Accounting Changes and Error Corrections (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Oct. 01, 2020	Jul. 02, 2020	Apr. 02, 2020	Dec. 31, 2019	Sep. 26, 2019	Jun. 27, 2019	Mar. 28, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Item Effected [Line Items]
Cash and cash equivalents	$ 1,873.3				$ 2,350.5				$ 1,873.3	$ 2,350.5	$ 773.6	$ 423.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	1,893.1				2,367.2				1,893.1	2,367.2	794.1	445.5
Restricted Cash, Current	0.3				0.3				0.3	0.3	0.3	2.2
Accounts Receivable, after Allowance for Credit Loss, Current	484.4				546.4				484.4	546.4
Revenues	876.6	$ 806.3	$ 644.6	$ 1,077.3	1,959.3	$ 1,919.9	$ 2,016.1	$ 1,967.8	3,404.8	7,863.1	7,222.0
Cost of Goods and Services Sold									3,845.5	6,786.4	6,135.9
Income Tax Expense (Benefit)									220.2	(132.8)	(139.8)
Net income	$ (295.9)	$ (155.5)	$ (255.9)	$ (163.0)	$ 67.7	$ 131.3	$ 168.0	$ 163.1	$ (870.3)	$ 530.1	$ 617.0
Earnings Per Share, Basic	$ (2.85)	$ (1.50)	$ (2.46)	$ (1.57)	$ 0.65	$ 1.27	$ 1.62	$ 1.57	$ (8.38)	$ 5.11	$ 5.71
Earnings Per Share, Diluted	$ (2.85)	$ (1.50)	$ (2.46)	$ (1.57)	$ 0.65	$ 1.26	$ 1.61	$ 1.55	$ (8.38)	$ 5.06	$ 5.65
Unbilled Receivables, Current	$ 368.4				$ 528.3				$ 368.4	$ 528.3
Total current assets	1,422.3				1,118.8				1,422.3	1,118.8
Other Assets, Current	336.3				98.7				336.3	98.7
Unbilled Receivable, Non Current	4.4				6.4				4.4	6.4
Other Assets, Noncurrent	83.6				76.8				83.6	76.8
Assets	8,383.9				7,606.0				8,383.9	7,606.0
Accrued Liabilities, Current	365.6				240.2				365.6	240.2
Billings in Excess of Cost, Current	97.6				158.3				97.6	158.3
Provision for Loss on Contracts	184.6				83.9				184.6	83.9
Deferred Revenue, Current	22.2				14.8				22.2	14.8
Other Liabilities, Current	58.4				39.3				58.4	39.3
Billings in Excess of Cost, Noncurrent	372.0				356.3				372.0	356.3
Provision for Loss on Contacts, Non Current	561.4				163.5				561.4	163.5
Deferred Revenue and Credits, Noncurrent	38.9				34.4				38.9	34.4
Retained Earnings (Accumulated Deficit)	2,326.4				3,201.3				2,326.4	3,201.3
Liabilities and Equity	8,383.9				7,606.0				8,383.9	7,606.0
Selling, General and Administrative Expense									237.4	261.4	$ 210.4
Other Nonoperating Income (Expense)									(77.8)	(5.8)	(7.0)
Restricted Cash and Investments, Noncurrent	$ 19.5				$ 16.4				$ 19.5	$ 16.4	$ 20.2	$ 20.0