayments of Debt		(534.9)
Collection on (repayment of) intercompany debt	12.5	(2.0)
Payments Related to Tax Withholding for Share-based Compensation	(2.9)
Proceeds from Issuance of Long-term Debt		535.0
Debt issuance and financing costs		(4.7)
Proceeds from (Payments for) Other Financing Activities	(165.2)
Excess tax benefit of share-based payment arrangements	0.2
Net cash used in financing activities	(162.1)	(13.3)
Net (decrease) increase in cash and cash equivalents for the period	(97.9)	369.0
Cash and cash equivalents, beginning of period	894.2	354.6
Cash and cash equivalents, end of period	$ 796.3	723.6
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Ownership percentage in domestic subsidiaries	100.00%
Condensed Consolidating Statements of Operations [Abstract]
Net revenues	$ 95.0	58.1
Operating costs and expenses
Cost of sales	91.7	54.8
Selling, general and administrative	0.7	1.3
Research and development	0.5
Total operating costs and expenses	92.9	56.1
Operating income	2.1	2.0
Other expense, net		0.1
Income (loss) before income taxes and equity in net loss of affiliates and subsidiaries	2.1	2.1
Income tax provision	(0.8)	(0.8)
Income (loss) Before Equity In Net Income (Loss) Of Affiliates and Subsidiaries	1.3	1.3
Net income	1.3	1.3
Comprehensive Income, Net of Tax, Attributable to Parent	1.3	1.3
Current assets
Accounts receivable, net			35.9	27.1
Inventory			175.2	179.4
Other current assets			2.3	1.9
Total current assets			213.4	208.4
Property, plant and equipment, net			366.2	364.2
Other assets			82.1	82.7
Total assets			661.7	655.3
Current liabilities
Accounts payable			283.4	276.4
Accrued expenses			1.0	0.5
Deferred grant income liability - current			11.4	10.8
Total current liabilities			295.8	287.7
Deferred grant income liability - non-current			52.5	55.6
Total equity			313.4	312.0
Total liabilities and equity			661.7	655.3
Operating activities
Net cash (used in) operating activities	7.1	9.7
Investing activities
Purchase of property, plant and equipment	(7.1)	(9.7)
Net cash used in investing activities	(7.1)	(9.7)
Financing activities
Repayments of Debt		0.0
Payments Related to Tax Withholding for Share-based Compensation	0.0
Proceeds from (Payments for) Other Financing Activities	0.0
Non-Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Operations [Abstract]
Net revenues	215.9	186.2
Operating costs and expenses
Cost of sales	192.7	162.6
Selling, general and administrative	3.6	2.5
Research and development	0.6	0.7
Total operating costs and expenses	196.9	165.8
Operating income	19.0	20.4
Interest expense and financing fee amortization	(2.1)	(2.0)
Other expense, net	(4.1)	(6.0)
Income (loss) before income taxes and equity in net loss of affiliates and subsidiaries	12.8	12.4
Income tax provision	(2.9)	(1.8)
Income (loss) Before Equity In Net Income (Loss) Of Affiliates and Subsidiaries	9.9	10.6
Equity in net income of affiliate	0.6	0.3
Net income	10.5	10.9
Total other comprehensive income (loss)	(8.8)	(15.1)
Comprehensive Income, Net of Tax, Attributable to Parent	1.7	(4.2)
Current assets
Cash and cash equivalents	63.1	23.3	26.6	63.1
Accounts receivable, net			211.8	189.4
Inventory			351.6	365.9
Other current assets			3.8	4.1
Total current assets			593.8	622.5
Property, plant and equipment, net			188.0	193.4
Pension assets			13.2	13.6
Investment in subsidiary				0.1
Other assets			21.3	21.3
Total assets			816.3	850.9
Current liabilities
Accounts payable			151.1	169.4
Accrued expenses			34.1	34.7
Profit sharing			0.7	3.3
Current portion of long-term debt			3.0	2.7
Deferred revenue, short-term			2.9	3.8
Deferred grant income liability - current			1.2	1.1
Other current liabilities			2.8	3.0
Total current liabilities			195.8	218.0
Long-term debt			257.6	270.6
Deferred grant income liability - non-current			25.7	26.7
Deferred revenue and other deferred credits			4.7	4.4
Other liabilities			25.1	25.3
Total equity			307.4	305.9
Total liabilities and equity			816.3	850.9
Operating activities
Net cash (used in) operating activities	(14.8)	5.6
Investing activities
Purchase of property, plant and equipment	(6.0)	(4.5)
Net cash used in investing activities	(6.0)	(4.5)
Financing activities
Principal payments of debt	(0.8)	(0.8)
Repayments of Debt		0.0
Collection on (repayment of) intercompany debt	(12.5)	2.0
Payments Related to Tax Withholding for Share-based Compensation	0.0
Proceeds from (Payments for) Other Financing Activities	0.0
Net cash used in financing activities	(13.3)	1.2
Effect of exchange rate changes on cash and cash equivalents	(2.4)	0.3
Net (decrease) increase in cash and cash equivalents for the period	(36.5)	2.6
Cash and cash equivalents, beginning of period	63.1	23.3
Cash and cash equivalents, end of period	26.6	25.9
Consolidating Adjustments [Member]
Condensed Consolidating Statements of Operations [Abstract]
Net revenues	(139.8)	(121.1)
Operating costs and expenses
Cost of sales	(139.8)	(121.1)
Total operating costs and expenses	(139.8)	(121.1)
Interest expense and financing fee amortization	2.0	1.9
Other expense, net	(2.0)	(1.9)
Equity in net income of affiliate	(0.6)	(0.3)
Equity in net income of subsidiaries	(183.2)	(195.8)
Net income	(183.8)	(196.1)
Total other comprehensive income (loss)	16.8	14.0
Comprehensive Income, Net of Tax, Attributable to Parent	(167.0)	(182.1)
Current assets
Accounts receivable, net			(362.5)	(365.8)
Inventory				0.1
Total current assets			(362.5)	(365.7)
Investment in subsidiary			(744.5)	(907.4)
Equity In Net Assets Of Subsidiaries			(1,917.0)	(1,750.5)
Other assets			(328.5)	(340.9)
Total assets			(3,352.5)	(3,364.5)
Current liabilities
Accounts payable			(362.5)	(365.8)
Total current liabilities			(362.5)	(365.8)
Long-term debt			(248.5)	(261.0)
Other liabilities			(80.0)	(80.0)
Total equity			(2,661.5)	(2,657.7)
Total liabilities and equity			$ (3,352.5)	$ (3,364.5)
Financing activities
Repayments of Debt		$ 0.0
Payments Related to Tax Withholding for Share-based Compensation	0.0
Proceeds from (Payments for) Other Financing Activities	$ 0.0