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	411.0	368.4
Inventory, net	1,325.7	1,422.3
Other current assets	121.1	336.3
Total current assets	3,816.3	4,485.0
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	0.0	4.4
Pension assets	487.2	455.9
Deferred Income Tax Assets, Net	0.0	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	57.0
Long-term Debt and Lease Obligation, Current	47.8	340.7
Operating Lease, Liability, Current	8.3	5.5
Customer Advances, Current	116.0	18.9
Contract with Customer, Liability, Current	109.9	97.6
Provision for Loss on Contracts	284.0	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	372.0
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	26.0	13.0
Deferred income taxes	422.2	437.0
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	857.0
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